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Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod. The end of the rod attached to the crank moves in a circular motion, while the other end is usually constrained to move in a linear sliding motion, in and out.
The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crankset or a brace and bit drill. In this case a person's arm or leg serves as the connecting rod, applying reciprocating force to the crank. Often there is a bar perpendicular to the other end of the arm, often with a freely rotatable handle on it to hold in the hand, or in the case of operation by a foot (usually with a second arm for the other foot), with a freely rotatable pedal.
1.1 Hand-powered cranks
1.2 Foot-powered cranks
1.3 Engines
3.1 Western World
3.1.1 Classical Antiquity
3.1.2 Middle Ages
3.1.3 Renaissance
3.2 Far East
5.1 Bibliography
A crank
Hand crank on a pencil sharpener
Familiar examples include:
Hand-powered cranks
Mechanical pencil sharpener
Fishing reel and other reels for cables, wires, ropes, etc.
Manually operated car window
The crank set that drives a trikke through its handles.
Foot-powered cranks
The crankset that drives a bicycle via the pedals.
Treadle sewing machine
Almost all reciprocating engines use cranks to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft.
The displacement of the end of the connecting rod is approximately proportional to the cosine of the angle of rotation of the crank, when it is measured from top dead center (TDC). So the reciprocating motion created by a steadily rotating crank and connecting rod is approximately simple harmonic motion:
where x is the distance of the end of the connecting rod from the crank axle, l is the length of the connecting rod, r is the length of the crank, and α is the angle of the crank measured from top dead center (TDC). Technically, the reciprocating motion of the connecting rod departs slightly from sinusoidal motion due to the changing angle of the connecting rod during the cycle.
The mechanical advantage of a crank, the ratio between the force on the connecting rod and the torque on the shaft, varies throughout the crank's cycle. The relationship between the two is approximately:
where is the torque and F is the force on the connecting rod. For a given force on the crank, the torque is maximum at crank angles of α = 90° or 270° from TDC. When the crank is driven by the connecting rod, a problem arises when the crank is at top dead centre (0°) or bottom dead centre (180°). At these points in the crank's cycle, a force on the connecting rod causes no torque on the crank. Therefore if the crank is stationary and happens to be at one of these two points, it cannot be started moving by the connecting rod. For this reason, in steam locomotives, whose wheels are driven by cranks, the two connecting rods are attached to the wheels at points 90° apart, so that regardless of the position of the wheels when the engine starts, at least one connecting rod will be able to exert torque to start the train.
See also: Roman technology and List of Roman watermills
Roman crank handle from Augusta Raurica, dated to the 2nd century AD[1]
The eccentrically mounted handle of the rotary handmill which appeared in 5th century BC Celtiberian Spain and ultimately spread across the Roman Empire constitutes a crank.[2][3][4] A Roman iron crankshaft of yet unknown purpose dating to the 2nd century AD was excavated in Augusta Raurica, Switzerland. The 82.5 cm long piece has fitted to one end a 15 cm long bronze handle, the other handle being lost.[5][1]
A ca. 40 cm long true iron crank was excavated, along with a pair of shattered mill-stones of 50−65 cm diameter and diverse iron items, in Aschheim, close to Munich. The crank-operated Roman mill is dated to the late 2nd century AD.[6] An often cited modern reconstruction of a bucket-chain pump driven by hand-cranked flywheels from the Nemi ships has been dismissed though as "archaeological fantasy".[7]
Roman Hierapolis sawmill from the 3rd century AD, the earliest known machine to combine a crank with a connecting rod.[8]
The earliest evidence, anywhere in the world, for the crank combined with a connecting rod in a machine appears in the late Roman Hierapolis sawmill from the 3rd century AD and two Roman stone sawmills at Gerasa, Roman Syria, and Ephesus, Asia Minor (both 6th century AD).[8] On the pediment of the Hierapolis mill, a waterwheel fed by a mill race is shown powering via a gear train two frame saws which cut rectangular blocks by the way of some kind of connecting rods and, through mechanical necessity, cranks. The accompanying inscription is in Greek.[9]
The crank and connecting rod mechanisms of the other two archaeologically attested sawmills worked without a gear train.[10][11] In ancient literature, we find a reference to the workings of water-powered marble saws close to Trier, now Germany, by the late 4th century poet Ausonius;[8] about the same time, these mill types seem also to be indicated by the Christian saint Gregory of Nyssa from Anatolia, demonstrating a diversified use of water-power in many parts of the Roman Empire[12] The three finds push back the date of the invention of the crank and connecting rod back by a full millennium;[8] for the first time, all essential components of the much later steam engine were assembled by one technological culture:
With the crank and connecting rod system, all elements for constructing a steam engine (invented in 1712) — Hero's aeolipile (generating steam power), the cylinder and piston (in metal force pumps), non-return valves (in water pumps), gearing (in water mills and clocks) — were known in Roman times.[13]
See also: Medieval technology
Vigevano's war carriage
A rotary grindstone − the earliest representation thereof −[14] which is operated by a crank handle is shown in the Carolingian manuscript Utrecht Psalter; the pen drawing of around 830 goes back to a late antique original.[15] A musical tract ascribed to the abbot Odo of Cluny (ca. 878−942) describes a fretted stringed instrument which was sounded by a resined wheel turned with a crank; the device later appears in two 12th century illuminated manuscripts.[14] There are also two pictures of Fortuna cranking her wheel of destiny from this and the following century.[14]
The use of crank handles in trepanation drills was depicted in the 1887 edition of the Dictionnaire des Antiquités Grecques et Romaines to the credit of the Spanish Muslim surgeon Abu al-Qasim al-Zahrawi; however, the existence of such a device cannot be confirmed by the original illuminations and thus has to be discounted.[16] The Benedictine monk Theophilus Presbyter (c. 1070−1125) described crank handles "used in the turning of casting cores".[17]
The Italian physician Guido da Vigevano (c. 1280−1349), planning for a new crusade, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels (center of image).[18] The Luttrell Psalter, dating to around 1340, describes a grindstone which was rotated by two cranks, one at each end of its axle; the geared hand-mill, operated either with one or two cranks, appeared later in the 15th century;[19]
Medieval cranes were occasionally powered by cranks, although more often by windlasses.[20]
See also: Renaissance technology
15th century paddle-wheel boat whose paddles are turned by single-throw crankshafts (Anonymous of the Hussite Wars)
The crank became common in Europe by the early 15th century, often seen in the works of those such as the German military engineer Konrad Kyeser.[19] Devices depicted in Kyeser's Bellifortis include cranked windlasses (instead of spoke-wheels) for spanning siege crossbows, cranked chain of buckets for water-lifting and cranks fitted to a wheel of bells.[19] Kyeser also equipped the Archimedes screws for water-raising with a crank handle, an innovation which subsequently replaced the ancient practice of working the pipe by treading.[21] The earliest evidence for the fitting of a well-hoist with cranks is found in a miniature of c. 1425 in the German Hausbuch of the Mendel Foundation.[22]
German crossbowman cocking his weapon with a cranked rack-and-pinion device (ca. 1493)
The first depictions of the compound crank in the carpenter's brace appear between 1420 and 1430 in various northern European artwork.[23] The rapid adoption of the compound crank can be traced in the works of the Anonymous of the Hussite Wars, an unknown German engineer writing on the state of the military technology of his day: first, the connecting-rod, applied to cranks, reappeared, second, double compound cranks also began to be equipped with connecting-rods and third, the flywheel was employed for these cranks to get them over the 'dead-spot'.
One of the drawings of the Anonymous of the Hussite Wars shows a boat with a pair of paddle-wheels at each end turned by men operating compound cranks (see above). The concept was much improved by the Italian Roberto Valturio in 1463, who devised a boat with five sets, where the parallel cranks are all joined to a single power source by one connecting-rod, an idea also taken up by his compatriot Francesco di Giorgio.[24]
Water-raising pump powered by crank and connecting rod mechanism (Georg Andreas Böckler, 1661)
In Renaissance Italy, the earliest evidence of a compound crank and connecting-rod is found in the sketch books of Taccola, but the device is still mechanically misunderstood.[25] A sound grasp of the crank motion involved demonstrates a little later Pisanello who painted a piston-pump driven by a water-wheel and operated by two simple cranks and two connecting-rods.[25]
The 15th century also saw the introduction of cranked rack-and-pinion devices, called cranequins, which were fitted to the crossbow's stock as a means of exerting even more force while spanning the missile weapon (see right).[26] In the textile industry, cranked reels for winding skeins of yarn were introduced.[19]
Around 1480, the early medieval rotary grindstone was improved with a treadle and crank mechanism. Cranks mounted on push-carts first appear in a German engraving of 1589.[27]
From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period: Agostino Ramelli's The Diverse and Artifactitious Machines of 1588 alone depicts eighteen examples, a number which rises in the Theatrum Machinarum Novum by Georg Andreas Böckler to 45 different machines, one third of the total.[28]
Tibetan operating a quern (1938). The perpendicular handle of such rotary handmills works as a crank.[3][4]
The earliest true crank handle in Han China occurs, as Han era glazed-earthenware tomb models portray, in an agricultural winnowing fan,[29] dated no later than 200 AD.[30] The crank was used thereafter in China for silk-reeling and hemp-spinning, in the water-powered flour-sifter, for hydraulic-powered metallurgic bellows, and in the well windlass.[31] However, the potential of the crank of converting circular motion into reciprocal one never seems to have been fully realized in China, and the crank was typically absent from such machines until the turn of the 20th century.[32]
While the US-American historian of technology Lynn White could not find "firm evidence of even the simplest application of the crank until al-Jazari's book of A.D. 1206",[19] the crank appears according to Beeston in the mid-9th century in several of the hydraulic devices described by the Banū Mūsā brothers in their Book of Ingenious Devices.[33] These devices, however, made only partial rotations and could not transmit much power,[34] although only a small modification would have been required to convert it to a crankshaft.[35]
Al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machine in two of his water-raising machines.[36] His twin-cylinder pump incorporated a crankshaft,[37] but the device was unnecessarily complex indicating that he still did not fully understand the concept of power conversion.[38] After al-Jazari cranks in Islamic technology are not traceable until an early 15th century copy of the Mechanics of the ancient Greek engineer Hero of Alexandria.[16]
Cranks were formerly common on some machines in the early 20th century; for example almost all phonographs before the 1930s were powered by clockwork motors wound with cranks, and internal combustion engines of automobiles were usually started with cranks (known as starting handles in the UK), before electric starters came into general use.
Piston motion equations
Nothing grinder
Sun and planet gear
^ a b Schiöler 2009, pp. 113f.
^ Date: Frankel 2003, pp. 17–19
^ a b Ritti, Grewe & Kessener 2007, p. 159
^ a b Lucas 2005, p. 5, fn. 9
^ Laur-Belart 1988, p. 51–52, 56, fig. 42
^ Volpert 1997, pp. 195, 199
^ White, Jr. 1962, pp. 105f.; Oleson 1984, pp. 230f.
^ a b c d Ritti, Grewe & Kessener 2007, p. 161:
Because of the findings at Ephesus and Gerasa the invention of the crank and connecting rod system has had to be redated from the 13th to the 6th c; now the Hierapolis relief takes it back another three centuries, which confirms that water-powered stone saw mills were indeed in use when Ausonius wrote his Mosella.
^ Ritti, Grewe & Kessener 2007, pp. 139–141
^ Mangartz 2006, pp. 579f.
^ Wilson 2002, p. 16
^ Ritti, Grewe & Kessener 2007, p. 156, fn. 74
^ a b c White, Jr. 1962, p. 110
^ Hägermann & Schneider 1997, pp. 425f.
^ a b White, Jr. 1962, p. 170
^ Needham 1986, pp. 112–113.
^ Hall 1979, p. 80
^ a b c d e White, Jr. 1962, p. 111
^ White, Jr. 1962, pp. 105, 111, 168
^ White, Jr. 1962, p. 167; Hall 1979, p. 52
^ White, Jr. 1962, p. 112
^ Hall 1979, pp. 74f.
^ N. Sivin; Needham, Joseph (August 1968), "Review: Science and Civilisation in China by Joseph Needham", Journal of Asian Studies (Association for Asian Studies) 27 (4): 859–864 [862], doi:10.2307/2051584, JSTOR 2051584
^ White, Jr. 1962, p. 104:
Yet a student of the Chinese technology of the early twentieth century remarks that even a generation ago the Chinese had not 'reached that stage where continuous rotary motion is substituted for reciprocating motion in technical contrivances such as the drill, lathe, saw, etc. To take this step familiarity with the crank is necessary. The crank in its simple rudimentary form we find in the [modern] Chinese windlass, which use of the device, however, has apparently not given the impulse to change reciprocating into circular motion in other contrivances'. In China the crank was known, but remained dormant for at least nineteen centuries, its explosive potential for applied mechanics being unrecognized and unexploited.
^ A. F. L. Beeston, M. J. L. Young, J. D. Latham, Robert Bertram Serjeant (1990), The Cambridge History of Arabic Literature, Cambridge University Press, p. 266, ISBN 0521327636
^ al-Hassan & Hill 1992, pp. 45, 61
^ Banu Musa, Donald Routledge Hill (1979), The book of ingenious devices (Kitāb al-ḥiyal), Springer, pp. 23–4, ISBN 9027708339
^ Ahmad Y Hassan. The Crank-Connecting Rod System in a Continuously Rotating Machine.
^ Sally Ganchy, Sarah Gancher (2009), Islam and Science, Medicine, and Technology, The Rosen Publishing Group, p. 41, ISBN 1435850661
However, that al-Jazari did not entirely grasp the meaning of the crank for joining reciprocating with rotary motion is shown by his extraordinarily complex pump powered through a cog-wheel mounted eccentrically on its axle.
Frankel, Rafael (2003), "The Olynthus Mill, Its Origin, and Diffusion: Typology and Distribution", American Journal of Archaeology 107 (1): 1–21
Hall, Bert S. (1979), The Technological Illustrations of the So-Called "Anonymous of the Hussite Wars". Codex Latinus Monacensis 197, Part 1, Wiesbaden: Dr. Ludwig Reichert Verlag, ISBN 3-920153-93-6
Hägermann, Dieter; Schneider, Helmuth (1997), Propyläen Technikgeschichte. Landbau und Handwerk, 750 v. Chr. bis 1000 n. Chr. (2nd ed.), Berlin, ISBN 3-549-05632-X
al-Hassan, Ahmad Y.; Hill, Donald R. (1992), Islamic Technology. An Illustrated History, Cambridge University Press, ISBN 0-521-422396
Lucas, Adam Robert (2005), "Industrial Milling in the Ancient and Medieval Worlds. A Survey of the Evidence for an Industrial Revolution in Medieval Europe", Technology and Culture 46 (1): 1–30, doi:10.1353/tech.2005.0026
Laur-Belart, Rudolf (1988), Führer durch Augusta Raurica (5th ed.), Augst
Mangartz, Fritz (2006), "Zur Rekonstruktion der wassergetriebenen byzantinischen Steinsägemaschine von Ephesos, Türkei. Vorbericht", Archäologisches Korrespondenzblatt 36 (1): 573–590
Needham, Joseph (1991), Science and Civilisation in China: Volume 4, Physics and Physical Technology: Part 2, Mechanical Engineering, Cambridge University Press, ISBN 0521058031 .
Oleson, John Peter (1984), Greek and Roman Mechanical Water-Lifting Devices: The History of a Technology, University of Toronto Press, ISBN 90-277-1693-5
Volpert, Hans-Peter (1997), "Eine römische Kurbelmühle aus Aschheim, Lkr. München", Bericht der bayerischen Bodendenkmalpflege 38: 193–199, ISBN 3-7749-2903-3
White, Jr., Lynn (1962), Medieval Technology and Social Change, Oxford: At the Clarendon Press
Ritti, Tullia; Grewe, Klaus; Kessener, Paul (2007), "A Relief of a Water-powered Stone Saw Mill on a Sarcophagus at Hierapolis and its Implications", Journal of Roman Archaeology 20: 138–163
Schiöler, Thorkild (2009), "Die Kurbelwelle von Augst und die römische Steinsägemühle", Helvetia Archaeologica 40 (159/160): 113–124
Crank highlight: Hypervideo of construction and operation of a four cylinder internal combustion engine courtesy of Ford Motor Company
Kinematic Models for Design Digital Library (KMODDL) - Movies and photos of hundreds of working mechanical-systems models at Cornell University. Also includes an e-book library of classic texts on mechanical design and engineering.
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Evans · Peaucellier–Lipkin · Sector straight-line · Watt's (parallel)
Hemi · Recuperator · Turbo-compounding
Piston engine configurations
Crank (person)
Virtuous circle and vicious circle
crank mechanism — alkūninis mechanizmas statusas T sritis Energetika apibrėžtis Keturgrandis svirtinis mechanizmas, keičiantis sukamąjį judesį slenkamuoju arba atvirkščiai. atitikmenys: angl. crank and connecting rod assembly; crank mechanism vok. Kurbelgetriebe,… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas
slider-crank mechanism — ▪ mechanics arrangement of mechanical parts designed to convert straight line motion to rotary motion, as in a reciprocating piston engine, or to convert rotary motion to straight line motion, as in a reciprocating piston pump. The basic nature… … Universalium
Crank — may refer to: Contents 1 Mechanism 2 People 3 Places 4 … Wikipedia
crank and connecting-rod assembly — alkūninis mechanizmas statusas T sritis Energetika apibrėžtis Keturgrandis svirtinis mechanizmas, keičiantis sukamąjį judesį slenkamuoju arba atvirkščiai. atitikmenys: angl. crank and connecting rod assembly; crank mechanism vok. Kurbelgetriebe,… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas
Crank (person) — Crank is a pejorative term used for a person who unshakably holds a belief that most of his or her contemporaries consider to be false.[1] A cranky belief is so wildly at variance with commonly accepted belief as to be ludicrous. Cranks… … Wikipedia
crank — In a mechanical linkage or mechanism, a link that can turn about a center of rotation. The crank's center of rotation is in the pivot, usually the axis of the crankshaft, that connects the crank to the adjacent link. A crank is arranged for… … Aviation dictionary
eccentric-and-rod mechanism — ▪ mechanics arrangement of mechanical parts used to obtain a reciprocating straight line motion from a rotating shaft; it serves the same purpose as a slider crank mechanism and is particularly useful when the required stroke of the… … Universalium
eccentric and rod mechanism — Arrangement of mechanical parts used to obtain a reciprocating straight line motion from a rotating shaft. It serves the same purpose as a slider crank mechanism and is particularly useful when the required stroke of the reciprocating motion is… … Universalium
Antikythera mechanism — The Antikythera mechanism (main fragment) The Antikythera mechanism ( / … Wikipedia
Eccentric (mechanism) — An eccentric in mechanical engineering is a circular disk ( eccentric sheave ) solidly fixed to a rotating axle with its centre offset from that of the axle (hence the word eccentric , out of the centre). It is most often employed in steam… … Wikipedia


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Drugs & Diseases > Hematology
Sickle Cell Disease Clinical Presentation
Author: Joseph E Maakaron, MD; Chief Editor: Emmanuel C Besa, MD more...
Sections Sickle Cell Disease
Baseline Blood Study Abnormalities
Suggested Routine Clinical Laboratory Evaluations
Laboratory Studies in the Ill Child
Nuclear Medicine Scans
Transcranial Doppler Ultrasonography
Abdominal Ultrasonography
Hydroxyurea Therapy
Management of Ophthalmic Manifestations
Vaso-Occlusive Crisis Management
Control of Acute Pain
Treatment of Acute Chest Syndrome
Control of Chronic Pain
Management of Chronic Anemia
Prevention and Treatment of Infections
Treatment of Gallstones
Treatment of Priapism
Treatment of Leg Ulcers
Stroke Prevention
Treatment of Pulmonary Hypertension
Sickle Cell Nephropathy
Treatment of Other Complications
Diet and Activity Restrictions
Investigational Treatments
Guidelines Summary
Sleep-Disordered Breathing
Cerebrovascular Complications
Transfusion Support
Hematopoietic Stem Cell Transplantation (HSCT)
Antimetabolites
Opioid Analgesics
Nonsteroidal Analgesics
Hemoglobin Oxygen-Affinity Modulators
P-Selectin Inhibitor
Phosphodiesterase Type 5 Inhibitors
Endothelin Receptor Antagonists
Iron Chelators
Adrenergic Agonists
Sickle cell disease (SCD) usually manifests early in childhood. For the first 6 months of life, infants are protected largely by elevated levels of Hb F; soon thereafter, the condition becomes evident.
The most common clinical manifestation of SCD is vaso-occlusive crisis. A vaso-occlusive crisis occurs when the microcirculation is obstructed by sickled RBCs, causing ischemic injury to the organ supplied and resultant pain. Pain crises constitute the most distinguishing clinical feature of sickle cell disease and are the leading cause of emergency department visits and hospitalizations for affected patients.
Approximately half the individuals with homozygous Hb S disease experience vaso-occlusive crisis. The frequency of crisis is extremely variable. Some have as many as 6 or more episodes annually, whereas others may have episodes only at great intervals or none at all. Each individual typically has a consistent pattern for crisis frequency.
Pain crises begin suddenly. The crisis may last several hours to several days and terminate as abruptly as it began.
The pain can affect any body part. It often involves the abdomen, bones, joints, and soft tissue, and it may present as dactylitis (bilateral painful and swollen hands and/or feet in children), acute joint necrosis or avascular necrosis, or acute abdomen. [31] With repeated episodes in the spleen, infarctions and autosplenectomy predisposing to life-threatening infection are usual. The liver also may infarct and progress to failure with time. Papillary necrosis is a common renal manifestation of vaso-occlusion, leading to isosthenuria (ie, inability to concentrate urine).
Severe deep pain is present in the extremities, involving long bones. Abdominal pain can be severe, resembling acute abdomen; it may result from referred pain from other sites or intra-abdominal solid organ or soft tissue infarction. Reactive ileus leads to intestinal distention and pain.
The face also may be involved. Pain may be accompanied by fever, malaise, and leukocytosis.
Bone pain is often due to bone marrow infarction. Certain patterns are predictable, since pain tends to involve bones with the most bone marrow activity and because marrow activity changes with age. During the first 18 months of life, the metatarsals and metacarpals can be involved, presenting as dactylitis or hand-foot syndrome.
As the child grows older, pain often involves the long bones of the extremities, sites that retain marrow activity during childhood. Proximity to the joints and occasional sympathetic effusions lead to the belief that the pain involves the joints. As marrow activity recedes further during adolescence, pain involves the vertebral bodies, especially in the lumbar region.
Although the above patterns describe commonly encountered presentations, any area with blood supply and sensory nerves can be affected.
Triggers of vaso-occlusive crisis
Often, no precipitating cause can be identified. However, because deoxygenated hemoglobin S (HbS) becomes semisolid, the most likely physiologic trigger of vaso-occlusive crises is hypoxemia. This may be due to acute chest syndrome or accompany respiratory complications.
Dehydration can precipitate pain, since acidosis results in a shift of the oxygen dissociation curve (Bohr effect), causing hemoglobin to desaturate more readily. Hemoconcentration also is a common mechanism.
Another common trigger is changes in body temperature—whether an increase due to fever or a decrease due to environmental temperature change. Lowered body temperature likely leads to crises as the result of peripheral vasoconstriction. Patients should wear proper clothing and avoid exposure to ensure normal core temperature.
Chronic pain in SCD
Many individuals with SCD experience chronic low-level pain, mainly in bones and joints. Intermittent vaso-occlusive crises may be superimposed, or chronic low-level pain may be the only expression of the disease.
Anemia is universally present. It is chronic and hemolytic in nature and usually very well tolerated. While patients with an Hb level of 6-7 g/dL who are able to participate in the activities of daily life in a normal fashion are not uncommon, their tolerance for exercise and exertion tends to be very limited.
Anemia may be complicated with megaloblastic changes secondary to folate deficiency. These result from increased RBC turnover and folate utilization. Periodic bouts of hyperhemolysis may occur.
Children exhibit few manifestations of anemia because they readily adjust by increasing heart rate and stroke volume; however, they have decreased stamina, which may be noted on the playground or when participating in physical education class.
Aplastic crisis
A serious complication is the aplastic crisis. This is caused by infection with Parvovirus B-19 (B19V). This virus causes fifth disease, a normally benign childhood disorder associated with fever, malaise, and a mild rash. This virus infects RBC progenitors in bone marrow, resulting in impaired cell division for a few days. Healthy people experience, at most, a slight drop in hematocrit, since the half-life of normal erythrocytes in the circulation is 40-60 days. In people with SCD, however, the RBC lifespan is greatly shortened (usually 10-20 days), and a very rapid drop in Hb occurs. The condition is self-limited, with bone marrow recovery occurring in 7-10 days, followed by brisk reticulocytosis.
Splenic sequestration
Splenic sequestration occurs with highest frequency during the first 5 years of life in children with sickle cell anemia. Splenic sequestration can occur at any age in individuals with other sickle syndromes. This complication is characterized by the onset of life-threatening anemia with rapid enlargement of the spleen and high reticulocyte count.
Splenic sequestration is a medical emergency that demands prompt and appropriate treatment. Parents should be familiar with the signs and symptoms of splenic sequestration crises. Children should be seen as rapidly as possible in the emergency room. Treatment of the acute episode requires early recognition, careful monitoring, and aggressive transfusion support. Because these episodes tend to recur, many advocate long-term transfusion in young children and splenectomy in older children.
As HbS replaces HbF in the early months of life, problems associated with sickling and red cell membrane damage begin. The resulting rigid cells progressively obstruct and damage the spleen, which leads to functional asplenia. This, along with other abnormalities, results in extreme susceptibility to infection.
Organisms that pose the greatest danger include encapsulated respiratory bacteria, particularly Streptococcus pneumoniae. The mortality rate of such infections has been reported to be as high as 10-30%. Consider osteomyelitis when dealing with a combination of persistent pain and fever. Bone that is involved with infarct-related vaso-occlusive pain is prone to infection. Staphylococcus and Salmonella are the 2 most likely organisms responsible for osteomyelitis.
During adult life, infections with gram-negative organisms, especially Salmonella, predominate. Of special concern is the frequent occurrence of Salmonella osteomyelitis in areas of bone weakened by infarction.
Effects on growth and maturation
During childhood and adolescence, SCD is associated with growth retardation, delayed sexual maturation, and being underweight. Rhodes et al demonstrated that growth delays during puberty in adolescents with SCD is independently associated with decreased Hb concentration and increased total energy expenditure. [32]
Rhodes et al found that children with SCD progressed more slowly through puberty than healthy control children. Affected pubertal males were shorter and had significantly slower height growth than their unaffected counterparts, with a decline in height over time; however, their annual weight increases did not differ. In addition, the mean fat free mass increments in affected males and females were significantly less than those of the control children. [32]
Hand-foot syndrome
Infants with SCD may develop hand-foot syndrome, a dactylitis presenting as exquisite pain and soft tissue swelling of the dorsum of the hands and feet. The syndrome develops suddenly and lasts 1-2 weeks. Hand-foot syndrome occurs between age 6 months and 3 years; it is not seen after age 5 years because hematopoiesis in the small bones of the hands and feet ceases at this age. Osteomyelitis is the major differential diagnosis.
Cortical thinning and destruction of the metacarpal and metatarsal bones appear on radiographs 3-5 weeks after the swelling begins. Leukocytosis or erythema does not accompany the swelling.
Acute chest syndrome
In young children, the acute chest syndrome consists of chest pain, fever, cough, tachypnea, leukocytosis, and pulmonary infiltrates in the upper lobes. Adults are usually afebrile and dyspneic with severe chest pain and multilobar and lower lobe disease.
Acute chest syndrome is a medical emergency and must be treated immediately. Patients are otherwise at risk for developing acute respiratory distress syndrome.
Acute chest syndrome probably begins with infarction of ribs, leading to chest splinting and atelectasis. Because the appearance of radiographic changes may be delayed, the diagnosis may not be recognized immediately.
In children, acute chest syndrome is usually due to infection. Other etiologies include pulmonary infarction and fat embolism resulting from bone marrow infarction. Recognition of the specific cause is less critical than the ability to assess the management and pace of the lung injury.
Central nervous system involvement
Central nervous system involvement is one of the most devastating aspects of SCD. It is most prevalent in childhood and adolescence. The most severe manifestation is stroke, resulting in varying degrees of neurological deficit. Stroke affects 30% of children and 11% of patients by 20 years. It is usually ischemic in children and hemorrhagic in adults. [33]
Hemiparesis is the usual presentation. Other deficits may be found, depending on the location of the infarct.
Convulsions are frequently associated with stroke. Convulsions occur as an isolated event but also appear in the setting of evolving acute chest syndrome, pain crisis, aplastic crisis, and priapism. Rapid and excessive blood transfusion to a hemoglobin level of greater than 12 g/dL increases blood viscosity and can lead to stroke.
Children with sickle cell disease may have various anatomic and physiologic abnormalities that involve the CNS even if they appear to be neurologically healthy. These silent brain infarcts occur in 17% of patients and may be associated with deterioration in cognitive function, with effects on learning and behavior; these infarcts may increase the potential risk for clinical and subclinical damage to the CNS.
Hemorrhagic stroke is often caused by rupture of aneurysms that might be a result of vascular injury and tend to occur later in life. Moya moya, a proliferation of small fragile vessels found in patients with stenotic lesions, can also lead to cerebral hemorrhage. Hemorrhagic stroke is associated with a mortality rate of more than 29%.
Cardiac involvement
The heart is involved due to chronic anemia and microinfarcts. Hemolysis and blood transfusion lead to hemosiderin deposition in the myocardium. Both ventricles and the left atrium are all dilated.
A study by Nicholson et al also indicated that coronary artery dilation is common in children with SCD. The prevalence of coronary artery ectasia in patients with SCD was 17.7%, compared with 2.3% for the general population. [34] Furthermore, a systolic murmur is usually present, with wide radiation over the precordium.
Cholelithiasis
Cholelithiasis is common in children with SCD, as chronic hemolysis with hyperbilirubinemia is associated with the formation of bile stones. Cholelithiasis may be asymptomatic or result in acute cholecystitis, requiring surgical intervention. The liver may also become involved. Cholecystitis or common bile duct obstruction can occur.
Consider cholecystitis in a child who presents with right upper quadrant pain, especially if associated with fatty food. Consider common bile duct blockage when a child presents with right upper quadrant pain and dramatically elevated conjugated hyperbilirubinemia.
Renal involvement
The kidneys lose concentrating capacity. Isosthenuria results in a large loss of water, further contributing to dehydration in these patients. Renal failure may ensue, usually preceded by proteinuria. Nephrotic syndrome is uncommon but may occur.
Eye involvement
Paraorbital facial infarction may result in ptosis. Retinal vascular changes also occur. A proliferative retinitis is common in Hb SC disease and may lead to loss of vision. See Ophthalmic Manifestations of Sickle Cell Anemia for a complete discussion of this topic.
Leg ulcers
Leg ulcers are a chronic painful problem. They result from minor injury to the area around the malleoli. Because of relatively poor circulation, compounded by sickling and microinfarcts, healing is delayed and infection becomes established.
Priapism
Priapism, defined as a sustained, painful, and unwanted erection, is a well-recognized complication of SCD. Priapism tends to occur repeatedly. When it is prolonged, it may lead to impotence.
According to one study, the mean age at which priapism occurs is 12 years, and, by age 20 years, as many as 89% of males with sickle cell disease have experienced one or more episodes of priapism. Priapism can be classified as prolonged if it lasts for more than 3 hours or as stuttering if it lasts for more than a few minutes but less than 3 hours and resolves spontaneously. Stuttering episodes may recur or develop into more prolonged events.
Prolonged priapism is an emergency that requires urologic consultation. Recurrent episodes of priapism can result in fibrosis and impotence, even when adequate treatment is attempted.
Avascular necrosis
Vascular occlusion can result in avascular necrosis (AVN) of the femoral or humeral head and subsequent infarction and collapse at either site. AVN of the femoral head presents a greater problem because of weight bearing. Patients with high baseline hemoglobin levels are at increased risk. Approximately 30% of all patients with SCD have hip pathology by age 30 years.
The natural history of symptomatic hip disease in patients with sickle cell disease who are treated conservatively varies with the patient's age. In skeletally immature patients aged 12 years or younger, treatment with analgesics, NSAIDs, and protected weight bearing usually results in healing and remodeling of the involved capital epiphysis, similar to that observed in Legg-Calve-Perthes disease. This approach results in preservation of the joint despite the persistence of deformity, such as coxa magna and coxa plana.
In contrast, conservative management of osteonecrosis usually fails in older adolescents and adults. Progressive flattening and collapse of the femoral head results in painful secondary degenerative arthritis.
Blood in the pulmonary circulation is deoxygenated, resulting in a high degree of polymer formation. The lungs develop areas of microinfarction and microthrombi that hinder the flow of blood. The resulting areas that lack oxygenation aggravate the sickling process. Pulmonary hypertension may develop. This may be due in part to the depletion of nitric oxide. Various studies have found that more than 40% of adults with SCD have pulmonary hypertension that worsens with age.
This is increasingly recognized as a serious complication of sickle cell disease, with an incidence as high as 31.8%. [35, 36] Familial clustering has also been recognized. Hemolysis, chronic hypoxia caused by sickle cell disease, and pulmonary disease (eg, recurrent acute chest syndrome, asthma, obstructive sleep apnea) are contributing factors.
Pulmonary hypertension is characterized by a regurgitant pulmonary (tricuspid) jet velocity of more than 2.5 m/s by echocardiography. Recently, there has been a lot of debate about the positive predictive value of measuring tricuspid regurgitant jet velocity. A recent study found that in a population of sickle cell patients, 25% had a tricuspid regurgitant jet of more than 2.5 m/s, but only 6% had actual pulmonary hypertension on right-sided heart catheterization. [37] It is associated with a high mortality rate in adult patients. Children with pulmonary hypertension have lower mortality, but the disease is associated with high morbidity.
Physical findings are not specific. Scleral icterus is present, and, upon ophthalmoscopic examination of the conjunctiva with the +40 lens, abnormal or corkscrew-shaped blood vessels may be seen. The mucous membranes are pale. A systolic murmur may be heard over the entire precordium.
Hypotension and tachycardia may be signs of septic shock or splenic sequestration crisis. With the severe anemia that accompanies aplastic crisis, patients may exhibit signs of high-output heart failure.
Orthostasis suggests hypovolemia. Tachypnea suggests pneumonia, heart failure, or acute chest syndrome. Dyspnea suggests acute chest syndrome, pulmonary hypertension, and/or heart failure.
Fever suggests infection in children; however, it is less significant in adults unless it is a high-grade fever. Examine the head and neck for meningeal signs or possible source of infection (eg, otitis, sinusitis).
Auscultate the heart to search for signs of congestive heart failure. Auscultate the lungs for signs of pneumonia, heart failure, or acute chest syndrome (similar to pulmonary embolism). Palpate for tenderness (abdomen, extremities, back, chest, femoral head) and hepatosplenomegaly.
In childhood, splenomegaly may be present, although this is not present in adults due to autosplenectomy. Spleen size should be measured, and parents should be made aware of it. A tongue blade may be used as a "spleen stick" in a small child, with the upper end of the blade corresponding to the nipple in the midclavicular line and a marking made on the stick corresponding to the edge of the spleen.
Growth parameters show patients falling below the growth isobars. This usually occurs around the prepubertal age because of delayed puberty.
Observe for pallor, icterus, and erythema or edema of the extremities or joints. In adults, leg ulcers may be found over the malleoli. Perform a neurological examination to search for focal neurological deficits.
Ocular manifestations
Sickle cell vasoocclusive events can affect every vascular bed in the eye, often with visually devastating consequences in advanced stages of the disease.
Anterior segment abnormalities include the following:
Segmentation "corkscrew" conjunctival vessel, more commonly seen in the inferior bulbar conjunctiva
Iris infarct and atrophy
Phthisis bulbi
Hyphema
The abnormalities of the posterior segment can be divided into 6 categories, as follows [38, 39, 40, 41] :
Optic disc changes
Posterior retinal and macular vascular occlusionChronic macular changes (sickling maculopathy)
Choroidal vascular occlusions
Nonproliferative retinal changes
Proliferative retinal changes
Intravascular occlusions on the surface of the optic disc appear ophthalmoscopically as dark-red intravascular spots. These occlusions are transient and do not produce any clinical impairment. [42] These changes are most common in hemoglobin SS disease but can also occur in patients with hemoglobin SC and hemoglobin S.
Posterior retinal and macular vascular occlusions
Retinal artery occlusions are either central or branch. Peripapillary or macular arteriolar occlusions are rare. Retinal vein occlusions also are rare with SCD.
Chronic macular changes
Chronic macular vascular occlusions occur in SCD. These are manifested by microaneurysms resembling dots, hairpin-shaped vascular loops, and abnormal foveal avascular zone (FAZ).
This is an extremely rare manifestation of SCD. Only 3 cases have been reported thus far in the literature.
Nonproliferative or background sickle retinopathy includes the following manifestations:
Venous tortuosity
Salmon-patch hemorrhage
Schisis cavity
The black sunburst
Venous tortuosity probably is due to arteriovenous shunting from the retinal periphery. It can occur in many patients with hemoglobin SS and hemoglobin SC disease.
Salmon-patch hemorrhages are superficial intraretinal hemorrhages. They are usually seen in the mid periphery of the retina adjacent to a retinal arteriole.
The schisis cavity is a space caused by the disappearance of the intraretinal hemorrhage. Nonproliferative sickle retinopathy features iridescent spots and glistening refractive bodies in the schisis cavity.
The black sunburst consists of round chorioretinal scars usually located in the equatorial fundus. These lesions result from pigment accumulated around the vessels. They do not cause any visual symptoms.
Proliferative sickle retinopathy
Proliferative sickle retinopathy (PSR) is the most severe ocular change in SCD. This is a peripheral retinal change most frequent in patients with hemoglobin SC but also can be present in patients with hemoglobin S–thalassemia disease, homozygous hemoglobin SS, and hemoglobin AS and hemoglobin AC disease. [43, 44]
PSR is progressive. A desirable objective is to treat the neovascular tissue before a vitreous hemorrhage occurs.
Goldberg classified PSR into the following 5 stages:
Peripheral arteriolar occlusions
Arteriolar-venular anastomosis
Neovascular proliferation
Vitreous hemorrhage
In stage I, the peripheral arteriolar vessels occlude, with anteriorly located avascular vessels evident. Early in the process, the occluded arterioles are dark-red lines, but eventually they turn into silver-wire–appearing vessels.
In stage II, peripheral arteriolar-venular anastomosis occurs as the eye adjusts to peripheral arteriolar occlusion, and blood is diverted from the occluded arterioles into the adjacent venules. Peripheral to these anastomoses, no perfusion is present.
In stage III, new vessel formation occurs at the junction of the vascular and avascular retina. These neovascular tufts resemble sea fans. Initially, the sea fans can be fed by a single arteriole and draining vessel.
Later, as the sea fan grows in size, it is difficult to distinguish the major feeding and draining vessels. The sea fans may acquire a glial and fibrotic tissue envelope. This envelope may pull on the vitreous. A full-thickness retinal break, which may lead to total rhegmatogenous retinal detachment, may occur.
Meningitis is 200 times more common in children with HbSS. Consider lumbar puncture in children with fever who appear toxic and in those with neurologic findings such as neck stiffness, positive Brudzinski or Kernig signs, or focal deficits. Meningeal signs are not reliable if the children are irritable and inconsolable.
Skeletal manifestations
The characteristic appearance in children with sickle cell disease includes frontal and parietal bossing and prominent maxilla due to marrow hyperplasia expanding the bone. The extremities may appear proportionately longer than normal because there is often flattening of the vertebrae. Bone marrow expansion often causes maxillary hypertrophy with overbite; orthodontics consultations are recommended to prevent or correct this problem.
The physical findings of acute infarction include local effects from swelling of the affected bone, such as proptosis or ophthalmoplegia from orbital bone infarction. Also present is pain, swelling, and warmth of the involved extremity, such on the dorsa of the hands and feet in patients with dactylitis.
Sequelae of chronic infarction include structural and functional orthopedic abnormalities. Examples include an immobile or nonfunctional shoulder joint, abnormal hip growth and deformity, secondary osteoarthritis, shortened fingers and toes, and kyphoscoliosis.
Hand-foot syndrome, or aseptic dactylitis, is a common presentation of sickle cell disease. This condition is caused by infarction of bone marrow and cortical bone in the metacarpals, metatarsals, and proximal phalanges. Hand-foot syndrome is usually one of the earliest manifestations of the disease.
Acute bone pain crisis
Acute bone pain crisis is caused by bone marrow ischemia or infarction. These crises usually start after age 2-3 years and occur as gnawing, progressive pain, most commonly in the humerus, tibia, and femur and less commonly in the facial bones. Periarticular pain and joint effusion, often associated with a sickle cell crisis, are considered a result of ischemia and infarction of the synovium and adjacent bone and bone marrow.
Patients with acute bone pain crisis usually present with fever, leukocytosis, and warmth and tenderness around the affected joints. This process tends to affect the knees and elbows, mimicking rheumatic fever and septic arthritis.
In adolescence and adulthood, the most prominent complication is osteonecrosis of 1 or more epiphyses, usually of the femoral or humeral heads. Chronic pain is often associated with later stages of osteonecrosis, particularly in the femoral head. Pain due to avascular necrosis is most notable with weight bearing on the joint. Patients often have pain associated with functional limitation of the affected joint.
Patients with sickle cell disease are prone to infection of the bone and bone marrow in areas of infarction and necrosis. Although Staphylococcus aureus is the most common cause of osteomyelitis in the general population, studies have shown that in patients with sickle cell disease, the relative incidence of Salmonella osteomyelitis is twice that of staphylococcal infection.
Nephrologic manifestations
See Nephrologic Manifestations of Sickle Cell Disease for more information on this topic.
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Leen JS, Ratnakaram R, Del Priore LV, Bhagat N, Zarbin MA. Anterior segment ischemia after vitrectomy in sickle cell disease. Retina. 2002 Apr. 22 (2):216-9. [Medline].
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Rogovik AL, Li Y, Kirby MA, Friedman JN, Goldman RD. Admission and length of stay due to painful vasoocclusive crisis in children. Am J Emerg Med. 2009 Sep. 27(7):797-801. [Medline].
Wang WC, Ware RE, Miller ST, et al. Hydroxycarbamide in very young children with sickle-cell anaemia: a multicentre, randomised, controlled trial (BABY HUG). Lancet. 2011 May 14. 377(9778):1663-72. [Medline].
Gladwin MT, Kato GJ, Weiner D, et al. Nitric oxide for inhalation in the acute treatment of sickle cell pain crisis: a randomized controlled trial. JAMA. 2011 Mar 2. 305(9):893-902. [Medline].
[Guideline] Howard J, Hart N, Roberts-Harewood M, Cummins M, Awogbade M, Davis B, et al. Guideline on the management of acute chest syndrome in sickle cell disease. Br J Haematol. 2015 May. 169 (4):492-505. [Medline]. [Full Text].
Styles L, Wager CG, Labotka RJ, Smith-Whitley K, Thompson AA, Lane PA, et al. Refining the value of secretory phospholipase A2 as a predictor of acute chest syndrome in sickle cell disease: results of a feasibility study (PROACTIVE). Br J Haematol. 2012 Jun. 157 (5):627-36. [Medline]. [Full Text].
Ogunlesi F, Heeney MM, Koumbourlis AC. Systemic corticosteroids in acute chest syndrome: friend or foe?. Paediatr Respir Rev. 2014 Mar. 15 (1):24-7. [Medline].
[Guideline] Brandow AM, Carroll CP, Creary S, Edwards-Elliott R, Glassberg J, Hurley RW, et al. American Society of Hematology 2020 guidelines for sickle cell disease: management of acute and chronic pain. Blood Adv. 2020 Jun 23. 4 (12):2656-2701. [Medline]. [Full Text].
Goodwin EF, Partain PI, Lebensburger JD, Fineberg NS, Howard TH. Elective cholecystectomy reduces morbidity of cholelithiasis in pediatric sickle cell disease. Pediatr Blood Cancer. 2016 Sep 19. [Medline].
Rogers ZR. Priapism in sickle cell disease. Hematol Oncol Clin North Am. 2005 Oct. 19(5):917-28, viii. [Medline].
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Freed J, Talano J, Small T, Ricci A, Cairo MS. Allogeneic cellular and autologous stem cell therapy for sickle cell disease: 'whom, when and how'. Bone Marrow Transplant. 2012 Dec. 47 (12):1489-98. [Medline]. [Full Text].
Ware RE, Helms RW, SWiTCH Investigators. Stroke With Transfusions Changing to Hydroxyurea (SWiTCH). Blood. 2012 Apr 26. 119 (17):3925-32. [Medline].
Ware RE, Davis BR, Schultz WH, Brown RC, Aygun B, et al. Hydroxycarbamide versus chronic transfusion for maintenance of transcranial doppler flow velocities in children with sickle cell anaemia-TCD With Transfusions Changing to Hydroxyurea (TWiTCH): a multicentre, open-label, phase 3, non-inferiority trial. Lancet. 2016 Feb 13. 387 (10019):661-70. [Medline].
Walters MC, De Castro LM, Sullivan KM, Krishnamurti L, Kamani N, Bredeson C, et al. Indications and Results of HLA-Identical Sibling Hematopoietic Cell Transplantation for Sickle Cell Disease. Biol Blood Marrow Transplant. 2016 Feb. 22 (2):207-211. [Medline]. [Full Text].
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[Guideline] Liem RI, Lanzkron S, D Coates T, DeCastro L, Desai AA, Ataga KI, et al. American Society of Hematology 2019 guidelines for sickle cell disease: cardiopulmonary and kidney disease. Blood Adv. 2019 Dec 10. 3 (23):3867-3897. [Medline]. [Full Text].
[Guideline] DeBaun MR, Jordan LC, King AA, Schatz J, Vichinsky E, Fox CK, et al. American Society of Hematology 2020 guidelines for sickle cell disease: prevention, diagnosis, and treatment of cerebrovascular disease in children and adults. Blood Adv. 2020 Apr 28. 4 (8):1554-1588. [Medline]. [Full Text].
[Guideline] Chou ST, Alsawas M, Fasano RM, Field JJ, Hendrickson JE, Howard J, et al. American Society of Hematology 2020 guidelines for sickle cell disease: transfusion support. Blood Adv. 2020 Jan 28. 4 (2):327-355. [Medline]. [Full Text].
Kanter J, Liem RI, Bernaudin F, Bolaños-Meade J, Fitzhugh CD, Hankins JS, et al. American Society of Hematology 2021 guidelines for sickle cell disease: stem cell transplantation. Blood Adv. 2021 Sep 28. 5 (18):3668-3689. [Medline]. [Full Text].
Molecular and cellular changes of hemoglobin S.
Skeletal sickle cell anemia. H vertebrae. Lateral view of the spine shows angular depression of the central portion of each upper and lower endplate.
Peripheral blood with sickled cells at 400X magnification. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.
Peripheral blood smear with sickled cells at 1000X magnification. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.
Peripheral blood smear with Howell-Jolly body, indicating functional asplenism. Courtesy of U. Woermann, MD, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland.
Effects of therapy with hydroxyurea.
Skeletal sickle cell anemia. Bone-within-bone appearance. Following multiple infarctions of the long bones, sclerosis may assume the appearance of a bone within a bone, reflecting the old cortex within the new cortex.
A 12-year-old boy with HgbSS disease presents to the pediatric emergency department after his mother tried to wake him for school this morning and noted altered mental status, left-sided gaze paralysis with his head tilted to the left, and flaccid paralysis of the right arm and leg. A CT scan of the brain was obtained immediately.
Embolic stroke of the left middle cerebral artery. SCD is the most common cause of stroke in children and one of the most devastating complications of SCD. Clinically overt strokes are typically due to embolism of the intracranial internal carotid artery and proximal middle cerebral artery (MCA), while "silent strokes" more typically occur in the smaller lacunar and penetrating arteries. As RBCs undergo sickling and hemolysis within the cerebral circulation, they adhere to the vascular endothelium and promote a hypercoaguable state and fuel thromboembolism formation. Treatment options include prophylactic therapy with hydroxyurea to promote HgbF concentrations and monitoring via transcranial Doppler to evaluate MCA blood flow velocity. Children found to have high velocities are at increased risk for stroke and commonly receive RBC transfusions to decrease the concentration of HgbS.
The spleen enlarges during the first year of life in SCD, as it becomes congested with trapped slow-flowing sickled cells within the splenic sinuses and reticuloendothelial system. The histology image shown demonstrates splenic congestion from sequestered sickled RBCs (arrows). Microvascular occlusions produce chronic tissue hypoxia and microinfarctions. Over time, fibrosis induces autosplenectomy. With functional asplenia, patients are particularly susceptible to infection by the encapsulated organisms Streptococcus pneumoniae and Haemophilus influenzae. Vaccination and prophylactic daily penicillin throughout childhood are mainstays of treatment to prevent sepsis and meningitis
Splenic sequestration is an important cause of morbidity that occurs when sudden splenic pooling of blood within the reticuloendothelial system causes an acute drop in circulatory volume and shock-like symptoms (hypotension, tachycardia) with a rigid distended abdomen. It is an acute emergency and can be fatal in 1-2 hours secondary to circulatory hypovolemia. Treatment is with volume resuscitation and blood transfusion. The CT image shown demonstrates splenomegaly with a mass-like process (arrows) from splenic sequestration.
Patients with SCD are also at increased risk of developing pulmonary arterial hypertension (PAH). The etiology is most likely multifactorial but likely related to increased cardiac output secondary to underlying chronic anemia. Impedance to the elevated blood flow will cause further dilation and increase in pulmonary pressures. Postsickling changes including interstitial fibrosis secondary to vaso-occlusive crisis of ACS and hypoperfusion with resultant hypoxia of the pulmonary vascular beds are both proposed offenders inciting further dilation and elevation of pulmonary pressures. A pulmonary arteriogram depicting the markedly dilated vascular supply of the lungs seen in PAH is shown.
Proliferative sickle cell retinopathy. Sickle cell retinopathy is believed to be vaso-occlusion of peripheral arterioles of the retina leading to retinal hypoxia, ischemia, and infarction. New vessels then form at the junction of the vascular and avascular areas of retina. This neovascularization of retinal tissue and resultant traction of fibrovascularization places patients at risk for vitreous hemorrhage (arrows) and retinal detachment. Another common ocular manifestation is hyphema. Anterior chamber bleeding occurs spontaneously, but sickled erythrocytes obstruct the trabecular meshwork leading to significant elevations of intraocular pressure. Patients are particularly susceptible to glaucomatous optic nerve damage from even mildly elevated intraocular pressures. Pressures greater than 36 mm Hg for 24 hours are an indication for surgical drainage in both SCD and sickle cell trait, regardless of the size of hyphema. Image courtesy of the National Eye Institute, National Institutes of Health (NEI/NIH).
A 19-year-old man with known HgbSS disease presents because his girlfriend reports his eyes are yellow. He has no complaints. Physical exam is notable for mild abdominal pain, but is otherwise within normal limits. What imaging test is warranted for this work-up? The image shown is of a male child with similar symptoms. Image courtesy of Wikimedia Commons.
Right upper quadrant ultrasoundChronic hemolysis of sickled cells in HgbSS disease and high heme turnover yields hyperbilirubinemia and is associated with increased formation of bile stones. Stone formation occurs as substances in bile reach concentrations that approach the limits of their solubility. As saturation levels are reached, crystals precipitate, become trapped in mucus, and produce sludge (shown). Over time, the crystals aggregate and form stones. Occlusion of the biliary tree by sludge and/or stones produces clinical disease, typically right upper quadrant pain. The scleral icterus seen in the image of the previous slide is most likely secondary to the elevated circulating levels of bilirubin as a result of an acute hemolytic event (such as an acute vaso-occlusive crisis).
Renal papillary necrosisThe microvascular beds of the renal parenchyma are susceptible to sickling and vaso-occlusive crisis because of their inherent low-oxygen and high-osmolarity state. Depending on the location of occlusion, symptoms vary from a decreased ability to concentrate urine (yielding nocturia and polyuria), a disruption of exchange mechanisms (yielding hyperkalemia) or hematuria, which further damages renal tubules. In renal papillary necrosis, repeated vascular occlusion infarcts the renal medullary pyramids and papillae. This causes sloughing of papillae, which obstructs the urinary tract. Treatment options include hydration, high-dose antibiotics for resulting pyelonephritis, and possible percutaneous nephrostomy tube or invasive retrieval of sloughed papillae in acute urinary obstruction. The intravenous pyelogram demonstrates the "egg-in-a-cup" appearance of sloughed renal papillae (arrows) secondary to renal papillary necrosis.
Skeletal sickle cell anemia. Hand-foot syndrome. Soft tissue swelling with periosteal new-bone formation and a moth-eaten lytic process at the proximal aspect of the fourth phalanx.
Skeletal sickle cell anemia. Advanced dactylitis. Lytic processes are present at the first and fifth metacarpals, along with periostitis, which is most prominent in the third metacarpal.
Skeletal sickle cell anemia. Expanded medullary cavity. The diploic space is markedly widened due to marrow hyperplasia. Trabeculae are oriented perpendicular to the inner table, giving a hair-on-end appearance.
Skeletal sickle cell anemia. Detailed view of the expanded medullary cavity in the same patient as in the previous image.
Skeletal sickle cell anemia. Osteonecrosis. Image shows flattening of the femoral heads with a mixture of sclerosis and lucency characteristic of osteonecrosis.
Skeletal sickle cell anemia. Osteonecrosis. Detail of the right hip.
Skeletal sickle cell anemia. Osteonecrosis. Detail of the left hip.
Skeletal sickle cell anemia. Bone infarct. Image shows patchy sclerosis of the humeral head and shaft representing multiple prior bone infarcts.
Skeletal sickle cell anemia. Chronic infarcts and secondary osteoarthritis. Image shows advanced changes of irregular sclerosis and lucency on both sides of the knee joint reflecting numerous prior infarcts. The joint surfaces are irregular and the cartilages are narrowed due to secondary osteoarthritis.
Skeletal sickle cell anemia. Osteonecrosis. Coronal T1-weighted MRI shows a slightly flattened femoral head with a serpentine margin of low signal intensity around an area of ischemic marrow with signal intensity similar to that of fat.
Skeletal sickle cell anemia. Osteonecrosis in the same patient as in the previous image. Coronal T2-weighted MRI shows a serpentine area of low signal intensity and additional focal areas of abnormal low signal intensity in the femoral head; these findings reflect collapse of bone and sclerosis.
Skeletal sickle cell anemia. Osteomyelitis. CT scan in a soft tissue window demonstrates a large abscess in the left thigh encircling the femur, with hypoattenuating pus surrounded by a rim of vivid enhancement.
Skeletal sickle cell anemia. Osteomyelitis and bone-within-bone. Bone-window CT scan in the same patient as in the previous image shows a bone-within-bone appearance (concentric rings of cortical bone) in the right femur. On the left, a sinus tract (cloaca) traverses the lateral aspect of the femoral cortex, and a small, shardlike sequestrum is present deep to the sinus tract.
Skeletal sickle cell anemia. Bone scan of bone infarct shows an area of increased uptake in the distal femoral metaphysis corresponding to the infarct demonstrated on the previous plain radiograph.
Table. Schedule of Laboratory Tests for Patients With Sickle Cell Disease
CBC count with WBC differential,
reticulocyte count
>24 mo
every 3 mo
Percent Hb F
Renal function (creatinine, BUN, urinalysis)
≥ 12 mo
Hepatobiliary function (ALT, fractionated bilirubin)
Pulmonary function (transcutaneous O2 saturation)
Joseph E Maakaron, MD Research Fellow, Department of Internal Medicine, Division of Hematology/Oncology, American University of Beirut Medical Center, Lebanon
Ali T Taher, MD, PhD, FRCP Professor of Medicine, Associate Chair of Research, Department of Internal Medicine, Division of Hematology/Oncology, Director of Research, NK Basile Cancer Center, American University of Beirut Medical Center, Lebanon
Jeanne Yu, PharmD
Emmanuel C Besa, MD Professor Emeritus, Department of Medicine, Division of Hematologic Malignancies and Hematopoietic Stem Cell Transplantation, Kimmel Cancer Center, Jefferson Medical College of Thomas Jefferson University
Emmanuel C Besa, MD is a member of the following medical societies: American Association for Cancer Education, American Society of Clinical Oncology, American College of Clinical Pharmacology, American Federation for Medical Research, American Society of Hematology, New York Academy of Sciences
Mark Ventocilla, OD, FAAO Chief Executive Officer, Elder Eye Care Group, PLC; Chief Executive Officer, Mark Ventocilla, OD, Inc; President, California Eye Wear, Oakwood Optical
Mark Ventocilla, OD, FAAO is a member of the following medical societies: American Academy of Optometry, American Optometric Association
Roy Alson, MD, PhD, FACEP, FAAEM Associate Professor, Department of Emergency Medicine, Wake Forest University School of Medicine; Medical Director, Forsyth County EMS; Deputy Medical Advisor, North Carolina Office of EMS; Associate Medical Director, North Carolina Baptist AirCare
Roy Alson, MD, PhD, FACEP, FAAEM is a member of the following medical societies: Air Medical Physician Association, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, National Association of EMS Physicians, North Carolina Medical Society, Society for Academic Emergency Medicine, and World Association for Disaster and Emergency Medicine
Jeffrey L Arnold, MD, FACEP Chairman, Department of Emergency Medicine, Santa Clara Valley Medical Center
Jeffrey L Arnold, MD, FACEP is a member of the following medical societies: American Academy of Emergency Medicine and American College of Physicians
Robert J Arceci, MD, PhD King Fahd Professor of Pediatric Oncology, Professor of Pediatrics, Oncology and the Cellular and Molecular Medicine Graduate Program, Kimmel Comprehensive Cancer Center at Johns Hopkins University School of Medicine
Robert J Arceci, MD, PhD is a member of the following medical societies: American Association for Cancer Research, American Association for the Advancement of Science, American Pediatric Society, American Society of Hematology, and American Society of Pediatric Hematology/Oncology
Wadie F Bahou, MD Chief, Division of Hematology, Hematology/Oncology Fellowship Director, Professor, Department of Internal Medicine, State University of New York at Stony Brook
Wadie F Bahou, MD is a member of the following medical societies: American Society of Hematology
Dvorah Balsam, MD Chief, Division of Pediatric Radiology, Nassau University Medical Center; Professor, Department of Clinical Radiology, State University of New York at Stony Brook
Salvatore Bertolone, MD Director, Division of Pediatric Hematology/Oncology, Department of Pediatrics, Kosair Children's Hospital; Professor, University of Louisville School of Medicine
Salvatore Bertolone, MD is a member of the following medical societies: American Academy of Pediatrics, American Association for Cancer Education, American Association of Blood Banks, American Cancer Society, American Society of Hematology, American Society of Pediatric Hematology/Oncology, and Kentucky Medical Association
Barry E Brenner, MD, PhD, FACEP Professor of Emergency Medicine, Professor of Internal Medicine, Program Director, Emergency Medicine, Case Medical Center, University Hospitals, Case Western Reserve University School of Medicine
Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences,and Society for Academic Emergency Medicine
Marcel E Conrad, MD Distinguished Professor of Medicine (Retired), University of South Alabama College of Medicine
Marcel E Conrad, MD is a member of the following medical societies: Alpha Omega Alpha, American Association for the Advancement of Science, American Association of Blood Banks, American Chemical Society, American College of Physicians, American Physiological Society, American Society for Clinical Investigation, American Society of Hematology, Association of American Physicians, Association of Military Surgeons of the US, International Society of Hematology, Society for Experimental Biology and Medicine, and Southwest Oncology Group
Disclosure: No financial interests None None
Nedra R Dodds, MD Medical Director, Opulence Aesthetic Medicine
Nedra R Dodds, MD is a member of the following medical societies: American Academy of Anti-Aging Medicine, American Academy of Cosmetic Surgery, American College of Emergency Physicians, American Medical Association, National Medical Association, and Society for Academic Emergency Medicine
James L Harper, MD Associate Professor, Department of Pediatrics, Division of Hematology/Oncology and Bone Marrow Transplantation, Associate Chairman for Education, Department of Pediatrics, University of Nebraska Medical Center; Assistant Clinical Professor, Department of Pediatrics, Creighton University School of Medicine; Director, Continuing Medical Education, Children's Memorial Hospital; Pediatric Director, Nebraska Regional Hemophilia Treatment Center
James L Harper, MD is a member of the following medical societies: American Academy of Pediatrics, American Association for Cancer Research, American Federation for Clinical Research, American Society of Hematology, American Society of Pediatric Hematology/Oncology, Council on Medical Student Education in Pediatrics, and Hemophilia and Thrombosis Research Society
Adlette Inati, MD Head, Division of Pediatric Hematology-Oncology, Medical Director, Children's Center for Cancer and Blood Diseases, Rafik Hariri University Hospital; Research Associate, Balamand University; Head of Post Bone Marrow Transplant Clinic and Consultant Hematologist, Chronic Care Center; Founding Faculty, Lebanese American University School of Medicine, Lebanon
Adlette Inati, MD is a member of the following medical societies: Alpha Omega Alpha, American Society of Hematology, European Hematology Association, and International Society of Hematology
Ziad N Kazzi, MD Assistant Professor, Department of Emergency Medicine, Emory University; Medical Toxicologist, Georgia Poison Center
Ziad N Kazzi, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Emergency Physicians, and American College of Medical Toxicology
Ashok B Raj, MD Associate Professor, Section of Pediatric Hematology and Oncology, Department of Pediatrics, Kosair Children's Hospital, University of Louisville School of Medicine
Ashok B Raj, MD is a member of the following medical societies: American Academy of Pediatrics, American Society of Pediatric Hematology/Oncology, Children's Oncology Group, and Kentucky Medical Association
Sharada A Sarnaik, MBBS Professor of Pediatrics, Wayne State University School of Medicine; Director, Sickle Cell Center, Attending Hematologist/Oncologist, Children's Hospital of Michigan
Sharada A Sarnaik, MBBS is a member of the following medical societies: American Association of Blood Banks, American Association of University Professors, American Society of Hematology, American Society of Pediatric Hematology/Oncology, New York Academy of Sciences, and Society for Pediatric Research
Hosseinali Shahidi, MD, MPH Assistant Professor, Departments of Emergency Medicine and Pediatrics, State University of New York and Health Science Center at Brooklyn
Hosseinali Shahidi, MD, MPH is a member of the following medical societies: American Academy of Pediatrics, American College of Emergency Physicians, and American Public Health Association
Garry Wilkes MBBS, FACEM, Director of Emergency Medicine, Calvary Hospital, Canberra, ACT; Adjunct Associate Professor, Edith Cowan University; Clinical Associate Professor, Rural Clinical School, University of Western Australia
Mary L Windle, PharmD, Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Ulrich Josef Woermann, MD Consulting Staff, Division of Instructional Media, Institute for Medical Education, University of Bern, Switzerland
Grace M Young, MD Associate Professor, Department of Pediatrics, University of Maryland Medical Center
Grace M Young, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Emergency Physicians
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redpajama_set_name: RedPajamaCommonCrawl


The WordPress editor hasn't seen big changes over the years since its creation. Now we are seeing a complete revamp of the editing experience with the WordPress new editor – Gutenberg. The name coming from Johannes Gutenberg, who introduced printing to Europe with the printing press movable type in 1439.
This project is being developed as Gutenberg plugin has plans to be merged to WordPress core around August as announced in WordCamp Europe by Matt Mullenweg (WordPress founder).
There are lots of resources out there talking about Gutenberg, what is it, how to use it, and how to extend and develop on top of it. In this article, I will not add to those great resources but instead will talk about how we – WordPress Beirut Community, contributed to this project by translating it into Arabic.
In Beirut, Lebanon I initiated the first WordPress Meetup in July 2017 (1 year ago), we were meeting monthly to discuss WordPress related topics varied from beginner to advanced level. After 12 monthly meetups, the community was mature enough to start something new! Something that will engage more people. We – wpBeirut Meetup organizers – agreed that we need to increase members familiarity with contributing to Open Source, but we need an easy starting point, a place where the members can feel engaged and can contribute without a high prerequisite level of skills. Here came WordPress Translations!
We decided to meet monthly and contribute for 2 hours/month to WordPress Translations, believing that doing something small and continuous will have good results. At the end, we were able to increase the progress of the Arabic Gutenberg translations from 8% to 100%.
On 19 June we gathered at a coffee shop, 6 of the community members showed up after our call to volunteer. We were able to complete till 59% of the strings during 2 hours.
On 19 July we gathered for the second time in the same coffee shop and again 6 members showed up. This time we were able to complete 100% of the strings during another 2 hours.
Do you want to contribute to WordPress Translations? Check the First Steps here.


text:
Eadwine est un ealdorman du Sussex mort en 982.

Il apparaît comme témoin sur une charte du roi Æthelred le Malavisé en 982, ainsi que sur une autre charte, probablement fausse, datée de 956 (peut-être une erreur pour 976). Les deux chartes l'appellent Eaduuine dux. Le manuscrit C de la Chronique anglo-saxonne, rédigé à l'abbaye d'Abingdon, indique qu'il est mort en 982 et a été inhumé dans cette même abbaye.

Références

Bibliographie

 .

Liens externes

  Eadwine sur

Ealdorman
Décès en 982
Personnalité anglaise du Xe siècle

redpajama_set_name: RedPajamaWikipedia


The Epson 1-Year Replacement Extended Service Contract for Business Scanners Valued up to $100 extends the existing 1-year limited warranty to two (2) years from the original product purchase date. This 1-year Extended Service Plan must be purchased while the product is covered under the standard warranty. Coverage with this option expires two (2) years from the original product purchase date.


text:
I Khleang sono due edifici simili costruiti sul lato orientale della piazza reale di Angkor Thom, ad Angkor in Cambogia.

Il nome significa "il tempio deposito", ma è improbabile siano serviti a tale scopo e il loro utilizzo è sconosciuto. Inoltre furono costruiti in date diverse. Si pensa che il Khleang settentrionale sia stato costruito per primo, durante il regno di Jayaviravarman, ivi menzionato in numerose iscrizioni, o di Jayavarman V. Ha forma cruciforme, con un lato lungo in senso N-S di 40 metri per 4,7 e una torre centrale sul ramo breve a dividere in due la lunga sala.

Il Khleang meridionale fu costruito durante il regno di Suryavarman I, salito al potere dopo un periodo di guerra civile, forse per ragioni di simmetria. La forma della pianta è circa la stessa (manca la suddivisione interna presente in quello nord) ma la larghezza è minore, solo 4,2 metri. Risulta inoltre costruito con cura minore e non completato.

Le costruzioni non hanno tetto ma sono presenti dei buchi che indicano la presenza di un tetto ligneo. Travi di legno furono usate anche per sostenere gli architravi, che crollarono dopo il deterioramento del materiale organico.

La sobrietà delle linee, la mancanza di decorazioni esterne nonché i caratteristici capitelli e architravi, che riportano un makara centrale, hanno portato all'identificazione di uno stile architettonico che da essi ha preso il nome e comprende anche Ta Keo e Phimeanakas.

Note

Bibliografia

Voci correlate
Architettura della Cambogia

Altri progetti

Collegamenti esterni

Siti archeologici della Cambogia
Siti archeologici angkoriani


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