Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. The body normally attempts to compensate for this homeostatically, but if this fails or is overridden, the blood pH will rise, leading to respiratory alkalosis. The symptoms of respiratory alkalosis include: dizziness, tingling in the lips, hands or feet, headache, weakness, fainting, and seizures. In extreme cases it may cause carpopedal spasms, a flapping and contraction of the hands and feet.Factors that may induce or sustain hyperventilation include: physiological stress, anxiety or panic disorder, high altitude, head injury, stroke, respiratory disorders such as asthma, pneumonia, or hyperventilation syndrome, cardiovascular problems such as pulmonary embolisms, anemia, an incorrectly calibrated medical respirator, and adverse reactions to certain drugs. Hyperventilation can also be  induced intentionally to achieve an altered state of consciousness such as in the choking game, during breathwork, or in an attempt to extend a breath-hold dive. See also
List of terms of lung size and activity
Control of respiration
Choking game a game which may involve hyperventilation in order to induce temporary syncope and euphoria
Respiratory alkalosis
Kussmaul breathing
Shallow water blackout, the role of hyperventilation in some drowning incidents

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Cervical lymphadenopathy refers to lymphadenopathy of the cervical lymph nodes (the glands in the neck). The term lymphadenopathy strictly speaking refers to disease of the lymph nodes, though it is often used to describe the enlargement of the lymph nodes. Similarly, the term lymphadenitis refers to inflammation of a lymph node, but often it is used as a synonym of lymphadenopathy. Cervical lymphadenopathy is a sign or a symptom, not a diagnosis. The causes are varied, and may be inflammatory, degenerative, or neoplastic. In adults, healthy lymph nodes can be palpable (able to be felt), in the axilla, neck and groin. In children up to the age of 12 cervical nodes up to 1 cm in size may be palpable and this may not signify any disease. If nodes heal by resolution or scarring after being inflamed, they may remain palpable thereafter. In children, most palpable cervical lymphadenopathy is reactive or infective. In individuals over the age of 50, metastatic enlargement from cancers (most commonly squamous cell carcinomas) of the aerodigestive tract should be considered. Classification
Cervical lymphadenopathy can be thought of as local where only the cervical lymph nodes are affected, or general where all the lymph nodes of the body are affected. Causes
Infection
Pericoronitis
Staphylococcal lymphadenitis
Mycobacterial lymphadenitis
Rubella
Cat scratch fever
Infectious mononucleosis
Streptococcal pharyngitis
Viral respiratory infection
Toxoplasmosis
Tuberculosis
Brucellosis
Primary herpes simplex infection (primary herpetic gingivostomatitis)
Syphilis (secondary)
Cytomegalovirus
Human immunodeficiency virus
Histoplasmosis
Chicken pox

Malignancy
Lymph nodes may become enlarged in malignant disease. This cervical lymphadenopathy may be reactive or metastatic.