In1959,AveryandMeaddiscoveredthatinprematureinfantswhodiedofhyalinemembranedisease(HMD),thelungsweredeficientinsurfactant.HMD,alsoknownasinfantrespiratory distress syndrome, ischaracterizedbyprogressiveatelectasisandrespiratoryfailureinprematureinfants.Itisamajorcauseofmorbidityandmortalityintheneonatalperiod.Themajorsurfactantdeficiencyinpremature 1.
Gas flows from areas of higher pressure to areas of lower pressure. Positive transpulmonary pressure is needed to increase lung volume. The pressure across the respiratory system is 0 at points of no airflow (end inspiration and end exhalation). At functional residual capacity (FRC), the pressure difference across the respiratory system is 0, and lung elastic recoil pressure, which operates to decrease lung volume, and the pressure generated by the chest wall to become larger are equal and opposite.
2.
Pressure gradients in the respiratory system are created by the active contraction and subsequent relaxation of the muscles of respiration.
3.
Lung volumes are determined by the balance between the lung’s elastic recoil properties and the properties of the muscles of the chest wall.
Gibson GJ, Pride NB. Lung distensibility: the static pressurevolume curve of the lungs and its use in clinical assessment. Br J Dis Chest. 1976;70:143184.
Jobe AH. The alveolar lining layer: a review of studies on its role in pulmonary mechanics and in the pathogenesis of atelectasis, by Mary Ellen Avery, MD, Pediatrics, 1962:30:324330. Pediatrics. 1998;102(S1):234235.
infantsislackofphosphatidylglycerol.Ingeneral,asthelevelofphosphatidylglycerolincreasesinamnioticfluid,theinfantmortalityratedecreases.ResearchinthisfieldhasculminatedinsuccessfulattemptstotreatHMDinprematureinfantswithsurfactantreplacementtherapy.Today,surfactantreplacementtherapyisstandardcareforprematureinfants.
4.
Total lung capacity (TLC) is equal to the total volume of air that can be exhaled after a maximal inspiration (vital capacity [VC]) and the air remaining in the lung after a maximal exhalation (residual volume [RV]).
5.
Lung compliance is a measure of the elastic properties of the lung. Elastic recoil is lost in patients with emphysema, and this loss is associated with an increase in lung compliance, whereas in diseases associated with pulmonary fibrosis, lung compliance is decreased.
6.
The surface tensionreducing and antisticking properties of surfactant increase lung compliance, decrease the work of breathing, and help stabilize alveoli of different size.
Lumb AB. Nunn’s Applied Respiratory Physiology. 8th ed. St. Louis: Elsevier; 2016.
Mead J, Macklem PT, vol eds. American Physiological Society Handbook of Physiology: The Respiratory System, vol. 3: Mechanics. Bethesda, MD: American Physiological Society; 1986.
Otis AB. A perspective of respiratory mechanics. J Appl Physiol. 1983;54:11831187.
Otis AB, Fenn WO, Rahn H. Mechanics of breathing in man. J Appl Physiol. 1950;2:592607.
Upon completion of this chapter the student should be able to answer the following questions: 1.
Describe air flow in the airways.
2.
Define resistance and its affect upon airflow in the airways.
3.
List and describe two categories of factors that contribute to airway resistance.
4.
List the features of a spirogram and flow volume curve.
5.