Lung compliance is:
Correct Answer: dV/dP
Description: Ans. B.dV/dP (Ref. Ganong Physiology 23rd/ pg. 654-657; Figure 35-10). The change in lung volume per unit change in the airway pressure (DV/DP) is the stretchability (compliance) of the lungs and chest wall.0 It is in pulmonary fibrosis, pneumonia, and pulmonary edema; increased in emphysema and normal aging. COMPLIANCE OF THE LUNGS & CHEST WALL # The interaction between the recoil of the lungs and recoil of the chest can be demonstrated in living subjects through a spirometer that has a valve just beyond the mouthpiece. # The respiratory muscles are then relaxed while the pressure in the airway is recorded. The procedure is repeated after inhaling or actively exhaling various volumes. The curve of airway pressure obtained in this way, plotted against volume, is the relaxation pressure curve of the total respiratory system. # The pressure is zero at a lung volume that corresponds to the volume of gas in the lungs at the end of quiet expiration (functional residual capacity, or FRC; also known as relaxation volume). It is positive at greater volumes and negative at smaller volumes. # The change in lung volume per unit change in airway pressure (V/P) is the compliance (stretchability) of the lungs and chest wall. It is normally measured in the pressure range where the relaxation pressure curve is steepest, and the normal value is approximately 0.2 L/cm H-,0. However, compliance depends on lung volume; an individual with only one lung has approximately half the V for a given P. # Compliance is also slightly greater when measured during deflation than when measured during inflation. Consequently, it is more informative to examine the whole pressure - volume curve. # The curve is shifted downward and to the right (compliance is decreased) by pulmonary congestion and interstitial pulmonary fibrosis. Pulmonary fibrosis is a progressive restrictive airway disease of unknown cause in which there is stiffening and scarring of the lung. The curve is shifted upward and to the left (compliance is increased) in emphysema. It should be noted that compliance is a static measure of lung and chest recoil. # The resistance of the lung and chest is the pressure difference required for a unit of air flow; this measurement, which is dynamic rather than static, also takes into account the resistance to air flow in the airways. Educational point: The total compliance of both lungs together in the normal adult human being averages about 200 mil- liliters of air %imeter of water transpulmonary pressure. That is, every time the transpulmonary pressure increases 1 centimeter of water, the lung volume, after 10 to 20 seconds, will expand 200 milliliters.
Category:
Unknown
Get More
Subject Mock Tests
Practice with over 200,000 questions from various medical subjects and improve your knowledge.
Attempt a mock test nowMock Exam
Take an exam with 100 random questions selected from all subjects to test your knowledge.
Coming SoonGet More
Subject Mock Tests
Try practicing mock tests with over 200,000 questions from various medical subjects.
Attempt a mock test now