<prompt> Slope of pressure volume curve of lung represents:Compliance of lungConductanceSurface tensionTranspulmonary pressure  <response>: Ans. a Compliance of lung. Ref. Ganong Physiology 23rd pg. 654-657; Figure 35-10Lung compliance is an index of lung distensibility or the ease with which the lungs are expanded; thus, compliance is the inverse of elastic recoil. Compliance is defined as the ratio of change of lung volume to the change in pressure required to inflate the lung dVdP. Compliance decreases in patients with pulmonary edema or surfactant deficiency and increases when there is a loss of elastic fibers in the lungs, such as occurs in patients with emphysema and with aging.MECHANICS OF BREATHING - Compliance of the lungs chest wall Curve of airway pressure plotted against volume, is 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 relaxation volume, which equals the functional residual capacity. It is positive at greater volumes and negative at smaller volumes. The change in lung volume per unit change in the airway pressure DVDP is the stretchability compliance of the lungs and chest wall.Q It is normally measured in the pressure range where the relaxation pressure curve is steepest, and the normal value is approximately 0.2 Lcm H2O. The curve is shifted downward and to the right compliance is decreased by pulmonary congestion and interstitial pulmonary fibrosis; pulmonary fibrosis is a progressive 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. Two major forces contribute to lung compliance:o tissue elastic forces ando surface tension forces.Q 