Lung compliance is greatest at/during:
Static compliance of the lung is 200 mL/cm H2O. However, the compliance goes on changing with stages of a respiratory cycle. This changing compliance is 'dynamic compliance' of the lung. At the sta of inspiration, with smaller diameter of the alveoli, the surfactant molecules are concentrated over a small surface area; it makes the surfactant more effective in reducing the surface tension. Lower the surface tension, less is the collapsibility and greater is the distensibility (i.e., compliance). By the end of inspiration (with enlarged alveoli), surfactant molecules spread, making the surfactant less efficient in reducing surface tension. Greater the surface tension, lower is the compliance. However, if inspiration and expiration are compared, compliance will be more during expiration. During expiration, alveoli are becoming small and concentrating the surfactant molecules. The surface tension will be low; compliance will be high during expiration. So the lung compliance is greatest at the end of expiration.
Sta of inspiration
Mid-inspiration
End-inspiration
End-expiration
Respiratory System Pa 1