Lung compliance and its transient elevations measured with pulse-flow method

Abstract

A pulse-flow method of measuring static lung compliance (CL) [sensitive to rapid transients in CL] is described. CL is measured by blowing air at a constant flow into the mouth and lungs for 2 s and calculated by dividing airflow in 1/s by the change in transpulmonary pressure in cm H2O/s. Pulse and static inspiratory CL was measured in 5 normals, 4 obstructives, 5 obese and 2 patients with pulmonary fibrosis. Pulse CL after tidal breathing was correlated with static CL measured after deep breaths (r = 0.96). Pulse CL after deep breaths was higher than pulse CL after tidal breathing (P < 0.01) and than static CL after deep breaths (P < 0.05). In all subjects the lower the forced expiratory volume in 1 s, expressed as a percentage of vital capacity (FEV1/FVC), the greater the increase in pulse CL after a deep breath will be (r = 0.93). After deep breaths pulse CL fell from maximum CL to base-line CL at a rate related to 1/t2 where t equals the time in seconds from the last deep breath. The increase in CL after a deep breath is related to the degree of airway obstruction; the subsequent fall in CL is related to 1/t2.