The Maximum Expiratory Flow Rate and Volume Dependent Respiratory Resistance in Small Airway Obstruction

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Abstract
In 8 healthy subjects (group A) and 4 subjects with respiratory symptoms (group B), the lung pressure-volume curve (P-V curve), maximum expiratory flow-volume curve (MEFVC) and respiratory resistance (Rrs) at all vital capacities were measured. To avoid laryngeal artifact on a mouth pressure, an intratracheal catheter was used for measurement of Rrs which was obtained with 3 cps oscillatory forced pressure. Group B did not show a different elastic recoil from group A. In comparison of the maximum expiratory flow .ovrhdot.V max at 80, 70, 60 and 50% of the total lung capacity (TLC), .ovrhdot.V max of group B showed lower values than that of group A. Rrs was almost the same in both groups from 70% TLC upwards, but Rrs of group B was higher than that of group A from 65% TLC downwards. Since the lung elastic recoil pressures (Pst (1)) in the 2 groups were not different and Rrs''s were different significantly only at low lung volumes, the decrease in .ovrhdot.V max of group B was supposed to be due to the increased Rrs which might reflect small airway obstruction.

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