Lung tissue resistance and pulmonary hysteresis.

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Abstract
Using a plethysmographic method, lung tissue resistance (Rlt) was determined in 5 healthy subjects breathing at 5 different breathing patterns. By measuring at a constant mean flow rate of about 0.5 liter/sec., a direct relationship between Rlt and the size of the tidal volume was found. In subjects breathing with similar tidal volumes, only a slight increase of work done per breath against Rlt could be detected by doubling the mean flow rate; accordingly, Rlt, expressed in centimeters H2O/liter/sec., was considerably lower in hyperventilating subjects. Very high values of Rlt were obtained near full inspiratory position when breathing with medium-sized tidal volumes. These observations and the previously stated inverse relationship between Rlt and the vital capacity or the compliance, respectively, suggest the interpretation that Rlt is not an ohmic resistance, but that its value, as determined by the method described, mainly represents the degree of retarded elastic response of the lung. Therefore, an attempt was made to explain these findings on the basis of well-known phenomena such as nonflow resistive volume-pressure hysteresis and stress relaxation.