Some Effects of Respiratory Frequency on Pulmonary Mechanics*

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Abstract
This study was undertaken to determine the effect of respiratory frequency on the pulmonary mechanics of normal adults. Nine healthy young adults sat in a body plethysmo-graph with the head protruding while respiration was driven by sinusoidal plethysmograph pressures at a series of frequencies from 10 to 132 cycles per minute. Esophageal and plethysmograph pressures and air flow rate and volume were measured simultaneously. The total thoracic, pulmonary, and chest wall compliances and resistances decreased as frequency of respiration increased. The variations are significant over a wide but not narrow range of frequencies. The total thoracic, pulmonary, and chest wall impedances decreased with increasing respiratory frequency and approached their respective resistances at the higher frequencies. The phase angle between pressure and flow and the time constant also varied inversely with frequency. The absolute values are generally consistent with previous observations at isolated frequencies. The results support the concept that pulmonary compliance and resistance are frequency dependent even in normal subjects.