Ventilatory response to high-frequency airway oscillation in humans

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Abstract
To investigate respiratory control during high-frequency oscillation (HFO), ventilation was monitored in conscious humans by respiratory inductive plethysmography during application at the mouth of high-frequency pressure oscillations. Studies were conducted before and after airway and pharyngeal anesthesia. During HFO, breathing became slow and deep with an increase in tidal volume (VT) of 37% (P < 0.01) and inspiratory duration (TI) of 34% (P < 0.01). Timing ratio (TI/TT) increased 14% (P < 0.05) and respiratory frequency (f) decreased 12% (P < 0.01). Mean inspiratory flow (VT/TI) did not change during HFO. Following airway anesthesia, VT increased only 26% during HFO (P < 0.01), whereas significant changes in TI, TI/TT, and f were not observed. Pharyngeal anesthesia failed to diminish the effect of HFO on TI, TT or f, although the increase in VT was reduced. HFO presented in this manner alters inspiratory timing without affecting the level of inspiratory activity. Receptors in the larynx and/or lower airways may in part mediate the response.