The pattern of breathing in man in response to sine waves of alveolar carbon dioxide and hypoxia.

Abstract

Sine waves of alveolar CO2 at constant high alveolar O2, and sine waves of alveolar hypoxia (1/(PA, O2 -C) where C congruent to 32 torr) at constant alveolar CO2 have been administered to three subjects in each case. Six different periods of the sine waves were studied, ranging between 900 and 30 s for the CO2 sine waves and 300 and 20 s for the hypoxic sine waves. The sinusoidal variations in inspiratory and expiratory volumes (VT, I, VT, E), durations (TI, TE) and mean flows (vI, vE) produced by these manoeuvres were calculated, and the results analysed from the phase shifts of the responses. For the CO2 sine-wave results, the peak in the TI oscillation generally appeared after the minima for VT, I and vI, but before their maxima. The peak in the TE oscillation was variable. For the hypoxic sine-wave results, the peak in the TI oscillation showed no over-all tendency to lead or lag the peaks of VT, I and vI. The peak in the TE oscillation generally appeared after the maxima for VT, E and vE but before their minima. For the CO2 sine-wave results, expiratory mean flow led inspiratory mean flow, with the volumes showing no significant difference. For the hypoxic sine-wave results expiratory volumes and mean flows led inspiratory volumes and mean flows. The results are discussed in relation to the transient responses of the components of breathing pattern obtained from other perturbations of chemical drive.