Human breathing pattern responses to loading with increased background impedance.

We determined the influence of the background level of mechanical impedance on the respiratory responses to very small mechanical loads, at or below the threshold for conscious perception. We used a pseudorandom load application technique to estimate the immediate pattern responses from the zeroth lag of the cross correlation between the load application sequence and the respiratory pattern components of tidal volume (VT), inspiratory and expiratory time (TI and TE), and the instantaneous respiratory frequency (f), minute ventilation (VI), and mean inspiratory flow (VT/TI). Elevation of the background resistance served to reduce the TI and TE responses to small perturbations in resistance from those in the control background state, which resulted in generally smaller perturbations of f, VI, and VT/TI. Elevation of the background elastance, however, served to initiate a TI reduction not seen in the control state but did not appreciably affect the rest of the pattern responses to the load perturbations. Thus the neural reflexes involved in breath-by-breath pattern regulation are modulated by the background level of the respiratory impedance, as well as by the type and size of the load perturbation.