Immediate human breathing pattern responses to loads near the perceptual threshold

Abstract

Breathing pattern responses to small mechanical loads added pseudorandomly to the external airway of human subjects were measured using flow-resistive and elastic loads above and below the threshold for detectability of some subjects. The zeroth lag of the computed cross-correlations between the loading sequence and the various aspects of the breathing pattern response was used as an index of the immediate response to loading. All subjects showed an immediate reduction in tidal volume (VT) and expiratory duration (TE) in response to elastic loading, but inspiratory duration (TI) responded variably. Respiratory frequency (f) was increased, and minute ventilation (V) and mean inspiratory flow (VT/TI) decreased immediately in all subjects. Resistance loading, on the other hand, tended to prolong TI and TE immediately such that f fell. VT responses were variable, and both V and VT/TI fell. The responses to imperceptible loads reflect mainly the action of neural reflexes and characteristics intrinsic to the respiratory muscles and configuration of the chest and abdomen. A mathematical simulation was used to show that the TE responses in particular may indicate the action of subconscious neural reflexes.