Mechanical factors in breathing pattern regulation in humans.

Abstract

The adult human breathing pattern is a complex product of neural, humoral, and perceptual factors, each of which is influenced by changes in the respiratory mechanics. The regulation of this pattern is qualitatively consistent with hypotheses based upon optimization criteria and involves alteration of both the respiratory frequency (f) and tidal volume (VT) as their product of minute ventilation ( $$\dot V$$ ) varies. The particular f-VT relationship followed both in theory and observed response is influenced by changes in respiratory mechanics produced by loading. Within the breath, volume and durations of inspiration and expiration also respond to applied loads. The inspiratory terminating threshold curve is shifted to the left by elastic (E) loading and to the right by flow resistive (R) loading. Regulation of the end-expiratory volume (EEV) is provided by regulation of laryngeal resistance, control of inspiratory muscle tone during expiration, and activation of expiratory muscles. Separation of the contributions of humoral, subconscious neural, and perceptual reflexes responding to loading is important to enable assessment of the effects of sleep or pathology upon specific aspects of pattern regulation. A loading technique is described that permits the reliable estimation of breathing pattern responses to mechanical loads below the threshold for conscious perception, producing immediate response estimates attributable only to neural reflexes and intrinsic muscle characteristics.