Temporal variations in the pattern of breathing.

Breath-to-breath variations in the pattern of breathing can occur as uncorrelated random variations ("white noise"), correlated random changes, or as one of two types of nonrandom variations: periodic oscillations or nonrandom nonperiodic fluctuations. White noise is probably present in all physiological processes. In many cases, periodic variations are due to oscillations originating in chemoreflex feedback loops. It has long been hypothesized that correlated random variations in breathing pattern are due to central neutral "memory" mechanisms, but part of this behavior might be due to chemoreflex mechanisms. Recently it has been concluded that nonlinear interactions between pulmonary and airway afferent activities and integrative central respiratory mechanisms can produce nonrandom nonperiodic (and also periodic) variability of the respiratory pattern. These latter studies have provided new insights about the behavioral relevance of the integrative character of central respiratory mechanisms and the time-varying nature of pulmonary afferent activities and have emphasized the importance of identifying the physiological bases for these phenomena. These and other findings are interpreted assuming that respiratory rhythm generation/pattern formation occurs via a nonlinear oscillator, and novel inferences concerning temporal variations of the breathing pattern are proposed.