Control of arrhythmic breathing in aerial breathers

Arrhythmic breathing patterns of two basic types occur among the air-breathing vertebrates. These patterns, which appear to be dependent more on inputs from peripheral receptor groups than on a central generator, allow significant fluctuations in the partial pressures of O2 and CO2 in lungs, blood, and tissues with accompanying fluctuations of pH in body fluids. The major components of each pattern are the size and timing of each breath, the length of each episode of breathing, and the length of the pause between episodes of breathing. While each of these components appears to be under separate control, the relative roles of the various receptor groups in the control of each remain unclear. Similarities between data collected from reptiles and hibernating mammals suggest that the arrhythmic breathing patterns seen under physiological conditions in all air-breathing vertebrates may be manifestations of a common control system. The conversion from continuous to arrhythmic breathing seen in mammals entering hibernation further suggests that both continuous and arrhythmic breathing are manifestations of a common control system. The two distinct arrhythmic breathing patterns appear to arise from differences in the supramedullary integration of vagal input in different species. It is suggested that under conditions of reduced metabolic demand, these arrhythmic breathing patterns may represent an adaptive strategy which, in part, serves to reduce the energetic cost of ventilation.