A theoretical study of the effect of circadian rhythms on sleep-induced periodic breathing and apnoea.

This study employed a mathematical model of the respiratory control system to test the plausibility of the hypothesis that circadian rhythms in respiratory control can significantly influence respiratory stability at sleep onset. Computer simulations utilized a standardized "normal" sleep onset effect, superimposed upon systematic changes in chemoreflex parameters that mimicked the peaks and troughs of normal and high amplitude circadian rhythms. The analysis predicted that circadian influences may augment sleep-induced periodic breathing in nocturnal sleep compared with daytime naps. Furthermore, increased circadian amplitude of chemoreflex threshold, or absence of a circadian rhythm in peripheral chemosensitivity, each acted to stabilize respiration during daytime sleep onset and promote periodic breathing during nocturnal sleep onset. High amplitude circadian rhythms in respiratory control were predicted to cause an increasing number and duration of obstructive apnoeas from early to late night. It is suggested that the circadian timing system creates a nocturnal window of respiratory vulnerability and that abnormal circadian rhythms could potentially induce nocturnal sleep apnoea, even in individuals with normal sleep mechanisms.