Sleep apnea and its causes.

Perspectivesver long periods oftime, months and years, arterial Pco2 and P02 are closely regulated, but over shorter periods, constancy of arterial blood gas tensions is perhaps an impractical or even an undesirable objective.It is now appreciated that fluctuation within limits is an inherent feature ofnormal function and that there are cycles of activity and rest that modify re- spiratory regulation as well as other regulatory processes (1, 2).Many of these cycles, like the sleep-waking cycle, are circadian, with a period of -24 h, and seem to be keyed to the revolution of the earth.Sleep, like breathing, seems to be essential to health, and adverse physiological and psychological consequences occur with sleep deprivation (3, 4).However, the need to adjust breathing to physiological requirements during both sleep and wakefulness complicates the task of the respiratory control system because sleep alters the response characteristics of the respiratory con- troller and the performance of the respiratory muscles.There may be a hierarchy of neurological organization that governs physiological regulations that determines priorities and arbitrates among conflicting demands as activity levels change.In some individuals with the sleep apnea syndrome, adequate sleep and sufficiently stable breathing, both necessary to prevent dangerous fluctuations in blood gas tensions, seem to be in- compatible (5,6).Sleep is interspersed with periods when airflow stops and profound hypoxemia develops.Sometimes it seems as if death is averted only by arousal and the termination of sleep.While the biochemical basis of neither sleep nor breathing are known, much has been learned in recent years about sleep and about the mechanisms by which it affects respiratory control.Several effective methods of treatment of the sleep apnea syn- drome have been developed based on our understanding of the effects of sleep on breathing.Breathing during sleep.Neither sleep nor wakefulness are uniform states.Even in awake individuals, cyclic changes in breathing with both long and short periods can be obvious at altitude and can be discerned at sea level by sophisticated math-