Respiratory muscle activation by chemical stimuli in awake and sleeping dogs.

The present findings in awake and sleeping dogs confirm the early observations in anesthetized cats (Bainton et al., 1978; Sears et al., 1982), and more recent studies in awake and sleeping humans (Takasaki et al., 1989), that suggest an asymmetry in pattern of respiratory motoneuron and muscle activation by central and peripheral chemoreceptor stimulation, with central chemoreceptor stimulation driving both inspiratory and expiratory mechanisms, and peripheral chemoreceptor stimulation driving inspiratory and inhibiting expiratory mechanisms. Because REM sleep inhibits the nondiaphragmatic muscles, which include the expiratory muscles, there is a reduction in CO2 response during this sleep stage. In contrast because the response to hypoxia is mediated predominantly by the diaphragm, which is not generally inhibited by REM sleep, there is less effect of REM sleep on the overall response to hypoxia. In addition to being of basic importance, these concepts may have important clinical implications.