Central respiratory carbon dioxide chemosensitivity does not decrease during sleep

The ventilatory response to CO2 decreases during slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep compared with awake levels. However, it is not known to what extent this can be attributed to decreased sensitivity of the CO2 chemoreflex. Mechanical factors during sleep may decrease ventilatory output, or PCO2 at the central chemoreceptor may not increase to the same degree as PaCO2, particularly during REM sleep when brain blood flow (BBF) is increased. In 10 goats, we measured the ventilatory (VI), diaphragmatic electromyogram (EMGdI), and BBF responses to CO2 rebreathing during each sleep-wake state. delta VI/delta PaCO2 decreased from wakefulness to SWS (p less than 0.05) and REM sleep (p less than 0.05). In contrast, delta EMGdI/delta PaCO2 was decreased only during REM sleep (p less than 0.05). Concurrently, delta BBF/delta PaCO2 increased during REM sleep (p less than 0.05) compared with the awake state or SWS. A significant reciprocal correlation existed between delta EMGdI/delta PaCO2 and delta BBF/delta PaCO2 across sleep states (r = -0.786). When EMGdI was related to directly measured cerebral venous PCO2 (n = 4), a single linear function (r = 0.894) was found, independent of sleep-wake state. Similar results were obtained during quasi-steady-state hypercapnia. We conclude that central CO2 chemosensitivity is intact during sleep.