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 Pa(CO₂), particularly during REM sleep when brain blood flow (BBF) is increased. In 10 goats, we measured the ventilatory (V̇I), diaphragmatic electromyogram (EMGdl), and BBF responses to CO₂ rebreathing during each sleep-wake state. ΔV̇I/ΔPa(CO₂) decreased from wakefulness to SWS (p < 0.05) and REM sleep (p < 0.05). In contrast, ΔEMGdi/ΔPa(CO₂) was decreased only during REM sleep (p < 0.05). Concurrently, ΔBBF/ΔPa(CO₂) increased during REM sleep (p < 0.05) compared with the awake state or SWS. A significant reciprocal correlation existed between ΔEMGdi/ΔPa(CO₂) and ΔBBF/ΔPa(CO₂) across sleep states (r = -0.786). When EMGdl 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.