Correlation between Ventilation and Brain Blood Flow during Sleep

As bstract. The relationships between brain blood flow (BBF) and ventilation (VI) were studied during sleep in 13 goats. Unilateral BBF was continuously mea-sured with an electromagnetic flow probe; total and re-gional BBF were assessed by the radioactive microsphere technique in four animals. Interacting changes in VI and BBF occurred during both slow wave (SWS) and rapid eye movement (REM) sleep. During SWS, significant de-creases in VI and increases in arterial Pco2 occurred com-pared to wakefulness. BBF during SWS correlated linearly with arterial CO2 tension (PaCO2); and the relationship was similar to that for awake goats breathing CO2. During REM sleep, VI was significantly less than both the awake (W) and SWS states due principally to a decrease in tidal volume. BBF during REM sleep was significantly and substantially increased compared with both the W and SWS states; this increase was shared by all brain areas. The increase in BBF during REM sleep was greater than that predicted from changes in PaCO2. In five goats pro-vided with chronic sagittal sinus fistulae, arteriovenous oxygen difference was measured in separate studies and found to be significantly lower during REM sleep com-pared with W; brain 02 consumption was similar in mag-nitude in the REM and W states. Thus, the high BBF of REM sleep was also unexplained by an increase of brain metabolic activity. We conclude that, during SWS, increases in BBF are explained by hypoventilation and hypercapnia. In con-trast, during REM sleep, BBF is substantially in excess Address all correspondence and reprint requests to Dr. T. V. Santiago