The intrasleep relationship between wake and stage 4 examined by transition probability analysis

The relationship between wake and stage 4 of slow-wave sleep (SWS), in particular the previously observed deficiency in SWS accompanying sleep containing long-wake periods, is examined in this study of 147 health subjects. Stage shift comportment is compared between those NREM/REM cycles with wake periods greater than 3 minutes and those with less, using the method of transition probabilities. It is shown that these long wake interruptions occur preferentially in light sleep, and systematically disrupt the regular normal descent towards SWS, but do not significantly reduce the number of SWS episodes. There is at the same time, however, a reduction in the average duration of stage 4 periods of SWS which accounts for the observed reduction in the total amount of SWS.