Fifteen recumbent young health volunteers underwent 24-h beat-to-beat blood pressure (BP) and interbeat interval (IBI) recordings to explore the effects of wake and polygraphically recorded sleep on the nyctohemeral variations in the spectral frequency components of BP and IBI and in the arterial baroreflex sensitivity (BRS), independent of the confounding effects of changes in posture and physical activity. Spectral analysis of BP and IBI provided markers of sympathetic and vagal controls and of arterial BRS. When falling asleep, the low-frequency (LF) BP and IBI components showed a marked decrease while there was a clear-cut increase in the high-frequency (HF) IBI component. In contrast, only a slight nighttime rapid eye movement-related arterial BRS increase was observed. The final morning awakening induced a pronounced decrease in arterial BRS and the HF IBI component while there was a marked rise in the LF BP component. Hence, a clear 24-h variation in sympathetic and vagal tone but not in arterial BRS persists, independent of changes in activity and position.

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We hypothesize that sleep apnea-hypopnea alters interaction between cardiac vagal modulation and sleep delta EEG. Sleep apnea-hypopnea syndrome (SAHS) is related to cardiovascular complications in men. SAHS patients show higher sympathetic activity than normal subjects. In healthy men, non-rapid eye movement (NREM) sleep is associated with cardiac vagal influence, whereas rapid eye movement (REM) sleep is linked to cardiac sympathetic activity. Interaction between cardiac autonomic modulation and delta sleep EEG is not altered across a life span nor is the delay between appearances of modifications in both signals. Healthy controls, moderate SAHS, and severe SAHS patients were compared across the first three NREM-REM cycles. Spectral analysis was applied to ECG and EEG signals. High frequency (HF) and low frequency (LF) of heart rate variability (HRV), ratio of LF/HF, and normalized (nu) delta power were obtained. A coherency analysis between HF(nu) and delta was performed, as well as a correlation analysis between obstructive apnea index (AI) or hypopnea index (HI) and gain, coherence, or phase shift. HRV components were similar between groups. In each group, HF(nu) was larger during NREM, while LF(nu) predominated across REM and wake stages. Coherence and gain between HF(nu) and delta decreased from controls to severe SAHS patients. In SAHS patients, the delay between modifications in HF(nu) and delta did not differ from zero. AI and HI correlated negatively with coherence, while HI correlated negatively with gain only. Apneas-hypopneas affect the link between cardiac sympathetic and vagal modulation and delta EEG demonstrated by the loss of cardiac autonomic activity fluctuations across shifts in sleep stages. Obstructive apneas and hypopneas alter the interaction between both signals differently.

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