Jean Ehrhart

Dynamic heart rate variability: a tool for exploring sympathovagal balance continuously during sleep in men

We have recently demonstrated that the overnight profiles of cardiac interbeat autocorrelation coefficient of R-R intervals (rRR) calculated at 1-min intervals are related to the changes in sleep electroencephalographic (EEG) mean frequency, which reflect depth of sleep. Other quantitative measures of the Poincaré plots, i.e., the standard deviation of normal R-R intervals (SDNN) and the root mean square difference among successive R-R normal intervals (RMSSD), are commonly used to evaluate heart rate variability. The present study was designed to compare the nocturnal profiles of rRR, SDNN, and RMSSD with the R-R spectral power components: high-frequency (HF) power, reflecting parasympathetic activity; low-frequency (LF) power, reflecting a predominance of sympathetic activity with a parasympathetic component; and the LF-to-HF ratio (LF/HF), regarded as an index of sympathovagal balance. rRR, SDNN, RMSSD, and the spectral power components were calculated every 5 min during sleep in 15 healthy subjects. The overnight profiles of rRR and LF/HF showed coordinate variations with highly significant correlation coefficients (P < 0.001 in all subjects). SDNN correlated with LF power (P < 0.001), and RMSSD correlated with HF power (P < 0.001). The overnight profiles of rRR and EEG mean frequency were found to be closely related with highly cross-correlated coefficients (P < 0. 001). SDNN and EEG mean frequency were also highly cross correlated (P < 0.001 in all subjects but 1). No systematic relationship was found between RMSSD and EEG mean frequency. In conclusion, rRR appears to be a new tool for evaluating the dynamic beat-to-beat interval behavior and the sympathovagal balance continuously during sleep. This nonlinear method may provide new insight into autonomic disorders.We have recently demonstrated that the overnight profiles of cardiac interbeat autocorrelation coefficient of R-R intervals ( r RR) calculated at 1-min intervals are related to the changes in sleep electroencephalographic (EEG) mean frequency, which reflect depth of sleep. Other quantitative measures of the Poincaré plots, i.e., the standard deviation of normal R-R intervals (SDNN) and the root mean square difference among successive R-R normal intervals (RMSSD), are commonly used to evaluate heart rate variability. The present study was designed to compare the nocturnal profiles of r RR, SDNN, and RMSSD with the R-R spectral power components: high-frequency (HF) power, reflecting parasympathetic activity; low-frequency (LF) power, reflecting a predominance of sympathetic activity with a parasympathetic component; and the LF-to-HF ratio (LF/HF), regarded as an index of sympathovagal balance. r RR, SDNN, RMSSD, and the spectral power components were calculated every 5 min during sleep in 15 healthy subjects. The overnight profiles of r RR and LF/HF showed coordinate variations with highly significant correlation coefficients ( P < 0.001 in all subjects). SDNN correlated with LF power ( P < 0.001), and RMSSD correlated with HF power ( P < 0.001). The overnight profiles of r RR and EEG mean frequency were found to be closely related with highly cross-correlated coefficients ( P < 0.001). SDNN and EEG mean frequency were also highly cross correlated ( P < 0.001 in all subjects but 1). No systematic relationship was found between RMSSD and EEG mean frequency. In conclusion, r RR appears to be a new tool for evaluating the dynamic beat-to-beat interval behavior and the sympathovagal balance continuously during sleep. This nonlinear method may provide new insight into autonomic disorders.

Age-related changes in cardiac autonomic control during sleep

Aging is commonly associated with decreased sleep quality and increased periodic breathing (PB) that can influence heart rate variability (HRV). Cardiac autonomic control, as inferred from HRV analysis, was determined, taking into account the sleep quality and breathing patterns. Two groups of 12 young (21.1 ± 0.8 years) and 12 older (64.9 ± 1.9 years) volunteers underwent electroencephalographic, cardiac, and respiratory recordings during one experimental night. Time and frequency domain indices of HRV were calculated in 5‐min segments, together with electroencephalographic and respiratory power spectra. In the elderly, large R–R oscillations in the very‐low frequency (VLF) range emerged, that reflected the frequency of PB observed in 18% of the sleep time. PB occurred more frequently during rapid eye movement sleep (REM) sleep and caused a significant (P < 0.02) increase in the standard deviation of normal R–R intervals (SDNN) and absolute low‐frequency (LF) power. With normal respiratory patterns, SDNN, absolute VLF, LF, and high frequency (HF) power fell during each sleep stage (P < 0.01) compared with young subjects, with no significant sleep‐stage dependent variations. An overall decrease (P < 0.01) in normalized HF/(LF + HF) was observed in the elderly, suggesting a predominant loss of parasympathetic activity which may be related to decreased slow‐wave sleep duration. These results indicate that two distinct breathing features, implying different levels of autonomic drive to the heart, influence HRV in the elderly during sleep. The breathing pattern must be considered to correctly interpret HRV in the elderly.

Sleep Processes Exert a Predominant Influence on the 24-h Profile of Heart Rate Variability

Adverse cardiovascular events are known to exhibit 24-h variations with a peak incidence in the morning hours and a nonuniform distribution during the night. The authors examined whether these 24-h variations could be related to circadian or sleep-related changes in heart rate (HR) and in HR variability (HRV). To differentiate the effect of circadian and sleep-related influences, independent of posture and of meal ingestion, seven normal subjects were studied over 24 h, once with nocturnal sleep from 2300 to 0700 h and once after a night of sleep deprivation followed by8hof daytime sleep from 0700 to 1500 h. The subjects were submitted to constant conditions (continuous enteral nutrition and bed rest). HRV was calculated every 5 min using two indexes: the standard deviation of normal R-R intervals (SDNN) and the ratio of low-frequency to low-frequency plus high-frequency power. Sleep processes exerted a predominant influence on the 24-h profiles of HR and HRV, with lowest HRV levels during slow wave sleep, high levels during REM sleep and intrasleep awakenings, and abrupt increases in HR at each transition from deeper sleep to lighter sleep or awakenings. The circadian influence was smaller, except for SDNN, which displayed a nocturnal increase of 140% whether the subjects slept or not. This study demonstrates that 24-h variations in HR and HRV are little influenced by the circadian clock and are mainly sleep-stage dependent. The results suggest an important role for exogenous factors in the morning increase in cardiovascular events. During sleep, the sudden rises in HR at each transition from deeper sleep to lighter sleep or awakenings might precipitate the adverse cardiac events.

Sleep deprivation blunts the night time increase in aldosterone release in humans

The aim of this study was to determine the effect of sleep deprivation on the 24‐h profile of aldosterone and its consequences on renal function. Aldosterone and its main hormonal regulatory factors, ACTH (evaluated by cortisol measurement) and the renin‐angiotensin system [RAS, evaluated by plasma renin activity (PRA) measurement] were determined every 10 min for 24 h in eight healthy subjects in the supine position, once with nocturnal sleep and once during total 24‐h sleep deprivation. Plasma Na+ and K+ were measured every 10 min in four of these subjects. In an additional group of 13 subjects under enteral nutrition, diuresis, natriuresis and kaliuresis were measured once during the sleep period (23.00–07.00 h) and once during a 23.00–07.00 hours sleep deprivation period. During sleep deprivation, aldosterone displayed lower plasma levels and pulse amplitude in the 23.00–07.00‐hour period than during sleep. Similarly, PRA showed reduced levels and lower pulse frequency and amplitude. Plasma cortisol levels were slightly enhanced during sleep deprivation. Overnight profiles of plasma K+ and Na+ were not affected. Diuresis and kaliuresis were not influenced by sleep deprivation. In contrast, natriuresis significantly increased during sleep deprivation. This study demonstrates that sleep deprivation modifies the 24‐h aldosterone profile by preventing the nocturnal increase in aldosterone release and leads to altered overnight hydromineral balance.

Alpha activity and cardiac correlates: three types of relationships during nocturnal sleep

OBJECTIVE We examined simultaneously alpha activity and cardiac changes during nocturnal sleep, in order to differentiate non-rapid eye movement (NREM) sleep, REM sleep, and intra-sleep awakening. METHODS Ten male subjects displaying occasionally spontaneous intra-sleep awakenings underwent EEG and cardiac recordings during one experimental night. The heart rate and heart rate variability were calculated over 5 min periods. Heart rate variability was estimated: (1) by the ratio of low frequency (LF) to high frequency (HF) power calculated from spectral analysis of R-R intervals; and (2) by the interbeat autocorrelation coefficient of R-R intervals (rRR). EEG spectral analysis was performed using a fast Fourier transform algorithm. RESULTS Three types of relationships between alpha waves (8-13 Hz) and cardiac correlates could be distinguished. During NREM sleep, alpha activity and cardiac correlates showed opposite variations, with high levels of alpha power associated with decreased heart rate, rRR and LF/HF ratio, indicating low sympathetic activity. Conversely, during REM sleep, alpha activity was low whereas heart rate, rRR, and the LF/HF ratio peaked, indicating high sympathetic activity. During intra-sleep awakenings, alpha activity and cardiac correlates both increased. No difference in time-course between alpha 1 (8-10 Hz) and alpha 2 (10-13 Hz) activity could be shown. Alpha waves occurred in fronto-central areas during slow wave sleep (SWS), migrated to posterior areas during REM sleep, and were localized in occipital areas during intra-sleep awakenings. CONCLUSIONS These results suggest that alpha waves are not simply a sign of arousal, as is commonly thought. Fronto-central alpha waves, associated with decreased heart rate, possibly reflect sleep-maintaining processes.

Time‐courses in renin and blood pressure during sleep in humans

We previously described a strong concordance between nocturnal oscillations in plasma renin activity (PRA) and the rapid eye movement (REM) and non‐REM (NREM) sleep cycles, but the mechanisms inducing PRA oscillations remain to be identified. This study was designed to examine whether they are linked to sleep stage‐related changes in arterial blood pressure (ABP). Analysis of sleep electroencephalographic (EEG) activity in the delta frequency band, intra‐arterial pressure, and PRA measured every 10 min was performed in eight healthy subjects. Simultaneously, the ratio of low frequency power to low frequency power + high frequency power [LF/(LF + HF)] was calculated using spectral analysis of R–R intervals. The cascade of physiological events that led to increased renin release during NREM sleep could be characterized. First, the LF/(LF + HF) ratio significantly (P < 10−4) decreased, indicating a reduction in sympathetic tone, concomitantly to a significant (P < 10−3) decrease in mean arterial pressure (MAP). Delta wave activity increased (P < 10−4) 10–20 min later and was associated with a lag of 0–10 min with a significant rise in PRA (P < 10−4). Rapid eye movement sleep was characterized by a significant increase (P < 10−4) in the LF/(LF + HF) ratio and a decrease (P < 10−4) in delta wave activity and PRA, whereas MAP levels were highly variable. Overnight cross‐correlation analysis revealed that MAP was inversely correlated with delta wave activity and with PRA (P < 0.01 in all subjects but one). These results suggest that pressure‐dependent mechanisms elicit the nocturnal PRA oscillations rather than common central processes controlling both the generation of slow waves and the release of renin from the kidney.

Advances of human core temperature minimum and maximal paradoxical sleep propensity by ambient thermal transients

By using slow thermal transients of reduced amplitude (+/- 3 degrees C (thermoneutrality in humans sleeping nude) during only 1 night (experimental, EX), we have advanced the minimum of rectal temperature (Tre) and the peak of their paradoxical sleep propensity (PPSP) of sleeping subjects. During this EX night Tre minimum was significantly (P = 0.0001) advanced by 143 min versus that observed during baseline night spent at thermoneutrality. The advance of PPSP was objectivated by the more rapid cumulation of paradoxical sleep (P = 0.02) during the second half of EX night, i.e. strictly after the occurrence (around 0330 h) of the new Tre minimum, and by the earlier occurrence of its barycentric point (P = 0.04) between 0330 and 0700 h. The involvement of the central thermoregulatory system on phase-shifting mechanisms is discussed.

Cardiovascular responses and electroencephalogram disturbances to intermittent noises : effects of nocturnal heat and daytime exposure

SummaryDuring sleep, in thermoneutral conditions, the noise of a passing vehicle induces a biphasic cardiac response, a transient peripheral vasoconstriction and sleep disturbances. The present study was performed to determine whether or not the physiological responses were modified in a hot environment or after daytime exposure to both heat and noise. Eight young men were exposed to a nocturnal thermoneutral (20° C) or hot (35° C) environment disturbed by traffic noise. During the night, the peak intensities were of 71 dB(A) for trucks, 67 dB(A) for motorbikes and 64 dB(A) for cars. The background noise level (pink noise) was set at 30 dB(A). The noises were randomly distributed at a rate of 9·h−1. Nights were equally preceded by day-time exposure to combined heat and noise or to no disturbance. During the day, the noises as well as the background noise levels were increased by 15 dB(A) and the rate was 48 · h−1. Electroencephalogram (EEG) measures of sleep, electrocardiograms and finger pulse amplitudes were continuously recorded. Regardless of the day condition, when compared with undisturbed nights, the nocturnal increase in the level of heart rate induced by heat exposure disappeared when noise was added. Percentages, delays, magnitudes and costs of cardiac and vascular responses as well as EEG events such as transient activation phases (TAP) due to noise were not affected by nocturnal thermal load or by the preceding daytime exposure to disturbances. Cardiovascular responses and TAP depended on the type of traffic noise and on the sleep stage during which noise occurred: motorbike noise provoked more disturbance than car or truck noise although the latter had the largest peak intensity. The TAP induced by noise were more frequent in stage 2 sleep than in other sleep stages. Cardiovascular responses were of lower amplitude in slow wave sleep (SWS) than in stage 2 sleep or in rapid eye movements (REM) sleep. These results suggested that the deleterious effect of noise on sleep depended on the type of noise (getting-up time and spectral composition) and that SWS was the least disturbed sleep stage when compared with stage 2 and REM sleep.

The circadian thyrotropin rhythm is delayed in regular night workers.

In order to determine whether the circadian thyrotropin (TSH) rhythm is adapted to a night-active schedule, plasma TSH and body temperature were measured for 28 h every 10-min in 8 regular night workers and in 8 day-active subjects. In night workers, the shift of 8-h in the sleep period induced a mean shift of 6 h 30 min of the TSH acrophase which remained located, as in day-active subjects, at about the time of sleep onset. The nadir of the body temperature rhythm was shifted by an equivalent amount and occurred systematically during the sleep period, so that both parameters maintained a fixed phase relationship. TSH and temperature rhythms had similar amplitudes in the two groups. However, mean TSH values in night workers returned more rapidly to basal values. These results demonstrate that, together with body temperature, TSH acrophase is adapted to regular night work, suggesting that TSH may be a good index for evaluating the orientation of the endogenous clock.

Effects of sleep inertia on cognitive performance following a 1-hour nap

Abstract This study investigated the effects of a 1-h nap on subsequent performance in spatial memory (SM) and logical reasoning (LR) tasks. The objective was to evaluate the duration of the effects of sleep inertia (SI). The performance was measured in two independent groups of subjects. The 1-h nap took place at 00:00 h in group 1 and at 03:00 h in group 2. In each task, the experimental design comprised one no-nap condition in which subjects had no sleep before the night tests, and a nap condition that comprised the 1-h nap followed by the test sessions. To measure the duration of SI effects, the subjects were tested in two 30-min sessions and the data in each session were analysed in sub-units of time of 3 min each. In each task the results showed no effects on accuracy, and no circadian effects of napping were found. In each task, analyses of pooled data of the two groups showed that the performance in the 1-h nap condition exhibited significant reductions of speed immediately following awakening, wh...