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

Summary During 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.     

Changes in human heart rate during sleep following daily physical exercise

Summary Four fit, healthy young men (aged 20) volunteered for the experiment. After a 5 day control period, they marched for 6 consecutive days (from 09:00 h to 17:00 h) for 34 km/day at a speed of 6 km/h, with an energy expenditure of 35% of individual max. A recovery period of 5 consecutive days began immediately after the exercise period. Sleep records and electrocardiograms were taken every night during the three periods from 22:00 h to 06:00 h.During the exercise period the night time heart rates increased by about 10%, compared to the previous control condition, and returned to normal during the recovery period.The relation between heart rate changes and sleep stages remained identical throughout the three experimental periods. Three subjects showed an increase in heart rate during paradoxical sleep, compared to the preceding slow wave sleep, while one subject experienced the reverse.The tonic increases in heart rate are discussed in relation to changes in body temperature, sleep patterns, blood composition and hormonal status induced by the physical exercise performed.Supported by grant N 77/1198 from the Direction des Recherches et Etudes Techniques (Délégation Ministérielle pour l'Armement)     

Peripheral thermal responsivity to facial cooling during sleep

A recently developed technique for examining thermal sensitivity during sleep was used to assess whether skin and core temperature responses to thermal stimulation were altered by sleep state. The technique was designed to probe thermal responsivity without altering core body temperature or inducing awakening. Twenty-seven young men and women were studied during a sleep deprivation night and a sleep night three nights later. Cold water stimulation of the face alternated with an equal period of rewarming across a 40-min cycle throughout the night. Skin temperature from the finger and rectal temperature were continuously assessed. Sleep continuity and architecture were largely uninfluenced by the thermal stimulation. Finger skin temperature decreased during cold facial stimulation in both sleep and waking states. Skin temperature changes during sleep were approximately one-fifth the magnitude of those during waking. Core temperature was minimally influenced. REM sleep was associated with a greater amplitude decrease in finger temperature than was non-REM (NREM) sleep. The results support the utility of the technique as a probe of thermal responsivity during sleep and suggest a reduction of thermal responsivity during sleep and, more tentatively, an altered responsivity during REM versus NREM sleep.     

Short-term cardiovascular responses to rapid whole-body tilting during exercise

Our objective was to characterize the responses of heart rate (HR) and arterial blood pressure (BP) to changes in posture during concomitant dynamic leg exercise. Ten men performed dynamic leg exercise at 50, 100, and 150 W and were rapidly and repeatedly tilted between supine (0°) and upright (80°) positions at 2-min intervals. Continuous recordings of BP and HR were made, and changes in central blood volume were estimated from transthoracic impedance. Short-lasting increases in BP were observed immediately upon tilting from the upright to the supine position (down-tilt), averaging +18 mmHg (50 W) to +31 mmHg (150 W), and there were equally short-lasting decreases in BP, ranging from −26 to −38 mmHg upon tilting from supine to upright (up-tilt). These components occurred for all pressure parameters (systolic, mean, diastolic, and pulse pressures). We propose that these transients reflect mainly tilt-induced changes in total peripheral resistance resulting from decreases and increases of the efficiency of the venous muscle pump. After 3–4 s (down-tilt) and 7–11 s (up-tilt) there were large HR transients in a direction opposite to the pressure transients. These HR transients were larger during the down-tilt (−15 to −26 beats · min⁻¹) than during the up-tilt (+13 to +17 beats · min⁻¹), and increased in amplitude with work intensity during the down-tilt. The tilt-induced HR fluctuations could be modelled as a basically linear function of an arterial baroreflex input from a site half-way between the heart and the carotid sinus, and with varying contributions of fast vagal and slow sympathetic HR responses resulting in attenuated tachycardic responses to hypotensive stimuli during exercise. Accepted: 24 August 1999     

Night-time sleep and daytime sleepiness in narcolepsy

This report describes night-time sleep and daytime sleepiness in a large (N=530) sample of patients meeting the International Classification of Sleep Disorders criteria for diagnosis of narcolepsy. Sleep data were obtained from polysomnographic recordings on two consecutive nights. Sleepiness was assessed using the Multiple Sleep Latency Test, the Maintenance of Wakefulness Test and the Epworth Sleepiness Scale. Analysis revealed that sleep was mild to moderately disturbed on both recording nights. A first-night effect was suggested by decreased REM latency and increased percentage REM and slow-wave sleep on the second night. Sleepiness and sleep disturbance varied across patient subgroups created based on patient ethnicity and on the presence/absence of cataplexy, sleep apnoea, and periodic limb movements. Covariation of sleep and sleepiness measures across patients was significant but weak. Strong association was found between subgroup means of sleep and sleep disturbance measures. The findings reported here show that sleepiness and sleep disturbance vary across patient subgroups and that sleep disturbance is related to, although unable to account, for the pathological sleepiness of narcolepsy.     

Memory Retrieval in Noise and Psychophysiological Response in the Young and Old

Both noise and aging induce changes in memory performance that have been attributed to physiological overarousal. The aim of the current experiment was to examine variation in performance due to noise and aging and to determine if this variation was related to variation in general arousal or, alternatively, to changes in processes specifically required by memory retrieval. The cardiovascular responses of young and old men (n=30) were compared during a memory retrieval task performed in acoustic noise. Noise (90dBA) and old age independently increased the number of associatively cued recall errors relative to orthographically cued recall errors. Despite the change in errors, changes in general arousal were not observed in response to noise in either young or old volunteers. The task sequence induced consistent cardiac and vascular responses which were related to attention and rehearsal requirements, and also to performance. This suggests that task processing induces supportive physiological changes rather than that physiological change (arousal) constrains performance. Noise and age may alter physiological change independently by altering task processing and requirements for physiological support.     

Plasma oxytocin is related to lower cardiovascular and sympathetic reactivity to stress

In addition to known reproductive and social affiliation functions, oxytocin (OT) has been identified as a cardiovascular hormone. OT synthesis and receptors are found in cardiac and vascular tissue. Animal studies suggest that OT activates an ‘anti-stress’ response that reduces cardiovascular and neuroendocrine stress reactivity. We tested 28 early postpartum mothers, obtaining multiple blood samples for OT, the sympathetic marker, norepinephrine (NE), and the lactation hormone, prolactin, while monitoring their cardiovascular responses to two stressors: public speaking and forehead cold pressor. Although plasma OT did not increase reliably from pre-stress levels during stressors, greater overall OT level was related to greater vasodilation and cardiac stroke volume responses to both tasks, to reduction in heart rate to the cold pressor, as well as to lower plasma NE and higher prolactin levels. In contrast, higher NE was linked to increases in heart rate and decreases in stroke volume. These data support a cardioprotective role for OT, which may influence the magnitude and hemodynamic determinants of cardiovascular stress responses.     

Autonomic control of the cardiovascular system during sleep in normal subjects

The autonomic control of heart rate and blood pressure during sleep is controversial: although it has been reported that vagal activity is more often lower in rapid eye movement sleep (REM) than in other stages of sleep (non-REM, NREM), the opposite has also been described. Initially, it was reported that baroreflex sensitivity (BRS) increases during sleep (REM and NREM), but in later studies, this was only partially confirmed. We therefore studied autonomic control of the cardiovascular (CV) system during sleep in 12 normal adults. The spectral components of the heart rate R-R interval, blood pressure (BP), and BRS were computed at low (LF) and actual breathing frequency (high frequency, HF). Analysis of sleep stage and a cycle-by-cycle stage II analysis were performed. CV variability is affected largely by sleep-stage and sleep-cycle organisation: NREM and the last cycle exhibit the greatest vagal activity and the lowest sympathetic activity. BRS estimation for both the LF and HF bands confirmed previous results obtained by pharmacological and spontaneous slope methods: BRS is greater during sleep than during nocturnal wake periods, and further increased in REM. BRS is frequency dependent: in NREM, the higher value of HF BRS compared to LF BRS favours the HF control of BP variability, whereas higher BRS HF and LF components contribute to the strongest control in REM. BRS variability exhibits no significant pattern during the night. Our results suggest that both sleep-cycle organisation and BRS estimation in the LF and HF bands should be considered in sleep studies of autonomic CV control. Electronic Publication     

Local sweating responses during recovery sleep after sleep deprivation in humans

Changes in the central control of sweating were investigated in five sleep-deprived subjects (kept awake for 40 h) during their recovery sleep under warm ambient conditions [operative temperature (T _o) was either 35 or 38° C]. Oesophageal (T _oes) and mean skin (T _sk) temperatures, chest sweat rate (m _sw,ch), and concomitant electro-encephalographic data were recorded. Throughout the night at 35 or 38° C T _o, m _sw,ch changes were measured at a constant local chest skin temperature (T _ch) of 35.5° C. The results showed that body temperatures (T _oes and T _sk) of sleep-deprived subjects were influenced by thermal and hypnogogic conditions. The m _sw,ch levels correlated positively with T _oes in the subjects studied during sleep stage 1–2 (light sleep: LS), sleep stage 3–4 (slow wave sleep: SWS) and rapid eye movement (REM) sleep. Contrary to what has been reported in normal sleep, firstly, the T _oes threshold for sweating onset differed between REM sleep and both LS and SWS, and, secondly, the slopes of the m _sw,ch versus T _oes relationships were unchanged between REM and non-REM (i.e. LS or SWS) sleep. The changes observed after sleep deprivation were hypothesized to be due to alterations in the functioning of the central nervous system controller.     

Sleep duration and cardiovascular responses to stress in undergraduate men

Short sleep has been related to incident cardiovascular disease, but physiological mechanisms accounting for this relationship are largely unknown. This study examines sleep duration and cardiovascular stress responses in 79 healthy, young men. Sleep duration was assessed by wrist actigraphy for seven nights. Participants then completed a series of laboratory stress tasks while heart rate and blood pressure were monitored. Shorter total sleep time was related to a greater reduction in high‐frequency heart rate variability during stress tasks, and to prolonged elevations in heart rate and diastolic pressure following tasks. Associations were independent of age, race, body mass index, caffeine intake, and smoking status. In sum, healthy young men with shorter actigraphy‐assessed sleep exhibit less cardiac vagal activity, and poorer heart rate and diastolic blood pressure recovery, upon encountering stressful stimuli, than those with longer sleep.     

Arterial pressure and heart rate changes during natural sleep in rat

Mean arterial pressure and heart rate data during quiet wakefulness and phases of sleep in conscious rat are sampled by a computer at a rate of 100/sec. Average values and variability expressed as standard deviation are computed for each recording session. Mean arterial pressure and heart rate and their variability decrease from quiet wakefulness to synchronized sleep. During desynchronized sleep, mean arterial pressure increases to the level of quiet wakefulness and is more variable than during synchronized sleep. Heart rate is lower and more uniform during sleep than during quiet wakefulness, and there is no difference between synchronized and desynchronized sleep except that a greater variability occurs during desynchronized sleep. The study shows that characteristic and specific cardiovascular changes accompany the phases of sleep and that a hierarchy of arterial pressure is present during the resting behavior in rat.     

Frontal brain asymmetry and transient cardiovascular responses to the perception of humor

The study examined the relationship of individual differences in prefrontal brain asymmetry, measured by the EEG in resting conditions, to the individual's responsivity in the context of humor (n = 42). Several weeks after the EEG recording, immediate cardiovascular responses to the perception of humor and behavioral indicators of humor processing were obtained in an experimental paradigm involving non-verbal cartoons. Relatively greater resting activity in the left than right prefrontal cortex, particularly at the ventrolateral positions, was associated with faster detection of humor, a more pronounced cardiac response to the perception of humor (heart rate and cardiac output), and more accessible internal positive affective states (indicated by faster reports of amusement levels). The study confirms and extends findings of the relevance of prefrontal brain asymmetry to affective responsivity, contributing evidence in the domain of positive affect and humor, and demonstrating relationships to the immediate cardiovascular response pattern to an emotional event.     

Autonomic arousals related to traffic noise during sleep

AIM: To analyze the heart rate (HR) response to traffic noise during sleep and the influence of acoustic parameters, time of night, and momentary sleep stage on these responses. PARTICIPANTS: Twelve women and 12 men (19-28 years). MEASUREMENTS AND RESULTS: The participants slept in the laboratory for 4 consecutive nights in each of 3 consecutive weeks and were exposed to aircraft, road, or rail traffic noise with weekly permutations. The 4 nights of each week consisted of a random sequence of a quiet night (32 dBA) and 3 nights during which aircraft, rail traffic, or road traffic noises occurred with maximum levels of 45-77 dBA. The polysomnogram and the electrocardiogram were recorded during all nights. In case of awakenings, the HR alterations consisted of monophasic elevations for >1 min, with mean maximum HR elevations of 30 bpm. Though obviously triggered by the noise events, the awakenings per se rather than the acoustical parameters determined the extent and pattern of the response. Without awakenings, HR responses were biphasic and consisted of initial accelerations with maximum HR elevations of about 9 bpm followed by decelerations below the baseline. These alterations were clearly influenced by the acoustic parameters (traffic mode, maximum level, rate of rise) as well as by the momentary sleep stage. CONCLUSIONS: Cardiac responses did not habituate to traffic noise within the night and may therefore play a key role in promoting traffic noise induced cardiovascular disease. If so, these consequences are more likely for responses accompanied by awakenings than for situations without awakenings.     

Effect of arm position on cardiovascular responses during isometric handgrips

Summary Sixteen subjects (eight women and eight men, age 20–25 years) carried out in the seated position, isometric contractions sustained until exhaustion of the digital flexors. The subject's arm was placed in two positions, high and low. The muscle tensions used were 30, 40 and 50% of maximum voluntary contraction (MVC). Under these conditions, for a given relative force, the duration of contraction (limit-time) was not modified by the arm position. In the male subjects, increases in heart rate (HR) and systolic blood pressure (SBP) were slightly more pronounced in the low than the high position, but the differences were not significant. Limit times in the high position were similar to those in the low position, and, in the absence of an increase in HR and SBP, this seemed to be due to an increase in cardiac output consequent upon a transient improvement in venous return together with an increase in the coefficient of oxygen utilization.     

Electroencephalogram asymmetry and spectral power during sleep in the northern fur seal

The fur seal (Callorhinus ursinus), a member of the Pinniped family, displays a highly expressed electroencephalogram (EEG) asymmetry during slow wave sleep (SWS), which is comparable with the unihemispheric sleep in cetaceans. In this study, we investigated the EEG asymmetry in the fur seal using spectral analysis. Four young (2-3 years old) seals were implanted with EEG electrodes for polygraphic sleep recording. In each animal, EEG spectral power in the frequency range of 1.2-16 Hz was computed in symmetrical cortical recordings over two consecutive nights. The degree of EEG asymmetry was measured by using the asymmetry index [AI = (L - R)/(L + R), where L and R are the spectral powers in the left and right hemispheres, respectively]. In fur seals, EEG asymmetry, as measured by the percent of 20-s epochs with absolute AI > 0.3 and >0.6, was expressed in the entire frequency range (1.2-16 Hz). The asymmetry was significantly greater during SWS (25.6-44.2% of all SWS epochs had an absolute AI > 0.3 and 2.1-12.2% of all epochs had AI > 0.6) than during quiet waking (11.0-20.3% and 0-1.9% of all waking epochs, respectively) and REM sleep (4.2-8.9% of all REM sleep epochs and no epochs, respectively). EEG asymmetry was recorded during both low- and high-voltage SWS, and was maximal in the range of 1.2-4 and 12-16 Hz. As shown in this study, the degree of EEG asymmetry and the frequency range in which it is expressed during SWS in fur seals are profoundly different from those of terrestrial mammals and birds.     

A behavioural test to assess daytime sleepiness in obstructive sleep apnoea

Daytime sleepiness is an important symptom of obstructive sleep apnoea syndrome (OSAS). The standard tests for its objective quantification use EEG recordings, and are time consuming and expensive, which makes them difficult to use for large studies. This study assesses the ability of a simple test of sustained ‘wakefulness’ to discriminate the excessive somnolence of severe symptomatic obstructive sleep apnoea from normality, and compares its results to the traditional EEG based Maintenance of Wakefulness Test (MWT). Ten subjects (7M 3F) with severe sleep apnoea (>4% SaO₂ dip rate median 32.7 (90% central range 9.7–65.6)) and symptoms of daytime sleepiness, (Epworth Sleepiness Score (ESS)17(10–24)) and 10 normal subjects (4M 6F, ESS 3.5(1–8)) were studied. The MWT and the behavioural test (Oxford SLEep Resistance test – OSLER test) were performed on each subject in random order on 2 separate days. The protocol for both tests was the same with 4 × 40 min sleep resistance challenges throughout the day while sound isolated in a darkened room. During the OSLER test subjects were asked to press a switch in response to a light emitting diode (LED), which was lit for 1 s in every three. Both the switch and the light were connected to a computer that stored both the number of times the light was illuminated and whether a correct response was made. The OSLER test discriminated the normal subjects from the sleep apnoea group (mean sleep latency (min) normal group 39.8, OSA group 10.5) as well as the traditional MWT (normal group 38.1, OSA group 7.3) and was much simpler to administer. This test has the advantage that sleep onset is defined objectively and automatically as a failure to respond to the light, rather than from EEG interpretation, which is inevitably partly subjective. This technique may provide a simple and robust method of objectively quantifying daytime sleepiness for large studies.     

Ten-year stability of cardiovascular responses to laboratory stressors

In this study we examined test-retest stability of cardiovascular stress responses over a decade of the life span. Participants were 55 male college undergraduates. 19 years of age at initial testing, and 29 years of age at follow-up testing Stressors were a foot cold pressor and an aversive reaction time task. Cardiovascular measures included systolic and diastolic blood pressure, heart rate, and preejection period. For cold pressor, the magnitude and pattern of cardiovascular responses remained unchanged at the 10-year follow-up. For the reaction time task, the characteristic cardiovascular response patterns was preserved but with significant attenuation of magnitude. The present findings are consistent with previous observations of temporal stability but over a substantially longer test-retest interval. The long-term stability of stress responses is discussed in the context of stress test methodology, behavioral response demands, and maturation of the physiological systems involved in cardiovascular response expression.     

Cardiovascular responses to railway noise during sleep in young and middle-aged adults

The aim of this study was to investigate the effects of nocturnal railway noise on cardiovascular reactivity in young (25.8 ± 2.6 years) and middle-aged (52.2 ± 2.5 years) adults during sleep. Thirty-eight subjects slept three nights in the laboratory at 1-week interval. They were exposed to 48 randomized pass-bys of Freight, Passenger and Automotive trains either at an 8-h equivalent sound level of 40 dBA (Moderate) and 50 dBA (High) or at a silent Control night. Heart rate response (HRR), heart response amplitude (HRA), heart response latency (HRL) and finger pulse response (FPR), finger pulse amplitude (FPA) and finger pulse latency (FPL) were recorded to measure cardiovascular reactivity after each noise onset and for time-matched pseudo-noises in the control condition. Results show that Freight trains produced the highest cardiac response (increased HRR, HRA and HRL) compared to Passenger and Automotive. But the vascular response was similar whatever the type of train. Juniors exhibited an increased HRR and HRA as compared to seniors, but there was no age difference on vasoconstriction, except a shorter FPL in seniors. Noise level produced dose-dependent effects on all the cardiovascular indices. Sleep stage at noise occurrence was ineffective for cardiac response, but FPA was reduced when noise occurred during REM sleep. In conclusion, our study is in favor of an important impact of nocturnal railway noise on the cardiovascular system of sleeping subjects. In the limit of the samples studied, Freight trains are the most harmful, probably more because of their special length (duration) than because of their speed (rise time).     

Oculomotor changes are associated to daytime sleepiness in the multiple sleep latency test

Sleep onsets in the diurnal multiple sleep latency test (MSLT), following different sleep lengths of the preceding night sleep (8, 5, 4, 3, 2, 1 h) and following the corresponding recovery nights, were considered for a study on changes of oculomotor activity during sleep onset. The study aimed to assess the individual time course in spontaneous blinks (SBs) and slow eye movements (SEMs) during the sleep onset period and also the relationship with sleep latencies in the MSLT. Group analyses compared oculomotor changes between conditions characterized by a different level of daytime sleepiness. The results show a clear inverse relation between the two oculomotor measures, with a linear SB decrease and quadratic SEM increase across the wake-sleep transition. A 150 s sample of SB and SEM activity at the start of MSLT trials correlates with individual subsequent sleep latency. Finally, mean changes in daytime sleepiness as measured by the MSLT are paralleled by coherent oculomotor changes, with a significant linear decrease of SB as sleepiness increases as a consequence of previous sleep reduction. Both individual and group results show that endogenous blinking is associated with moderate changes in daytime sleepiness.     

Comparison of cardiovascular responses to noise during waking and sleeping in humans

Eighty subjects, 40 men and 40 women, were allocated to one of two groups according to their self-estimated high or low sensitivity to noise. In the first part of the experiment, they were exposed to sequences of common noises during the morning or the afternoon. The heart-rate and finger-pulse responses were measured and recorded in relation to sensitivity, sex of subjects, and time of day. The different types of noise were compared for both responses. The heart-rate response showed differences between sensitivity groups but not between noises. In contrast, no significant differences were obtained between sensitivity groups when using the finger-pulse response, but clear differences were observed between noises. In a second part of the experiment, 10 men and 10 women subjects were selected from the previous two sensitivity groups. These 20 subjects were exposed during sleep to the same noises as during the daytime. Heart-rate and finger-pulse responses during sleep were significantly greater than during waking, and they did not differ significantly with respect to sensitivity to noise or gender. These two autonomic responses showed differences between noises that appeared to be related to their noise-equivalent-level value. Compared with the silent baseline night, the sleep pattern showed no significant modification in the night of noise disturbance, except for the frequency of transient activation phases, which was significantly increased in the latter.