Electroencephalogram and cardiovascular responses to noise during daytime sleep in shiftworkers

Summary Intermittent noise occurring during sleep has been found to induce heart rate, peripheral vasomotor and electroencephalogram (EEG) changes. This study analysed these responses during the daytime and night-time sleep of shiftworkers doing a three shift system, to determine the influence of the inversion of the sleep-wake cycle on the sensitivity to noise. A group of 14 shiftworkers [aged 37 (SD 5) years] underwent an habituation daytime sleep, two experimental daytime sleeps and a night-time sleep. Traffic noises were presented during sleep [truck, 71 dB(A); motorbike, 67 dB(A); and car, 64 dB(A)] at a rate of nine each hour. The EEG measurements of sleep, electrocardiogram and finger pulse amplitude were recorded continuously. The results were expressed by computing the percentage of observed cardiac response (%HRR) and vasoconstrictive response (%FPR), magnitude of heart rate variation (heart rate response; HRR), percentage of reduction of the digital blood flow (finger pulse response, FPR), cardiac cost (CC = % HRR x HRR) and vasomotor cost (VC = % FPR x FPR). The results showed that, compared to night-time sleep, there was change in the structure of daytime sleep, that is an increase in slow wave sleep (SWS), especially stage 4 sleep decrease of stage 2 and rapid eye movement (REM) sleep latencies, and an earlier SWS and REM sleep barycentric point. During daytime sleep the % FPR was significantly smaller in SWS than in stage 2 or REM sleep. Large differences were observed in % HRR, HRR and CC between daytime sleep stages (SWS less than stage 2 less than REM sleep). These differences were not observed during night-time sleep. Moreover, compared to night-time sleep, CC was increased during daytime REM sleep and decreased during daytime SWS. The inversion of the sleep-wake cycle in shiftworkers, did not influence the overall cardiovascular reactivity to noise. This was explained by a compensatory effect due to an increase in this reactivity during daytime REM sleep and its decrease in daytime SWS. The second reason is due to an increase in the percentage of stage 4 sleep during daytime sleep (less disturbed by noise than other sleep stages). This increased percentage of stage 4 sleep was probably a consequence of the partial sleep deprivation occurring after a week working on nightshift.     

Habituation of the infant arousal response.

STUDY OBJECTIVES: Arousal is considered to be an important protective response in a sleeping infant and its depression could leave an infant vulnerable to a life threatening stimulus. We found previously that arousal to a non-respiratory (tactile) stimulus occurs in a sequence of events that begins with spinal, followed by brainstem responses, and then a cortical electroencephalographic (EEG) arousal response. We hypothesized that repeated stimuli would depress the arousal responses by habituation and that spinal and brainstem responses would be more resistant to habituation than cortical responses. PARTICIPANTS: We studied 22 normal infants. INTERVENTIONS: The infants underwent polysomnographic monitoring during a daytime nap. Tactile stimuli was applied to the infants foot at 5-second intervals. MEASUREMENTS AND RESULTS: We found that spinal, brainstem, and cortical responses occurred on the first trial of each test. Repeated trials during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep resulted in a decrease in the incidence of each individual response and eventually elimination of the arousal responses. Cortical responses were eliminated first, followed by brainstem responses and finally spinal responses. The elimination of each of the responses occurred more rapidly during REM sleep that during NREM sleep. CONCLUSIONS: Habituation of the infant arousal sequence occurs with repeated tactile stimulation. There is a serial habituation of responses from the cortical to the spinal level, which occurs more rapidly during REM sleep. Rapid habituation to innocuous stimuli is probably beneficial in avoiding detrimental sleep disruptions. However, in situations requiring the protective functions of arousal, such habituation could be detrimental to an infant.     

EEG AND AUTONOMIC RESPONSE PATTERN DURING WAKING AND SLEEP STAGES

The response hierarchy of EEG and autonomic variables to tones of increasing intensity was studied during waking and sleep stages 2, REM, and SW (3 & 4 combined). Tones of 1000 Hz (5 sec duration, 55 sec ISI) were presented to 35 young adult male subjects. During waking, the tones began below awake auditory threshold and increased by 5 db until a motor response (button press) was made. During sleep, tones began at awake threshold and went to arousal threshold, i.e., motor response and/or an EEG change indicative of arousal. Changes in EEG, finger pulse amplitude, heart rate, skin potential, skin resistance, and respiration period were measured for each stimulus and were compared to a pseudostimulus response scored 25 sec prior to the actual stimulus. In the awake state, statistically significant responses (p < .05) were found for EEG, finger pulse, heart rate early deceleration, skin potential, and skin resistance to the tone at awake threshold, but not to tones at lesser db levels. During sleep, significant EEG responses were present to tones 30–25 db below arousal threshold, finger pulse 20–15 db below, and heart rate acceleration 20–5 db below. Significant skin potential, skin resistance, and motor responses were seen only at arousal threshold. Thus, in sleep, in contrast to waking, there were clear responses to stimuli below the arousal threshold, and there was definite ordering of the appearance of the various responses: EEG preceded the cardiovascular, with electrodermal and motor occurring only at arousal. This order was constant over sleep stages. Arousal thresholds were very similar across sleep stages in day sleepers (approximately 35 db above awake threshold). The threshold during stage 2 for night sleepers was about 15 db lower than that for day sleepers.     

Directing Attention Toward Stimuli Affects the P300 But Not the Orienting Response

Whether attending to stimuli affects the orienting response and its habituation is not yet clear. EEG alpha suppression responses, electrodermal responses, and EEG evoked potential responses of two groups of subjects were compared. The Attend group was given instructions to pay attention to and count the 59 moderate intensity clicks (interstimulus interval = 15 sec). The Ignore group was instructed to “try not to let the clicks disturb your relaxed state.” Separate ANOVAs with repeated measures were used to evaluate all measures, and all showed significant effects for click repetition (habituation). Alpha suppression and change in log conductance showed no differences related to group. The P300 component of the average evoked potentials was significantly larger for the Attend group. We concluded that attending to, versus ignoring, stimuli does not have an appreciable effect on these two traditional measures of the orienting response, but it does affect the evoked potentials. The relationship between attention and “significance” is discussed.     

Habituation During Sleeping and Waking

EEG and autonomic habituation were studied during sleep stages 2 and REM. and during awake. Repeated presentations of the same stimulus to the same subjects within sleep stages and when awake permitted evaluation of habituation between tone sets within stag 2, REM, and awake, and from sleep to awake. Forty-six subjects were exposed to 800 Hz. 75 dB, 1- or 2-sec tones, presented in sets of 20 tones. During steep, there was no habituation of the EEC response. Habituation occurred for both FPR and HRR during stage 2, with no evidence of within-stage. between tone set habituation. No significant habituation occurred during REM for HRR or FPR. Evoked skin resistance responses were rare during both stage 2 and RKM. In the awake state, HRR was unresponsive but all other variables showed habituation. Tones presented during the night had no effect on the awake response.     

Habituation of the Orienting Response in Sleep

This experiment was designed with stimulus parameters deliberately chosen to maximize the probability of observing habituation of the orienting response (OR) in sleep: weak stimulus, short interstimulas interval. with test for both dishabituation and spontaneous recovery, Habituation of finger plethysmograph. heart rate, skin potential. and skin resistance responses was studied in delta sleep and RKM sleep in 46 male undergraduate volunteers. There was significant habituation of both finger plethysmograph and heart rate responses in both delta and REM sleep, as well as dishabituation and spontaneous recovery. None of these effects was observed in the electrodermal measures. Results were compared with other studies of habituation of the OR in sleep, as well as theories of habituation. The authors do not interpret the results as demonstrating learning during steep.     

Cerebrovascular response to arousal from NREM and REM sleep

STUDY OBJECTIVE: To determine the effect of arousal from sleep on cerebral blood flow velocity (CBFV) in relation to associated ventilatory and systemic hemodynamic changes. PARTICIPANTS: Eleven healthy individuals (6 men, 5 women). MEASUREMENTS: Pulsed Doppler ultrasonography was used to measure CBFV in the middle cerebral artery with simultaneous measurements of sleep state (EEG, EOG, and EMG), ventilation (inductance plethysmography), heart rate (ECG), and arterial pressure (finger plethysmography). Arousals were induced by auditory tones (range: 40-80 dB; duration: 0.5 sec). Cardiovascular responses were examined beat-by-beat for 30 sec before and 30 sec after auditory tones. RESULTS: During NREM sleep, CBFV declined following arousals (-15% +/- 2%; group mean +/- SEM) with a nadir at 9 sec after the auditory tone, followed by a gradual return to baseline. Mean arterial pressure (MAP; +20% +/- 1%) and heart rate (HR; +17% +/- 2%) increased with peaks at 5 and 3 sec after the auditory tone, respectively. Minute ventilation (VE) was increased (+35% +/- 10%) for 2 breaths after the auditory tone. In contrast, during REM sleep, CBFV increased following arousals (+15% +/- 3%) with a peak at 3 sec. MAP (+17% +/- 2%) and HR (+15% +/- 2%) increased during arousals from REM sleep with peaks at 5 and 3 sec post tone. VE increased (+16% +/- 7%) in a smaller, more sustained manner during arousals from REM sleep. CONCLUSIONS: Arousals from NREM sleep transiently reduce CBFV, whereas arousals from REM sleep transiently increase CBFV, despite qualitatively and quantitatively similar increases in MAP, HR, and VE in the two sleep states.     

Effects of a Change in Tone Frequency on the Habituated Orienting Response of the Sleeping Rat

EEG arousal and heart rate responses to change in tone frequency following habituation training were studied during slow wave sleep in the rat. Rats were exposed to sequences of 12 tone pulses. Habituation stimuli (trials 1-7) had a frequency of 16 kHz. The frequency of the following (test) trials was changed to either 5, 12, 14, 22, or 40 kHz. Hearing level was held constant for all frequencies. Test trials were repeated five times to study rehabituation. The results indicate that heart rate deceleration is an indicator of the orienting reflex and its magnitude is a positive function of the amount of frequency change of the stimulus. Large frequency changes in either direction relative to the habituation frequency lead to re-evocation of the habituated EEG arousal and heart rate deceleration, with subsequent rehabituation. Small tone-frequency changes do not result in EEG arousal or heart rate deceleration responses that differ from the responses to the habituated frequency. Heart rate acceleration shows neither short-term habituation nor significant reaction to any of the test frequencies.     

Auditory Evoked Potential in Stage 2 and REM Sleep During a 30-Day Exposure to Tone Pulses

Ten subjects were exposed to 3.5K Hz tone pulses of 660 msec duration, presented 24-hr-per-day for 30 days. The interstimulus interval was 22 sec. There were 10 days each at 80, 85, and 90 dB in that order. The average evoked potential (AEP) at C₃ referenced to linked mastoids was obtained from contiguous stage 2 and REM sleep segments on the first, second, and last recorded nights of tone-pulse exposure. The AEP was consistently larger in stage 2 than in REM sleep. In both stage 2 and REM sleep, AEP amplitude on the second recorded night bore no consistent relationship to first or last recorded night AEPs. Only the N2–P3 amplitude yielded consistent decreases, with 9 of 10 subjects in both stage 2 and REM sleep having smaller N2–P3 amplitudes on the last than on the first recorded night. There were no changes in latency of any component. During sleep there is little, if any, habituation of the auditory AEP during long-duration exposures to nonmeaningful stimuli, and certainly no extinction of the AEP under these conditions.     

Sleep disturbances due to exposure to tone pulses throughout the night

Sleep electroencephalograms (EEGs) and subjective reports data were obtained from six subjects (male college students) during 2 nights of baseline observation and 5 experimental nights of exposure to a 90-100 dB, 25 ms, 1,000 c/s tone pulse with various interstimulus intervals. The first of the 5 experimental nights started with an intertone interval of 80 s. On each of the following 4 nights, the intertone interval was fixed at 40-, 10-, 2.5-, or 1-s intervals, respectively. With the intensification of noise stimulus by shortening the intervals of tone pulses, a progressive disruption of nightly EEG sleep patterns was observed as follows: (a) increased frequency of awakenings and sleep stage changes during the night, (b) prolonged sleep latency, and (c) increased percentage of time spent in stage 1 sleep. However, total sleep time, REM latency, inter-REM intervals, and the percentages of time in stages 2, 3, 4, and REM sleep did not change significantly. The degree of subjective sleep disturbance was highly associated with objective measures of nightly EEG sleep patterns.     

Nightmares do result in psychophysiological arousal: A multimeasure ambulatory assessment study

Individuals who frequently experience nightmares report compromised sleep quality, poor daytime mood, and functioning. Previous research has aimed at linking these impairments with altered sleep architecture, but results were inconclusive. One plausible explanation is that only a few studies recorded markers of autonomic nervous system activity. For the first time, this study collected such markers under ecologically valid conditions with ambulatory assessment. In 19 individuals with frequent nightmares (≥1 nightmare/week) and 19 healthy control participants (<1 nightmare/month), measures indicating autonomic activation (heart rate, heart rate variability, respiration cycle length, electrodermal fluctuations, EEG arousals, saliva cortisol, REM density) were collected while applying ambulatory polysomnographic assessment during 3 consecutive nights. When nightmare participants reported a nightmare, we analyzed the last 5 min of REM sleep before awakening and compared these data to their non‐nightmares as well as to the dream episodes of control participants. Overall, there were no general differences in autonomic activation of nightmare sufferers compared to control participants. However, when nightmare participants experienced nightmares, autonomic activation was markedly increased compared to their own non‐nightmares and, to some extent, to control participant’s dreams. Significant intraindividual differences were found for all autonomic measures except in participant’s EEG arousals and cortisol levels. Group differences were found in EEG arousals and heart rate. In conclusion, ambulatory polysomnography demonstrates that nightmares are accompanied by increased autonomic activation. Results support the notion of impaired self‐reported sleep quality caused by one’s autonomic response rather than altered sleep pattern.     

Habituation of heart rate in functionally decorticate rats

Habituation of acoustically evoked heart rate responses and retention of this habituation was studied in functionally decorticate rats. An improved technique to induce cortical spreading depression (CSD) resulted in a pronounced and continuous depression of electroencephalographic activity. In Experiment 1, short-term habituation (STH) was demonstrated in decorticate rats and surgical controls; long-term habituation (LTH, 24 hr) occurred only in intact animals. In Experiment 2, only CSD groups were used. As in the first experiment, STH but not LTH was obtained under CSD. However, there was clear evidence that habituation could be retained subcortically for 30 min. It is concluded that the rat's cortex is not necessary for habituation of acoustically evoked heart rate responses and retention of this habituation over a moderately long interval. However, the results suggest that the cortex is involved in LTH and that the neuronal substrates of STH and LTH are, in significant part, different.     

Effects of intravenous catheter on sleep in healthy men and in depressed patients

The effects of intravenous catheter and nocturnal blood samplings at frequent intervals on sleep electroencephalogram (EEG) variables were investigated in 8 male healthy controls and 12 depressed patients, who were studied in the same experimental conditions. After one night of habituation, sleep was recorded during 4 consecutive nights in the sleep laboratory. A catheter was inserted around noon the day before the fourth night, and blood was sampled every 15 min for 25 h. The night-to-night comparison of sleep EEG variables did not show significant sleep continuity modifications in the control subjects, other than a weak trend toward an increase in nocturnal awakenings during the night with the catheter. A lengthening of sleep onset latency during the fourth night was found in the depressed patients. No significant changes were detected in percentage of rapid eye movement (REM) sleep in the two groups. However, a gradual increase in Stage 3 was observed across the 4 nights in the control subjects. These results indicate that intravenous blood sampling via a catheter can be performed without inducing significant disruption of sleep length and structure.     

Possible influence of AMPD1 on cholinergic neurotransmission and sleep

It is known that adenosine excess due to monophosphate deaminase deficiency (AMPD1) can be linked to muscle problems. Recently, Perumal et al., 2014 reported a first case of possible impact of AMPD1 on sleep, REM sleep and cholinergic neurotransmission. We report a second patient with similar sleep complaints: long sleep duration with residual daytime sleepiness and a need to sleep after exercise. On polysomnography we observed a long sleep duration, with high sleep efficiency and a SOREMP; on MSLT a shortened sleep latency and 4 SOREMPS were observed. Frequency power spectral heart rate analysis during slow wave sleep, REM sleep and wakefulness revealed an increased parasympathetic tone. In conclusion, AMPD1 could have a profound influence on cholinergic neurotransmission and sleep; further studies are mandatory.     

Cardiovascular and autonomic response to environmental noise during sleep in night shift workers

Polysomnograph, beat-by-beat heart rate and blood pressure were monitored in night shift workers exposed to environmental and laboratory noise events during day sleep. The study was carried out in a sleep laboratory. Subjects were nine young, healthy female night shift workers. Recorded noises from trucks, civilian aircraft, low altitude military aircraft and tones were presented at 55, 65, and 75 L(Amax). Sleep stage, heart rate, and systolic and diastolic blood pressures before and immediately after onset of noise events were compared. Spectral analyses of heart rate and blood pressure variabilities were used to compare sympathetic and parasympathetic nervous tone in 10-min. intervals containing noise and quiet. Heart rate was responsive to noise level but not noise type. Blood pressure increased primarily to sounds of sudden onset. Noise-induced awakening and alpha EEG responses were related to BP increase. Increase in HR was greatest when subjects were awakened by noise or already awake. Spectral analysis of BP variabilities indicated increased sympathetic vascular tone due to noise. Similar analyses of HR data indicated no noise effect. No habituation to noise was apparent over three consecutive sleep sessions. It was concluded that over the range of noise levels used, heart rate responds to noise level during sleep; blood pressure to sounds of sudden onset. Spectral analysis of blood pressure variabilities is a sensitive measure of autonomic nervous response to environmental noise and should also be studied in subjects sleeping at home.     

Studies of Information Processing in Sleep

Two studies of information processing in normal human sleep are reported. In Experiment I it was found that subjects responded differentially in stage 2 sleep to “own name,”“other name,” and tone stimuli (decreasing in that order) as reflected in both the finger plethysmograph (FP)and heart rate (HR) and to some extent the EEG K-complex response, and similarly in REM sleep as reflected in the FP measure and to some extent the HR measure, but not in sleep stage 3–4. In Experiment II it was found that conditioned discrimination acquired during wakefulness persisted in sleep stage 4, as reflected in the FP and HR measures, and sleep stage 2, as reflected in the K-complex response, but not in REM sleep. Results are compared to other studies of information processing in sleep. It is concluded that the results appear to indicate differential availability of the mechanisms of long-term memory, short-term memory, and stimulus preprocessing in the various stages of sleep. The authors further noted a bifurcation of the autonomic nervous system in sleep into two discrete effector limbs: electrodermal and cardiovascular.     

Behavioral versus EEG-based monitoring of all-night sleep/wake patterns

Faint tones were presented at intervals (average 16 s) throughout a night's sleep; whenever they heard them, subjects pressed a palm-mounted button to switch them off. At the same time, electroencephalogram (EEG) was recorded. Button-press responses occurred in all EEG stages of sleep except Stage 4, although there was only one behavioral response (BR) in Stage 3 and one in REM. The mean probability of response (PR)/Stage was Stage 1 = 0.235, Stage 2 = 0.016, Stage 3 = 0.001, Stage 4 = 0.000, Stage REM = 0.0004. Also, responses sometimes failed to occur in EEG Stage wake (PR = 0.94), particularly near sleep onset. If the criterion for wakefulness is cognitive response to external stimulation, only in EEG Stages 3, 4, and REM can accurate distinctions between sleep and wakefulness be made. If EEG is the criterion, then the data suggest that cognitive response is possible during Stages 1 and 2 "sleep." The concept of a sleep onset period (SOP), characterized by lengthening response times and intermittent response failure (thereby reflecting neither true sleep or wakefulness), may provide a useful resolution of this definitional dilemma.     

Modification of EEG asymmetry induced by auditory biofeedback loop during REM sleep in man

Several studies have emphasized the relationship between (1) rapid eye movement sleep (REM sleep) and learning, and (2) between REM sleep and asymmetry in EEG activity. Since we have shown that obtaining operant conditioned responses via auditory biofeedback during REM sleep is feasible, we demonstrate here that REM contingent auditory stimulations (white noise stimulation or interruption of a continuous white noise stimulation) lead to differential changes in phasic and tonic components of REM sleep. Whereas during baseline nights a relative right activation is found in the medium bands of EEG frequencies, our procedure seems to induce a systematic interhemispheric change during experimental nights. A new approach to the information processing hypothesis during REM sleep is proposed in terms of functional lateralized modifications of the EEG.     

NOCTURNAL EEG-GSR PROFILES: THE INFLUENCE OF PRESLEEP STATES

The number of nocturnal galvanic skin responses-(GSRs) varied widely between the electroencephalograph (EEG) stages of sleep as well as from night to night and from person to person. As others have found, non-specific GSRs occurred much more frequently during stage IV than other EEG stages, and were rare in stage REM. However, night-to-night variation and individual differences were related to the presleep state of the person. In general, electrodermal activity increased in all EEG stages as daytime stress increased, being especially great on nights preceding important school examinations. The nocturnal EEG profile was also related to the presleep state, the percentage of stage IV decreasing as daytime stress increased. The percentage of stage REM showed no systematic relation to stress. The occurrence of GSR “storms” during slow-wave sleep is consistent with the notion of release of cortical or other inhibitory influences during this state, but another mechanism is needed to explain the fact that presleep stress increases the frequency of GSRs in all stages of sleep, while simultaneously decreasing the percentage of slow-wave sleep.     

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.