Tone intensity and rise-decay time effects on cardiac responses during sleep

Evoked K-complexes and altered interaction between the central and autonomic nervous systems during sleep in alcohol use disorder

There is evidence for impairment in both central nervous system (CNS) and autonomic nervous system (ANS) function with prolonged alcohol use. While these impairments persist into abstinence, partial recovery of function has been demonstrated in both systems during sleep. To investigate potential ANS dysfunction associated with cortical CNS responses (impairment in CNS-ANS coupling), we assessed phasic heart rate (HR) fluctuation associated with tones that did and those that did not elicit a K-complex (KC) during stable N2 non-rapid eye movement (NREM) sleep in a group of 16 recently abstinent alcohol use disorder (AUD) patients (41.6 ± 8.5 years) and a group of 13 sex- and age-matched control participants (46.6 ± 9.3 years). Electroencephalogram (EEG) and electrocardiogram (ECG) data were recorded throughout the night. Alcohol consumption questionnaires were also administered to the AUD patients. AUD patients had elevated HR compared to controls at baseline prior to tone presentation. The HR fluctuation associated with KCs elicited by tone presentation was significantly smaller in amplitude, and tended to be delayed in time, in the AUD group compared with the control group, and the subsequent deceleration was also smaller in AUD patients. In both groups, the increase in HR was larger and occurred earlier when KCs were produced than when they were not, and there was no difference in the magnitude of the KC effect between groups. Phasic HR changes associated with KCs elicited by tones are impaired in AUD participants, reflecting ANS dysfunction possibly caused by an alteration of cardiac vagal trafficking. However, only the timing of the HR response was found to relate to estimated lifetime alcohol consumption in AUD. The clinical meaning and implications of these novel findings need to be determined.

K-Complexes: Interaction between the Central and Autonomic Nervous Systems during Sleep

STUDY OBJECTIVES

To investigate the relationship between K-complexes (KCs) and cardiac functioning.

METHODS

Forty healthy adolescents aged 16-22 y (19 females) participated in the study. Heart rate (HR) fluctuations associated with spontaneous and evoked KCs were investigated on two nights, one with (event-related potential night) and one without auditory tones presented across the night.

RESULTS

There was a clear biphasic cardiac response to evoked and spontaneous KCs, with an initial acceleration in HR followed by a deceleration (P < 0.001). HR acceleration occurred immediately to KCs in response to tones presented in the first third of the interbeat interval, but was delayed a beat when the tone occurred later in the cardiac cycle (P < 0.05). Sex differences were also evident. Pretone baseline HR was higher, and the magnitude of the HR response was blunted and delayed, in female compared to male adolescents (P < 0.001). Also, pretone baseline HR was lower when a tone elicited a KC compared to when it did not (P < 0.001), suggesting that KCs are possibly more likely to be elicited by external stimuli in states of reduced cardiac activation.

CONCLUSIONS

The strict dependency observed between KCs and cardiac control indicates a potential role of KCs in modulating the cardiovascular system during sleep. Sex differences in the KC-cardiac response indicate the sensitivity of this measure in capturing sex differences in cardiac regulatory physiology.

Living alongside railway tracks: Long-term effects of nocturnal noise on sleep and cardiovascular reactivity as a function of age

Very few studies were devoted to permanent effects of nocturnal railway noise on sleep and cardiovascular reactivity. We investigated the effects of nocturnal railway noise on sleep and cardiovascular response in young and middle-aged adults living for many years either near a railway track or in a quiet area. Forty subjects (50% males) divided into two age groups (juniors: 26.2+/-3.6 and seniors: 56.2+/-4.2) participated in this experiment. Half of them lived near a railway track (RW group: 2.6 to 19 years) and the other half in a quiet environment (QE group: 8.1 to 14.2 years). After an adaptation night, all subjects underwent two nights in the laboratory: one control night and one noisy night (30 by-passes of a freight train). Sleep and cardiovascular modifications were assessed in response to noise. Sleep fragmentation indices were lower in RW subjects compared to QE whatever their age. In response to noise, there was a higher cardiovascular response rate to noise in RW juniors and a lower cardiovascular response rate in RW seniors compared to their age-paired QE counterparts. In conclusion, permanent exposure to nocturnal railway noise leads to decreased sleep fragmentation and to cardiovascular habituation. It is suggested that during the initial period experienced by residents living near railway tracks, nocturnal railway noise could induce a sensitization process on the autonomic response to noise reflecting a startle/defense reflex due to its functional significance, which progressively turns to habituation in the long-term if no adverse effect is experienced.

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).

The heart rate deceleratory response in low-risk human fetuses: effect of stimulus intensity on response topography

The purpose of this study was to determine the effect of stimulus intensity on heart rate response in 18 low-risk human fetuses between 37 and 40 weeks gestation. Each fetus was stimulated in quiet sleep with a 30-s voice sound at intensities of 80 dB and 90 dB. The fetal cardiac electrical signal was captured transabdominally at a rate of 1024 Hz and fetal R-waves were extracted using adaptive signal-processing techniques. We found that fetuses generally exhibited a 5- to 10-s decrease in heart rate following stimulus onset at an intensity of 80 dB. The response pattern changed from deceleratory to acceleratory when stimulus intensity was increased to 90 dB. Our findings suggest that a heart rate deceleration at low-stimulus intensity may be a component of the orienting reflex in the human fetus.

Effects of rate of tone-pip stimulation on the evoked K-Complex

The effects of rate of presentation on the evoked K-Complex were examined. In different conditions, brief duration tone pips were presented every 5, 10 or 30 s. Trials were sorted into those on which a K-Complex was or was not elicited and averaged separately. The evoked K-Complex consisted of two different negative components peaking at approximately 350 and 550 ms (respectively), followed by a positive component peaking at approximately 900 ms. K-Complexes were elicited more often in Stage 2 early and 2 late than in slow-wave sleep although the differences were not significant. K-Complexes were elicited more often in the Long ISI compared to the Short and Medium ISI conditions. When a K-Complex was evoked, the amplitude of N350 and N550 was greater for the Long ISI than for the Short or Medium ISI conditions. P900 amplitude remained invariant regardless of the ISI. A micro-analysis was carried out whenever 3 consecutive occurring K-Complexes were elicited. During the Short and Medium ISI conditions, N350 and N550 following the second and third occurrence of the K-Complex were significantly attenuated compared to the first occurrence. There was no difference in N350 and N550 amplitudes among the 3 consecutive occurrences during the Long ISI condition. The decay in amplitude over consecutive occurrences of the K-Complex might be a reflection of either habituation or refractory processes.

Developmental constraints on the expression of behavioral and heart-rate orienting responses: II. The role of ambient temperature

The effect of ambient temperature on the expression of behavioral and heart-rate orienting responses to a novel olfactory stimulus was examined in rats 1-18 days of age. There was no effect of ambient temperature on the behavioral orienting responses at any age. Ambient temperature did influence the expression of the heart-rate orienting response and did so differentially as a function of age. The implications of these findings for developmental models of attention and cognition are discussed.

Stimulus rise time, intensity and the elicitation of unconditioned cardiac and electrodermal responses

In recent discussions on the differentiation of orienting, startle and defense responses, the importance of stimulus rise time for the elicitation of different cardiac response patterns was re-emphasized. Especially, it has been claimed that phasic accelerative heart rate (HR) responses-interpreted as indicators of startle-might not only be evoked by auditory stimuli with instantaneous rise times and high intensities, but also by low to moderate stimulus intensities with sudden onsets. The present study examined this question by manipulating rise time (instantaneous vs. 50 ms) and intensity (60 vs. 95 dB). Subjects (N = 120) were randomly assigned to one of the four independent groups. They performed a habituation experiment in which 12 tones of 1000 Hz with a constant interstimulus interval of 90 s were presented. On trial 13, a change in rise time was introduced by reversing the rise time condition in each group (i.e., from instantaneous to 50 ms and vice versa). Examination of HR changes across 4 poststimulus seconds, of maximal HR deceleration and acceleration, as well as examination of magnitude of skin conductance responses (SCRs) indicated clear intensity effects. Rise time, on the other hand, had no effects on HR and SC that could be interpreted as indicative of startle. Thus, it could neither be observed that instantaneous rise time led to stronger accelerative HR responses nor that the combination of instantaneous rise time and high intensity elicited anything but a dominant accelerative response pattern. These findings were also obtained when the first four trials were analyzed separately. As a consequence of stimulus change, larger SCRs as well as larger decelerative HR responses were observed without, however, being affected by the direction of the change in rise time. In sum, the present study suggests that the role attributed to rise time with respect to eliciting qualitatively different cardiac response patterns has been exaggerated. The consequences for the differentiation of different unconditioned responses are briefly addressed.

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.

Preconditioning and excitability of the human orbicularis oculi reflex as a function of state

Reflex excitability and unstimulated activity of orbicularis oculi were found to vary as a function of state but the effects of weak conditioning stimuli, preceding reflex stimulation by 30--210 msec, were independent of state. Electromyographic activity was recorded from 23 young adults: 12 subjects with eyes closed during quiet wakefulness, 3 subjects during all-night sleep, 8 subjects during an afternoon nap. Stimulation with a 50 msec, 105 dB(A) white noise burst elicited a reflex response in 92% of waking trials and 87% of trials during REM sleep, but responses occurred in only 54% of trials during NREM sleep. Further, response latency was longer and magnitude less during the NREM state. Despite the differences in reflex excitability associated with state, state did not affect the modifications of reflex activity produced by a 20 msec, 70 dB(A) conditioning tone. At all lead intervals, reflex magnitude was reduced by the weak prestimulation even though, at the shortest interval, reflex activity was initiated more rapidly. The discordant changes in reflex size and latency have been seen in previous waking studies and appear to be mediated by different mechanisms. The persistence of both effects during sleep suggests that neither effect depends on high-level central processes.

Precocious cardiac orienting in a human anencephalic infant

An anencephalic infant, 3 to 6 weeks old, responded to acoustic stimulation with cardiac decelerations typical of the response pattern seen in normal, older infants. Such precocity implies unexpected competence of lower brain structures and suggests that, in the normal infant, feedback from immature higher centers may sometimes interfere with rather than modulate the functioning of lower centers.

Tail artery response to sound in the unanesthetized rat

Arterial pulsations have been recorded indirectly from the surface of the rat's tail. Slight heating of restrained unanesthetized rats produces vasodilatation and large amplitude pulsations that are influenced by sensory stimuli, in this case, sound. The surface-recorded pulse volume was found to be proportional to pulse pressure, indicating vasoconstriction as the cause of the decline of the pulse amplitude. A one-second noise burst elicited vasoconstriction, the duration of which was proportional to sound level and occurred as low as at hearing threshold. Under the specified conditions, reproducibility was good with no significant habituation both within session, and between sessions with a one week interval. The warming of the rats was found to be critical for the sound-elicited reactions; responses were obtained only within a narrow, individual temperature-range. The possibilities of using tail vasoconstriction for evaluation of hearing was pointed out, as well as for studies of noise effects on peripheral circulation.