The effect of CNS activation versus EEG arousal during sleep on heart rate response and daytime tests

Distinction between epileptic and non-epileptic arousal by heart rate change

OBJECTIVE

We investigated the difference in heart rate (HR) change between epileptic and non-epileptic arousals in adult patients with epilepsy (PWE).

METHODS

This is a case-control study conducted at the University Hospitals of Cleveland Medical Center. Inclusion criteria are (1) adult (≥18 years old) PWE who had arousal related to a focal aware or impaired awareness automatism seizure with or without focal to bilateral tonic-clonic seizure during an Epilepsy Monitoring Unit (EMU) admission between January 2009 and January 2021 or (2) adult PWE who had a non-epileptic arousal during an EMU admission between July 2020 and January 2021. Outcomes are (1) a percent change in baseline HR within 60 s after arousal and (2) the highest percent change in baseline HR within a 10-s sliding time window within 60 s after arousal.

RESULTS

We included 20 non-epileptic arousals from 20 adult PWE and 29 epileptic arousals with seizures from 29 adult PWE. Within 60 s after arousal, HR increased by a median of 86.7% (interquartile range (IQR), 52.7%-121.3%) in the epileptic arousal group compared to a median of 26.1% (12.9%-43.3%) in the non-epileptic arousal group (p < 0.001). The cut-off value was 48.7%. The area under the curve (AUC), sensitivity, and specificity were 0.85, 0.79, and 0.80, respectively. More than 70.1% was only in the epileptic arousals, with 100% specificity. Within 10 s of the greatest change, HR increased by 36.5 (18.7%-48.4%) in the epileptic arousal group compared to 17.7 (10.9%-23.7%) in the non-epileptic arousal group (p < 0.001). The cut-off value was 36.5%. The AUC, sensitivity, and specificity were 0.79, 0.52, and 0.95, respectively. More than 48.1% was only in the epileptic arousals, with 100% specificity.

SIGNIFICANCE

Tachycardia during epileptic arousals was significantly higher and more robust compared to tachycardia during non-epileptic arousals.

Recent Progress in Long-Term Sleep Monitoring Technology

Sleep is an essential physiological activity, accounting for about one-third of our lives, which significantly impacts our memory, mood, health, and children's growth. Especially after the COVID-19 epidemic, sleep health issues have attracted more attention. In recent years, with the development of wearable electronic devices, there have been more and more studies, products, or solutions related to sleep monitoring. Many mature technologies, such as polysomnography, have been applied to clinical practice. However, it is urgent to develop wearable or non-contacting electronic devices suitable for household continuous sleep monitoring. This paper first introduces the basic knowledge of sleep and the significance of sleep monitoring. Then, according to the types of physiological signals monitored, this paper describes the research progress of bioelectrical signals, biomechanical signals, and biochemical signals used for sleep monitoring. However, it is not ideal to monitor the sleep quality for the whole night based on only one signal. Therefore, this paper reviews the research on multi-signal monitoring and introduces systematic sleep monitoring schemes. Finally, a conclusion and discussion of sleep monitoring are presented to propose potential future directions and prospects for sleep monitoring.

Exclusion of EEG-based arousals in wake epochs of polysomnography leads to underestimation of the arousal index

STUDY OBJECTIVES

There is an internal contradiction in current American Academy of Sleep Medicine (AASM) standards for arousal index (AI) calculation in polysomnography (PSG), in that arousals in sleep and wake epochs are counted, but only sleep time is used in the denominator. This study aimed to investigate the impact of including arousals scored in wake epochs on the AI.

METHODS

We compared arousal indices including (AI_inc) vs. excluding (AI_exc) awake-epoch arousals from 100 consecutive PSGs conducted for investigation of possible OSA. To determine the AI that most closely approximated 'truth', AI_inc and AI_exc were compared to an AI calculated from continuous sleep analysis (AI_cont) in a 20 PSG subgroup.

RESULTS

The median (IQR) increase in AI_inc was 5.2/h (3.5, 8.1) vs. AI_exc (AI_inc = 28.0/h (18.4, 38.9) vs. AI_exc = 22.9/h (13.1, 31.3)), equating to an increase of 25.3% (15.6, 40.8). As the AI increased, the difference increased (p < .001), with decreasing sleep efficiency and increasing AHI the strongest predictors of the difference between AI_exc and AI_inc. The absolute AI_exc-AI_cont difference (7.7/h (5.1, 13.6)) was significantly greater than the AI_inc-AI_cont difference (1.2/h (0.6, 5.7); z = -3.099, p = .002).

CONCLUSIONS

There was a notable increase in AI when including wake-epoch arousals, particularly with more severe OSA or reduced sleep efficiency. However, the AI including wake-epoch arousals best matched the 'true' continuous sleep scoring arousal index. Our study informs clinical and research practice, highlights epoch scoring pitfalls, and supports the current AASM standard arousal reporting approach for future standards.

The Different Facets of Heart Rate Variability in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), a heterogeneous and multifactorial sleep related breathing disorder with high prevalence, is a recognized risk factor for cardiovascular morbidity and mortality. Autonomic dysfunction leads to adverse cardiovascular outcomes in diverse pathways. Heart rate is a complex physiological process involving neurovisceral networks and relative regulatory mechanisms such as thermoregulation, renin-angiotensin-aldosterone mechanisms, and metabolic mechanisms. Heart rate variability (HRV) is considered as a reliable and non-invasive measure of autonomic modulation response and adaptation to endogenous and exogenous stimuli. HRV measures may add a new dimension to help understand the interplay between cardiac and nervous system involvement in OSA. The aim of this review is to introduce the various applications of HRV in different aspects of OSA to examine the impaired neuro-cardiac modulation. More specifically, the topics covered include: HRV time windows, sleep staging, arousal, sleepiness, hypoxia, mental illness, and mortality and morbidity. All of these aspects show pathways in the clinical implementation of HRV to screen, diagnose, classify, and predict patients as a reasonable and more convenient alternative to current measures.

Sympathetic activity contributes to the fMRI signal

The interpretation of functional magnetic resonance imaging (fMRI) studies of brain activity is often hampered by the presence of brain-wide signal variations that may arise from a variety of neuronal and non-neuronal sources. Recent work suggests a contribution from the sympathetic vascular innervation, which may affect the fMRI signal through its putative and poorly understood role in cerebral blood flow (CBF) regulation. By analyzing fMRI and (electro-) physiological signals concurrently acquired during sleep, we found that widespread fMRI signal changes often co-occur with electroencephalography (EEG) K-complexes, signatures of sub-cortical arousal, and episodic drops in finger skin vascular tone; phenomena that have been associated with intermittent sympathetic activity. These findings support the notion that the extrinsic sympathetic innervation of the cerebral vasculature contributes to CBF regulation and the fMRI signal. Accounting for this mechanism could help separate systemic from local signal contributions and improve interpretation of fMRI studies.

Contribution of systemic vascular effects to fMRI activity in white matter

To investigate a potential contribution of systemic physiology to recently reported BOLD fMRI signals in white matter, we compared photo-plethysmography (PPG) and whole-brain fMRI signals recorded simultaneously during long resting-state scans from an overnight sleep study. We found that intermittent drops in the amplitude of the PPG signal exhibited strong and widespread correlations with the fMRI signal, both in white matter (WM) and in gray matter (GM). The WM signal pattern resembled that seen in previous resting-state fMRI studies and closely tracked the location of medullary veins. Its temporal cross-correlation with the PPG amplitude was bipolar, with an early negative value. In GM, the correlation was consistently positive. Consistent with previous studies comparing physiological signals with fMRI, these findings point to a systemic vascular contribution to WM fMRI signals. The PPG drops are interpreted as systemic vasoconstrictive events, possibly related to intermittent increases in sympathetic tone related to fluctuations in arousal state. The counter-intuitive polarity of the WM signal is explained by long blood transit times in the medullary vasculature of WM, which cause blood oxygenation loss and a substantial timing mismatch between blood volume and blood oxygenation effects. A similar mechanism may explain previous findings of negative WM signals around large draining veins during both task- and resting-state fMRI.

Humor drawings evoked temporal and spectral EEG processes

The study aimed to explore the humor processing elicited through the manipulation of artistic drawings. Using the Comprehension-Elaboration Theory of humor as the main research background, the experiment manipulated the head portraits of celebrities based on the independent variables of facial deformation (large/small) and addition of affective features (positive/negative). A 64-channel electroencephalography was recorded in 30 participants while viewing the incongruous drawings of celebrities. The electroencephalography temporal and spectral responses were measured during the three stages of humor which included incongruity detection, incongruity comprehension and elaboration of humor. Analysis of event-related potentials indicated that for humorous vs non-humorous drawings, facial deformation and the addition of affective features significantly affected the degree of humor elicited, specifically: large > small deformation; negative > positive affective features. The N170, N270, N400, N600-800 and N900-1200 components showed significant differences, particularly in the right prefrontal and frontal regions. Analysis of event-related spectral perturbation showed significant differences in the theta band evoked in the anterior cingulate cortex, parietal region and posterior cingulate cortex; and in the alpha and beta bands in the motor areas. These regions are involved in emotional processing, memory retrieval, and laughter and feelings of amusement induced by elaboration of the situation.

Sleep disturbances in irritable bowel syndrome: a systematic review

BACKGROUND

Sleep disturbances are well-documented among persons with irritable bowel syndrome (IBS). Difficulty in falling asleep, shorter sleep time, frequent arousal and awakenings, or non-restorative sleep are the most common manifestations. Sleep disturbances are also related to a higher risk of having IBS. Some researchers have provided evidence of a positive association between poorer subjective sleep quality and increased severity and frequency in gastrointestinal (GI) symptoms in those with IBS. However, findings from studies using objective sleep and activity measures, such as polysomnography and actigraphy, are inconclusive.

PURPOSE

This systematic review of the literature between 1990 and 2015 evaluates the evidence of sleep disturbances in adults with IBS and their relationship with GI symptoms.

Relationship between arousal intensity and heart rate response to arousal

STUDY OBJECTIVES

The visual appearance of cortical arousals varies considerably, from barely meeting scoring criteria to very intense arousals. Arousal from sleep is associated with an increase in heart rate (HR). Our objective was to quantify the intensity of arousals in an objective manner using the time and frequency characteristics of the electroencephalogram (EEG) and to determine whether HR response to arousal correlates with arousal intensity so determined.

DESIGN

Post hoc analysis of 20 preexisting polysomnography (PSG) files.

SETTING

Research and Development Laboratory (YRT Limited).

PARTICIPANTS

N/A.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Arousals were scored using the American Academy of Sleep Medicine criteria. The EEG signals' time and frequency characteristics were determined using wavelet analysis. An automatic algorithm was developed to scale arousal intensity based on the change in wavelet features and data from a training set obtained from 271 arousals visually scaled between zero and nine (most intense). There were 2,695 arousals in 20 PSGs that were scaled. HR response (ΔHR) was defined as the difference between the highest HR in the interval [arousal-onset to (arousal-end +8 sec)] and the highest HR between 2 and 12 sec preceding arousal onset. There was a strong correlation between arousal scale and ΔHR within each subject (average r: 0.95 ± 0.04). The slope of the relationship varied among subjects (0.7-2.4 min(-1)/unit scale).

CONCLUSIONS

Arousal intensity, quantified by wavelet transform, is strongly associated with arousal-related tachycardia, and the gain of the relationship varies among subjects. Quantifying arousal intensity in PSGs provides additional information that may be clinically relevant.

Contribution of arousal from sleep to postevent tachycardia in patients with obstructive sleep apnea

STUDY OBJECTIVES

Heart rate increases after obstructive events in patients with obstructive sleep apnea (OSA). This response is generally attributed to arousal from sleep. Opening of the obstructed airway, however, is associated with ventilatory and hemodynamic changes that could result in physiologic responses unrelated to arousal. Our objective was to determine the contribution of these physiologic responses to postevent tachycardia.

DESIGN

Analysis of data obtained during previous research protocols.

SETTING

Academic sleep laboratory.

PARTICIPANTS

Twenty patients with severe OSA.

INTERVENTIONS

Patients were placed on a continuous positive airway pressure (CPAP) device. CPAP was reduced during sleep to different levels (dial-downs), producing obstructive events of varying severity. Some dial-downs with severe obstruction were maintained until spontaneous airway opening. In others, CPAP was increased after three obstructed breaths, terminating the events approximately 10 sec before spontaneous termination in long dial-downs.

MEASUREMENT AND RESULTS

Beat-by-beat heart rate (HR) was measured for 20 sec following airway opening. Spontaneous opening during sustained dial-downs occurred 21.9 ± 8.4 sec after dial-down, was associated with arousal, and resulted in the greatest postevent tachycardia (7.8 ± 4.0 min(-1)). However, deliberate termination of events (12.2 ± 2.6 sec after dial-down) was also followed by tachycardia that, in the absence of cortical arousal, showed a dose-response behavior, increasing with severity of obstruction and without apparent threshold. ΔHR following deliberately brief, severe obstruction (3.8 ± 3.0 min(-1)) was approximately half the ΔHR that followed spontaneous opening of equally severe obstructions despite the shorter duration and absence of cortical arousal.

CONCLUSIONS

Postevent tachycardia is due in large part to physiologic (arousal-unrelated) responses that occur upon relief of obstruction.

Progressive changes in cortical state before and after spontaneous arousals from sleep in elderly and middle-aged women

Arousals are often considered to be events which have an abrupt onset and offset, indicating abrupt changes in the state of the cortex. We hypothesized that cortical state, as reflected in electroencephalograph (EEG) signals, exhibits progressive systematic changes before and after a spontaneous, isolated arousal and that the time courses of the spectral components of the EEG before and after an arousal would differ between healthy middle-aged and elderly subjects. We analyzed the power spectrum and Sample Entropy of the C3A2 EEG before and after isolated arousals from 20 middle-aged (47.2±2.0 years) and 20 elderly (78.4±3.8 years) women using polysomnograms from the Sleep Heart Health Study database. In middle-aged women, all EEG spectral band powers <16 Hz exhibited a significant increase relative to baseline at some time in the 21 s before an arousal, but only low- (0.2-2.0 Hz) and high-frequency (2.0-4.0 Hz) delta increased in elderly and only during the last 7 s pre-arousal. Post-arousal, all frequency bands below 12 Hz transiently fell below pre-arousal baseline in both age groups. Consistent with these findings, Sample Entropy decreased steadily before an arousal, increased markedly during the arousal, and remained above pre-arousal baseline levels for ∼30 s after the arousal. In middle-aged, but not in elderly, women the presence of early pre-arousal low delta power was associated with shorter arousals. We propose that this attenuation of the effect of the arousing stimulus may be related to the slow (<1 Hz) cortical state oscillation, and that prolonged alterations of cortical state due to arousals may contribute to the poor correlation between indices of arousals and indices of sleepiness or impaired cognitive function.

Cardiorespiratory response to spontaneous cortical arousals during stage 2 and rapid eye movement sleep in healthy children

Arousal from sleep is associated with transient and abrupt cardiorespiratory changes, and elevated arousals associated with sleep disorders may trigger adverse cardiovascular sequela. In this paper, we provide the first data in children on cardiorespiratory responses to cortical arousal. Heart rate and ventilatory responses to arousal from stage 2 and rapid eye movement (REM) sleep were investigated in 40 normal, healthy Caucasian children (age: 7.7 +/- 2.6 years; body mass index z-score: 0.30 +/- 0.8). All children underwent overnight polysomnography studies. Cortical arousals were scored according to standard criteria. Heart rate changes were assessed over 30 s, starting 15 s prior to cortical arousal onset. Breathing rates were quantified three breaths before and after arousal onset. Arousals from stage 2 as well as REM sleep resulted in an R-R interval shortening of about 15%, independent of age and gender. The R-R interval shortening initiated at least 3 s before the cortical arousal onset. The breathing interval immediately after cortical arousal onset was significantly shortened (P < 0.001). In conclusion, cortical arousals in children are associated with an increase in breathing rate and significant heart rate accelerations, which typically precede the cortical arousal onset.

Cervical column morphology in adult patients with obstructive sleep apnoea

Cervical column morphology was examined in adult patients with obstructive sleep apnoea (OSA) and compared with the cervical morphology of an adult control group with neutral occlusion, normal craniofacial morphology, and no history of sleep apnoea. The sleep apnoea group consisted of 91 patients, 16 females aged 29-59 years (mean 49.4 years) and 75 males aged 27-65 years (mean 49.0 years). All patients were diagnosed with OSA by overnight polysomnography. The control group consisted of 21 subjects, 15 females aged 23-40 years (mean 29.2 years) and 6 males aged 25-44 years (mean 32.8 years). From each individual, a visual assessment of the cervical column was performed on the radiograph. Differences in the cervical column morphology, between the genders and the groups were assessed by Fisher's exact test and the effect of age by logistic regression analysis. In the OSA group, 46.2 per cent had fusion anomalies of the cervical column and 5.5 per cent a posterior arch deficiency. Fusion anomalies occurred in 26.4 per cent as fusions between two cervical vertebrae. Block fusions occurred in 12.1 per cent and occipitalization in 14.3 per cent. A posterior arch deficiency occurred in 2.2 per cent as a partial cleft of C1 and in 3.3 per cent as dehiscence of C3 and C4. No statistical gender differences were found in the occurrence of morphological characteristics of the cervical column. The fusion anomalies of the cervical column occurred significantly more often in the OSA group. The results indicate that the morphological deviations of the upper cervical vertebrae play a role in the phenotypical subdivision and diagnosis of OSA.

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.

An ECG-based algorithm for the automatic identification of autonomic activations associated with cortical arousal

OBJECTIVES

EEG arousals are associated with autonomic activations. Visual EEG arousal scoring is time consuming and suffers from low interobserver agreement. We hypothesized that information on changes in heart rate alone suffice to predict the occurrence of cortical arousal.

METHODS

Two visual AASM EEG arousal scorings of 56 healthy subject nights (mean age 37.0 +/- 12.8 years, 26 male) were obtained. For each of 5 heartbeats following the onset of 3581 consensus EEG arousals and of an equal number of control conditions, differences to a moving median were calculated and used to estimate likelihood ratios (LRs) for 10 categories of heartbeat differences. Comparable to 5 consecutive diagnostic tests, these LRs were used to calculate the probability of heart rate responses being associated with cortical arousals.

RESULTS

EEG and ECG arousal indexes agreed well across a wide range of decision thresholds, resulting in a receiver operating characteristic (ROC) with an area under the curve of 0.91. For the decision threshold chosen for the final analyses, a sensitivity of 68.1% and a specificity of 95.2% were obtained. ECG and EEG arousal indexes were poorly correlated (r = 0.19, P <0.001, ICC = 0.186), which could in part be attributed to 3 outliers. The Bland-Altman plot showed an unbiased estimation of EEG arousal indexes by ECG arousal indexes with a standard deviation of +/- 7.9 arousals per hour sleep. In about two-thirds of all cases, ECG arousal scoring was matched by at least one (22.2%) or by both (42.5%) of the visual scorings. Sensitivity of the algorithm increased with increasing duration of EEG arousals. The ECG algorithm was also successfully validated with 30 different nights of 10 subjects (mean age 35.3 [ 13.6 years, 5 male).

CONCLUSIONS

In its current version, the ECG algorithm cannot replace visual EEG arousal scoring. Sensitivity for detecting <10-s EEG arousals needs to be improved. However, in a nonclinical population, it may be valuable to supplement visual EEG arousal scoring by this automatic, objective, reproducible, cheap, and time-saving method.