Jo M. Solet

Measuring sleep: Accuracy, sensitivity, and specificity of wrist actigraphy compared to polysomnography

OBJECTIVES We validated actigraphy for detecting sleep and wakefulness versus polysomnography (PSG). DESIGN Actigraphy and polysomnography were simultaneously collected during sleep laboratory admissions. All studies involved 8.5 h time in bed, except for sleep restriction studies. Epochs (30-sec; n = 232,849) were characterized for sensitivity (actigraphy = sleep when PSG = sleep), specificity (actigraphy = wake when PSG = wake), and accuracy (total proportion correct); the amount of wakefulness after sleep onset (WASO) was also assessed. A generalized estimating equation (GEE) model included age, gender, insomnia diagnosis, and daytime/nighttime sleep timing factors. SETTING Controlled sleep laboratory conditions. PARTICIPANTS Young and older adults, healthy or chronic primary insomniac (PI) patients, and daytime sleep of 23 night-workers (n = 77, age 35.0 ± 12.5, 30F, mean nights = 3.2). INTERVENTIONS N/A. MEASUREMENTS AND RESULTS Overall, sensitivity (0.965) and accuracy (0.863) were high, whereas specificity (0.329) was low; each was only slightly modified by gender, insomnia, day/night sleep timing (magnitude of change < 0.04). Increasing age slightly reduced specificity. Mean WASO/night was 49.1 min by PSG compared to 36.8 min/night by actigraphy (β = 0.81; CI = 0.42, 1.21), unbiased when WASO < 30 min/night, and overestimated when WASO > 30 min/night. CONCLUSIONS This validation quantifies strengths and weaknesses of actigraphy as a tool measuring sleep in clinical and population studies. Overall, the participant-specific accuracy is relatively high, and for most participants, above 80%. We validate this finding across multiple nights and a variety of adults across much of the young to midlife years, in both men and women, in those with and without insomnia, and in 77 participants. We conclude that actigraphy is overall a useful and valid means for estimating total sleep time and wakefulness after sleep onset in field and workplace studies, with some limitations in specificity.

Spontaneous brain rhythms predict sleep stability in the face of noise

Quality sleep is an essential part of health and well-being. Yet fractured sleep is disturbingly prevalent in our society, partly due to insults from a variety of noises [1]. Common experience suggests that this fragility of sleep is highly variable between people, but it is unclear what mechanisms drive these differences. Here we show that it is possible to predict an individuals ability to maintain sleep in the face of sound using spontaneous brain rhythms from electroencephalography (EEG). The sleep spindle is a thalamocortical rhythm manifested on the EEG as a brief 11-15 Hz oscillation and is thought to be capable of modulating the influence of external stimuli [2]. Its rate of occurrence, while variable across people, is stable across nights [3]. We found that individuals who generated more sleep spindles during a quiet night of sleep went on to exhibit higher tolerance for noise during a subsequent, noisy night of sleep. This result shows that the sleeping brains spontaneous activity heralds individual resilience to disruptive stimuli. Our finding sets the stage for future studies that attempt to augment spindle production to enhance sleep continuity when confronted with noise.

Sleep Disruption due to Hospital Noises: A Prospective Evaluation

Background Sleep plays a critical role in maintaining health and well-being; however, patients who are hospitalized are frequently exposed to noise that can disrupt sleep. Efforts to attenuate hospital noise have been limited by incomplete information on the interaction between sounds and sleep physiology. Objective To determine profiles of acoustic disruption of sleep by examining the cortical (encephalographic) arousal responses during sleep to typical hospital noises by sound level and type and sleep stage. Design 3-day polysomnographic study. Setting Sound-attenuated sleep laboratory. Participants Volunteer sample of 12 healthy participants. Intervention Baseline (sham) night followed by 2 intervention nights with controlled presentation of 14 sounds that are common in hospitals (for example, voice, intravenous alarm, phone, ice machine, outside traffic, and helicopter). The sounds were administered at calibrated, increasing decibel levels (40 to 70 dBA [decibels, adjusted for the range of normal hearing]) during specific sleep stages. Measurements Encephalographic arousals, by using established criteria, during rapid eye movement (REM) sleep and non-REM (NREM) sleep stages 2 and 3. Results Sound presentations yielded arousal response curves that varied because of sound level and type and sleep stage. Electronic sounds were more arousing than other sounds, including human voices, and there were large differences in responses by sound type. As expected, sounds in NREM stage 3 were less likely to cause arousals than sounds in NREM stage 2; unexpectedly, the probability of arousal to sounds presented in REM sleep varied less by sound type than when presented in NREM sleep and caused a greater and more sustained elevation of instantaneous heart rate. Limitations The study included only 12 participants. Results for these healthy persons may underestimate the effects of noise on sleep in patients who are hospitalized. Conclusion Sounds during sleep influence both cortical brain activity and cardiovascular function. This study systematically quantifies the disruptive capacity of a range of hospital sounds on sleep, providing evidence that is essential to improving the acoustic environments of new and existing health care facilities to enable the highest quality of care. Primary funding source Academy of Architecture for Health, Facilities Guidelines Institute, and The Center for Health Design.

Gender Differences in Research Grant Applications and Funding Outcomes for Medical School Faculty

PURPOSE To evaluate whether there were differences in acquisition of research grant support between male and female faculty at eight Harvard Medical School-affiliated institutions. METHODS Data were obtained from the participating institutions on all research grant applications submitted by full-time faculty from 2001 through 2003. Data were analyzed by gender and faculty rank of applicant, source of support (federal or nonfederal), funding outcome, amount of funding requested, and amount of funding awarded. RESULTS Data on 6319 grant applications submitted by 2480 faculty applicants were analyzed. Women represented 29% of investigators and submitted 26% of all grant requests. There were significant gender differences in the mean number of submissions per applicant (women 2.3, men 2.7), success rate (women 41%, men 45%), number of years requested (women 3.1, men 3.4), median annual amount requested (women

Covert waking brain activity reveals instantaneous sleep depth.

115,325, men

Decrease in as‐needed sedative use by limiting nighttime sleep disruptions from hospital staff

150,000), mean number of years awarded (women 2.9, men 3.2), and median annual amount awarded (women

Managing alarm fatigue in cardiac care

98,094, men

Sleep disruption due to hospital noises

125,000). After controlling for academic rank, grant success rates were not significantly different between women and men, although submission rates by women were significantly lower at the lowest faculty rank. Although there was no difference in the proportion of money awarded to money requested, women were awarded significantly less money than men at the ranks of instructor and associate professor. More men than women applied to the National Institutes of Health, which awarded higher dollar amounts than other funding sources. CONCLUSIONS Gender disparity in grant funding is largely explained by gender disparities in academic rank. Controlling for rank, women and men were equally successful in acquiring grants. However, gender differences in grant application behavior at lower academic ranks also contribute to gender disparity in grant funding for medical science.

Translating Sleep Science Into Policy

The neural correlates of the wake-sleep continuum remain incompletely understood, limiting the development of adaptive drug delivery systems for promoting sleep maintenance. The most useful measure for resolving early positions along this continuum is the alpha oscillation, an 8–13 Hz electroencephalographic rhythm prominent over posterior scalp locations. The brain activation signature of wakefulness, alpha expression discloses immediate levels of alertness and dissipates in concert with fading awareness as sleep begins. This brain activity pattern, however, is largely ignored once sleep begins. Here we show that the intensity of spectral power in the alpha band actually continues to disclose instantaneous responsiveness to noise—a measure of sleep depth—throughout a night of sleep. By systematically challenging sleep with realistic and varied acoustic disruption, we found that sleepers exhibited markedly greater sensitivity to sounds during moments of elevated alpha expression. This result demonstrates that alpha power is not a binary marker of the transition between sleep and wakefulness, but carries rich information about immediate sleep stability. Further, it shows that an empirical and ecologically relevant form of sleep depth is revealed in real-time by EEG spectral content in the alpha band, a measure that affords prediction on the order of minutes. This signal, which transcends the boundaries of classical sleep stages, could potentially be used for real-time feedback to novel, adaptive drug delivery systems for inducing sleep.