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Introduction Sleep initiation and maintenance are linked to thermoregulation. In Parkinson's disease (PD), thermoregulatory dysfunction potentially worsens sleep disorders. However, the association between thermoregulation and sleep quality in patients with PD remains unclear. We aimed to examine the association between skin temperature, a measure of heat dissipation, and actigraphic sleep metrics in PD.Methods In this cross-sectional study with 186 outpatients with PD and 580 non-PD controls, we measured wrist skin temperature (WST) and actigraphic sleep quality for seven days in PD and two days in controls in real-life settings. Linear mixed-effect models were used to examine the association between nighttime WST and sleep quality.Results Nighttime WST in PD was significantly lower than that in controls (adjusted difference 0.39 [95 % confidence interval, 0.23–0.54] °C, P < 0.001). In patients with PD, changes in sleep efficiency, wake after sleep onset, total sleep time, and log-transformed fragmentation index per 1 °C increase in nighttime WST were 3.2 (95 % CI, 2.4–3.9) %, −10.3 (95 % CI, −13.6, −7.1) minutes, 13.4 (95 % CI, 9.1–17.8) minutes, and −0.09 (95 % CI: −0.12, −0.06), respectively, independent of potential confounders. Significant interactions were observed between nighttime WST and the presence of PD for sleep efficiency, wake after sleep onset, and total sleep time.Conclusions: Within-individual changes in nighttime WST were significantly associated with changes in actigraphic sleep measures in PD. Interventional studies are necessary that address the limitations and potential biases of this study to elucidate whether cutaneous temperature modulation can enhance the quality of sleep in PD.

Simple Summary: Human rhythmicity is subjected to the workings of the internal circadian clock, but it is also influenced by environmental time (mainly the light-dark cycle) and social timing imposed by the official time at our location, as well as by our work schedule. When a misalignment among these times occurs, an internal order impairment appears, which affects our health. Western Spain (GMT+1/+2) and Portugal (GMT0/+1) share similar longitudes (sun time) but have different official times, and thus they provide a "natural experiment" to assess how this discrepancy affects circadian rhythmicity and sleep in people with no work duties (>65 years). Although sleep duration was not affected, the circadian rhythms in the Portuguese were more robust, especially during weekdays, while higher desynchronization tended to occur in the Spaniards. Once official time was corrected by GMT0, meals took place later in Spain than in Portugal, especially as the day progressed, indicating the possible deleterious effect on circadian system robustness when official time is misaligned with its corresponding geographical time zone. Human circadian rhythmicity is subjected to the internal circadian clock, the sun and social clocks (official time, social/work schedules). The discrepancy among these clocks, as occurs when official time does not match its geographical time zone, may produce circadian disruption. Western Spain (GMT+1/+2) and Portugal (GMT0/+1) share similar longitudes (sun time) but have different official times. This provides a unique opportunity to evaluate the effects of official time on circadian rhythmicity and sleep in elderly and retired populations (with no remunerated duties presumed, although other social commitments may be present) at both locations. Although both populations slept enough for their age (7–8 h), circadian robustness (e.g., interdaily stability, relative amplitude) was greater in Portugal, especially during weekdays, while greater desynchronization (both body temperature vs. motor activity and body temperature vs. light exposure) tended to occur in the Spaniards. Once corrected by GMT0, meals took place later in Spain than in Portugal, especially as the day progresses, and a possible interplay between bed/meal timings and internal desynchronization was found. Our results point to the possible deleterious effect on circadian system robustness when official time is misaligned with its geographical time zone. [ABSTRACT FROM AUTHOR]

Currently, people in crowded indoor spaces are required to wear a variety of personal protective equipment to curb the spread of COVID-19. This study aimed to investigate the effects of wearing four types of personal protective equipment (unprotected, wearing masks, wearing face shield and wearing medical protective clothing) on human thermal perception and physiological responses in indoor crowded spaces in summer. The experiment was conducted in a climate chamber designed to simulate the indoor crowded spaces. Environmental parameters of climate chamber (air temperature, relative humidity and wind speed), physiological parameters of subjects (wrist skin temperature and pulse rate), and subjective perceptions (thermal sensation and thermal comfort) were collected during the experiment. The experimental results showed that medical protective clothing has the most obvious blocking effect on heat exchange between human and environment. Thermal sensation in state 4 (wearing medical protective clothing) was significantly (p < 0.05) higher than that in other states. The study of physiological parameters showed that the wrist skin temperature and pulse rate under different protection states increased with the increase of room temperature. Through regression analysis, the thermal sensation estimation model of protective personnel in indoor crowded spaces based on wrist skin temperature and pulse rate was established. The adjusted R2 and RMSE of all models were above 82% and less than 1, indicating that the established thermal sensation model had a good prediction effect. [ABSTRACT FROM AUTHOR]

Human circadian rhythmicity is subjected to the internal circadian clock, the sun and social clocks (official time, social/work schedules). The discrepancy among these clocks, as occurs when official time does not match its geographical time zone, may produce circadian disruption. Western Spain (GMT+1/+2) and Portugal (GMT0/+1) share similar longitudes (sun time) but have different official times. This provides a unique opportunity to evaluate the effects of official time on circadian rhythmicity and sleep in elderly and retired populations (with no remunerated duties presumed, although other social commitments may be present) at both locations. Although both populations slept enough for their age (7–8 h), circadian robustness (e.g., interdaily stability, relative amplitude) was greater in Portugal, especially during weekdays, while greater desynchronization (both body temperature vs. motor activity and body temperature vs. light exposure) tended to occur in the Spaniards. Once corrected by GMT0, meals took place later in Spain than in Portugal, especially as the day progresses, and a possible interplay between bed/meal timings and internal desynchronization was found. Our results point to the possible deleterious effect on circadian system robustness when official time is misaligned with its geographical time zone.

The present study examines whether the daily rhythm of distal skin temperature (DST) is associated with brown adipose tissue (BAT) metabolism as determined by 18F-fluorodeoxyglucose (18F-FDG) uptake in young adults. Using a wireless thermometer (iButton) worn on the nondominant wrist, DST was measured in 77 subjects (26% male; age 22 ± 2 years; body mass index 25.2 ± 4.8 kg/m2) for 7 consecutive days. The temperatures to which they were habitually exposed over the day were also recorded. The interday stability of DST was calculated from the collected data, along with the intraday variability and relative amplitude; the mean temperature of the 5 and 10 consecutive hours with the maximum and minimum DST values, respectively; and when these hours occurred. Following exposure to cold, BAT volume and mean and peak standardized 18F-FDG uptake (SUVmean and SUVpeak) were determined for each subject via static 18F-FDG positron emission tomography/computed tomography scanning. Relative amplitude and the time at which the 10 consecutive hours of minimum DST values occurred were positively associated with BAT volume, SUVmean, and SUVpeak (p ≤ 0.02), whereas the mean DST of that period was inversely associated with the latter BAT variables (p ≤ 0.01). The interday stability and intraday variability of the DST were also associated (directly and inversely, respectively) with BAT SUVpeak (p ≤ 0.02 for both). All of these associations disappeared, however, when the analyses were adjusted for the ambient temperature to which the subjects were habitually exposed. Thus, the relationship between the daily rhythm of DST and BAT activity estimated by 18F-FDG uptake is masked by environmental and likely behavioral factors. Of note is that those participants exposed to the lowest ambient temperature showed 3 to 5 times more BAT volume and activity compared with subjects who were exposed to a warmer ambient temperature. [ABSTRACT FROM AUTHOR]

Thermal comfort is an essential environmental factor related to quality of life and work effectiveness. We assessed the feasibility of wrist skin temperature monitoring for estimating subjective thermal sensation. We invented a wrist band that simultaneously monitors skin temperatures from the wrist (i.e., the radial artery and ulnar artery regions, and upper wrist) and the fingertip. Skin temperatures from eight healthy subjects were acquired while thermal sensation varied. To develop a thermal sensation estimation model, the mean skin temperature, temperature gradient, time differential of the temperatures, and average power of frequency band were calculated. A thermal sensation estimation model using temperatures of the fingertip and wrist showed the highest accuracy (mean root mean square error [RMSE]: 1.26 ± 0.31). An estimation model based on the three wrist skin temperatures showed a slightly better result to the model that used a single fingertip skin temperature (mean RMSE: 1.39 ± 0.18). When a personalized thermal sensation estimation model based on three wrist skin temperatures was used, the mean RMSE was 1.06 ± 0.29, and the correlation coefficient was 0.89. Thermal sensation estimation technology based on wrist skin temperatures, and combined with wearable devices may facilitate intelligent control of one's thermal environment. [ABSTRACT FROM AUTHOR]

Parameters describing the bedroom environment and sleep quality were measured overnight for one week in 84 randomly selected actual bedrooms in Denmark from September to December 2020. The median age of participants was 26 years (interquartile range (IQR) [24-32] years); 41 were males. Carbon dioxide (CO 2), temperature, and relative humidity were measured continuously. Sleep quality was assessed by the Groningen Sleep Quality Scale (GSQS) on two mornings and was assessed using wrist-worn sleep trackers. Skin temperature was monitored continuously. Bedroom indoor air quality (IAQ) was rated by participants on two occasions just before sleep in the evening and upon waking up in the morning. Measurements from 75 bedrooms were complete. The median [IQR] of mean CO 2 , air temperature and relative humidity measured during sleep were 1,120 [741–4,804] ppm, 23.4 [22.3–24.4]°C, and 48.6 [44.7–55.4]%. The median [IQR] of GSQS was 4.0 [1.0–6.0] suggesting medium to poor subjectively rated sleep quality; the objectively measured sleep efficiency, and percentage of light, deep and REM sleep were in normal ranges: 88.1 [86.1–89.5]%, 59.4 [54.9–64.5]%, 18.3 [15.0–21.7]%, and 23.0 [18.4–26.4]%. The subjectively-assessed sleep quality decreased when perceived IAQ was reduced. Opening the bedroom door or window, which is a proxy for enhanced ventilation, also improved subjectively-assessed sleep quality and IAQ. The cross-sectional nature of the study prompts the validation of the present results with protocols that include measurements of other pollutants besides CO 2 as well as the examination of underlying mechanisms. Nevertheless, they strongly suggest that keeping high bedroom IAQ is essential. • Sleeping with either windows or doors open improved subjective-rated sleep quality. • Poorer perceived air quality decreased subjective-rated sleep quality. • Higher CO 2 levels increased the drop in skin temperature during sleep. • A higher drop in skin temperature increased the fraction of deep sleep. [ABSTRACT FROM AUTHOR]

• Four human subject experiments were performed to investigate the characteristics of wrist skin temperature (WST) during sleep. • WST was linearly and synchronically correlated with the mean skin temperature (MST) calculated using Hardy & Dubois's seven-point method. • WST is advantageous for measuring skin temperature in field study and optimal control of sleeping thermal environment. Wrist skin temperature has been validated to be sensitive to the thermal state of awake people, but its correlation with thermal state of sleeping people has not been investigated. In the present study four human subject experiments were performed on both young and elderly subjects in different seasons (winter, transition, summer). Their skin temperatures were continuously measured during the whole night sleep at wrist (WST) and at the normally accepted seven points (forehead, chest, posterior forearm, hand, anterior thigh, anterior calf, and foot) proposed by Hardy & Dubois. The WST was compared with the mean skin temperature (MST) calculated with Hardy & Dubois's seven-point method. The results show that the WST was moderately and positively correlated with MST, with the Pearson's R value ranged from 0.44 to 0.63. When comparing the variation of WST and MST throughout the whole-night sleep, the averaged maximum crossing correlation coefficient was 0.56 (Q1 = 0.4, Q3 = 0.7) and the lag time was on average −10.4 min (Q1 = -11.0, Q3 = 0.0 min), indicating that the WST was synchronically correlated with MST. Similar to MST, the WST could differentiate sleeping micro thermal environments which were created by different combinations of indoor temperature and bedding thermal insulation. These results suggest that the WST was linearly and synchronically correlated with the MST calculated using Hardy & Dubois's seven-point method. Thus, the skin temperature at wrist could provide information on thermal state of human body when people asleep, making it possible to measure skin temperature in field studies and to personally and energy efficiently control the thermal environment for sleep. [ABSTRACT FROM AUTHOR]

Where people live and work together it is not always possible to modify the ambient temperature; ways must therefore be found that allow individuals to feel thermally comfortable in such settings. The Embr Wave® is a wrist-worn device marketed as a 'personal thermostat' that can apply a local cooling stimulus to the skin. The aim of the present study was to determine the effect of an intermittent mild cold stimulus of 25 °C for 15–20 s every 5 min over 3.5 days under free-living conditions on 1) skin temperature, 2) perception of skin temperature, 3) sleep quality and 4) resting energy expenditure (REE) in young, healthy adults. Ten subjects wore the device for 3.5 consecutive days. This intervention reduced distal skin temperature after correcting for personal ambient temperature (P < 0.05), but did not affect the subjects' the perception of skin temperature, sleep quality or REE (all P ≥ 0.051). Thus, this intermittent mild cold regime can reduce distal skin temperature, and wearing it under free-living conditions for 3.5 days does not seem to impair the perception of skin temperature and sleep quality or modify REE. • An intermittent cold regime reduces distal skin temperature after 3.5 days. • An intermittent cold regime does not modify perception of skin temperature after 3.5 days. • An intermittent cold regime does not impair sleep quality after 3.5 days. • An intermittent cold regime does not modify resting energy expenditure after 3.5 days. New & noteworthy: Cold exposure has been suggested as an effective therapy for improving metabolic health, but better study interventions are needed. This study provides evidence that an intermittent mild cold regimen on the right wrist is able to decrease distal skin temperature in both hands after 3.5 days activation, yet other metabolic parameters were not affected. [ABSTRACT FROM AUTHOR]

Core and peripheral body temperatures are affected by changes in reproductive hormones during the menstrual cycle. Women worldwide use the basal body temperature (BBT) method to aid and prevent conception. However, prior research suggests that taking one's daily temperature can prove inconvenient and subject to environmental factors. We investigate whether a more automatic, non-invasive temperature measurement system can detect changes in temperature across the menstrual cycle. We examined how wrist skin temperature (WST), measured with wearable sensors, correlates with urinary tests of ovulation and may serve as a new method of fertility tracking. One hundred and thirty-six eumenorrheic, non-pregnant women participated in an observational study. Participants wore WST biosensors during sleep and reported their daily activities. An at-home luteinizing hormone (LH) test was used to confirm ovulation. WST was recorded across 437 cycles (mean cycles/participant = 3.21, S.D. = 2.25). We tested the relationship between the fertile window and WST temperature shifts, using the BBT three-over-six rule. A sustained 3-day temperature shift was observed in 357/437 cycles (82%), with the lowest cycle temperature occurring in the fertile window 41% of the time. Most temporal shifts (307/357, 86%) occurred on ovulation day (OV) or later. The average early-luteal phase temperature was 0.33°C higher than in the fertile window. Menstrual cycle changes in WST were impervious to lifestyle factors, like having sex, alcohol, or eating prior to bed, that, in prior work, have been shown to obfuscate BBT readings. Although currently costlier than BBT, the present study suggests that WST could be a promising, convenient parameter for future multiparameter fertility awareness methods., (© 2018 The Author(s).)

Thermal comfort is an essential environmental factor related to quality of life and work effectiveness. We assessed the feasibility of wrist skin temperature monitoring for estimating subjective thermal sensation. We invented a wrist band that simultaneously monitors skin temperatures from the wrist (i.e., the radial artery and ulnar artery regions, and upper wrist) and the fingertip. Skin temperatures from eight healthy subjects were acquired while thermal sensation varied. To develop a thermal sensation estimation model, the mean skin temperature, temperature gradient, time differential of the temperatures, and average power of frequency band were calculated. A thermal sensation estimation model using temperatures of the fingertip and wrist showed the highest accuracy (mean root mean square error [RMSE]: 1.26 ± 0.31). An estimation model based on the three wrist skin temperatures showed a slightly better result to the model that used a single fingertip skin temperature (mean RMSE: 1.39 ± 0.18). When a personalized thermal sensation estimation model based on three wrist skin temperatures was used, the mean RMSE was 1.06 ± 0.29, and the correlation coefficient was 0.89. Thermal sensation estimation technology based on wrist skin temperatures, and combined with wearable devices may facilitate intelligent control of one's thermal environment.