Circadian rhythms in bed rest: Monitoring core body temperature via heat-flux approach is superior to skin surface temperature

Simulated space environmental factors of weightlessness, noise and low atmospheric pressure differentially affect the diurnal rhythm and the gut microbiome

The circadian clock extensively regulates physiology and behavior. In space, astronauts encounter many environmental factors that are dramatically different from those on Earth; however, the effects of these factors on circadian rhythms and the mechanisms remain largely unknown. The present study aimed to investigate the changes in the mouse diurnal rhythm and gut microbiome under simulated space capsule conditions, including microgravity, noise and low atmospheric pressure (LAP). Noise and LAP were loaded in the capsule while the conditions in the animal room remained constant. The mice in the capsule showed disturbed locomotor rhythms and faster adaptation to a 6-h phase advance. RNA sequencing of hypothalamus samples containing the suprachiasmatic nucleus (SCN) revealed that microgravity simulated by hind limb unloading (HU) and exposure to noise and LAP led to decreases in the quantities of differentially expressed genes (DEGs), including circadian clock genes. Changes in the rhythmicity of genes implicated in pathways of cardiovascular deconditioning and more concentrated phases were found under HU or noise and LAP. Furthermore, 16S rRNA sequencing revealed dysbiosis in the gut microbiome, and noise and LAP may repress the temporal discrepancy in the microbiome community structure induced by microgravity. Changes in diurnal oscillations were observed in a number of gut bacteria with critical physiological consequences on metabolism and immunodefense. We also found that the superimposition of noise and LAP may repress normal changes in global gene expression and adaptation in the gut microbiome. Our data demonstrate that in addition to microgravity, exposure to noise and LAP affect the robustness of circadian rhythms and the community structure of the gut microbiome, and these factors may interfere with each other in their adaptation to respective conditions. These findings are important for furthering our understanding of the alterations in circadian rhythms in the complex environment of space.

Agreement of zero-heat-flux thermometry with the oesophageal and tympanic core temperature measurement in patient receiving major surgery

To identify and prevent perioperative hypothermia, most surgical patients require a non-invasive, accurate, convenient, and continuous core temperature method, especially for patients undergoing major surgery. This study validated the precision and accuracy of a cutaneous zero-heat-flux thermometer and its performance in detecting intraoperative hypothermia. Adults undergoing major non-cardiac surgeries with general anaesthesia were enrolled in the study. Core temperatures were measured with a zero-heat-flux thermometer, infrared tympanic membrane thermometer, and oesophagal monitoring at 15-minute intervals. Taking the average value of temperature measured in the tympanic membrane and oesophagus as a reference, we assessed the agreement using the Bland-Altman analysis and linear regression methods. Sensitivity, specificity, and predictive values of detecting hypothermia were estimated. 103 patients and one thousand sixty-eight sets of paired temperatures were analyzed. The mean difference between zero-heat-flux and the referenced measurements was -0.03 ± 0.25 °C, with 95% limits of agreement (-0.52 °C, 0.47 °C) was narrow, with 94.5% of the differences within 0.5 °C. Lin's concordance correlation coefficient was 0.90 (95%CI 0.89-0.92). The zero-heat-flux thermometry detected hypothermia with a sensitivity of 82% and a specificity of 90%. The zero-heat-flux thermometer is in good agreement with the reference core temperature based on tympanic and oesophagal temperature monitoring in patients undergoing major surgeries, and appears high performance in detecting hypothermia.

Comparing body temperature measurements using the double sensor method within a wearable device with oral and core body temperature measurements using medical grade thermometers-a short report

Introduction: Body temperature is essential for diagnosing, managing, and following multiple medical conditions. There are several methods and devices to measure body temperature, but most do not allow continuous and prolonged measurement of body temperature. Noninvasive skin temperature sensor combined with a heat flux sensor, also known as the "double sensor" technique, is becoming a valuable and simple method for frequently monitoring body temperature. Methods: Body temperature measurements using the "double sensor" method in a wearable monitoring device were compared with oral and core body temperature measurements using medical grade thermometers, analyzing data from two prospective clinical trials of different clinical scenarios. One study included 45 hospitalized COVID-19 patients in which oral measurements were taken using a hand-held device, and the second included 18 post-cardiac surgery patients in which rectal measurements were taken using a rectal probe. Results: In study 1, Bland-Altman analysis showed a bias of -0.04°C [0.34-(-0.43)°C, 95% LOA] with a correlation of 99.4% (p < 0.001). In study 2, Bland-Altman analysis showed a bias of 0.0°C [0.27-(-0.28)°C, 95% LOA], and the correlation was 99.3% (p < 0.001). In both studies, stratifying patients based on BMI and skin tone showed high accordance in all sub-groups. Discussion: The wearable monitor showed high correlation with oral and core body temperature measurements in different clinical scenarios.

Noninvasive and Continuous Monitoring of the Core Body Temperature through the Quantitative Measurement of Blood Perfusion Rate

Core body temperature (CBT) is one of the four vital signs that must be monitored continuously. The continuous recording of CBT is possible through invasive methods by inserting a temperature probe into specific body sites. We report a novel method to monitor CBT through the quantitative measurement of skin blood perfusion rate (ωb,skin). By monitoring the skin temperature, heat flux, and ωb,skin, the arterial blood temperature, equivalent to CBT, can be extracted. ωb,skin is quantitatively evaluated thermally via sinusoidal heating with regulated thermal penetration depth so that the blood perfusion rate is acquired only in the skin. Its quantification is significant because it indicates various physiological events including hyper- or hypothermia, tissue death, and delineation of tumors. A subject showed promising results with steady values of ωb,skin and CBT of 5.2 ± 1.05 × 10-4 s-1 and 36.51 ± 0.23 °C, respectively. For periods where the subject's actual CBT (axillary temperature) did not fall within the estimated range, the average deviation from the actual CBT was only 0.07 °C. This study aims to develop a competent methodology capable of continuously monitoring the CBT and blood perfusion rate at a distant location from the core body region for the diagnosis of a patient's health condition with wearable devices.

Acute Thermoregulatory and Cardiovascular Response to Submaximal Exercise in People With Multiple Sclerosis

Background

Heat sensitivity occurs in a high percentage of people with multiple sclerosis (PwMS), in response to environmental or exercise-induced increase in body temperature. However, the kinetic and magnitude of adaptation of the internal load and of the core body temperature (CBT) to a submaximal continuous exercise has been poorly addressed in PwMS; this may be relevant for the brief exercise bouts usually occurring in normal daily life. The aim of this work was to evaluate whether multiple sclerosis influences the acute adaptation of the internal load, the CBT and the perceptual load in response to a constant submaximal work step.

Methods

CBT has been continuously monitored (0.5 Hz) by a validated wearable heat-flux sensor and electrocardiography was recorded (250 Hz) by a wearable device during a standard 6-minute walk test (6MWT) in 14 PwMS (EDSS, 4.7 ± 1.2; disease duration: 13.0 ± 10.2 years; m ± SD) and 14 age, sex and BMI-matched healthy subjects (HS). The rate of perceived exertion (RPE) of the lower limbs was assessed during the 6MWT by the Borg scale (6-20).

Results

As expected, PwMS walked a significantly shorter distance (361 ± 98 m) than the HS group (613 ± 62 m, p<0.001 vs PwMS). However, the kinetics of adaptation of CBT and the magnitude of CBT change from baseline did not differ between groups. Similarly, heart rate (HR) kinetics and HR change from baseline were comparable between groups during the 6MWT. Finally, lower limbs RPE gradually increased during the exercise test, but without significant differences between groups.

Conclusion

The internal load, the metabolic heat production, and the perceptive load due to a standard submaximal walking exercise seems to be preserved in PwMS, suggesting a comparable acute heat production and dissipation during exercise. Therefore, it is unlikely that the different distance achieved during the 6MWT may be caused by altered thermoregulatory responses to exercise. Rather, this appears to be a consequence of the known increased energy cost of locomotion in PwMS.

Optimization of a Stacked-design Core-body-temperature Sensor for Long-period Human Trials

We fabricated a wearable sensor that can be attached to the skin surface and continuously measure core body temperature (CBT) wirelessly over a long period. CBT is calculated from skin-surface temperature and heat flux passing through the sensor. Since heat flux is lost to the surroundings of the probe, the slightest change in convection in daily life will degrade the measurement accuracy of the sensor. Accordingly, we previously proposed a heat-flux-path control structure to reduce the absolute amount of heat-flux loss. To make wearable sensors for long-term human trials, we proposed an integrated design in which a sensor probe, a circuit board, and a battery are stacked. We optimized the proposed design by computer simulation and evaluated the fabricated sensor by a phantom experiment in which the convectional state was changed. The evaluation results demonstrate that the sensor has limits of agreement (LOA) of [-0.13; 0.03]°C under 1-m/s-wind convection. Moreover, a preliminary human trial conducted under daily-life conditions (including convectional changes) demonstrated that the sensor has LOA of [-0.18; 0.22]°C. These results demonstrate that the fabricated sensor is suitable for CBT measurement.

Low Ambient Temperature Exposition Impairs the Accuracy of a Non-invasive Heat-Flux Thermometer

Background

Indirect core body temperature (CBT) monitoring from skin sensors is gaining attention for in-field applications thanks to non-invasivity, portability, and easy probe positioning. Among skin sensors, heat-flux devices, such as the so-called Double Sensor (DS), have demonstrated reliability under various experimental and clinical conditions. Still, their accuracy at low ambient temperatures is unknown. In this randomized cross-over trial, we tested the effects of cold temperature exposition on DS performance in tracking CBT.

Methods

Twenty-one participants were exposed to a warm (23.2 ± 0.4°C) and cold (−18.7 ± 1.0°C) room condition for 10 min, following a randomized cross-over design. The accuracy of the DS to estimate CBT in both settings was assessed by quantitative comparison with esophageal (reference) and tympanic (comparator) thermometers, using Bland–Altman and correlation analyses (Pearson’s correlation coefficient, r, and Lin’s concordance correlation coefficient, CCC).

Results

In the warm room setting, the DS showed a moderate agreement with the esophageal sensor [bias = 0.09 (−1.51; 1.69) °C, r = 0.40 (p = 0.069), CCC = 0.22 (−0.006; 0.43)] and tympanic sensor [bias = 2.74 (1.13; 4.35) °C, r = 0.54 (p < 0.05), CCC = 0.09 (0.008; 0.16)]. DS accuracy significantly deteriorated in the cold room setting, where DS temperature overestimated esophageal temperature [bias = 2.16 (−0.89; 5.22) °C, r = 0.02 (0.94), CCC = 0.002 (−0.05; 0.06)]. Previous exposition to the cold influenced temperature values measured by the DS in the warm room setting, where significant differences (p < 0.00001) in DS temperature were observed between randomization groups.

Conclusion

DS accuracy is influenced by environmental conditions and previous exposure to cold settings. These results suggest the present inadequacy of the DS device for in-field applications in low-temperature environments and advocate further technological advancements and proper sensor insulation to improve performance in these conditions.

Wearable Personal Core Body Temperature Measurement Considering Individual Differences and Dynamic Tissue Blood Perfusion

Accurate and continuous measurement of the human core body temperature by a wearable device is of great significance for human health care and disease monitoring. The current wearable thermometers ignore the physiological differences between individuals and the role of blood perfusion in thermoregulation, resulting in insufficient accuracy and limitations in terms of the measurement sites. This study proposed a novel personal model for measuring core body temperature by taking dynamic tissue blood perfusion and individual differences into consideration. The technique facilitates possible accurate core body temperature measurements from the skin surface of the wrist and forehead. First, the personal core body temperature model was established based on the thermal equilibrium between the human body and the measurement device, in which the tissue blood perfusion changes dynamically with tissue temperature. Then, the parameters of the personal model that imply individual physiological differences were obtained based on personal data collected daily. The results show that with the developed personal model, the accuracy of the measured body temperature from the wrist is close to that of the forehead model. The wrist model and the forehead model have a mean absolute error of 0.297 (SD=0.078) C and 0.224 (SD=0.071) C, respectively, which meets the accuracy and robustness requirements of practical applications. The personal models significantly improve the accuracy compared with that of the group model, especially for the wrist model.

Feasibility, acceptability and validation of wearable devices for climate change and health research in the low-resource contexts of Burkina Faso and Kenya: Study protocol

As the epidemiological transition progresses throughout sub-Saharan Africa, life lived with diseases is an increasingly important part of a population's burden of disease. The burden of disease of climate-sensitive health outcomes is projected to increase considerably within the next decades. Objectively measured, reliable population health data is still limited and is primarily based on perceived illness from recall. Technological advances like non-invasive, consumer-grade wearable devices may play a vital role in alleviating this data gap and in obtaining insights on the disease burden in vulnerable populations, such as heat stress on human cardiovascular response. The overall goal of this study is to investigate whether consumer-grade wearable devices are an acceptable, feasible and valid means to generate data on the individual level in low-resource contexts. Three hundred individuals are recruited from the two study locations in the Nouna health and demographic surveillance system (HDSS), Burkina Faso, and the Siaya HDSS, Kenya. Participants complete a structured questionnaire that comprises question items on acceptability and feasibility under the supervision of trained data collectors. Validity will be evaluated by comparing consumer-grade wearable devices to research-grade devices. Furthermore, we will collect demographic data as well as the data generated by wearable devices. This study will provide insights into the usage of consumer-grade wearable devices to measure individual vital signs in low-resource contexts, such as Burkina Faso and Kenya. Vital signs comprising activity (steps), sleep (duration, quality) and heart rate (hr) are important measures to gain insights on individual behavior and activity patterns in low-resource contexts. These vital signs may be associated with weather variables-as we gather them from weather stations that we have setup as part of this study to cover the whole Nouna and Siaya HDSSs-in order to explore changes in behavior and other variables, such as activity, sleep, hr, during extreme weather events like heat stress exposure. Furthermore, wearable data could be linked to health outcomes and weather events. As a result, consumer-grade wearables may serve as a supporting technology for generating reliable measurements in low-resource contexts and investigating key links between weather occurrences and health outcomes. Thus, wearable devices may provide insights to better inform mitigation and adaptation interventions in these low-resource settings that are direly faced by climate change-induced changes, such as extreme weather events.

Comparison of diurnal rectal and body surface temperatures in large white piglets during the hot-dry season in a tropical Guinea savannah

The aim of the study was to determine the differences in rectal and body surface temperatures and their extent of conformity using digital and infrared thermometers, respectively, in piglets during the hot-dry season in a tropical guinea savannah of Nigeria. Thirty Large White piglets of both sexes, aged 10-14 days, served as the experimental subjects. The rectal and surface body temperatures were recorded concurrently with those of the ambient dry- and wet-bulbs, during the day at 06:00, 09:00, 12:00, 15:00 and 18:00 h (GMT +1). There were significant (P < 0.05) diurnal variations in all body and ambient temperature readings, with the highest values obtained in the afternoon (at 15:00 h GMT + 1). The mean diurnal rectal and body surface temperatures in the piglets at 09:00-18:00 h were significantly higher (P < 0.001) than the corresponding values at 06:00 h. The overall mean rectal temperature (39.00 ± 0.04 °C) was higher (P < 0.01) than body surface temperature recorded for the eye (38.05 ± 0.04 °C), ear (38.10 ± 0.07 °C), head (37.97 ± 0.05 °C), nose (35.68 ± 0.13 °C), scapula (38.16 ± 0.06 °C), thigh (38.00 ± 0.06 °C), back (38.02 ± 0.06 °C) and hoof (36.83 ± 0.07 °C). The largest and smallest mean difference between rectal and body surface temperatures was -3.32 ± 0.12 °C and -0.84 ± 0.06 °C for the temperature of the nose and scapula, respectively. The positive correlation (P < 0.05) between body temperatures (rectal and surface) of the piglets with ambient temperature implied that the later had a tremendous effect on the former. Body surface temperatures at the region of eye, ear, head, nose, scapula, thigh, back and hoof had significantly (P < 0.0001) linear and positive relationships with rectal temperature. In conclusion, the similar diurnal trends, highly significant correlation coefficients and linear relationships between the rectal and body surface temperatures suggest that the later may serve as valid and reliable estimates of the former in piglets.

Long-Term Bed Rest Delays the Circadian Phase of Core Body Temperature

Spaceflight can be associated with sleep loss and circadian misalignment as a result of non-24 h light-dark cycles, operational shifts in work/rest cycles, high workload under pressure, and psychological factors. Head-down tilt bed rest (HDBR) is an established model to mimic some of the physiological and psychological adaptions observed in spaceflight. Data on the effects of HDBR on circadian rhythms are scarce. To address this gap, we analyzed the change in the circadian rhythm of core body temperature (CBT) in two 60-day HDBR studies sponsored by the European Space Agency [n = 13 men, age: 31.1 ± 8.2 years (M ± SD)]. CBT was recorded for 36 h using a non-invasive and validated dual-sensor heatflux technology during the 3rd and the 8th week of HDBR. Bed rest induced a significant phase delay from the 3rd to the 8th week of HDBR (16.23 vs. 16.68 h, p = 0.005, g = 0.85) irrespective of the study site (p = 0.416, g = −0.46), corresponding to an average phase delay of about 0.9 min per day of HDBR. In conclusion, long-term bed rest weakens the entrainment of the circadian system to the 24-h day. We attribute this effect to the immobilization and reduced physical activity levels associated with HDBR. Given the critical role of diurnal rhythms for various physiological functions and behavior, our findings highlight the importance of monitoring circadian rhythms in circumstances in which gravity or physical activity levels are altered.

Assessing rectal temperature with a novel non-invasive sensor

Athletes, soldiers, and workers who perform intense physical activities under extreme hot conditions might encounter increased physiological thermal strain. Consequently, the increase in body core temperature (T_c) might result in heat exhaustion and heatstroke. Thus, continuously following changes in T_c is of utmost importance. Recently, the Tcore sensor (Dräger, Germany), which employs a unique dual-sensor heat flux technology, became commercially available to measure T_c, in a hospital-controlled environment. This study aimed to evaluate the possibility of using the Tcore sensor to accurately monitor rectal temperature (T_re), reflecting T_c, under exercise-heat stress. Thirteen healthy young males completed the study protocol, consisting of 90 min of moderate exercise (walking on a treadmill - 5 km/h, 4% elevation) under controlled hot/dry and hot/wet climatic conditions (30 °C/60% rh, 34 °C/40% rh, and 40 °C/40% rh). Tcore sensors were placed on the forehead and the left wrist. Temperatures from both Tcore sensors were recorded continuously together with T_re using a rectal thermistor. The original algorithm used by the company to estimate T_re from the Tcore sensor was found to be inadequate under the study's conditions and new models for the forehead and the wrist measurements were developed. Nearly 150,000 measurement sets (after filtering) were used to build independent MATLAB software algorithms and test their reliability according to the cross-validation algorithm. Bland-Altman analysis was used to compare between the results obtained by the new models to T_re. The database consisted of a large T_re range (36.5-38.9 °C). The mean errors of the models were close to zero, and the mean absolute errors were 0.20 ± 0.16 °C and 0.27 ± 0.20 °C for the forehead and wrist, respectively. 95% of the measurements from the forehead model and 86% from the wrist model were within ±0.5 °C of T_re, and 78% (forehead) and 64% (wrist) were within ±0.3 °C. Root Mean Square Deviation (RMSD) values were 0.29 °C and 0.40 °C for the forehead and wrist models, respectively. The developed models show the feasibility to use the Tcore sensor for assessing T_re under exercise-heat conditions. Furthermore, the sensor was found to be adequate for use on the wrist as well, which might be more practical for use in field conditions.

COVID-19-The largest isolation study in history: the value of shared learnings from spaceflight analogs

The world is currently experiencing the largest isolation experiment in history. In an attempt to slow down the spread of the COVID-19 pandemic numerous countries across the world have been shutting down economies, education, and public life. Governments have mandated strict regulations of quarantine and social distancing in an unprecedented manner. The effects of these measures on brain, behavior, neuro-humoral and immunological responses in humans are largely unknown. Life science research for space exploration has a long history in using high-fidelity spaceflight analogs to better understand the effect of prolonged isolation and confinement on genes, molecules, cells, neural circuits, and physiological systems to behavior. We here propose to leverage the extensive experience and data from these studies and build a bridge between spaceflight research and clinical settings to foster transdisciplinary approaches to characterize the neurobehavioral effects on the immune system and vice versa. These approaches are expected to develop innovative and efficient health screening tools, diagnostic systems, and treatments to mitigate health risks associated with isolation and confinement on Earth and during future exploratory spaceflight missions.

Non-invasive and wearable thermometer for continuous monitoring of core body temperature under various convective conditions

We describe the design of a thermometer that can be worn during everyday activities for monitoring core body temperature (CBT) at the skin surface. This sensor estimates the CBT by measuring the heat flux from the body core based on a thermal conductive model. The heat flux is usually affected by the ambient convective conditions (e.g. air conditioner or posture), which in turn affects the model's accuracy. Thus, we analytically investigated heat conduction and designed a sensor interface that would be robust to convection changes. We performed an in vitro experiment and a preliminary in vivo experiment. The accuracy of CBT in an in vitro experiments was 0.1°C for convective values ranging from 0 to 1.2 m/s. The wearable thermometer has high potential as non-invasive CBT monitor.

Clinical evaluation of fever-screening thermography: impact of consensus guidelines and facial measurement location

SIGNIFICANCE

Infrared thermographs (IRTs) have been used for fever screening during infectious disease epidemics, including severe acute respiratory syndrome, Ebola virus disease, and coronavirus disease 2019 (COVID-19). Although IRTs have significant potential for human body temperature measurement, the literature indicates inconsistent diagnostic performance, possibly due to wide variations in implemented methodology. A standardized method for IRT fever screening was recently published, but there is a lack of clinical data demonstrating its impact on IRT performance.

AIM

Perform a clinical study to assess the diagnostic effectiveness of standardized IRT-based fever screening and evaluate the effect of facial measurement location.

APPROACH

We performed a clinical study of 596 subjects. Temperatures from 17 facial locations were extracted from thermal images and compared with oral thermometry. Statistical analyses included calculation of receiver operating characteristic (ROC) curves and area under the curve (AUC) values for detection of febrile subjects.

RESULTS

Pearson correlation coefficients for IRT-based and reference (oral) temperatures were found to vary strongly with measurement location. Approaches based on maximum temperatures in either inner canthi or full-face regions indicated stronger discrimination ability than maximum forehead temperature (AUC values of 0.95 to 0.97 versus 0.86 to 0.87, respectively) and other specific facial locations. These values are markedly better than the vast majority of results found in prior human studies of IRT-based fever screening.

CONCLUSION

Our findings provide clinical confirmation of the utility of consensus approaches for fever screening, including the use of inner canthi temperatures, while also indicating that full-face maximum temperatures may provide an effective alternate approach.

Current Evidence for Continuous Vital Signs Monitoring by Wearable Wireless Devices in Hospitalized Adults: Systematic Review

BACKGROUND

Continuous monitoring of vital signs by using wearable wireless devices may allow for timely detection of clinical deterioration in patients in general wards in comparison to detection by standard intermittent vital signs measurements. A large number of studies on many different wearable devices have been reported in recent years, but a systematic review is not yet available to date.

OBJECTIVE

The aim of this study was to provide a systematic review for health care professionals regarding the current evidence about the validation, feasibility, clinical outcomes, and costs of wearable wireless devices for continuous monitoring of vital signs.

METHODS

A systematic and comprehensive search was performed using PubMed/MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials from January 2009 to September 2019 for studies that evaluated wearable wireless devices for continuous monitoring of vital signs in adults. Outcomes were structured by validation, feasibility, clinical outcomes, and costs. Risk of bias was determined by using the Mixed Methods Appraisal Tool, quality assessment of diagnostic accuracy studies 2nd edition, or quality of health economic studies tool.

RESULTS

In this review, 27 studies evaluating 13 different wearable wireless devices were included. These studies predominantly evaluated the validation or the feasibility outcomes of these devices. Only a few studies reported the clinical outcomes with these devices and they did not report a significantly better clinical outcome than the standard tools used for measuring vital signs. Cost outcomes were not reported in any study. The quality of the included studies was predominantly rated as low or moderate.

CONCLUSIONS

Wearable wireless continuous monitoring devices are mostly still in the clinical validation and feasibility testing phases. To date, there are no high quality large well-controlled studies of wearable wireless devices available that show a significant clinical benefit or cost-effectiveness. Such studies are needed to help health care professionals and administrators in their decision making regarding implementation of these devices on a large scale in clinical practice or in-home monitoring.

Sleep and thermoregulation

In homeothermic animals sleep preparatory behaviours often promote thermal efficiency, including warmth-seeking, adopting particular postures (curling up, head tucking) and nest building, all promoting warmer skin microclimates. Skin warmth induces NREM sleep and body cooling via circuitry that connects skin sensation to the preoptic hypothalamus. Coupling sleep induction and lower body temperature could serve to minimise energy expenditure or allow energy reallocation. Cooling during NREM sleep may also induce transcriptional changes in genes whose products facilitate housekeeping functions or measure the time spent sleeping.

Review on Wearables to Monitor Foot Temperature in Diabetic Patients

One of the diseases that could affect diabetic patients is the diabetic foot problem. Unnoticed minor injuries and subsequent infection can lead to ischemic ulceration, and may end in a foot amputation. Preliminary studies have shown that there is a positive relationship between increased skin temperature and the pre⁻ulceration phase. Hence, we have carried out a review on wearables, medical devices, and sensors used specifically for collecting vital data. In particular, we are interested in the measure of the foot⁻temperature. Since there is a large amount of this type of medical wearables, we will focus on those used to measure temperature and developed in Spain.

Prediction of Core Body Temperature Based on Skin Temperature, Heat Flux, and Heart Rate Under Different Exercise and Clothing Conditions in the Heat in Young Adult Males

Non-invasive, multi-parameter methods to estimate core body temperature offer several advantages for monitoring thermal strain, although further work is required to identify the most relevant predictor measures. This study aimed to compare the validity of an existing and two novel multi-parameter rectal temperature prediction models. Thirteen healthy male participants (age 30.9 ± 5.4 years) performed two experimental sessions. The experimental procedure comprised 15 min baseline seated rest (23.2 ± 0.3°C, 24.5 ± 1.6% relative humidity), followed by 15 min seated rest and cycling in a climatic chamber (35.4 ± 0.2°C, 56.5 ± 3.9% relative humidity; to +1.5°C or maximally 38.5°C rectal temperature, duration 20-60 min), with a final 30 min seated rest outside the chamber. In session 1, participants exercised at 75% of their heart rate maximum (HR max) and wore light athletic clothing (t-shirt and shorts), while in session 2, participants exercised at 50% HR max, wearing protective firefighter clothing (jacket and trousers). The first new prediction model, comprising the input of 18 non-invasive measures, i.e., insulated and non-insulated skin temperature, heat flux, and heart rate ("Max-Input Model", standard error of the estimate [SEE] = 0.28°C, R2 = 0.70), did not exceed the predictive power of a previously reported model which included six measures and no insulated skin temperatures (SEE = 0.28°C, R2 = 0.71). Moreover, a second new prediction model that contained only the two most relevant parameters (heart rate and insulated skin temperature at the scapula) performed similarly ("Min-Input Model", SEE = 0.29, R2 = 0.68). In conclusion, the "Min-Input Model" provided comparable validity and superior practicality (only two measurement parameters) for estimating rectal temperature versus two other models requiring six or more input measures.

Daily rhythms of rectal and body surface temperatures in donkeys during the cold-dry (harmattan) and hot-dry seasons in a tropical savannah

The aim of the study was to evaluate daily rhythms of rectal temperature (RT) and body surface temperature (BST) of adult, yearling and foal donkeys during the cold-dry (harmattan) and hot-dry seasons in a tropical savanna. The RTs and BSTs of 30 clinically healthy, free-ranging donkeys were recorded using digital and infrared thermometers. The RT and BST of each donkey and thermal environmental parameters inside the pen were measured bi-hourly from 0600 to 0600 hours (GM + 1) on each experimental day. Application of single cosinor procedure showed that RT and BST exhibited varying levels of daily rhythmicity in both seasons, with values usually higher during the afternoon periods of the photophase of the light/dark cycle. The oscillatory pattern differed with season, with greater amplitude recorded during the cold-dry season than the hot-dry season. The acrophases of the RT and BST were mostly restricted to the photophase of the light/dark cycle in both seasons. The mean values of RT in the adult (37.10 ± 0.10 °C), yearling (37.19 ± 0.10 °C) and foal (37.45 ± 0.11 °C) donkeys were higher (F = 93.41, P < 0.0001) during the hot-dry season than the cold-dry season (35.40 ± 0.05 °C, 35.50 ± 0.04 °C and 36.20 ± 0.05 °C, respectively). In conclusion, seasonal changes influenced significantly the daily rhythmicity of RT and BST in donkeys, kept under natural light/dark cycle.

Limb Skin Temperature as a Tool to Predict Orthostatic Instability

Orthostatic instability is one of the main consequences of weightlessness or gravity challenge and plays as well a crucial role in public health, being one of the most frequent disease of aging. Therefore, the assessment of effective countermeasures, or even the possibility to predict, and thus prevent orthostatic instability is of great importance. Heat stress affects orthostatic stability and may lead to impaired consciousness and decrease in cerebral perfusion, specifically during the exposure to G-forces. Conversely, peripheral cooling can prevent orthostatic intolerance – even in normothermic healthy subjects. Indicators of peripheral vasodilation, as elevated skin surface temperatures, may mirror blood decentralization and an increased risk of orthostatic instability. Therefore, the aim of this study was to quantify orthostatic instability risk, by assessing in 20 fighter jet pilot candidates’ cutaneous limb temperatures, with respect to the occurrence of G-force-induced almost loss of consciousness (ALOC), before and during exposure to a push-pull maneuver, i.e., head-down tilt, combined with lower body negative pressure. Peripheral skin temperatures from the upper and lower (both proximal and distal) extremities and core body temperature via heat-flux approach (i.e., the Double Sensor), were continuously measured before and during the maneuver. The 55% of subjects that suffered an ALOC during the procedure had higher upper arm and thigh temperatures at baseline compared to the 45% that remained stable. No difference in baseline core body temperature and distal limbs (both upper and lower) skin temperatures were found between the two groups. Therefore, peripheral skin temperature data could be considered a predicting factor for ALOC, prior to rapid onset acceleration. Moreover, these findings could also find applications in patient care settings such as in intensive care units.

Increased core body temperature in astronauts during long-duration space missions

Humans’ core body temperature (CBT) is strictly controlled within a narrow range. Various studies dealt with the impact of physical activity, clothing, and environmental factors on CBT regulation under terrestrial conditions. However, the effects of weightlessness on human thermoregulation are not well understood. Specifically, studies, investigating the effects of long-duration spaceflight on CBT at rest and during exercise are clearly lacking. We here show that during exercise CBT rises higher and faster in space than on Earth. Moreover, we observed for the first time a sustained increased astronauts’ CBT also under resting conditions. This increase of about 1 °C developed gradually over 2.5 months and was associated with augmented concentrations of interleukin-1 receptor antagonist, a key anti-inflammatory protein. Since even minor increases in CBT can impair physical and cognitive performance, both findings have a considerable impact on astronauts’ health and well-being during future long-term spaceflights. Moreover, our findings also pinpoint crucial physiological challenges for spacefaring civilizations, and raise questions about the assumption of a thermoregulatory set point in humans, and our evolutionary ability to adapt to climate changes on Earth.

Differences between the most used equations in BAT-human studies to estimate parameters of skin temperature in young lean men

Cold exposure is necessary to activate human brown adipose tissue (BAT), resulting in heat production. Skin temperature is an indirect measure to monitor the body's reaction to cold. The aim of this research was to study whether the most used equations to estimate parameters of skin temperature in BAT-human studies measure the same values of temperature in young lean men (n = 11: 23.4 ± 0.5 years, fat mass: 19.9 ± 1.2%). Skin temperature was measured with 26 ibuttons at 1-minute intervals in warm and cold room conditions. We used 12 equations to estimate parameters of mean, proximal, and distal skin temperature as well as skin temperature gradients. Data were analysed with Temperatus software. Significant differences were found across equations to measure the same parameters of skin temperature in warm and cold room conditions, hampering comparison across studies. Based on these findings, we suggest to use a set of 14 ibuttons at anatomical positions reported by ISO STANDARD 9886:2004 plus five ibuttons placed on the right supraclavicular fossa, right middle clavicular bone, right middle upper forearm, right top of forefinger, and right upper chest.

An IR Sensor Based Smart System to Approximate Core Body Temperature

Herein demonstrated experiment studies two methods, namely convection and body resistance, to approximate human core body temperature. The proposed system is highly energy efficient that consumes only 165 mW power and runs on 5 VDC source. The implemented solution employs an IR thermographic sensor of industry grade along with AT Mega 328 breakout board. Ordinarily, the IR sensor is placed 1.5-30 cm away from human forehead (i.e., non-invasive) and measured the raw data in terms of skin and ambient temperature which is then converted using appropriate approximation formula to find out core body temperature. The raw data is plotted, visualized, and stored instantaneously in a local machine by means of two tools such as Makerplot, and JAVA-JAR. The test is performed when human object is in complete rest and after 10 min of walk. Achieved results are compared with the CoreTemp CM-210 sensor (by Terumo, Japan) which is calculated to be 0.7 °F different from the average value of BCT, obtained by the proposed IR sensor system. Upon a slight modification, the presented model can be connected with a remotely placed Internet of Things cloud service, which may be useful to inform and predict the user's core body temperature through a probabilistic view. It is also comprehended that such system can be useful as wearable device to be worn on at the hat attachable way.