ClimApp-Integrating Personal Factors with Weather Forecasts for Individualised Warning and Guidance on Thermal Stress.

This paper describes the functional development of the ClimApp tool (available for free on iOS and Android devices), which combines current and 24 h weather forecasting with individual information to offer personalised guidance related to thermal exposure. Heat and cold stress assessments are based on ISO standards and thermal models where environmental settings and personal factors are integrated into the ClimApp index ranging from -4 (extremely cold) to +4 (extremely hot), while a range of -1 and +1 signifies low thermal stress. Advice for individuals or for groups is available, and the user can customise the model input according to their personal situation, including activity level, clothing, body characteristics, heat acclimatisation, indoor or outdoor situation, and geographical location. ClimApp output consists of a weather summary, a brief assessment of the thermal situation, and a thermal stress warning. Advice is provided via infographics and text depending on the user profile. ClimApp is available in 10 languages: English, Danish, Dutch, Swedish, Norwegian, Hellenic (Greek), Italian, German, Spanish and French. The tool also includes a research functionality providing a platform for worker and citizen science projects to collect individual data on physical thermal strain and the experienced thermal strain. The application may therefore improve the translation of heat and cold risk assessments and guidance for subpopulations. ClimApp provides the framework for personalising and downscaling weather reports, alerts and advice at the personal level, based on GPS location and adjustable input of individual factors.

Two isothermal challenges yield comparable physiological and subjective responses.

PURPOSE: Ventilated vests are developed to reduce thermal stress by enhancing convective and evaporative cooling from skin tissue underneath the vest. The purpose of this study is to investigate whether thermal stress is equal when a ventilated vest is worn compared to a no-vest situation with similar dry thermal resistance. METHODS: Nine healthy males walked on a treadmill (7 km h-1) for 45 min in a desert climate (34 °C, 20% relative humidity) with and without ventilated vest. Gastrointestinal temperature (Tgi), heart rate (HR), and skin temperature (Tsk) were continuously monitored. Local sweat rate (LSR) was assessed two times on six skin locations. Subjective ratings were assessed every 10 min. RESULTS: Final Tgi (37.6 ± 0.1 °C for vest and 37.6 ± 0.1 °C for no-vest), HR (133 ± 7 bpm and 133 ± 9 bpm) and mean Tsk (34.8 ± 0.7 °C and 34.9 ± 0.6 °C) were not different between conditions (p ≥ 0.163). Scapula skin temperature (Tscapula) under the vest tended to be lower (baseline to final: ΔTscapula = 0.35 ± 0.37 °C) than without vest (ΔTscapula = 0.74 ± 0.62 °C, p = 0.096). LSR at locations outside the vest did not differ with and without vest (p ≥ 0.271). Likewise, subjective responses did not differ between conditions (χ2 ≥ 0.143). CONCLUSIONS: We conclude that two systems with similar dry thermal resistance and, therefore, similar required evaporation, resulted in similar thermal stress during paced walking in a hot-dry environment. Local ventilation did not alter the sweating response on locations outside the vest.

Thermophysiological adaptations to passive mild heat acclimation.

Passive mild heat acclimation (PMHA) reflects realistic temperature challenges encountered in everyday life. Active heat acclimation, combining heat exposure and exercise, influences several important thermophysiological parameters; for example, it decreases core temperature and enhances heat exchange via the skin. However, it is unclear whether PMHA elicits comparable adaptations. Therefore, this study investigated the effect of PMHA on thermophysiological parameters. Participants were exposed to slightly increased temperatures (∼33°C/22% RH) for 6 h/d over 7 consecutive days. To study physiologic responses before and after PMHA, participants underwent a temperature ramp (UP), where ambient temperature increased from a thermoneutral value (28.8 ± 0.3°C) to 37.5 ± 0.6°C. During UP, core and skin temperature, water loss, cardiovascular parameters, skin blood flow and energy expenditure were measured. Three intervals were selected to compare data before and after PMHA: baseline (minutes 30-55: 28.44 ± 0.21°C), T1 (minutes 105-115: 33.29 ± 0.4°C) and T2 (minutes 130-140: 35.68 ± 0.61°C). After 7 d of PMHA, core (T1: -0.13 ± 0.13°C, P = 0.011; T2: -0.14 ± 0.15°C, P = 0.026) and proximal skin temperature (T1: -0.22 ± 0.29°C, P = 0.029) were lower during UP, whereas distal skin temperature was higher in a thermoneutral state (baseline: +0.74 ± 0.77°C, P = 0.009) and during UP (T1: +0.49 ± 0.76°C, P = .057 (not significant), T2:+0.51 ± 0.63°C, P = .022). Moreover, water loss was reduced (-30.5 ± 33.3 ml, P = 0.012) and both systolic (-7.7 ± 7.7 mmHg, P = 0.015) and diastolic (-4.4 ± 4.8 mmHg, P = 0.001) blood pressures were lowered in a thermoneutral state. During UP, only systolic blood pressure was decreased (T2: -6.1 ± 4.4 mmHg, P = 0.003). Skin blood flow was significantly decreased at T1 (-28.35 ± 38.96%, P = 0.037), yet energy expenditure remained unchanged. In conclusion, despite the mild heat stimulus, we show that PMHA induces distinct thermophysiological adaptations leading to increased resilience to heat.

Evaluating the performance of thermal sensation prediction with a biophysical model.

Neutral thermal sensation is expected for a human body in heat balance in near-steady-state thermal environments. The physiological thermoneutral zone (TNZ) is defined as the range of operative temperatures where the body can maintain such heat balance by actively adjusting body tissue insulation, but without regulatory increases in metabolic rate or sweating. These basic principles led to the hypothesis that thermal sensation relates to the operative temperature distance from the thermoneutral centroid (dTNZop ). This hypothesis was confirmed by data from respiratory climate chamber experiments. This paper explores the potential of such biophysical model for the prediction of thermal sensation under increased contextual variance. Data (798 votes, 47 participants) from a controlled office environment were used to analyze the predictive performance of the dTNZop model. The results showed a similar relationship between dTNZop and thermal sensation between the dataset used here and the previously used dataset. The predictive performance had the same magnitude as that of the PMV model; however, potential benefits of using a biophysical model are discussed. In conclusion, these findings confirm the potential of the biophysical model with regard to the understanding and prediction of human thermal sensation. Further work remains to make benefit of its full potential.

Local thermal sensation modeling-a review on the necessity and availability of local clothing properties and local metabolic heat production.

Local thermal sensation modeling gained importance due to developments in personalized and locally applied heating and cooling systems in office environments. The accuracy of these models depends on skin temperature prediction by thermophysiological models, which in turn rely on accurate environmental and personal input data. Environmental parameters are measured or prescribed, but personal factors such as clothing properties and metabolic rates have to be estimated. Data for estimating the overall values of clothing properties and metabolic rates are available in several papers and standards. However, local values are more difficult to retrieve. For local clothing, this study revealed that full and consistent data sets are not available in the published literature for typical office clothing sets. Furthermore, the values for local heat production were not verified for characteristic office activities, but were adapted empirically. Further analyses showed that variations in input parameters can lead to local skin temperature differences (∆Tskin,loc  = 0.4-4.4°C). These differences can affect the local sensation output, where ∆Tskin,loc  = 1°C is approximately one step on a 9-point thermal sensation scale. In conclusion, future research should include a systematic study of local clothing properties and the development of feasible methods for measuring and validating local heat production.

Thermal sensation: a mathematical model based on neurophysiology.

UNLABELLED: Thermal sensation has a large influence on thermal comfort, which is an important parameter for building performance. Understanding of thermal sensation may benefit from incorporating the physiology of thermal reception. The main issue is that humans do not sense temperature directly; the information is coded into neural discharge rates. This manuscript describes the development of a mathematical model of thermal sensation based on the neurophysiology of thermal reception. Experimental data from two independent studies were used to develop and validate the model. In both studies, skin and core temperature were measured. Thermal sensation votes were asked on the seven-point ASHRAE thermal sensation scale. For the development dataset, young adult males (N=12, 0.04Clo) were exposed to transient conditions; Tair 30-20-35-30°C. For validation, young adult males (N=8, 1.0Clo) were exposed to transient conditions; Tair: 17-25-17°C. The neurophysiological model significantly predicted thermal sensation for the development dataset (r2=0.89, P<0.001). Only information from warm-sensitive skin and core thermoreceptors was required. Validation revealed that the model predicted thermal sensation within acceptable range (root mean squared residual=0.38). The neurophysiological model captured the dynamics of thermal sensation. Therefore, the neurophysiological model of thermal sensation can be of great value in the design of high-performance buildings. PRACTICAL IMPLICATIONS: The presented method, based on neurophysiology, can be highly beneficial for predicting thermal sensation under complex environments with respect to transient environments.

Increased systolic blood pressure after mild cold and rewarming: relation to cold-induced thermogenesis and age.

AIM: Higher winter mortality in elderly has been associated with augmented systolic blood pressure (SBP) response and with impaired defense of core temperature. Here we investigated whether the augmented SBP upon mild cold exposure remains after a rewarming period, and whether SBP changes are linked to thermoregulation. Therefore, we tested the following hypotheses: cold-induced increase in SBP (1) remains augmented after rewarming in elderly compared to young adults (2) is related to non-shivering thermogenesis (NST) upon mild cold (3) is related to vasoconstriction upon mild cold. METHODS: Blood pressure, energy expenditure (EE), skin and core temperature, skin perfusion (abdomen, forearm, both sides of hand) and % body fat were measured in 12 young adults (Y) and 12 elderly (E). Supine subjects were exposed to a thermoneutral baseline 0.5 h (T(air) = 30.1°C), 1 h mild cold (T(air) = 20.7°C), 1 h rewarming (T(air) = 34.8°C) and 1 h baseline (T(air) = 30.5°C). RESULTS: Upon mild cold only the young adults showed significant NST (Y: +2.5 ± 0.6 W m(-2), P < 0.05). No significant age effects in vasoconstriction were observed. After rewarming per cent change in SBP (%ΔSBP) remained significantly increased in both age groups and was augmented in elderly (Y: +5.0% ± 1.2% vs. E: +14.7% ± 3.1%, P < 0.05). Regression analysis revealed that %ΔSBP significantly related to ΔEE upon mild cold (P < 0.01, r(2) = 0.35) and in elderly also to %body fat (P < 0.02, r(2) = 0.57). CONCLUSION: Individual changes in SBP after rewarming correlate negatively to NST. Elderly did not show NST, which explains the greater SBP increase in this group. In elderly a relatively large %body fat protected against the adverse effects of mild cold.

Cold-induced vasoconstriction at forearm and hand skin sites: the effect of age.

During mild cold exposure, elderly are at risk of hypothermia. In humans, glabrous skin at the hands is well adapted as a heat exchanger. Evidence exists that elderly show equal vasoconstriction due to local cooling at the ventral forearm, yet no age effects on vasoconstriction at hand skin have been studied. Here, we tested the hypotheses that at hand sites (a) elderly show equal vasoconstriction due to local cooling and (b) elderly show reduced response to noradrenergic stimuli. Skin perfusion and mean arterial pressure were measured in 16 young adults (Y: 18-28 years) and 16 elderly (E: 68-78 years). To study the effect of local vasoconstriction mechanisms local sympathetic nerve terminals were blocked by bretylium (BR). Baseline local skin temperature was clamped at 33 degrees C. Next, local temperature was reduced to 24 degrees C. After 15 min of local cooling, noradrenaline (NA) was administered to study the effect of neural vasoconstriction mechanisms. No significant age effect was observed in vasoconstriction due to local cooling at BR sites. After NA, vasoconstriction at the forearm showed a significant age effect; however, no significant age effect was found at the hand sites. [Change in CVC (% from baseline): Forearm Y: -76 +/- 3 vs. E: -60 +/- 5 (P < 0.01), dorsal hand Y: -74 +/- 4 vs. E: -72 +/- 4 (n.s.), ventral hand Y: -80 +/- 7 vs. E: -70 +/- 11 (n.s.)]. In conclusion, in contrast to results from the ventral forearm, elderly did not show a blunted response to local cooling and noradrenaline at hand skin sites. This indicates that at hand skin the noradrenergic mechanism of vasoconstriction is maintained with age.