Bioheat Transfer Basis of Human Thermoregulation: Principles and Applications

Thermoregulation is a process that is essential to the maintenance of life for all warm-blooded mammalian and avian species. It sustains a constant core body temperature in the face of a wide array of environmental thermal conditions and intensity of physical activities that generate internal heat. A primary component of thermoregulatory function is the movement of heat between the body core and the surface via the circulation of blood. The peripheral vasculature acts as a forced convection heat exchanger between blood and local peripheral tissues enabling heat to be conducted to the skin surface where is may be transferred to and from the environment via conduction, convection, radiation, and/or evaporation of water as local conditions dictate. Humans have evolved a particular vascular structure in glabrous (hairless) skin that is especially well suited for heat exchange. These vessels are called arteriovenous anastomoses (AVAs) and can vasodilate to large diameters and accommodate high flow rates. We report herein a new technology based on a physiological principle that enables simple and safe access to the thermoregulatory control system that allow manipulation of thermoregulatory function. The technology operates by applying a small amount of heating local to control tissue on the body surface overlying the cerebral spine that upregulates AVA perfusion. Under this action, heat exchangers can be applied to glabrous skin, preferably on the palms and soles, to alter the temperature of elevated blood flow prior to its return to the core. Therapeutic and prophylactic applications are discussed.

Climatological Nephropathy: An Overview

Globally hike in temperature provokes the heat waves, results in heat stress and becomes a silent health peril to the existing population. Today, heat stress or climatological stress is one of the dominant pathological conditions which comes in focus when the body means of handling its thermoregulatory function starts to fail, show its associated symptoms followed by eventual loss of consciousness and finally death. The condition of heat stress along with intermittent dehydration worsens the renal damage and enhances the risk of Acute Kidney Injury (AKI), results in chronic kidney disease (CKD). Therefore, CKD comes up as a leading cause of death, specifically in those patients having long-lasting medical conditions like heart problem, hypertension, diabetes and obesity etc. High temperature, work rate, humidity and working time wearing accessories, all become mitigating factors for causing heat stress. Distinguish molecular ups and downs specifically decrease production of uric acid (polyol-fructokinase pathway), increase ROS (oxidative stress), intracellular Ca2+ overload (mitochondrial dysfunctioning) and decrease NO (vascular endothelial dysfunctioning) has been responsible for the severe outcomes of Climatological Nephropathy (CN) or Heat Stress Nephropathy (HSN). However, prevention is the best approach to dealing with heat-related illness, therefore, the Government established some valuable policies as a preventive measures. This review epitomizes the alarming outcomes of the heat stress followed by recurrent dehydration and also enlightened the global talk of HSN, pathogenicity, molecular level peculiarities and recommended measures for HSN. Key words: Acute Kidney Injury, Chronic Kidney Disease, Nephropathy, Mitochondrial Dysfunctioning.

Lizards and snakes from the earliest Miocene of Saint-Gérand-le-Puy, France: an anatomical and histological approach of some of the oldest Neogene squamates from Europe

Background The earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates (i.e., lizards and snakes), witnessing a high diversity of taxa, including an array of extinct forms but also representatives of extant genera. We here conduct a taxonomical survey along with a histological/microanatomical approach on new squamate remains from the earliest Miocene of Saint-Gérand-le-Puy, France, an area that has been well known for its fossil discoveries since the nineteenth century. Results We document new occurrences of taxa, among which, the lacertid Janosikia and the anguid Ophisaurus holeci, were previously unknown from France. We provide a detailed description of the anatomical structures of the various cranial and postcranial remains of lizards and snakes from Saint-Gérand-le-Puy. By applying micro-CT scanning in the most complete cranial elements of our sample, we decipher previously unknown microanatomical features. We report in detail the subsurface distribution and 3D connectivity of vascular channels in the anguid parietal. The fine meshwork of channels and cavities or sinuses in the parietal of Ophisaurus could indicate some thermoregulatory function, as it has recently been demonstrated for other vertebrate groups, providing implications for the palaeophysiology of this earliest Miocene anguine lizard. Conclusions A combination of anatomical and micro-anatomical/histological approach, aided by micro-CT scanning, enabled the documentation of these new earliest Miocene squamate remains. A distinct geographic expansion is provided for the extinct anguine Ophisaurus holeci and the lacertid Janosikia (the closest relative of the extant insular Gallotia from the Canary Islands).

Differentiating ability of haematological indicators: comparative blood test of sympatric rodent species of the subfamily Arvicolinae (Clethrionomys glareolus, Clethrionomys rutilus, and Craseomys rufocanus)

Among the representatives of the subfamily Arvicolinae the interspecific differences (Clethrionomys glareolus, Clethrionomys rutilus, and Craseomys rufocanus) in the respiratory capacity of red blood and the immune status are presented in conjunction with the basal metabolic rate, the level of sociality and eurybionism, and thermoregulatory function. The degree of differentiation of voles in terms of haematological parameters has corresponded to the level of phylogenetic relationships between species. Correct conduct of interspecific comparisons of haematological parameters of voles is possible only within the same reproductive-age groups.

The effect of seasonal acclimatization on whole-body heat loss response during exercise in a hot humid environment with different air velocity

Seasonal acclimatization from winter to summer is known to enhance thermoeffector responses in hot-dry environments during exercise whilst its impact on sweat evaporation and core temperature (Tcore) responses in hot-humid environments remains unknown. We therefore sought to determine whether seasonal acclimatization is able to modulate whole-body sweat rate (WBSR), evaporated sweat rate, sweating efficiency and thermoregulatory function during cycling exercise in a hot-humid environment (32∘C, 75% RH). We also determined whether the increase in air-velocity, could enhance evaporated sweat rate and sweating efficiency before and after seasonal acclimatization. Twelve males cycled for 1-hour at 40% VO2max in winter (pre-acclimatization) and repeated the trial again in summer (after-acclimatization). For the last 20-min of cycling at a steady-state of Tcore, air-velocity increased from 0.2 (0.04) m/s to 1.1 (0.02) m/s by using an electric fan located in front of the participant. Seasonal acclimatization enhanced WBSR, unevaporated sweat rate, local sweat rate and mean skin temperature compared to pre-acclimatization state (all P<0.05) whilst sweating efficiency was lower (P<0.01) until the 55-min of exercise. Tcore and evaporated sweat rate were unaltered by acclimatization status (all P>0.70). In conclusion, seasonal acclimatization enhances thermoeffector responses but does not attenuate Tcore during exercise in a hot-humid environment. Furthermore, increasing air-velocity enhances evaporated sweat rate and sweating efficiency irrespective of acclimated state.

Partial submergence: An undescribed behavioral adjustment for thermoregulation at high ambient temperature in Aeshnidae

Many insects including odonates thermoregulate using a combination of behavioral and physiological mechanisms. At high ambient temperature (Ta), these mechanisms include decreased heat production and increased heat loss. Heat production can be reduced by decreasing activity. Heat loss can be enhanced by perching in a shaded microhabitat where temperature is cooler than in the surrounding environment. Aeshnids, which are intermittent endotherms, increase heat loss at high Ta; also by increasing hemolymph circulation from the thorax, where most metabolic heat is produced, to the abdomen, where it dissipates to the environment by convection. While studying two aeshnid species (Anax junius and Rhionaeschna multicolor) at a Sonoran Desert (Arizona, USA) stream, I observed partially submerged mature individuals of both sexes of these species. This heretofore undescribed behavior was seen only at Ta; ≥ 43 °C and almost exclusively during the hottest part of the day (15:00–17:00 hr), when the daily difference between Ta; and water temperature (Tw) was, on average, largest. A cooling effect of partial submergence behavior on body temperature would, therefore, presumably be most effective also during this period. Several percher species of libellulids were present at the study site. These dragonflies are not known to use endothermy for thermoregulation or to increase hemolymph circulation to the abdomen to dissipate heat at high Ta;, and none was ever observed to partially submerge. It is suggested in aeshnids that partial submergence at high Ta; serves a thermoregulatory function by facilitating body heat dissipation from the abdomen.

Biologically inspired flexible photonic films for efficient passive radiative cooling

Temperature is a fundamental parameter for all forms of lives. Natural evolution has resulted in organisms which have excellent thermoregulation capabilities in extreme climates. Bioinspired materials that mimic biological solution for thermoregulation have proven promising for passive radiative cooling. However, scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging. Herein, we design and demonstrate biologically inspired photonic materials for passive radiative cooling, after discovery of longicorn beetles’ excellent thermoregulatory function with their dual-scale fluffs. The natural fluffs exhibit a finely structured triangular cross-section with two thermoregulatory effects which effectively reflects sunlight and emits thermal radiation, thereby decreasing the beetles’ body temperature. Inspired by the finding, a photonic film consisting of a micropyramid-arrayed polymer matrix with random ceramic particles is fabricated with high throughput. The film reflects ∼95% of solar irradiance and exhibits an infrared emissivity >0.96. The effective cooling power is found to be ∼90.8 W⋅m−2and a temperature decrease of up to 5.1 °C is recorded under direct sunlight. Additionally, the film exhibits hydrophobicity, superior flexibility, and strong mechanical strength, which is promising for thermal management in various electronic devices and wearable products. Our work paves the way for designing and fabrication of high-performance thermal regulation materials.

Context-dependent effects of relative temperature extremes on bill morphology in a songbird

Species increasingly face environmental extremes. Morphological responses to changes in average environmental conditions are well documented, but responses to environmental extremes remain poorly understood. We used museum specimens to investigate relationships between a thermoregulatory morphological trait, bird bill surface area (SA) and a measure of short-term relative temperature extremity (RTE), which quantifies the degree that temperature maxima or minima diverge from the 5-year norm. Using a widespread, generalist species, Junco hyemalis , we found that SA exhibited different patterns of association with RTE depending on the overall temperature regime and on precipitation. While thermoregulatory function predicts larger SA at higher RTE, we found this only when the RTE existed in an environmental context that opposed it: atypically cold minimum temperature in a warm climate, or atypically warm maximum temperature in a cool climate. When environmental context amplified the RTE, we found a negative relationship between SA and RTE. We also found that the strength of associations between SA and RTE increased with precipitation. Our results suggest that trait responses to environmental variation may qualitatively differ depending on the overall environmental context, and that environmental change that extremifies already-extreme environments may produce responses that cannot be predicted from observations in less-extreme contexts.