Skin blood flow rate estimation through functions infrared imaging analysis

Females utilize thermal behavior more than males during low intensity aerobic exercise. Core temperature is elevated during high vs. low intensity aerobic exercise because of greater heat production. Thus, thermal behavior is greater during high intensity exercise because of the heightened stimulus to behave. It is unknown if sex modulates thermal behavior during high intensity exercise. PURPOSE: Test the hypothesis that thermal behavior differs between males and females during high intensity exercise and recovery. METHODS: 10 males (M) and 10 females (F) (23±3y) underwent 30 min of cycling exercise at a power output that elicited 80±5% (F) and 78±4% (M) of VO2peak (P=0.28) followed by 120 min seated recovery in a 27±1°C, 21±2% relative humidity environment. Subjects were instructed to maintain a thermally comfortable neck temperature throughout using a custom-made neck device. Neck device temperature provided an index of thermal behavior. Mean skin (10 site) and core (intestinal) temperatures, mean skin wettedness (8 site), neck device temperature, skin blood flow (laser Doppler) and local sweat rate (ventilated capsule) were measured continually. RESULTS: There were no sex differences in heat production during exercise (F: 399±68, M: 429±62 W/m2, P=0.39). During exercise, core and mean skin temperatures, skin wettedness, skin blood flow and local sweat rate increased, while neck device temperature decreased (all P<0.01). There were no sex differences in core (F: 37.7±0.2, M: 37.9±0.3°C, P> 0.50), mean skin (F: 32.6±0.3, M: 32.6±0.3°C, P>0.99) or neck device (F: 12.1±10.6, M: 11.9±10.2°C, P>0.25) temperatures, mean skin wettedness (at 30 min: F: 0.50±0.06, M: 0.53±0.04 au, P>0.99), skin blood flow (F: 163±50, M: 172±36 PU, P>0.99) or local sweat rate (F: 0.72±0.20, M: 0.85±0.27 mg/cm2/min, P>0.33) during exercise (data reported at 30 min). During recovery, core and mean skin temperatures, mean skin wettedness, skin blood flow and local sweat rate decreased, and neck device temperature increased back towards pre-exercise levels (all P<0.01). There were no differences in the dynamics of these changes between sexes (all P>0.16). CONCLUSIONS: Thermal behavior during and following high intensity aerobic exercise does not differ between males and females. This study was funded by lululemon athletica inc.

We compared two methods of partitional calorimetry to calculate heat storage and heat debt during cold air (0°C) exposure causing mild core cooling. Twelve participants performed a 5 min baseline in thermoneutral conditions (∼22.0°C, ∼50% relative humidity) followed by cold air exposure (∼0°C) until rectal temperature was reduced by ∆-0.5°C. Partitional calorimetry was used to calculate avenues of heat exchange (radiative, convective, and evaporative), heat storage, and heat debt continuously throughout cold exposure. We compared deriving these variables using prediction equations based on environmental and participant characteristics (PCALEquation Method) versus using measurement tools such as humidity sensors and heat flux discs (PCALHeat Flux Method). There were significant differences between methods (all p≤0.001) for determining heat exchange, heat storage, and heat debt. At ∆-0.5°C, PCALHeat Flux Method had greater levels of radiative and convective heat exchange (PCALHeat Flux Method: -143.0±16.8 W∙m2 vs PCALEquation Method: -123.0±12.9 W∙m2, p≤0.001), evaporative heat exchange (PCALHeat Flux Method: -9.0±1.7 W∙m2 vs PCALEquation Method: -4.1±0.0 W∙m2, p≤0.001), heat storage (PCALHeat Flux Method: -15.0±31.0 W∙m2 vs PCALEquation Method: +6.0±25.9 W∙m2, p=0.020), and heat debt (PCALHeat Flux Method: -692.0±315.0 kJ vs PCALEquation Method: -422.0±136.0 kJ, p≤0.001). Overall, this study found the largest discrepancies between the two methods were when the environmental conditions and skin temperature were in high flux, as well as when core temperature was reduced by ∆-0.5°C. The use of PCALHeat Flux Method may be more advantageous to use in the cold to provide a higher resolution measurement of cold strain.

The reactivity of skin blood flow and heart rate to periodic thermal stimulation was studied in 10 term small-for-gestational age (SGA) infants, in 9 preterm and 8 term normal-sized infants during the first two postnatal months. During the first postnatal days, the increase in thermally stimulated skin blood flow oscillations was absent in SGA infants but was clearly present in both preterm (p < 0.01) and term (p < 0.01) normal-sized infants. The responsiveness of SGA infants improved during the follow-up (p < 0.05). The response of the periodic heart rate variability of SGA and preterm infants was inferior to term normal-sized infants until the age of 2 months. The cardiovascular responsiveness of growth-retarded infants seems abnormal during the first days of life, and may impair their ability to meet stress, e.g. changes of ambient temperature.

Vector Flow Imaging Compared with Conventional Doppler Ultrasound and Thermodilution for Estimation of Blood Flow in the Ascending Aorta

1. The influence of baroreceptor unloading on cutaneous vasodilatation was investigated in ten human subjects during dynamic supine cycle ergometer exercise at 28 degrees C. Increases in forearm skin blood flow (venous occlusion plethysmography) and arterial blood pressure (non-invasive) were measured and used to calculate forearm vascular conductance while local chest sweating rate was measured by dew-point hygrometry. Subjects performed two similar exercise protocols with and without baroreceptor unloading induced by application of -40 mmHg lower body negative pressure (LBNP). The LBNP condition was reversed (i.e. either removed or applied) after 15 min while exercise continued for an additional 20 min. 2. During exercise without LBNP, the body core temperature threshold for vasodilatation (measured as oesophageal temperature, Tc) averaged 37.06 +/- 0.12 degrees C (+/- S.E.M.) and increased to 37.30 +/- 0.09 degrees C (P < 0.05) during exercise with LBNP. The rate of rise of forearm vascular conductance (FVC) per unit increase in Tc (an expression of thermal sensitivity) and peak FVC at 15 min was significantly attenuated during baroreceptor unloading. These effects were rapidly reversed when LBNP was turned off. 3. Baroreceptor unloading during the first 15 min of exercise attenuated the local chest sweating rate, which was also reversed when LBNP was removed. 4. The time course and quickness in which baroreceptor unloading modulated thermoregulatory control of skin blood flow and local chest sweat rate suggests that the interaction between these two homeostatic mechanisms is primarily neurally mediated. The ability of baroreceptor activity to modulate both control of skin blood flow and sweating suggests a common site of interaction, more proximal than the effector organs, and involving the active vasodilator system.

A theoretical method for cylinder-to-cylinder radiative heat exchange is formulated by utilizing a sphere approximation method. The sphere approximation method requires dividing the cylinders into smaller connected spheres and applying a previously published numerical method for near-field sphere-to-sphere radiative exchange. The overall radiative power exchange is obtained by an additive ray-tracing assumption. These results are compared to results produced by a rigorous cylinder-to-cylinder radiative heat exchange method. The heat exchange of nanorods is plotted vs. the gap to assess the impact of near-field radiative transfer as the gap decreases. The unit sphere method is applied to nanorod configurations having length-to-diameter ratios of 3:1, 5:1, and 7:1. Graphical results of energy vs. nanorod radii are presented. A nanoradii/gap dimensionless relationship caused by geometric effects is found and related to power for nanorods of different aspect ratios and temperatures. A V-shaped configuration is considered, with the results plotted for heat exchange vs. angle. An assessment of the number of spheres required to produce an accurate approximation of the V-shaped configuration of nanorods is presented. An error analysis of this method based on a ray-blocking assumption from neighboring spheres is discussed.

This paper theoretically examines the impact of thermal buoyancy on human skin tissue’s blood flow, heat exchange and their interaction with the surrounding environment using a two phase mathematical model that relies on continuity, momentum and energy conservation equations in continuum mechanics. The tissue blood flows and heat transfer characteristics are determined numerically based on Darcy’s Brinkman model for a saturated porous medium coupled with modified Pennes bioheat equation while analytical approach is employed to tackle the model of interacting surrounding environmental buoyancy driven air flow with heat sink. The influence of embedded biophysical parameters on the skin tissue’s blood flow rate and temperature distribution together with friction coefficient at skin tissue surface and Nusselt number are display graphically and discussed quantitatively. It is found that a boost in thermal buoyancy enhances skin tissue heat transfer and blood flow rates.

Methysergide is a serotonin antagonist and has been demonstrated to reduce wound blood flow and edema formation. We have determined the effect of methysergide on protein kinetics in normal and scalded skin of anesthetized rabbits. L-[ring-(13)C(6)]- or L-[ring-(2)H(5)]phenylalanine was used to reflect skin protein kinetics by use of an ear model, and L-[1-(13)C]leucine was used to reflect whole body protein kinetics. The results were that infusion of methysergide (2-3 mg. kg(-1). h(-1)) reduced the blood flow rate in normal skin by 50% without changing skin or whole body protein kinetics. After scald injury on the ear, administration of methysergide for 48 h reduced the weight of scalded ears (43 +/- 4 vs. 30 +/- 5 g, P < 0.01) and ear blood flow rate (42.6 +/- 4.9 vs. 5.8 +/- 1.0 ml. 100 g(-1). min(-1), P < 0.0001) and did not change wound protein kinetics. Methysergide reduced arteriovenous shunting and maintained inward phenylalanine transport from the blood to the skin pool. Using the microsphere technique, we found that the infusion of methysergide decreased blood perfusion by 33-36% in both normal and scalded ear skin. We conclude that methysergide administration reduces nonnutritive, as opposed to nutritive, blood flow in normal and scalded skin.

Enhancement of topical delivery of drugs via direct penetration by reducing blood flow rate in skin

We investigated the near-field radiative heat transfer between general materials and metamaterials. We studied the effects of metamaterial parameters on the radiative heat exchange and used three kinds of natural or artificially-constructed materials such as Al, boron-doped Si and metamaterials as examples. We calculated and analyzed the near-field radiative heat transfer processes between two semi-infinite bodies. The numerical results indicate that the radiative heat exchange between the two different materials may be less or more than the radiative heat exchange between the corresponding identical materials. It was found out to depend on the radiative properties of the materials. The work would provide a valuable reference for the selection of practical materials.

Highlights Equations for a modified steady-state thermal balance model solved with a spreadsheet are described. The modified model describes heat exchange between lactating cows and the surrounding environment. New relations were used for tissue insulation, sweat rate, longwave radiation, and convective heat exchange. A companion paper compares model results to published body temperatures, respiration rates, and skin temperatures. Abstract. Dairy cow heat stress impacts cow well-being, reduces milk yield, and leads to economic losses. Understanding heat stress mechanics supports ongoing and future efforts to mitigate heat stress. The purpose of this project was to modify a steady-state heat transfer model developed by McGovern and Bruce (2000) by incorporating work by Berman (2005), McArthur (1987), Turnpenny et al. (2000a,b), Thompson et al. (2014), Gwadera et al. (2017), two new empirical relations for tissue insulation and sweat rate, and a new solution method that allowed for overlapping changes in heat exchange. The modified model describes heat exchange between a lactating cow and the environment through respiration, convection, sweating, and shortwave and longwave radiation. This article describes the process-based model equations, compares results from the two new empirical relations used to published work, and presents the inputs and results for a cow on pasture in sunlight. The modified model, which can be solved with a spreadsheet, provides insight into factors and processes that affect lactating cow heat exchange. A companion paper compares the modified model results with published average measured body temperatures, respiration rates, and skin temperatures and unpublished body temperature data for cows on pasture in the sunshine. Keywords: Body temperature, Dairy, Heat stress, Lactating cow, Respiration rate, Thermal balance model.

The thermal state of a two-layer semitransparent system located on an opaque semi-infinite substrate was numerically analyzed under condition of radiation and convective heat exchange with surrounding environment at the external boundary. The problem statement simulates the heating by solar radiation of a hypothetical snow-ice cover consisting of two layers with different absorption and scattering. It was shown that subsurface or deeper regions of the medium can be heated by incident external radiation more intensively in dependence of the optical thickness of the layers, the predominance of absorption or scattering in them. Experimental verification of the results of numerical analysis was obtained.

This paper presents an experimental study of radiant cooling for building air-conditioning in a tropical climate. To prevent condensation of moisture on the cooling panel, the temperature of chilled water supplied to the panel was limited to 25°C. This led to the limitations of heat extraction capacity at the panel and its application to only space with low thermal load and low metabolic rate activity of people in the space. A simple calculation of radiative and convective heat exchange between the interior room surfaces and the room air was applied to determine the rate of heat extraction by the panels. The calculation results can match well with the measurement results. Using a comfort index of predicted mean vote (PMV), the results from experiments show that thermal comfort could be achieved with the application of radiant cooling.

Complex heat transfer in radiant chambers of technological furnaces of the petrochemical industry is considered. The object of research is a vertically located flat channel, approximately simulating a radiant chamber. The walls of the channel are formed by a refractory lining and a tubular screen with a known temperature. The chamber volume is filled with selectively emitting, absorbing and weakly scattering media of gaseous fuel combustion products. The research method is based on the numerical solution of two-dimensional integro-differential equations of radiation gas dynamics, closed by a two-parameter model of turbulent convection. The influence of the modes of organization of the combustion process, the radiation properties of the combustion products and refractory lining on the distribution of heat fluxes and the characteristics of the total heat transfer are considered.

Influence of ash deposit chemistry and structure on physical and transport properties