Whole-body temperature gradients under surface,perfusion, and combined surface/perfusion hypothermia

Using various methods of hypothermia and halothane-diethyl ether azeotrope anesthesia whole-body temperature gradients were evaluated in 20 adult mongrel dogs. Simultaneous measurements were taken of brain, rectal, esophageal, pharyngeal, liver, jugular vein, shoulder muscle, thigh muscle, and subcutaneous temperatures during (i) surface, (ii) perfusion (slow and rapid cooling), and (iii) combined surface/perfusion methods of hypothermia. Throughout cooling and rewarming core temperature gradients averaged 1.2 °C and during circulatory arrest core temperatures decreased an average of 0.3 °C under pure surface hypothermia. Animals, thermoregulated by extracorporeal methods only, developed larger core temperature gradients during cooling and a significant increase (average = 3.1 °C) was noted in core temperatures during circulatory arrest. This pattern was particularly pronounced during rapid perfusion cooling. Hypothermia induction by combined surface/perfusion, in contrast to pure perfusion methods, resulted in smaller gradients without remarkable increase in core temperature (average = 1.3 °C) during the arrest period. These findings when correlated with the shorter total operating time and ease of operative management and resuscitation lead us to the conclusion that combined surface/ perfusion hypothermia techniques have certain advantages over either pure surface or pure perfusion techniques alone.     

An assessment of skin temperature gradients in a tropical primate using infrared thermography and subcutaneous implants

Infrared thermography has become a useful tool to assess surface temperatures of animals for thermoregulatory research. However, surface temperatures are an endpoint along the body's core-shell temperature gradient. Skin and fur are the peripheral tissues most exposed to ambient thermal conditions and are known to serve as thermosensors that initiate thermoregulatory responses. Yet relatively little is known about how surface temperatures of wild mammals measured by infrared thermography relate to subcutaneous temperatures. Moreover, this relationship may differ with the degree that fur covers the body. To assess the relationship between temperatures and temperature gradients in peripheral tissues between furred and bare areas, we collected data from wild mantled howling monkeys (Alouatta palliata) in Costa Rica. We used infrared thermography to measure surface temperatures of the furred dorsum and bare facial areas of the body, recorded concurrent subcutaneous temperatures in the dorsum, and measured ambient thermal conditions via a weather station. Temperature gradients through cutaneous tissues (subcutaneous-surface temperature) and surface temperature gradients (surface-ambient temperature) were calculated. Our results indicate that there are differences in temperatures and temperature gradients in furred versus bare areas of mantled howlers. Under natural thermal conditions experienced by wild animals, the bare facial areas were warmer than temperatures in the furred dorsum, and cutaneous temperature gradients in the face were more variable than the dorsum, consistent with these bare areas acting as thermal windows. Cutaneous temperature gradients in the dorsum were more closely linked to subcutaneous temperatures, while facial temperature gradients were more heavily influenced by ambient conditions. These findings indicate that despite the insulative properties of fur, for mantled howling monkeys surface temperatures of furred areas still demonstrate a relationship with subcutaneous temperatures. Given that most mammals possess dense fur, this provides insight for using infrared imaging in thermoregulatory studies of wild animals lacking bare skin.     

The Effect of Temperature Gradients on Stress Development During Cryopreservation via Vitrification

This study addresses the problem of thermal stress development in bulky specimens during cryopreservation via vitrification (vitreous means glassy in Latin). While this study is a part of an ongoing effort to associate the developing mechanical stress with the relevant physical properties of the cryopreserved media and to its the thermal history, the current paper focuses exclusively on the role of temperature gradients. Temperature gradients arise due to the high cooling rates necessary to facilitate vitrification; the resulting non-uniform temperature distribution leads to differential thermal strain, possibly resulting in cracking. The cooling rate is assumed constant on the outer surface in this study, and the material properties are assumed constant. It is demonstrated that under these assumptions, mechanical stress develops only when the temperature distribution in the specimen approaches thermal equilibrium at a cryogenic storage temperature. It is shown that the maximum possible stresses for a given cooling rate can be computed with a simple thermo-elastic analysis; these stresses are associated with cooling to sufficiently low temperatures and are independent of the variation of viscosity with temperature. Analytic estimates for these stresses are obtained for several idealized shapes, while finite element analysis is used to determine stresses for geometries used in cryopreservation practice. Stresses that develop under a wider range of storage temperatures are also studied with finite element analysis, and the results are summarized with suitable normalizations. It is found that no stresses arise if cooling ceases above the set-temperature, which defines the transition from viscous-dominated to elastic-dominated behavior; the set-temperature is determined principally by the dependency of viscosity upon temperature. Strategies for rapidly reaching low temperatures and avoiding high stresses are inferred from the results.     

Skin temperature changes in humans induced by local peripheral cooling

Local peripheral cooling (immerson of legs up to the knees into 12°C water) increased heart rate and blood pressure by 10–20% within the first 3–10 min of cooling. During further cooling heart rate remained elevated, while systolic and diastolic blood pressures decreased to the control value. Data on heart rate indicate a permanent activation of the sympathetic nervous system during local cooling.Skin temperatures (measured topically by thermosensors) decreased on some non-cooled areas of the body (fingers, palms and thighs) immediately after the start of local cooling. On the other hand, skin temperatures on chest and forehead were not influenced. During cooling skin temperatures on thighs remained low, but skin temperatures on fingers tended to increase. Changes in skin temperatures on non-cooled areas of the body indicate that a permanent and generalized activation of the sympathetic nervous system occurs during local cooling.Cold induced cycles of vasodilation (CIVD) were observed on fingers, palms and forearms during local cooling. Minute cycles in skin temperatures were observed on forehead, thighs and chest. Minute cycles coincided with those in the heart rate, indicating a permanent, generalized but discontinuous control of vasomotion by the sympathetic nervous system during local cooling.Infrared thermographic recordings from different body areas indicated that local peripheral cooling lowered skin temperatures in all areas of the body within 5 min. Distant areas of the body (extremities) and pectoral muscles showed greater hypothermia than abdominal areas and head. After 10 min of cooling average skin temperatures in all areas of the body returned to the original level and further fluctuated at approximately 10–15 min intervals.Data indicate that during local cooling skin blood flow in all areas of the body surface permanently fluctuates forming a mosaic of dynamic changes in skin temperatures. Since tympanic temperature increases, while skin temperature decreases immediately after the start of the local cooling, it appears that the initial vasoconstrictor response is being controlled independently of the central temperature input.     

Measurement of torso skin temperature under clothing

The influence of clothing on skin temperature distributions of the torso was investigated during and after cold exposure. Volunteers were cooled for one hour at 5 degrees C while wearing clothing designed to have insulation which was intended to be relatively uniformly distributed. Three different thicknesses of clothing were used. Following thermistor measurements of skin temperatures during the cold exposures, clothing was quickly removed from the upper parts of the body to enable thermographic investigations of the temperature distributions of the front of the bare torso. The evolution of temperature distributions were then studied at different ambient temperatures (5 degrees C and 20 degrees C) as a function of the thickness of the insulation which had previously been worn. The patterns of the temperature distributions, and the range and standard deviation of torso temperatures were all found to be relatively constant in spite of the different thicknesses of clothing worn or in the time-variant mean torso temperatures which resulted. The front torso sites normally used for the determination of mean skin temperatures were found to be on portions of the torso which were cooler than the surrounding regions. It was concluded that a site midway between the umbilicus and a nipple yields a more accurate estimate of mean torso temperature in the conditions of the present study.     

Temperature gradient across the skin's layers has no influence on local skin vasomotor responses

The normal negative temperature gradient within the skin of the cheek was reversed by simultaneously heating the skin externally with an infrared lamp and cooling it internally, inside the mouth, with ice. Cutaneous blood flow was measured locally under four different conditions: negative and positive gradient of local skin temperature in hypothermia and hyperthermia. There were no significant differences between negative and positive skin temperature gradients. Cutaneous blood flow depended on the core body temperature. These results show that the local skin temperature gradient can not induce vasomotor responses.     

Characterization of performance of multihole nozzle in cryospray

Present study deals with improvement in conventional technique of spraying liquid nitrogen on cancerous lesions to improve its efficacy. It is an attempt to demarcate the variation in outcome when cryogen is sprayed through customised multi-hole nozzle (MHN). Influence of mass flow rate on cryoablation while varying the number of holes in MHNs is analysed experimentally. Another section of study focuses on the impact of the rate of evaporation of cryogen when margin among the holes is changed. Total 6 MHNs are fabricated while changing their geometrical parameters. Single freeze-thaw cycle is carried out to spray liquid nitrogen on tissue mimicking gel with a spraying distance of 18 mm. Temperature profile captured through infrared images advocates that lethal area formed through the application of MHNs with 5 holes is larger than MHNs with 4 holes on the surface of gel. It reflects the influence of central hole on necrosis. In order to necrotize lesion through freezing, the most desired cooling rate (CR) varies from 50^∘C/min to 200^∘C/min. It is achieved up to a depth of 2 mm below the gel surface and in a radius of 10 mm from the centre of spray (CS) for all MHNs, except 4C. Most optimised margin in terms of cryoablation is also estimated in the study. MHN with 1.5 mm margin provides the most optimised results in terms of cryoablation when MHNs with the central hole are considered while MHN with 1 mm margin provides most optimised result when MHNs without central hole are considered. On the basis of observations made through thermal images it can be said that multiple freezing fronts are not observed on the gel surface which aids in the formation of lone giant ice ball. This provides an extra edge to the treatment methodology because alteration in the dimensions of necrotic zone can be made by changing the duration of spray. Larger lateral spread of necrotic zone will also reduce the number of sittings required for the treatment of larger lesions.     

Regional hyperthermia by magnetic induction in a beagle dog model: analysis of thermal dosimetry

We have investigated magnetic induction heating techniques for achieving normal tissue hyperthermia in a beagle dog model to clarify the physics and physiology of "regional heating," to develop an animal model of regional heating in humans, and to develop a method of rapid regional heating in dogs for a normal visceral tissue toxicity study. Heating was done with a concentric coil or a coaxial pair of coils applied to the abdominal region, and with or without surface cooling blankets in each case. Thermometers were placed at multiple visceral and subcutaneous sites including an intraarterial thermocouple at the aortic arch level. With either electrode arrangement and no surface cooling, whole-body hyperthermia ( WBH ) at 42 degrees C was produced within 30 to 55 min with 250 W applied power; the 42 degrees C state could be maintained with 40 to 60 W of power. Thermal gradients in these cases reflected nonuniform power deposition superimposed upon arterial temperature elevation. With surface cooling blankets added, systemic heating was significantly reduced, and temperature gradients again reflected the nonuniform power deposition. Regional heating in a dog produces WBH unless sufficient surface cooling is used to provide a heat dissipation rate balancing the heat absorption rate; this latter case best models the use of inductive techniques in humans. The coaxial pair of coils, without surface cooling, produced rapid WBH and the visceral temperature maximum and minimum were within Tesoph + 0.21 degrees C and Tesoph - 0.07 degrees C, respectively (95% confidence index; Tesoph = esophageal temperature). This is an appropriate technique for the proposed toxicity study.     

Three-dimensional model on thermal response of skin subject to laser heating

A three-dimensional (3D) multilayer model based on the skin physical structure is developed to investigate the transient thermal response of human skin subject to laser heating. The temperature distribution of the skin is modeled by the bioheat transfer equation, and the influence of laser heating is expressed as a source term where the strength of the source is a product of a Gaussian shaped incident irradiance, an exponentially shaped axial attenuation, and a time function. The water evaporation and diffusion is included in the model by adding two terms regarding the heat loss due to the evaporation and diffusion, where the rate of water evaporation is determined based on the theory of laminar boundary layer. Cryogen spray cooling (CSC) in laser therapy is studied, as well as its effect on the skin thermal response. The time-dependent equation is discretized using the finite difference method with the Crank-Nicholson scheme and the stability of the numerical method is analyzed. The large sparse linear system resulted from discretizing the governing partial differential equation is solved by a GMRES solver and the expected simulation results are obtained.     

Three-dimensional model on thermal response of skin subject to laser heating

A three-dimensional (3D) multilayer model based on the skin physical structure is developed to investigate the transient thermal response of human skin subject to laser heating. The temperature distribution of the skin is modeled by the bioheat transfer equation, and the influence of laser heating is expressed as a source term where the strength of the source is a product of a Gaussian shaped incident irradiance, an exponentially shaped axial attenuation, and a time function. The water evaporation and diffusion is included in the model by adding two terms regarding the heat loss due to the evaporation and diffusion, where the rate of water evaporation is determined based on the theory of laminar boundary layer. Cryogen spray cooling (CSC) in laser therapy is studied, as well as its effect on the skin thermal response. The time-dependent equation is discretized using the finite difference method with the Crank–Nicholson scheme and the stability of the numerical method is analyzed. The large sparse linear system resulted from discretizing the governing partial differential equation is solved by a GMRES solver and the expected simulation results are obtained.     

The human thermal portrait and its relations with aerobic working capacity and the blood lactate level

In a study on 53 healthy male volunteers with the use of an infrared thermograph, data that the thermal portrait, i.e., skin temperature distribution, under the conditions of muscular rest and minimal chemical thermoregulation activation is related to the maximal aerobic capacity (r = + 0.6) and the lactate level after critical muscle load (r = −0.7) were obtained. A series of pilot experiments on six volunteers showed that acute regional cooling (by placing feet into ice-cold water for 1 min) led to temperature rise in some local areas of the breast and back skin and increase in oxygen uptake, pulmonary ventilation and the respiratory quotient. Simultaneously, the lactate level in peripheral blood was reduced. On the basis of these results, it was assumed that brown adipose tissue (BAT) activity influenced the thermal portrait formation in the case of environmental temperature below thermoneutral. This hypothesis makes it possible to explain a negative correlation between the skin temperature and the body mass index and a twofold increase in the oxygen uptake during acute cold exposure. Nevertheless, further investigations are necessary to clarify the physiological mechanisms underlying the significant correlation between skin temperatures at rest under thermoneutral conditions and the maximal aerobic capacity, anaerobic threshold and lactate accumulation after critical muscle load.     

Heat transfer analysis of skin during thermal therapy using thermal wave equation

Specifying exact geometry of vessel network and its effect on temperature distribution in living tissues is one of the most complicated problems of the bioheat field. In this paper, the effects of blood vessels on temperature distribution in a skin tissue subjected to various thermal therapy conditions are investigated. Present model consists of counter-current multilevel vessel network embedded in a three-dimensional triple-layered skin structure. Branching angles of vessels are calculated using the physiological principle of minimum work. Length and diameter ratios are specified using length doubling rule and Cube law, respectively. By solving continuity, momentum and energy equations for blood flow and Pennes and modified Pennes bioheat equations for the tissue, temperature distributions in the tissue are measured. Effects of considering modified Pennes bioheat equation are investigated, comprehensively. It is also observed that blood has an impressive role in temperature distribution of the tissue, especially at high temperatures. The effects of different parameters such as boundary conditions, relaxation time, thermal properties of skin, metabolism and pulse heat flux on temperature distribution are investigated. Tremendous effect of boundary condition type at the lower boundary is noted. It seems that neither insulation nor constant temperature at this boundary can completely describe the real physical phenomena. It is expected that real temperature at the lower levels is somewhat between two predicted values. The effect of temperature on the thermal properties of skin tissue is considered. It is shown that considering temperature dependent values for thermal conductivity is important in the temperature distribution estimation of skin tissue; however, the effect of temperature dependent values for specific heat capacity is negligible. It is seen that considering modified Pennes equation in processes with high heat flux during low times is significant.     

Thermal detection of embedded tumors using infrared imaging

Breast cancer is the most common cancer among women. Thermography, also known as thermal or infrared imaging, is a procedure to determine if an abnormality is present in the breast tissue temperature distribution. This abnormality in temperature distribution might indicate the presence of an embedded tumor. Although thermography is currently used to indicate the presence of an abnormality, there are no standard procedures to interpret these and determine the location of an embedded tumor. This research is a first step towards this direction. It explores the relationship between the characteristics (location and power) of an embedded heat source and the resulting temperature distribution on the surface. Experiments were conducted using a resistance heater that was embedded in agar in order to simulate the heat produced by a tumor in the biological tissue. The resulting temperature distribution on the surface was imaged using an infrared camera. In order to estimate the location and heat generation rate of the source from these temperature distributions, a genetic algorithm was used as the estimation method. The genetic algorithm utilizes a finite difference scheme for the direct solution of the Pennes bioheat equation. It was determined that a genetic algorithm based approach is well suited for the estimation problem since both the depth and the heat generation rate of the heat source were accurately predicted.     

Temperature regulation of marine mammals

A mathematical model of heat loss from an aquatic animal to the surrounding water is presented. Heat is generated in metabolically active tissues and distributed by circulating blood and by conduction. The time dependent radial temperature profile of the animal is numerically solved from heat transfer equations by a computer. The model is applied to large whales, porpoises, and seals. For the whales, blood circulation to the dermal layer below appendage and body skin surfaces proved to be essential for sufficient heat dissipation. When decreasing the blood flow below a certain value (dependent on sea temperature and whale activity) the large whales would overheat. Blubber thickness was found to be of minor importance in whale thermoregulation, because the blubber coat can be bypassed by blood circulation. On the other hand, it is in general not possible for small porpoises and seals to stay warm in the coldest waters using normal mammalian resting metabolic rates, even if the peripheral circulation is shut off (or artery-vein heat exchangers used). Heat loss can be reduced if the outermost tissue layers are allowed to cool. This is achieved by minimizing convective radial heat flow via the circulation. (For large whales even minute radial blood flow raises the muscle temperatures to the core temperature level.) Seasonal acclimatization of harbour seals is explained by changes in their effective insulation thickness. Differences in whale activity induce changes in the temperature profile mainly within the first few centimeters from the skin surface. These superficial temperatures, if known, could be used to estimate whale metabolic rates. Since they drop close to the sea water temperature within minutes after whale death, the measurements should be done of live whales.     

The effect of surface cooling on blood flow distribution in infant pigs with mature left to right shunts

Surface cooling as an adjunct to cardiopulmonary bypass, core cooling, and circulatory arrest has been effectively used to produce more homogeneous cooling and better tissue preservation. A previous study, using pigs with newly created aortopulmonary shunts, revealed a redistribution of blood flow away from the kidneys and viscera during surface cooling that did not occur in normal pigs. The present study tests the hypothesis that pigs with mature aortopulmonary shunts behave in a similar manner. Group I (N = 7, unshunted pigs) and Group II (N = 7, shunted pigs) underwent surface cooling and blood flow distribution measurements by microspheres at 37, 32, 28, and 25 degrees C. Both Groups I and II experienced a decrease in cardiac output with hypothermia. Group II had decreased absolute tissue flow to the viscera, kidneys, muscle, and skin at 37 degrees C compared with Group I, even before the onset of hypothermia. During hypothermia, Group I experienced a decrease in all tissue flows, but Group II had a decrease only in visceral and renal flows at 25 degrees C. Blood flow distribution, as a percentage of cardiac output, showed little change (decrease only in skin) in Group I with hypothermia. In Group II, however, a maldistribution of cardiac output developed resulting in decreased percentage of cardiac output to the kidneys and viscera and an increased percentage of cardiac output to the lungs that was confirmed by an increase in the Qp/Qs ratio.(ABSTRACT TRUNCATED AT 250 WORDS)     

Global‐scale species distributions predict temperature‐related changes in species composition of rocky shore communities in Britain

Changes in rocky shore community composition as responses to climatic fluctuations and anthropogenic warming can be shown by changes in average species thermal affinities. In this study, we derived thermal affinities for European Atlantic rocky intertidal species by matching their known distributions to patterns in average annual sea surface temperature. Average thermal affinities (the Community Temperature Index, CTI) tracked patterns in sea surface temperature from Portugal to Norway, but CTI for communities of macroalgae and plant species changed less than those composed of animal species. This reduced response was in line with the expectation that communities with a smaller range of thermal affinities among species would change less in composition along thermal gradients and over time. Local‐scale patterns in CTI over wave exposure gradients suggested that canopy macroalgae allow species with ranges centred in cooler than local temperatures (‘cold‐affinity’) to persist in otherwise too‐warm conditions. In annual surveys of rocky shores, communities of animal species in Shetland showed a shift in dominance towards warm‐affinity species (‘thermophilization’) with local warming from 1980 to 2018 but the community of plant and macroalgal species did not. From 2002 to 2018, communities in southwest Britain showed the reverse trend in CTI: declining average thermal affinities over a period of modest temperature decline. Despite the cooling, trends in species abundance were in line with the general mechanism of direction and magnitude of long‐term trends depending on the difference between species thermal affinities and local temperatures. Cold‐affinity species increased during cooling and warm‐affinity ones decreased. The consistency of responses across different communities and with general expectations based on species thermal characteristics suggests strong predictive accuracy of responses of community composition to anthropogenic warming.     

Effect of skin surface cooling on central venous pressure during orthostatic challenge

Orthostatic stress leads to a reduction in central venous pressure (CVP), which is an index of cardiac preload. Skin surface cooling has been shown to improve orthostatic tolerance, although the mechanism resulting in this outcome is unclear. One possible mechanism may be that skin surface cooling attenuates the drop in CVP during an orthostatic challenge, thereby preserving cardiac filling. To test this hypothesis, CVP, arterial blood pressure, heart rate, and skin blood flow, as well as skin and sublingual temperatures, were recorded in nine healthy subjects during lower body negative pressure (LBNP) in both normothermic and skin surface cooling conditions. Cardiac output was also measured via acetylene rebreathing. Progressive LBNP was applied at -10, -15, -20, and -40 mmHg at 5 min/stage. Before LBNP, skin surface cooling lowered mean skin temperature, increased CVP, and increased mean arterial blood pressure (all P < 0.001) but did not change mean heart rate (P = 0.38). Compared with normothermic conditions, arterial blood pressure remained elevated throughout progressive LBNP. Although progressive LBNP decreased CVP under both thermal conditions, during cooling CVP at each stage of LBNP was significantly greater relative to normothermia. Moreover, at higher levels of LBNP with skin cooling, stroke volume was significantly greater relative to normothermic conditions. These data indicate that skin surface cooling induced an upward shift in CVP throughout LBNP, which may be a key factor for preserving preload, stroke volume, and blood pressure and improving orthostatic tolerance.     

A thermographic study of the effect of body composition and ambient temperature on the accuracy of mean skin temperature calculations

The problem associated with using measurements from a small number of sites to determine mean skin temperature was investigated by studying variations in distributions of skin temperatures of the bare torsos of humans exposed to ambient temperatures of 18, 23, and 28 degrees C. Following a 60 minute equilibration period the temperatures of four regions (chest, abdomen, upper back, and lower back) were measured using both thermistors and an infra-red thermographic system. Regions of the torso usually represented by a single temperature exhibited significant point-to-point temperature variations especially in chilled subjects. Also an earlier finding was confirmed: in that larger variations in skin temperature distributions occur as body fat content increases. Caution must therefore be used in applying the concept of a mean skin temperature derived from a few select sites, especially with nude subjects who are chilled or have a high body fat content.     

Computational model of vascular endothelial growth factor spatial distribution in muscle and pro-angiogenic cell therapy

Members of the vascular endothelial growth factor (VEGF) family of proteins are critical regulators of angiogenesis. VEGF concentration gradients are important for activation and chemotactic guidance of capillary sprouting, but measurement of these gradients in vivo is not currently possible. We have constructed a biophysically and molecularly detailed computational model to study microenvironmental transport of two isoforms of VEGF in rat extensor digitorum longus skeletal muscle under in vivo conditions. Using parameters based on experimental measurements, the model includes: VEGF secretion from muscle fibers; binding to the extracellular matrix; binding to and activation of endothelial cell surface VEGF receptors; and internalization. For 2-D cross sections of tissue, we analyzed predicted VEGF distributions, gradients, and receptor binding. Significant VEGF gradients (up to 12% change in VEGF concentration over 10 μm) were predicted in resting skeletal muscle with uniform VEGF secretion, due to non-uniform capillary distribution. These relative VEGF gradients were not sensitive to extracellular matrix composition, or to the overall VEGF expression level, but were dependent on VEGF receptor density and affinity, and internalization rate parameters. VEGF upregulation in a subset of fibers increased VEGF gradients, simulating transplantation of pro-angiogenic myoblasts, a possible therapy for ischemic diseases. The number and relative position of overexpressing fibers determined the VEGF gradients and distribution of VEGF receptor activation. With total VEGF expression level in the tissue unchanged, concentrating overexpression into a small number of adjacent fibers can increase the number of capillaries activated. The VEGF concentration gradients predicted for resting muscle (average 3% VEGF/10 μm) is sufficient for cellular sensing; the tip cell of a vessel sprout is approximately 50 μm long. The VEGF gradients also result in heterogeneity in the activation of blood vessel VEGF receptors. This first model of VEGF tissue transport and heterogeneity provides a platform for the design and evaluation of therapeutic approaches.     

Counterpoint to “Infrared cameras overestimate skin temperature during rewarming from cold exposure”

We evaluated the paper by Maley et al. (2020) in this journal “Infrared cameras overestimate skin temperature during rewarming from cold Exposure” for the evidence provided in support of its title and conclusions. Several methodological issues were identified as well as issues with the data interpretation: 1: Only one camera was used but a conclusion was made for ‘cameras’ in general; 2: The camera accuracy (±2 °C) is too low to do a meaningful comparison without using local reference values or an on-site calibrator with higher accuracy; 3: Thermistor measurements are taken as a gold standard while issues such as temperature gradients and taping are known; 4: Both methods are not compared at the same location and a natural, physiological, gradient may be present between their locations; 5. The impact of the sensor and tape on delays in the change of the underlying tissue temperature is not considered; 6: Only a single pixel was used for the analysis, which has been shown to be problematic.We concluded that the paper by Maley et al. does not provide conclusive evidence that infrared cameras overestimate skin temperature during rewarming from cold exposure.