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  • 1
    Electronic Resource
    Electronic Resource
    Predicting survival time for cold exposure (1995)
    Springer
    International journal of biometeorology 39 (1995), S. 94-102 
    Details
    ISSN: 1432-1254
    Keywords: Hypothermia ; Shivering ; Immersion ; Clothing ; Wind
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract The prediction of survival time (ST) for cold exposure is speculative as reliable controlled data of deep hypothermia are unavailable. At best, guidance can be obtained from case histories of accidental exposure. This study describes the development of a mathematical model for the prediction of ST under sedentary conditions in the cold. The model is based on steady-state heat conduction in a single cylinder comprised of a core and two concentric annular shells representing the fat plus skin and the clothing plus still boundary layer, respectively. The ambient condition can be either air or water; the distinction is made by assigning different values of insulation to the still boundary layer. Metabolic heat production (M) is comprised of resting and shivering components with the latter predicted by temperature signals from the core and skin. Where the cold exposure is too severe forM to balance heat loss, ST is largely determined by the rate of heat loss from the body. Where a balance occurs, ST is governed by the endurance time for shivering. End of survival is marked by the deep core temperature reaching a value of 30° C. The model was calibrated against survival data of cold water (0 to 20° C) immersion and then applied to cold air exposure. A sampling of ST predictions for the nude exposure of an average healthy male in relatively calm air (1 km/h wind speed) are the following: 1.8, 2.5, 4.1, 9.0, and 〉24 h for −30, −20, −10, 0, and 10° C, respectively. With two layers of loose clothing (average thickness of 1 mm each) in a 5 km/h wind, STs are 4.0, 5.6, 8.6, 15.4, and 〉24 h for −50, −40, −30, −20, and −10° C. The predicted STs must be weighted against the extrapolative nature of the model. At present, it would be prudent to use the predictions in a relative sense, that is, to compare or rank-order predicted STs for various combinations of ambient conditions and clothing protection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212587
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  • 2
    Electronic Resource
    Electronic Resource
    Calorimetry and respirometry in guinea pigs in hydrox and heliox at 10–60 atm (2000)
    Springer
    Pflügers Archiv 440 (2000), S. 843-851 
    Details
    ISSN: 1432-2013
    Keywords: Hydrogen diving Hyperbaria Thermoregulation Hydrogen narcosis HPNS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. We used direct calorimetry and respirometry to measure the total rate of heat loss (Q Σ) and of oxygen consumption ( $$ \mathop V\limits^ \bullet {\rm O}_{\rm 2} $$ ) in guinea pigs in 1-atm (0.1 MPa) air and at 10–60 atm in either heliox (98% He, 2% O2) or hydrox (98% H2, 2% O2). Our objective was to determine if the physiological responses to these two gas mixtures were different and, if so, whether the differences were attributable to the thermal characteristics of the gases alone or were confounded by additional mechanisms. At 10–40 atm, Q Σ and $$ \mathop V\limits^ \bullet {\rm O}_{\rm 2} $$ were not significantly different in the two gas mixtures, whereas at 60 atm, Q Σ and $$ \mathop V\limits^ \bullet {\rm O}_{\rm 2} $$ were significantly higher in heliox than in hydrox. The $$ \mathop V\limits^ \bullet {\rm O}_{\rm 2} /Q_{\rm \Sigma } $$ ratio suggested that the animals were not in thermal equilibrium in hyperbaria. Based solely on the differing thermal properties of the gas mixtures, a mathematical model predicted a Q Σ that was higher in hydrox than in heliox at all pressures. Two plausible explanations are suggested: one is an adaptive lowering of the surface temperature as a physiological response of the animal to the thermally more stressful hydrox environment, and the other is related to the narcotic suppression of the animal's activity by hydrox.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240000385
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  • 3
    Electronic Resource
    Electronic Resource
    Is energy substrate mobilization a limiting factor for cold thermogenesis? (1993)
    Springer
    European journal of applied physiology 67 (1993), S. 239-244 
    Details
    ISSN: 1439-6327
    Keywords: Body temperatures ; Energy metabolism ; Heat balance ; Heat production ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Energy substrate mobilization has been suggested as being a limiting factor for the rate of cold-induced thermogenesis (M), and consequently in delaying hypothermia. The evidence supporting this hypothesis in humans, however, is not convincing and the hypothesis has yet to be tested in a rigorous manner using a full heat balance analysis (partitional calorimetry). The goal of this study was therefore to re-investigate whether enhancing energy substrate mobilization by feeding cold-exposed subjects would improveM and affect heat debt (S; the minute-by-minute balance ofM and heat losses) as well as rectal (T re) and mean skin temperatures $$\bar T_{sk} $$ . Nine healthy semi-nude fasted subjects were exposed to 5° C (3 h at rest, 1 m · s−1 wind) on three occasions following the ingestion at min 0 and 90 of either: (1) a placebo, (2) 710 kJ of pure carbohydrates (100%-CHO), or (3) 710 kJ of a high-carbohydrate bar (High-CHO). As expected in the cold,T re andT sk decreased whereasM, S and heat losses increased (P〈0.01). However, there were no differences between treatments, including the finalT re [mean (SEM); 36.4 (0.2); 36.5 (0.3) and 36.5 (0.2)°C for the placebo, 100%-CHO and High-CHO tests, respectively]. During the 100%-CHO treatment, rates of carbohydrate oxidation were the highest and fat oxidation the lowest (P〈0.05), whereas the High-CHO treatment caused smaller changes. The results demonstrate that in the cold, enhancing energy substrate mobilization by ingesting substrates in the form of a supplement containing either mainly or only CHO does not cause detectable changes inM, heat loss,S or body temperatures, compared to the ingestion of a placebo. Under the present conditions, the results do not support the theory that energy substrate mobilization is a limiting factor for cold-induced thermogenesis in humans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00864222
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  • 4
    Electronic Resource
    Electronic Resource
    Prediction of the thermoregulatory response for clothed immersion in cold water (1989)
    Springer
    European journal of applied physiology 59 (1989), S. 334-341 
    Details
    ISSN: 1439-6327
    Keywords: Thermoregulation ; Mathematical model ; Cold-water immersion ; Clothing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A multi-compartmental thermoregulatory model was applied to data of ten resting clothed males immersed for 3 h in water at 10 and 15°C. Clothing consisted of a dry suit and either a light or heavy undergarment, representing a total insulation of 0.15 (0.95) or 0.20 m2°CW−1 (1.28 clo), respectively. Data were grouped according to low (〈14%) and high (14 to 24%) body fat individuals. Mean decreases in rectal temperature ranged from 0.79 to 1.38°C, mean decreases in the mean weighted skin temperature ranged from 6.3 to 10.2°C, and mean increases in the metabolic rate ranged from 33.9 to 80.8 W. The model consists of eight segments, each representing a specific region of the body. Each segment is comprised of compartments representing the core, muscle, fat, skin, and clothing. Each compartment is assigned thermophysical values of heat conduction and heat capacitance, and with the exception of clothing, physiological values of blood flow and metabolic heat production. During cold exposure, responses are directed towards increased heat production in the form of shivering and heat conservation in the form of vasoconstriction and convective heat exchange at the vascular level. Agreement between the model predictions and the experimental observations was obtained by adjusting the parameters governing these responses. These adjusted parameters were 1) the onset of limb shivering with an exponential half-time of 30 min, 2) the fractional value of 0.5 for the convective heat exchange between the core compartments of the limbs and the blood flowing through these compartments, 3) the fractional contribution of trunk shivering to overall shivering, which ranged from 0.77 to 0.95, and 4) the onset of vasoconstriction with exponential half-times that ranged from 3 to 25 min. Steady state was predicted to occur within 4 h and a heat balance analysis indicated that the limbs were responsible for most of the body's heat loss while acquiring most of their own heat from the trunk through convective heat exchange with the central blood.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02389807
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  • 5
    Electronic Resource
    Electronic Resource
    Forearm temperature profile during the transient phase of thermal stress (1992)
    Springer
    European journal of applied physiology 64 (1992), S. 395-401 
    Details
    ISSN: 1439-6327
    Keywords: Cold stress ; Cooling rate ; Intramuscular temperature ; Tissue temperature ; Transient response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The transient temperature response of the resting human forearm immersed in water at temperatures (T w) ranging from 15 to 36°C was investigated. Tissue temperature (T t) was continuously monitored by a calibrated multicouple probe during the 3-h immersions.T t was measured every 5 mm, from the longitudinal axis of the forearm to the skin surface. Skin temperature, rectal temperature, and blood flow ( $$\dot Q$$ ) were also measured during the immersions. The maximum rate of change of the forearm mean tissue temperature ( $$\dot T_{{\text{t, max}}}$$ ) occurred during the first 5 min of the immersion. $$\dot T_{{\text{t, max}}}$$ was linearly dependent onT w (P〈0.001), with mean values (SEM) ranging from −0.8 (0.1) °C · min−1 at 15°C to 0.2 (0.1) °C · min−1 at 36°C. The maximum rate of change of compartment mean temperature was dependent (P〈0.001) on the radial distance from the longitudinal axis of the forearm. The half-time for thermal steady state of the forearm mean tissue temperature was linearly dependent onT w between 30 and 36°C (P〈0.01), with mean values (SEM) ranging from 15.6 (0.6) min at 30°C to 9.7 (1.2) min at 36°C and not different between 15 and 30°C, averaging 16.2 (0.6) min. There was a significant linear relationship between the half-time for thermal steady-state of the compartment mean temperature and the radial distance from the longitudinal axis of the forearm for each value ofT w tested (P〈0.001). The data of the present study suggest that the forearm $$\dot Q$$ is an important determinant of the transient thermal response of the forearm tissue during thermal stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625057
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  • 6
    Electronic Resource
    Electronic Resource
    Prediction of shivering heat production from core and mean skin temperatures (1999)
    Springer
    European journal of applied physiology 79 (1999), S. 221-229 
    Details
    ISSN: 1439-6327
    Keywords: Key words Modeling ; Thermogenesis ; Hypothermia ; Cooling ; Rewarming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Prediction formulae of shivering metabolism (M shiv) are critical to the development of models of thermoregulation for cold exposure, especially when the extrapolation of survival times is required. Many such formulae, however, have been calibrated with data that are limited in their range of core temperatures (T c), seldom involving values of less than 36°C. Certain recent studies of cold-water immersion have reported T c as low as 33.25°C. These data comprise measurements of T c (esophageal) and mean skin temperature (T¯ s), and metabolism from 14 males [mean (SD); age = 28 (5) years; height = 1.78 (0.06) m; body mass = 77.7 (6.9) kg; body fat (BF) = 18.4 (4.5)%] during immersion in water as cold as 8°C for up to 1 h and subsequent self-rewarming via shivering under dry blanketed conditions. The data contain 3343 observations with mean (SD) T c and T¯ s of 35.92 (0.93)°C and 23.4 (8.9)°C, respectively, and have been used to re-examine the prediction of M shiv. Rates of changes of these temperatures were not used in the analysis. The best fit of the formulae, which are essentially algebraic constructs with and without setpoints, are those with a quadratic expression involving T¯ s. This is consistent with the findings of Benzinger (1969) who demonstrated that the thermosensitivity of skin is parabolic downwards with temperature peaking near a value of 20°C. Formulae that included a multiplicative interaction term between T c and T¯ s did not predict as well. The best prediction using 37°C and 33°C as the T c and T s setpoints, respectively, was found with BF as an attenuation factor: M shiv (W · m−2) = [155.5 · (37 − T c) + 47.0 · (33 − T¯ s) − 1.57 · (33 − T¯ s)2] (%BF)0.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004210050499
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of postural changes on body temperatures and heat balance (1996)
    Springer
    European journal of applied physiology 72 (1996), S. 451-459 
    Details
    ISSN: 1439-6327
    Keywords: Posture ; Tilt-table ; Thermoneutrality ; Heat storage ; Blood flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Early studies have demonstrated that rectal temperature (T re) decreases and mean skin temperature (T sk) increases in subjects changing their posture from standing to supine, and vice versa. Such changes have important implications insofar as thermal stress experiments are conducted and interpreted. However, the extent of these changes between steady-state conditions is not known. In addition, it is not known whether thermal balance is also affected by postural changes. To examine these questions, 11 healthy males were exposed to a thermoneutral air environment (28.2–28.5°C and 40% relative humidity) in various postures at rest. Body temperatures, heat losses, and metabolic rate were measured. Subjects wore shorts only and began in an upright posture (standing or sitting at an inclination of 7.5°) on a customized tilt-table. They were tilted twice, once into a supine position and then back to the original upright position. Each tilt occurred after steady state was satisfied based on the subject's circadian variation of T re determined previously in a 4.25 h control supine trial. Times to supine steady state following the first tilt were [mean (SE)] 92.6 (6.4) and 116.6 (5.1) min for the standing and sitting trials, respectively. Times to upright steady state following the second tilt were 107.9 (11.4) and 124.1 (9.0) min. Mean steady-state T re and T sk were 36.87 (0.07) and 34.04 (0.14), 37.47 (0.09) and 33.48 (0.14), and 37.26 (0.05) and 33.49 (0.10) °C for supine, standing, and sitting, respectively. Thermal balance was attained in all steady-state conditions, and allowing for a decrease in the weighting factor of T re for mean body temperature in the upright postures, it also appears that thermal balance was preserved between changes in posture. These results are consistent with no perceived changes by the subjects in their thermal comfort and skin wetness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242275
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