Conductive and convective heat flows of exercising humans in cold water

The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Shivering onset, metabolic response, and convective heat transfer during cold air exposure

The onset and intensity of shivering of various muscles during cold air exposure are quantified and related to increases in metabolic rate and convective heat loss. Thirteen male subjects resting in a supine position and wearing only shorts were exposed to 10 degrees C air (42% relative humidity and less than 0.4 m/s airflow) for 2 h. Measurements included surface electromyogram recordings at six muscle sites representing the trunk and limb regions of one side of the body, temperatures and heat fluxes at the same contralateral sites, and metabolic rate. The subjects were grouped according to lean (LEAN, n = 6) and average body fat (NORM, n = 7) content. While the rectal temperatures fluctuated slightly but not significantly during exposure, the skin temperature decreased greatly, more at the limb sites than at the trunk sites. Muscles of the trunk region began to shiver sooner and at a higher intensity than those of the limbs. The intensity of shivering and its increase over time of exposure were consistent with the increase in the convective heat transfer coefficient calculated from skin temperatures and heat fluxes. Both the onset of shivering and the magnitude of the increase in metabolic rate due to shivering were higher for the LEAN group than for the NORM group. A regression analysis indicates that, for a given decrease in mean skin temperature, the increase in metabolic rate due to shivering is attenuated by the square root of percent body fat. Thus the LEAN group shivered at higher intensity, resulting in higher increases in metabolic heat production and convective heat loss during cold air exposure than did the NORM group.     

Sampling variance of the correlation coefficients estimated from analyses of variance and covariance

Summary A generalized sampling variance of correlation coefficients is derived for phenotypic, genetic and en vironmental correlations estimated from nested analyses of variance and covarianee for the equal number case. A numerical example is presented to estimate the sampling variance for the genetic correlation coefficient based on the relationship among full sibs using unequal subclass numbers.Journal Paper No. 3472 of the Purdue University Agricultural Experiment Station. This research was supported, in part, by NIH Biometry Training Grant, GM-00024.     

Convective and radiative heat transfer coefficients for individual human body segments

 Human thermal physiological and comfort models will soon be able to simulate both transient and spatial inhomogeneities in the thermal environment. With this increasing detail comes the need for anatomically specific convective and radiative heat transfer coefficients for the human body. The present study used an articulated thermal manikin with 16 body segments (head, chest, back, upper arms, forearms, hands, pelvis, upper legs, lower legs, feet) to generate radiative heat transfer coefficients as well as natural- and forced-mode convective coefficients. The tests were conducted across a range of wind speeds from still air to 5.0 m/s, representing atmospheric conditions typical of both indoors and outdoors. Both standing and seated postures were investigated, as were eight different wind azimuth angles. The radiative heat transfer coefficient measured for the whole-body was 4.5 W/m² per K for both the seated and standing cases, closely matching the generally accepted whole-body value of 4.7 W/m² per K. Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.4 and 3.3 W/m² per K when standing and seated respectively. In the forced convective regime, heat transfer coefficients were higher for hands, feet and peripheral limbs compared to the central torso region. Wind direction had little effect on convective heat transfers from individual body segments. A general-purpose forced convection equation suitable for application to both seated and standing postures indoors was h _c=10.3v ^0.6 for the whole-body. Similar equations were generated for individual body segments in both seated and standing postures. Received: 21 May 1996/Accepted: 27 November 1996     

Air flow and convective heat loss from small mammals in laboratory metabolism chambers

1. 1.Thermal conductance was determined from cooling curves of Mus domesticus carcasses at air flow rates ranging from still air to 0.91·min⁻¹ STP. Thermal conductance was constant over this range of air flows. This indicates that free convection predominates over forced convection at these air flow rates.

2. 2.While non single set of conditions will be appropriate for all experiments, free convection conditions are appropriate for determination of minimal thermal conductance.

The sampling variance of the correlation coefficients estimated from two-fold nested and offspring-parent regression analyses

Summary A formula is presented for the large-sample variance of phenotypic, genetic and environmental correlation coefficients, estimated from two-fold nested genetic analyses of balanced or unbalanced offspring data. Where parents of these offspring are scored, offspring on parent regression estimates of genetic parameters may be obtained for each parental level of the nested model. The large-sample variance of the offspring-parent genetic correlation coefficients, computed from either level or by using mid-parent data, is given. The first formula is a correction and generalisation of an expression given by Grossman (1970), while the second formula is an extension of a relationship derived by Reeve (1955).     

Adjusting culture conditions to isolate thraustochytrids from temperate and cold environments in southern Argentina

To study thraustochytrids from temperate and cold environments of Southern Argentina, the standard cultivation methodologies have been modified because many of the microorganisms detected by microscopic examination in both the original samples and the colonized baits failed to be successfully isolated in standard culture media. As a result, 35 strains, most of them having a very low growth rate, were isolated. Alternative procedures are proposed according to the nature of the sample, the characteristics of the thraustochytrid to be isolated, and the presence of contaminating microorganisms. Modifications proposed include the use of a newly formulated culture medium (Mar Chiquita, containing glucose, gelatine hydrolysate, peptone, and corn steep liquor as main carbon and nitrogen sources). In addition, the effects of the nutrient composition and agar concentration of culture media on the relative growth rates of the isolates were studied in an attempt to determine the most suitable conditions for the cultivation of new strains of thraustochytrids. The goal of this study is to develop a standard methodology, allowing us to grow baitable “elusive” thraustochytrid strains, and that could be applied to improve the isolation and the study of the undocumented biodiversity of this group of microorganisms from different environments.     

Responses to heat and cold in lower mammals

A survey has been made of the literature pertaining to temperature regulation in the lower mammals.The following scheme represent a tentative outline of one probable evolutionary sequence of homeothermy: the first successful efforts to maintain a fairly uniform level of body temperature began on the psycho-physiological or behavioural level. The first directly physiological factor in the maintenance of homeothermy seems to have been a capacity for variation in metabolic heat production.The monotremes provides an example of a temperature regulation based solely on behaviour patterns and variation in heat production. The next factor to appear in the gradual development of refined homeothermy has been the regulation of physical heat exchange. A gradual improvement of such function is discernible along the phylum also correlated with increased thermal stress imposed by the environment. Regulation of physical heat exchange is first generally apparent in the marsupial order. The thermostatic arrangements responsible for efficient body temperature regulation have been developed gradually becoming increasingly complex and accurate. It is discussed how an efficient central nervous thermostatic control seems to have been the last factor developed to perfection in homeothermy.

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Zusammenfassung übersichtsrefrat über die Temperaturregulation in niederen SÄugern. Das folgende Schema ist ein vorlÄufiger Entwurf über die wahrscheinliche Ausbildung der Homeothermie wÄhrend der Evolution:die ersten wirksamen Einrichtungen zur Erhaltung einer ziemlich uniformen Korpertemperatur waren psycho-physiologische Funktionen und Eigenarten im Verhalten. Die erste ausschliesslich physiologische Funktion zur Erhaltung der Homeothermie scheint die FÄhigkeit zur Änderung der WÄrmebildung im Stoffwechsel gewesen zu sein.Die Monotremata sind ein Beispiel für Temperaturregulation, die allein durch Verhaltensformen und Änderung der WÄrmebildung bestimmt wird. Der nÄchste Schritt wÄhrend der graduellen Entwicklung zur ausgebildeten Homeothermie war die Regulierung des physikalischen WÄrmeaustausches.Eine zunehmende Verbesserung dieser Funktionen ist in dem Stamm zu beobachten. Sie ist verbunden mit verstÄrkter Hitzebelastung durch die Umwelt.Die Regulierung des physikalischen WÄrmeaustausches ist bei den Marsupialia erstmalig nachweisbar.Die Einrichtungen für wirksame Körpertemperaturregulation haben sich langsam entwickelt und wurden immer komplexer und genauer. Die Körpertemperaturkontrolle durch das Zentralnervensystem scheint die letzte Einrichtung zur Vervollkommung der Homeothermie gewesen zu sein.

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Résumé Ce travail passe en revue la régulation thermique des petits mammifères.Le schéma provisoire suivant indique les mécanismes possibles d'apparition de l'homéothermie pendant l'évolution: les premiers dispositifs efficaces maintenant une température corporelle à peu près constante étaient des fonctions psycho-physiologiques et des particularités du comportement. La première fonction purement physiologique contribuant à l'homéothermie semble avoir été la faculté de modifier la production de chaleur métabolique. Les monotrèmes sont un exemple de régulation thermique produite uniquement par des formes de comportement et par des changements de la production de chaleur. Le développement de l'homéothermie complète progressa ensuite par la régulation des échanges physiques de chaleur.Le perfectionnement de ces fonctions s'observe chez le phylum.Elle est liée à une surcharge de chaleur en provenance du milieu externe. La régulation des échanges physiques de chaleur est atteinte en premier par les marsupiaux. Les dispositifs efficaces de régulation de la température corporelle se sont développés lentement et sont devenus toujours plus précis et plus complexes. Le contrÔle de la température corporelle par le système nerveux central semble Être le dispositif le plus récent de l'homéothermie complète.

     

Tropomyosin-caldesmon/actomyosin systems in platelets and arterial smooth muscle: results from exchange experiments

Tropomyosin and caldesomon reciprocally control the actomyosin system in smooth muscle and some non-muscle cells. To compare this mechanism between arterial smooth muscle and platelets, we carried out extensive exchange experiments. Actin, myosin, tropomyosin from arterial smooth muscle cells and platelets were recombined and the effects of two species of caldesmon ('caldesmon77' and 'caldesmon140') on the ATPase activities of both systems were examined and analyzed by the method of analysis of variance. (a) The actomyosin system itself is different between artery and platelets, the difference being determined by myosin (P less than 0.05) and not by actin. (b) Platelet tropomyosin differentiates platelet actin from arterial actin (P less than 0.01), while arterial tropomyosin does not. Neither does tropomyosin differentiate myosin. (c) The effect of caldesmon77 differentiates the origins of myosin (P less than 0.01), actin (P less than 0.05) and tropomyosin (P less than 0.05). The effect of caldesmon140 differentiates the origin of myosin (P less than 0.05) and the actin-myosin 'interaction' (combination) (P less than 0.01), but not the origin of tropomyosin (P greater than 0.1). (1) It is concluded that actomyosin/tropomyosin-caldesmon system is distinguishable between platelets and artery. (2) It is suggested that caldesmon is an actomyosin inhibitor which may interact with myosin, in addition to actin and tropomyosin.