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- Karaki, Wafaa, et al.
(författare)
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Human thermal response with improved AVA modeling of the digits
- 2013
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 67, s. 41-52
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Tidskriftsartikel (refereegranskat)abstract
- The arterio-venous anastomoses (AVA) play a major role in the blood circulation in the peripheral body parts. In this work, the segmental bioheat model of Salloum et al. [1] is improved to accurately predict skin blood flow rate in the hands and fingers, and the local and overall human thermal responses in transient environments. The improvements in the model include: 1) extending the artery tree to include the arterial branching to the five fingers; 2) modelling and distribution of the blood flow between the deep and superficial veins in the peripherals; 3) adjusting arteries' radii during dilation and constriction; 4) innovative modelling of AVA of the fingers. The model focus is on the accurate blood flow calculation to the different body segments proposing a better blood control mechanism through relating the arterial tree radii as well as the AVA control mechanism to cardiac output. The skin blood flow and digits' dynamic thermal response predicted by the model were compared with published experimental values on body core and skin temperatures and local skin temperatures of fingers. Good agreement was obtained with experimentally reported values on average skin, core, and finger skin temperature response of subjects exposed to gradual decrease in air temperature from 32.3°C to 13°C. The new integrated AVA model of the fingers with the bioheat model is capable of predicting digits' dynamics thermal response with better accuracy than some previous models while also incorporating the complex central and local thermoregulatory functions.
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| 2. |
- Kuklane, Kalev, et al.
(författare)
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Does reduced heat production during mild whole body cooling override increased heat generation by pre-shivering muscle tension?
- 2011
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Ingår i: Environmental Ergonomics. ; XIV, s. 112-115
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Konferensbidrag (refereegranskat)abstract
- INTRODUCTION Preshivering thermogenesis (developing muscle tension) may not be noticed in static situations due to reduced metabolism under mild body cooling. This paper describes the observations of metabolic and heart rate changes under mild body cooling. METHODS Eight men participated in the study. The subjects were dressed in shorts, socks and shoes, and were seated. The air temperature (32 °C) was after 25 minutes gradually reduced to 13°C (0.2 °C/min). Rectal, finger, central skin and air temperatures were recorded. Heart rate was measured continuously. Oxygen consumption was analysed under 5 minutes at 30th and 90th minutes. RESULTS AND DISCUSSION Metabolic rates were commonly decreasing (57((+/-)8 at 30th and 55(+/-)11 W/m2 at 90th minute) during cooling. In one subject (quickest finger cooling and increased final core temperature) the metabolic rate did not reduce. His momentary AVAs reaction indicates a more complex neural input than core cooling. In one subject onset of strong shivering raised metabolism considerably. The mean heart rate of all subjects followed the major trend in metabolic rate (80(+/-)12 at 30th and 72(+/-)12 beats/min at 90th minute). CONCLUSION Increased metabolic rate under mild cooling was not observed, eventually due to the absence of strong enough thermo regulatory responses such as increased muscle tension and superficial shivering. There is a need to repeat the study involving EMG in order to separate thermoregulatory effects from postural effects.
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| 4. |
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| 5. |
- Vanggaard, Leif, et al.
(författare)
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Response patterns in finger and central body skin temperatures under mild whole body cooling
- 2011
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Ingår i: Environmental Ergonomics. ; XIV, s. 124-127
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Konferensbidrag (refereegranskat)abstract
- INTRODUCTION The actual heat loss may be underestimated especially in studies employing mild whole-body cooling, if AVA-rich distal areas are not taken into account. In the present report, we illustrate the skin temperature response pattern in fingers (rich in AVAs) to transient whole-body cooling as compared to non-acral body sites (without AVAs). METHODS Eight men participated in the study. During the test the subjects were dressed in shorts, socks and shoes and stayed seated with the arms on insulated supports at heart level. The air temperature of 32 °C was after 25 minutes gradually reduced to 13 °C (0.2 °C/min). Core, finger (sulcus lateral to the nailbed) and non-acral skin (8 points) temperatures were measured. RESULTS During cooling the mean skin temperature in all subjects decreased at a similar rate. Higher variation in the end of the cooling could be explained by differences in body fat (R2=0.902). Simultaneously, the finger cooling could start with up to about 1 hour difference in different subjects. DISCUSSION AND CONCLUSION Mean skin temperature did not give any idea on when the subjects left thermal neutrality. It is strongly recommended to measure finger (or toe) temperatures when maintaining the thermal comfort of the subjects in dynamic conditions is important.
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| 6. |
- Vanggaard, Leif, et al.
(författare)
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Thermal responses to whole-body cooling in air with special reference to arteriovenous anastomoses in fingers
- 2012
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961. ; 32:6, s. 463-469
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Tidskriftsartikel (refereegranskat)abstract
- The arteriovenous anastomoses (AVAs) in the distal parts of the extremities play a significant role in the heat exchange with the environment. The aim of the study was to examine the thermal responses to whole-body cooling in air, and especially the behaviour of finger skin temperature (Tf, rich in AVAs). Eight young men sat in minimal clothing at 32°C air temperature (Ta), which was then lowered gradually to 13°C in 100 min. In the beginning of cooling, Tf was high and fluctuating, and then suddenly exhibited a rapid fall, while temperatures in other skin sites fell fairly linearly along decreasing Ta to the end of cooling. During the period from start to the rapid fall in Tf, rectal temperature decreased from 37.4°C (SD 0.2) to 37.2°C (0.2), mean skin temperature (Tsk) from 34.6°C (05) to 31.2°C (2.0) and whole-body thermal sensation from ‘slightly warm/warm’ to ‘slightly cool/cold’. The start of the steep fall in Tf varied considerably between individuals in terms of time (2–75 min), Ta (16.7–32.0°C) and Tsk (28.8–34.7°C). On the other hand, the range of Tf at that point was narrower (32.1–35.8°C). The findings stress the importance of taking into account the distal skin temperatures in thermoregulatory studies in addition to the ordinarily used more proximal and central skin sites. Also, it might be advisable to start such experiments with relatively high and fluctuating Tf to guarantee that the thermal state of the subject is well defined.
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