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2007, Piran, Slovenia

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Non-thermal factors<br />

INDIVIDUAL VARIABILITY IN THE CORE INTERTHRESHOLD<br />

ZONE AS RELATED TO NON-THERMAL FACTORS<br />

Naoshi Kakitsuba 1 , Igor B. Mekjavic 2 , Tetsuo Katsuura 3<br />

1 Meijo University, JAPAN, 2 Jozef Stefan Institute, <strong>Slovenia</strong>,<br />

3 Faculty of Enineering., Chiba University, JAPAN<br />

Contact person: naoshi@ccmfs.meijo-u.ac.jp<br />

INTRODUCTION<br />

Regulation of internal body temperature in humans is characterized by heat loss and heat<br />

production responses. These responses are each initiated at specific combinations of core and<br />

skin temperature, and each has a unique response sensitivity. The manner in which<br />

thermoafferent signals from the core and periphery are integrated centrally has been the focus<br />

of many studies in the past. However, attention is shifting towards a better understanding of<br />

how non-thermal factors influence temperature regulation. Some non-thermal factors, such as<br />

aging for example, have been shown to affect all thermoregulatory responses, whereas others,<br />

only affect individual autonomic responses. Hypoglycemia, for example, only attenuates<br />

shivering, and dehydration only the sweating response. Parallel neurophysiological studies<br />

have provided neuroanatomical evidence explaining the manner in which some of these nonthermal<br />

factors alter the thermoregulatory responses. In the case of hypoglycemia and<br />

dehydration, it has been demonstrated that the majority of the hypothalamic cold and warm<br />

sensors are bimodal, responding to more than one stimulus modality. Some of the cold<br />

sensors are also glucosensitive, and some of the warm sensors are osmosensitive. During<br />

cooling, the cold sensors will be progressively more active, but their activity will be<br />

dependent on the level of plasma glucose. In the same manner, the activity of the warm<br />

sensors will be dependent on the plasma osmolality. The attenuated activity of the cold and<br />

warm sensors will be reflected in the shivering and sweating responses, respectively.<br />

Common to all studies investigating the effect of non-thermal factors is the use homogenous<br />

subject samples. Despite this homogeneity, there remains a substantial degree of individual<br />

variability in both the characteristics of the responses, as well as the manner in which nonthermal<br />

factors affect the individual responses. Since the focus of the studies is to elucidate<br />

how non-thermal factors influence temperature regulation, analysis of the results usually<br />

incorporates a comparison of averaged responses for conditions in which a given non-thermal<br />

response is maintained at different levels, and such analyses usually neglect individual<br />

variability. The present study focuses on this variability in the autonomic responses,<br />

specifically the variability in sweating and shivering, as related to non-thermal factors.<br />

METHODS<br />

Subjects: Thirty two healthy male subjects participated in the study (Table 1). They all gave<br />

informed consent to participate in the study, being fully aware that they could withdraw from<br />

the study without prejudice at any time. The protocol of the study was approved by the<br />

institutional ethics review process.<br />

Table 1 Subjects’ physical characteristics (n=32).<br />

Age<br />

yr<br />

Height<br />

cm<br />

Weight<br />

kg<br />

AD*<br />

m 2<br />

AD /Weight<br />

(m 2<br />

/kg×10 2<br />

Maximum<br />

Adiposity<br />

work load<br />

N.D.<br />

(W)<br />

means±SD 21.4±1.81 172.0±5.76 60.7±8.32 1.71±0.1 2.84±0.18 0.26±0.04 262.2±39.8<br />

2<br />

* AD: body surface area (m 2 )<br />

249

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