Biomedical subjects

H Janáková

Publications and source records attributed to H Janáková.

3 recordsLinked to original sources

PubMed1996

Change in sympathetic activity, cardiovascular functions and plasma hormone concentrations due to cold water immersion in men.

The purpose of this study was to determine whether or not repeated short-term cold water immersions can induce a change in the activity of the sympathetic nervous system and, consequently, in cardiovascular functions in healthy young athletes. Changes in some plasma hormone concentrations were also followed. A single cold water immersion (head-out, at 14 degrees C, for 1 h) increased sympathetic nervous system activity, as evidenced by a four-fold increase (P < 0.05) in plasma noradrenaline concentration. Plasma adrenaline and dopamine concentrations were not increased significantly. Plasma renin-angiotensin activity was reduced by half (P < 0.05) during immersion but plasma aldosterone concentration was unchanged. Stimulation of the sympathetic nervous system during immersion did not induce significant changes in heart rate, but induced peripheral vasoconstriction (as judged from a decrease in skin temperature) and a small increase (by 10%) in systolic and diastolic blood pressures. No clear change in reactivity of the sympathetic nervous system was observed due to repeated cold water immersions (three times a week, for 6 weeks). Neither the plasma renin-angiotensin activity, aldosterone concentration nor cardiovascular parameters were significantly influenced by repeated cold water immersions. A lowered diastolic pressure and an increase in peripheral vasoconstriction were observed after cold acclimation, however. Evidently, the repeated cold stimuli were not sufficient to induce significant adaptational changes in sympathetic activity and hormone production.

Acclimatization↗

PubMed1996

Changes in thermal homeostasis in humans due to repeated cold water immersions.

The purpose of this study was to monitor changes in body and skin temperatures, heat production, subjective shivering, cold sensation and body fat content in humans after intermittent cold water immersion. Repeated exposures of young sportsmen to cold water (head out, 14 degrees C, 1 h, 3 times per week for 4-6 weeks) induced changes in regulation of thermal homeostasis. "Cold acclimated" subjects exhibited an hypothermic type of adaptation. Central and peripheral body temperatures at rest and during cold immersion were lowered. The metabolic response to cold was delayed and subjective shivering was attenuated. The observed hypothermia was due to the shift of the threshold for induction of cold thermogenesis to lower body temperatures. "Cold acclimated" subjects also showed a lowered cold sensation. Because of the observed physiological changes, about 20% of the total heat production was saved during one cold water immersion of "cold acclimated" subjects. Maximal aerobic and anaerobic performances were not altered. No change in the thermosensitivity of the body temperature controller, as assessed from the unchanged slope of the relation between the deep body temperature and total heat production, was observed. Changes in cold sensation and regulation of cold thermogenesis were noticed first after four cold water immersions and persisted for at least 2 weeks after termination of the adaptation procedure. A trend towards a small increase in the body fat content was also observed. This finding, as well as the increased vasoconstriction, evidenced by the lowered skin temperature, indicate that slight changes in body insulation may also occur after "cold acclimation" in humans.

Acclimatization↗

PubMed1995

[Nutrient utilization during cold exposure and adaptation].

BACKGROUND: Repeated exposure to cold leads to a decline in the intensity of physiological defence reactions. In the complex of adaptational responses metabolic, thermogenic and insulation reactions predominate. The objective of the present investigation was to provide evidence of the predominating type of response of sportsmen exposed repeatedly to cold in an aqueous environment and to elucidate metabolic processes which serve to meet the energy demands of a certain type of adaptation to cold. METHODS AND RESULTS: The examination was made in a group of volunteers (men, mean age 21.0 +/- 1.8 years, height 1.80 +/- 0.04 m, body weight 77.0 +/- 3.1 kg, body fat 13.2 +/- 1.7%, anaerobic capacity expressed as maximum oxygen consumption 4.5 +/- 0.43 l.min-1). The cold acclimation programme involved immersion of the body into water 14 +/- 1 degree C 3 times a week for 1 month. During cold exposure the median body temperature before the acclimation programme dropped by 3.9 degrees C, after the acclimation programme by 4.1 degrees C. The total metabolic turnover after the programme declined by a 0.23 multiple of the metabolism at rest, at the end of the programme merely by a multiple of 0.07. During immersion the oxygen consumption doubled regardless of the stage of adaptation and an insignificant rise of non-esterified fatty acids occurred before the onset of the programme as well as after its termination. After the first exposure to cold a significant drop of the blood sugar was observed, while after the acclimation programme it increased insignificantly. The serum level of the thyroid stimulating hormone and triiodothyronine were affected only insignificantly by exposure to cold, the thyroxine level only at the borderline of significance before the onset of the acclimation programme. CONCLUSIONS: From values of the blood sugar level, respiratory quotient RQ, the non-esterified fatty acid level and body temperature at the periphery we may conclude that there is a restriction of the carbohydrate component as regards meeting energy demands of cold exposure before adaptation and a mixed type of meeting energy demands after termination of the cold acclimation programme.

Adaptation, Physiological↗