Thermal, Metabolic, and Cardiovascular Responses to Various Degrees of Cold Stress

Abstract

The metabolic, thermal, and cardiovascular responses of two male Caucasians to 1 2 h exposure to ambient temperature ranging between 28 degrees C and 5 degrees C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal times m- minus 2 times h- minus 1) = minus 2.79 Ta degrees C + 103.4, r = -0.97, P smaller than 0.001. During all exposures below 28 degrees C, the rate of decrease in mean skin temperature (Tsk) was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of Tsk steady state occurred at 90-120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output (Q) = minus 0.25 Ta degrees C + 14.0, r = minus 0.92, P smaller than 0.01. However, the primary reason for the increased Q, the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28-5 degrees C) was linearly related to decreasing ambients. The non-linear response of this parameter which occurred at 20 degrees C larger than or equal to Ta larger than or equal to 10 degrees C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.

Changes in dietary intake account for seasonal changes in cardiovascular disease risk factors

“…With regard to blood pressure, part of the observed rise seems to stem from a fall in temperature (Keatings & McCance, 1957) and its impact on peripheral resistance (Raven et al, 1970;Raven et al, 1975). Another potentially important`seasonal' risk factor is ®brinogen, which tends to rise in the winter (Van der Bom et al, 1997).…”

Changes in the peripheral blood flow in legs in response to the cold: own studies using plethysmography

“…[3][4][5] This is particularly visible in persons who Note: ABF = alternative blood flow; BI = base impedance; CT = crest time; CW = crest width; HR = heart rate; IR = impedance ratio; SR = slope ratio. Note: ABF = alternative blood flow; BI = base impedance; CT = crest time; CW = crest width; HR = heart rate; IR = impedance ratio; SR = slope ratio.…”

Relationship Between Outdoor Temperature And Blood Pressure

“…The multi-city Monica study [22] also reported findings consistent with those of our study, as have chamber studies on modest cold exposure. [18,19] Given that increased BP is a known risk factor of cardiovascular mortality and morbidity, these findings suggest that increase in blood pressure could be related to cold-induced cardiovascular mortality.…”

“…The effects of mild exposure to cold have been tested under controlled conditions, and the results have shown that short-term exposure to cold causes subcutaneous vasoconstriction that increases central blood volume that further increases BP. [18,19] However, the effects of temperature on BP under ambient conditions with changing air pressure and humidity, which may also include intermittent exposures as people go in and out of buildings, may differ substantially from those in chamber studies, and are not thoroughly studied. Two epidemiological studies from Europe have reported that systolic BP [20], or both systolic and diastolic blood pressure [21] decrease in association with increasing outdoor temperature.…”