ADRENERGIC, RESPIRATORY, AND CARDIOVASCULAR EFFECTS OF CORE COOLING IN HUMANS

The adrenergic, respiratory, and cardiovascular responses to isolated core cooling were assessed in awake human subjects. Mild core hypother mia was induced by intravenous infusion of 30 or 40 ml/kg of cold sali ne (4 degrees C) on 2 separate days. A warm intravenous infusion (30 m l/kg, 37 degrees C) was given on a third day as a control treatment. M ean norepinephrine concentration increased 400% and total body oxygen consumption increased 30% when core temperature decreased 0.7 degrees C. Mean norepinephrine concentration increased 700% and total body oxy gen consumption increased 112% when core temperature decreased 1.3 deg rees C. Core cooling was associated with peripheral vasoconstriction a nd increased mean arterial blood pressure, whereas heart rate was unch anged. Plasma epinephrine and cortisol concentrations were unchanged d uring core cooling. There were no changes in any measured parameter wi th the warm infusion. These findings suggest that mild hypothermia ind uced by isolated core cooling is associated with an adrenergic respons e characterized by peripheral sympathetic nervous system activation wi thout a significant adrenocortical or adrenomedullary response. The re spiratory and cardiovascular responses to core cooling are characteriz ed by a shivering-induced increase in metabolic rate, norepinephrine-m ediated peripheral vasoconstriction, and increased arterial blood pres sure.