Interactions between surface cooling and LBNP-induced central hypovolemia.

The interaction between whole body surface cooling (WBSC) and progressive lower body negative pressure (LBNP) to -50 torr was evaluated in nine healthy male volunteers, mean age 29 +/- 1.7 years. WBSC, accomplished by circulating 16 degrees C water through an Apollo cooling garment, produced a significant drop in mean skin temperature of 1.96 degrees C (p less than 0.001). Cardiac output (Q) was measured by the C2H2 rebreathing technique. Changes in leg volume (LgV) were monitored by a Whitney strain gauge. WBSC at rest produced a significant decrease in leg volume of 0.27 I (p less than 0.01). Heart rate decreased (-7 bpm, p less than 0.01) and systolic arterial blood pressure was increased (+6 torr, p less than 0.02). The hemodynamic effects of cooling were maintained throughout progressive levels of LBNP with consistently lower leg volumes and heart rates and higher stroke volumes and systolic pressure (p less than 0.01 for all measurements). The data suggest that WBSC produces a central displacement of cutaneous venous volume resulting in an increase in stroke volume.