Reflex cardiovascular responses to cold exposure of the face or foot.

Six subjects performed a breathholding maneuver during facial cooling and immersed their foot in cold water, without drugs and after the intravenous administration of propranolol plus atropine (P + A). Cardiac interval (INT), mean interval for longest consecutive 5 cycles (L5INT/5); systolic time intervals including electromechanical systole (EMS), left ventricular ejection time (LVET), pre-ejection period (PEP), and PEP/LVET; and systolic (SP) and diastolic pressures (DP) were monitored during supine rest, during apnea with a plastic bag of ice water on the face, and from 16-30th and 46-60th sec of 1-min periods of foot immersion in 4 degrees C water. P+A administration induced reduction in INT, L5INT/5, and LVET and increase in PEP, PEP/LVET, and DP. INT, L5INT/5, PEP, SP, and DP increased during facial cooling without drugs. Only the increases in INT and L5INT/5 were abolished by P+A and thus considered to result from reflexes mediated by vagal or sympathetic outflow to the heart. Reductions in INT, L5INT/5, EMS, PEP, and PEP/LVET at 16-30 sec of foot immersion without drugs were not observed after P+A; 46-60 sec responses neared resting values, however, with and without P+A. These results indicate an initial cardiac reflex response to foot immersion may be overpowered by the ventricular afterload and the foot immersion may be overpowered by the ventricular afterload and the baroreceptor response due to the increased arterial pressure.