1980 Volume 21 Issue 5 Pages 665-679
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°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 TNT, L5INT/5, EMS, PEP, and PEP/LVET at 16-30sec of foot immersion without drugs were not observed after P+A; 46-60sec 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 baroreceptor response due to the increased arterial pressure.
