Chronotropic response to intravenous infusion in the anesthetized dog

¹ Department of Physiology, Basic Medical Science Institute, Karachi, Pakistan

Ninety-four anesthetized dogs at normal body temperature received 293 intravenous saline infusions by gravity flow through either a femoral or jugular vein. Also nine dogs with body temperature lowered to 27 C received 30 similar infusions. Heart rate and blood pressure were monitored by transducer and oscillographic recording. The chronotropic response of the normothermic group varied with the preinfusion heart rate, with those below 140/min generally showing increases and those above showing no response or a decrease. Negative results with hypothermic animals also having slow preinfusion rates indicate the Bainbridge effect requires the slow preinfusion heart rate to be under vagal inhibition.