Effect of intravenous volume infusion on heart rate in unanesthetized dogs

¹ Cardiovascular Institute, Michael Reese Hospital and Medical Center, Chicago, Illinois

Fifteen untrained, unanesthetized dogs were infused intravenously with blood for 10 min at the rate of 100 ml/min. The heart rate changes so induced were compared with the heart rate existing initially. Systemic arterial and venous pressures were also recorded by means of indwelling catheters. The direction of change in heart rate was found to depend on the initial heart rate. When the initial heart rate was below 120 beats/min the infusion caused a tachycardia; above this initial rate a bradycardia was induced. Denervation was carried out in 26 other dogs. Sympathectomy and "total" denervation of the heart tended to abolish the induced tachycardia, but not the induced bradycardia. Vagotomy did not abolish the induced bradycardia. In ten vagotomized dogs the initial rate was above 120 beats/min.

Key Words: heart rate changes • cardioregulation • cardiac reflexes in unanesthetized dogs

Submitted on September 11, 1963