Phylogenesis of the Bainbridge reflex.

The effects of volume loading were examined on measurements of left ventricular (LV) pressure and heart rate in patients undergoing cardiac catheterization. These data were compared to those collected in conscious dogs and subhuman primates (baboons). In man acute volume loading increased LV end-diastolic pressure by 14 mmHg, but did not increase LV systolic pressure significantly. Similar increases in LV end-diastolic pressure were observed in conscious dogs and baboons. LV systolic pressure also did not rise in baboons, but did increase (+32 mmHg) with volume loading in dogs. In man volume loading increased heart rate by 15 beats/min, significantly less (P less than 0.01) than observed in baboons (+37 beats/min), and which in turn was significantly less than that observed in dogs (+88 beats/min). Thus, the Bainbridge reflex, i.e., the tachycardia that occurs with volume loading, appears to exist in primates including man. However, the extent of utilization of this reflex decreases significantly from nonprimate mammals (dogs) to subhuman primates (baboons) to man.