Coherence of cardiac output with rate changes.
In awake or lightly anesthetized dogs increases in heart rate (HR) induced by atrial pacing affect cardiac output (CO) and stroke volume (SV) in a predictable way that is represented by a SV-HR relationship (dSV/dHR). Under our experimental conditions where normal regulation of atrial rate was bypassed, atrial rate was the independent variable and CO and SV were dependent variables. As HR is increased, CO and SV are modified by reflex and other circulatory regulators. The dSV/dHR relation characterized the circulatory response to increasing HR. A single dSV/dHR curve consistently predicted responses under a number of different conditions (standing, recumbent, awake, various anesthetics, beta-adrenergic stimulation, or depression) and thus appeared as an expression of cardiac function. Alterations of the circulation by stellate ganglion or vagal stimulation, volume loading, aortic compression, and ventricular pacing were not represented by the same dSV/dHR function. The dSV/dHR function (including its linear version as reported by others for anesthetized dogs) showed that, when SVs were larger at low rates, maximum CO occurred at a higher HR. Recognition of this arithmetic-based feature resolves apparent contradictory findings reported in the literature.