Dynamic control of maximal ventricular elastance in conscious dogs before and after pacing-induced heart failure.

We identified the transfer functions relating beat-to-beat fluctuations in arterial blood pressure to maximal ventricular elastance (ABP-->E(max)) and beat-to-beat fluctuations in heart rate to E(max) (HR-->E(max)) to characterize the dynamic properties of the arterial ventricular contractility baroreflex and force-frequency relation, respectively, in three conscious dogs before and after pacing-induced heart failure. During the control condition, the average gain value, dominant time constant, and time delay were respectively -0.0374 ml(-1), 12.8 sec, and 2 sec for the ABP-->E(max) transfer function and 0.0137 mmHg/ml-bpm, 1.77 sec, and 0 sec for the HR-->E(max) transfer function. During the heart failure condition, both transfer functions were markedly depressed. These results are consistent with known physiology and previous studies and provide perhaps the first quantitative information on the dynamic control of E(max) during normal closed-loop operation.