Dynamic control of maximal ventricular elastance via the baroreflex and force-frequency relation in awake dogs before and after pacing-induced heart failure

We investigated to what extent maximal ventricular elastance ([E.sub.max]) is dynamically controlled by the arterial baroreflex and force-frequency relation in conscious dogs and to what extent these mechanisms are attenuated after the induction of heart failure (HF). We mathematically analyzed spontaneous beat-to-beat hemodynamic variability. First, we estimated [E.sub.max] for each beat during a baseline period using the ventricular unstressed volume determined with the traditional multiple beat method during vena cava occlusion. We then jointly identified the transfer functions (system gain value and time delay per frequency) relating beat-to-beat fluctuations in arterial blood pressure (ABP) to [E.sub.max] (ABP [right arrow] [E.sub.max]) and beat-to-beat fluctuations in heart rate (HR) to [E.sub.max] (HR [right arrow] [E.sub.max]) to characterize the dynamic properties of the arterial baroreflex and force-frequency relation, respectively. During the control condition, the ABP [right arrow] [E.sub.max] transfer function revealed that ABP perturbations caused opposite direction [E.sub.max] changes with a gain value of -0.023 [+ or -] 0.012 [ml.sup.-1] whereas the HR [right arrow] [E.sub.max] transfer function indicated that HR alterations caused same direction [E.sub.max] changes with a gain value of 0.013 [+ or -] 0.005 mmHg x [ml.sup.-1] x [(beats/min).sup.-1]. Both transfer functions behaved as low-pass filters. However, the ABP [right arrow] [E.sub.max] transfer function was more sluggish than the HR [right arrow][E.sub.max] transfer function with overall time constants (indicator of full system response time to a sudden input change) of 11.2 [+ or -] 2.8 and 1.7 [+ or -] 0.5 s (P < 0.05), respectively. During the HF condition, the ABP [right arrow] [E.sub.max] and HR [right arrow] [E.sub.max] transfer functions were markedly depressed with gain values reduced to -0.0002 [+ or -] 0.007 [ml.sup.-1] and -0.001 [+ or -] 0.004 mmHg x [ml.sup.-1] x [(beats/min).sup.-1] (p < 0.1). [E.sub.max] is rapidly and significantly controlled at rest, but this modulation is virtually abolished in HF. autonomic nervous system; beat-to-beat variability; system identification; Treppe effect; ventricular contractility doi: 10.1152/ajpheart.00922.2009.