CARDIAC SYMPATHETIC DENERVATION DOES NOT CHANGE THE LOAD DEPENDENCE OF THE LEFT-VENTRICULAR END-SYSTOLIC PRESSURE-VOLUME RELATIONSHIP IN DOGS

It has been shown that in the intact canine heart the left-ventricular end-systolic pressure/volume relation (ESPVR) depends on loading cond itions: an increase in arterial vascular resistance causes a leftwards shift and a steeper slope of the ESPVR, suggesting an increased inotr opic state. Our purpose was to investigate the possible contribution o f the sympathetic nervous system to this load sensitivity of the ESPVR , using intact, but denervated, hearts with normal coronary perfusion and afterload. We used two types of loading intervention: venous volum e infusion and gradual occlusion of the descending aorta. ESPVRs were obtained in six anaesthetized open-chest dogs, both before and after b ilateral ablation of the stellate ganglia. To exclude the influence of heart rate changes, bilateral vagotomy was performed and the heart wa s paced. The absence of (unpaced) heart rate changes in response to pr essure alterations was used to confirm total denervation. Left ventric ular pressure was measured with a micromanometer and volume with a con ductance catheter. ESPVRs were essentially linear and characterized by their slope (E(es)) and volume intercept at 12 kPa (V-12). We found t hat E(es) (P ( 0.0001) and V-12 (P < 0.05) were both significantly dif ferent during pressure and volume interventions (0.67 +/- 0.29 and 0.4 1 +/- 0.18kPa/ml for E(es) and 16.2 +/- 8.2 and 18.2 +/- 8.4 ml for V- 12 respectively). Denervation did not significantly affect the paramet ers of the ESPVR obtained by either volume infusion or aortic occlusio n. Two-way analysis of variance revealed no significant interactive ef fect between denervation and intervention, indicating that the sympath etic nervous system does not influence the load dependency of the ESPV R. The dP/dt(max): EDV relationship behaved similarly. These results s uggest that load dependency is an intrinsic property of the myocardium .