Alternative Approaches to the Assessment of the Systemic Circulation and Left Ventricular Performance: A Proof-of-Concept Study.

Background: The purpose of this article is to examine the systemic circulation and left ventricular (LV) performance by alternative, nonconventional approaches: systemic vascular conductance ( ) and the head-capacity relation (ie, the relation between LV pressure and cardiac output), respectively; in so doing, we aspired to present a novel and improved interpretation of integrated cardiovascular function.

Methods: In 16 open-chest, anaesthetized pigs, we measured LV pressure ( ), central aortic pressure ( ), and central venous pressure ( ) and aortic flow ( ). We calculated heart rate (HR), stroke volume, cardiac index (CI = cardiac output/body weight), mean P ( , and the average arteriovenous pressure difference ( );  = /( ). We studied the effects of changing loading conditions with the administration of phenylephrine ( ≥ +25 mm Hg), isoproterenol ( ∼+25%), sodium nitroprusside ( ≥ -25 mm Hg), and proximal aortic constriction (to maximize developed and minimize ).

Results: Sodium nitroprusside and isoproterenol increased compared with phenylephrine and constriction. A maximum head-capacity curve was derived from pooled data using nonlinear regression on the maximum values in bins 12.5 mL/min/kg wide. The head-capacity relation and the plots of conductance were combined using as a common axis, which illustrated that is the output of the heart and the input of the circulation.

Conclusions: Thus, at a given , determines the driving pressure and, thereby, . We also demonstrated how decreases in compensate for arterial hypotension by restoring the arteriovenous pressure difference and arterial pressure.