External cardiac pressures and the left ventricular pressure-volume relationship

Introduction

Wide variations in external cardiac pressures are known to occur in clinical situations and can have significant effects on cardiac performance [1,2]. We designed an experimental situation where external cardiac pressure conditions were controlled and adjusted to physiological extremes to mimic clinically relevant situations, while cardiac performance was assessed using left ventricular pressure-volume relationships (LVPVR) which are relatively preload and afterload independent.

Methods

Healthy adult pigs (n = 4) were anesthetized, received central vascular catheters, a pericardial catheter, and bilateral pleura drains. Left ventricular volume was assessed by the conductance technique [3]. External cardiac pressures were manipulated: pneumothorax (20 ml/kg air injected in the pleura), and pericardial infusion (mean pressure of +6 mmHg). End sytolic elastance (Ees), preload recruitable stroke work (PRSW), preload-adjusted maximal power (PWRmax/EDV2) [4].

Results

During pericardial infusion, where the end-systolic pressure was low and limited in beat-to-beat decrement during the preload reduction only elastance increased while the other derived systolic parameters decreased. During pleura insufflation, all the systolic function parameters increased.

Discussion

These data suggest that relatively load-independent means are needed to assess cardiac function in the setting of extreme extracardiac pressure. LVPVR provides beat-to-beat insight into heart function at wide ranges of loading conditions. Further work is warranted to validate clinically applicable means to implement this type of assessment, as well as to further develop reference methodology for experimental and clinical heart volume assessment.

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