Effects of arterial load variations on dynamic arterial elastance: an experimental study.

BACKGROUND.: Dynamic arterial elastance (Ea dyn ), the relationship between pulse pressure variation (PPV) and stroke volume variation (SVV), has been suggested as a functional assessment of arterial load. The aim of this study was to evaluate the impact of arterial load changes during acute pharmacological changes, fluid administration, and haemorrhage on Ea dyn .

METHODS.: Eighteen anaesthetized, mechanically ventilated New Zealand rabbits were studied. Arterial load changes were induced by phenylephrine ( n =9) or nitroprusside ( n =9). Thereafter, animals received a fluid bolus (10 ml kg -1 ), followed by stepwise bleeding (blood loss: 15 ml kg -1 ). The influence of arterial load and cardiac variables on PPV, SVV, and Ea dyn was analysed using a linear mixed-effects model analysis.

RESULTS.: After phenylephrine infusion, mean ( sd ) Ea dyn decreased from 0.89 (0.14) to 0.49 (0.12), P <0.001; whereas after administration of nitroprusside, Ea dyn increased from 0.80 (0.23) to 1.28 (0.21), P <0.0001. Overall, the fluid bolus decreased Ea dyn [from 0.89 (0.44) to 0.73 (0.35); P <0.01], and haemorrhage increased it [from 0.78 (0.23) to 0.95 (0.26), P =0.03]. Both PPV and SVV were associated with similar arterial factors (effective arterial elastance, arterial compliance, and resistance) and heart rate. Furthermore, PPV was also related to the acceleration and peak velocity of aortic blood flow. Both arterial and cardiac factors contributed to the evolution of Ea dyn throughout the experiment.

CONCLUSIONS.: Acute modifications of arterial load induced significant changes on Ea dyn ; vasodilatation increased Ea dyn , whereas vasoconstriction decreased it. The Ea dyn was associated with both arterial load and cardiac factors, suggesting that Ea dyn should be more properly considered as a ventriculo-arterial coupling index.