Ea/Ees and oscillatory power fraction capture complementary but distinct components of ventriculoarterial coupling: a...

Ventriculoarterial coupling (VAC), traditionally assessed using the invasive "gold standard" Ea/Ees ratio (arterial elastance to end-systolic elastance), is clinically important but requires approximations that are impractical at the bedside. Oscillatory power fraction (OPF), defined as the ratio of oscillatory to total hydraulic power and derived from synchronized aortic flow-pressure measurements, has been proposed as a pragmatic VAC surrogate. This study aimed to clarify the possible correlation between VAC and OPF in pharmacologically induced hemodynamic extremes.

In 14 juvenile pigs challenged with vasoactive (phenylephrine, nitroprusside) and cardioactive drugs (dobutamine, esmolol) titrated toward protocolized targets (± 40% MAP, ± 50% dP/dt), we obtained a comprehensive dataset using intracardiac conductance catheters, intraaortic pressure probes, and ascending aortic flow probes. Linear mixed models with animal as a random effect compared baseline and drug-effect states. The coupling of the two responses was assessed from each animal's baseline-to-effect change, corrected for measurement error estimated from the replicate recordings.

Ea/Ees changed by 10%-36% across the four interventions, whereas OPF changed by 1.5%-12%, and under phenylephrine and dobutamine, the change in OPF was negligible (|d| < 0.2, both p > 0.2) despite measurable changes in Ea/Ees. Esmolol was the only challenge under which both indices changed substantially in the same direction (Ea/Ees: + 35.4%, OPF: + 12.2%). Whether the magnitudes of the two responses were coupled could not be determined. Dobutamine markedly increased Ees, total power, and oscillatory power while preserving OPF despite a reduction in Ea/Ees, indicating improved VAC but stable pulsatile efficiency. Vasoactive drugs (phenylephrine, nitroprusside) substantially altered Ea/Ees without relevant OPF changes.

Ea/Ees and OPF are not interchangeable. OPF responded far less strongly than Ea/Ees to the loading changes imposed here and did not resolve them under two of the four challenges. This is consistent with the two indices reflecting predominantly steady and pulsatile aspects of arterial load, although the present data do not demonstrate that separation directly. While OPF cannot replace Ea/Ees, power-derived indices offer practical adjuncts for characterizing ventriculoarterial interactions and the effects of selected drugs at the intensive care bedside.