Assessment of right ventricular afterload by pressure waveform analysis in acute pulmonary hypertension

To characterize hydraulic right ventricle (RV) afterload by pulmonary arterial pressure waveform analysis in an acute pulmonary hypertension (PH) model.

Pulmonary artery (PA) flow and pressure were recorded in six anesthetized sheep. Acute isobaric PH was induced by phenylephrine (active) and PA mechanical constriction (passive). We estimated the amplitude of the forward and reflected pressure waves according to the inflection point. In most cases the inflection pressure was smooth, thus the inflection point was defined as the time at which the first derivative of pulmonary arterial pressure reached its first minimum. We calculated the input and characteristic (Z(C), time-domain Li method) impedances, the capacitance index (stroke volume/pulse pressure), the augmentation index (AI) (reflected pressure/pulse pressure), the fractional pulse pressure (pulse pressure/mean pressure) and the wasted energy generated by the RV due to wave reflection during ejection (E(W)).

Pulse pressure, fractional pulse pressure, AI and Z(C) increased and capacitance index decreased during passive PH with respect to control (P < 0.05). In contrast, Z(C) and the capacitance index did not change and E(W) and the AI decreased during active PH. Pulse pressure correlated with E(W) and Z(C) and the AI was correlated with E(W) (r > 0.6, P < 0.05).

PA pressure waveform analysis allows the quantification of the dynamic RV afterload. Prospective clinical studies will be necessary to validate this time-domain approach to evaluate the dynamic RV afterload in chronic PH.