A right ventricular pressure waveform based pulse contour cardiac output algorithm in canines.

Tracking changes in stroke volume or cardiac output (CO) can be useful in the diagnosis and treatment of various cardiac illnesses. Existing arterial pressure waveform based pulse contour CO algorithms perform poorly during altered systemic hemodynamics. In this study, a right ventricular pressure waveform based pulse contour CO algorithm was developed to estimate the amplitude and duration of a hypothetical triangular flow waveform in the pulmonary artery. This algorithm was tested against gold standard blood flow measurements in ten canines during acute perturbations to preload (inferior vena caval occlusion (IVCO), rapid saline infusion), afterload (descending aortic occlusion (DAO), serotonin, angiotensin II, sodium nitroprusside infusion), and cardiac contractility (dobutamine and propranolol infusion). The algorithm correctly predicted the changes in CO (r2 = 0.82) that varied from - 45 to 31% of the baseline levels. To explain this finding both the pulmonary arterial (PA) and the ascending aortic (AA) input impedances were modeled as three element windkessels. In the AA the peripheral resistance (from - 61 to 191%), characteristic impedance (from - 59 to 20%) and total arterial compliance (from - 49 to 34%) varied significantly with these perturbations. In contrast, these parameters in the PA changed little. In particular, except serotonin infusion, the characteristic impedance of the PA deviated only 6% (SD/mean) from baseline values. This suggests right ventricular pressure waveform based estimate of CO is possible during acute changes in left ventricular hemodynamics.