Non-invasive determination of cardiac output in pre-capillary pulmonary hypertension

Background Cardiac output (CO) is a major diagnostic and prognostic factor in pre-capillary pulmonary hypertension (PH). Reference methods for CO determination, like thermodilution (TD), require invasive procedures and allow only steady-state measurements. The Modelflow (MF) method is an appealing technique for this purpose as it allows non-invasive and beat-by- beat determination of CO. Methods We aimed to compare CO values obtained simultaneously from non-invasive pulse wave analysis by MF (COMF) and by TD (COTD) to determine its precision and accuracy in precapillary PH. The study was performed on 50 patients with pulmonary arterial hypertension (PAH) or chronic thrombo-embolic PH (CTEPH). CO was determined at rest in all patients (n = 50) and during nitric oxide vasoreactivity test, fluid challenge or exercise (n = 48). Results Baseline COMF and COTD were 6.18 ± 1.95 and 5.46 ± 1.95 L_min-1, respectively. Accuracy and precision were 0.72 and 1.04 L_min-1, respectively. Limits of agreement (LoA) ranged from -1.32 to 2.76 L_min-1. Percentage error (PE) was ±35.7%. Overall sensitivity and specificity of COMF for directional change were 95.2% and 82.4%, (n = 48) and 93.3% and 100% for directional changes during exercise (n = 16), respectively. After application of a correction factor (1.17 ± 0.25), neither proportional nor fixed bias was found for subsequent CO determination (n = 48). Accuracy was -0.03 L_min−1 and precision 0.61 L_min−1. LoA ranged from -1.23 to 1.17 L_min−1 and PE was ±19.8%. Conclusions After correction against a reference method, MF is precise and accurate enough to determine absolute values and beat-by-beat relative changes of CO in pre-capillary PH.