Determination of Cardiac Output in Pulmonary Hypertension Using Impedance Cardiography

Cardiac output (CO) is a prognostic factor in pulmonary hypertension (PH). Right heart catheterisation using the direct Fick method or thermodilution (TD) is the reference technique for CO measurement. Impedance cardiography (IPc) is a known non-invasive method of measuring CO.

In our study, we assume that the measurement of CO by IPc using the PHYSIOFLOW® system is as accurate as TD or using the direct Fick method in patients with PH in group 1 or group 4.

A total of 75 patients were enrolled in a prospective study carried out at the hypertension reference centre of Toulouse University Hospital. Right heart catheterisation was performed for the diagnosis or follow-up of the disease. CO was measured using the Fick method, TD, and IPc simultaneously. A Bland-Altman analysis was plotted.

CO was 5.7 ± 1.9 L/min as measured by the Fick method, 5.4 ± 1.5 L/min by TD, and 5.5 ± 1.7 L/min by IPc. The bias between CO measurements by IPc and the direct Fick method was 0.149 L/min (95% CI, -0.298 to 0.596). The bias between CO measurements by IPc and the TD method was -0.153 L/min (95% CI, -0.450 to 0.153). The correlation decreased with the more extreme CO values (< 3 L/min or > 7 L/min). A few factors changed the agreement between measurements (BMI or membership in group 4).

To conclude, this study shows that the measurement of CO by IPc in PH patients is reliable compared to the direct Fick method and TD obtained by right heart catheterisation. This accuracy decreases for extreme CO values.