Non-invasive estimations of ventricular ejection time and stroke volume: comparison of impedance cardiography and the Portapres 2

Stroke volume estimates and left ventricular ejection time (1) derived from calibrated finger pulse pressure recordings (Portapres 2, TNO-BMI, Amsterdam) based on the Model Flow method and (2) derived from impedance cardiography were compared in 20 student subjects. The recordings were made for seven conditions: supine rest, standing, mental arithmetic, ergometer exercise 50 W, motor performance test, reading aloud, and walking. Findings indicated that caution is required in assuming concurrent validity for both methods in tracking haemodynamic changes. Within-subject correlations were low or even negligible. Basic discrepancies were evident regarding the estimation of left ventricular ejection time but obviously more sources of measurement error exist which necessitate further research.