Measurement of cardiac output during exercise in healthy, trained humans using lithium dilution and pulse contour analysis

Abstract

The aim of this study was to evaluate the use of pulse contour analysis calibrated with lithium dilution in a single device (LiDCO™) for measurement of cardiac output (Q-dot) during exercise in healthy volunteers. We sought to; (a) compare pulse contour analysis (PulseCO) and lithium indicator dilution (LiDCO) for the measurement of Q-dot during exercise, and (b) assess the requirement for recalibration of PulseCO with LiDCO during exercise. Ten trained males performed multi-stage cycling exercise at intensities below and above ventilatory threshold before constant load maximal exercise to exhaustion. Uncalibrated PulseCO Q-dot (Q-dot raw) was compared to that calibrated with lithium dilution at baseline (Q-dot baseline), during submaximal exercise below (Q-dot low) and above (Q-dot high) ventilatory threshold, and at each exercise stage individually (Q-dot exercise). There was a significant difference between Q-dot baseline and all other calibration methods during exercise, but not at rest. No significant differences were observed between other methods. Closest agreement with Q-dot exercise was observed for Q-dot high (bias ± limits of agreement: 4.8 ± 30.0%). The difference between Q-dot exercise and both Q-dot low and Q-dot raw was characterized by low bias (4–7%) and wide limits of agreement (>±40%). Calibration of pulse contour analysis with lithium dilution prior to exercise leads to a systematic overestimation of exercising cardiac output. A single calibration performed during exercise above the ventilatory threshold provided acceptable limits of agreement with an approach incorporating multiple calibrations throughout exercise. Pulse contour analysis may be used for Q-dot measurement during exercise providing the system is calibrated during exercise.