EFFECTS OF BODY POSITION ON EXERCISE CAPACITY AND PULMONARY VASCULAR PRESSURE-FLOW RELATIONSHIPS

There has been revival of in interest in exercise testing of the pulmonary circulation for the diagnosis of pulmonary vascular disease, but there still is uncertainty about body position and the most relevant measurements. Doppler echocardiography pulmonary hemodynamic measurements were performed at progressively increased workload in 26 healthy adult volunteers in supine, semi-recumbent and upright positions which were randomly assigned at 24 hours intervals. Mean pulmonary artery pressure (mPAP) was estimated from the maximum tricuspid regurgitation jet velocity. Cardiac output (CO) was calculated from the left ventricular outflow velocity-time integral. Pulmonary vascular distensibility α-index, the % change of vessel diameter per mmHg of mPAP, was calculated from multi-point mPAP-CO plots. Body position did not affect maximum oxygen uptake (VO₂max), maximum respiratory exchange ratio, ventilatory equivalent for carbon dioxide or slope of mPAP-CO relationships which was on average of 1.5 ± 0.4 mmHg/L/min. Maximum mPAP, CO, and total pulmonary vascular resistance (TPR) were respectively of 34 ± 4 mmHg, 18 ± 3 L/min, and 1.9 ± 0.3 Wood units. However, the semi-recumbent position was associated with a 10 % decrease in maximum workload. Furthermore, CO-workload or CO-VO₂ relationships were nonlinear and too variable for a reliable prediction of CO. Thus, these results suggest that body position does not affect maximum exercise testing of the pulmonary circulation when results are expressed as mPAP-CO or maximum TPR. Maximum workload is decreased in semi-recumbent as compared to upright exercise. Workload or VO₂ cannot reliably be used as surrogates for CO.

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