Influence of Upright Versus Supine Position on Resting and Exercise Hemodynamics in Patients Assessed for Pulmonary Hypertension

Abstract

Background The aim of the present work was to study the influence of body position on resting and exercise pulmonary hemodynamics in patients assessed for pulmonary hypertension (PH). Methods and Results Data from 483 patients with suspected PH undergoing right heart catheterization for clinical indications (62% women, age 61±15 years, 246 precapillary PH, 48 postcapillary PH, 106 exercise PH, 83 no PH) were analyzed; 213 patients (main cohort, years 2016-2018) were examined at rest in upright (45°) and supine position, such as under upright exercise. Upright exercise hemodynamics were compared with 270 patients (historical cohort) undergoing supine exercise with the same protocol. Upright versus supine resting data revealed a lower mean pulmonary artery pressure 31±14 versus 32±13 mm Hg, pulmonary artery wedge pressure 11±4 versus 12±5 mm Hg, and cardiac index 2.9±0.7 versus 3.1±0.8 L/min per m², and higher pulmonary vascular resistance 4.1±3.1 versus 3.9±2.8 Wood P<0.001. Exercise data upright versus supine revealed higher work rates (53±26 versus 33±22 watt), and adjusting for differences in work rate and baseline values, higher end-exercise mean pulmonary artery pressure (52±19 versus 45±16 mm Hg, P=0.001), similar pulmonary artery wedge pressure and cardiac index, higher pulmonary vascular resistance (5.4±3.7 versus 4.5±3.4 Wood units, P=0.002), and higher mean pulmonary artery pressure/cardiac output (7.9±4.7 versus 7.1±4.1 Wood units, P=0.001). Conclusions Body position significantly affects resting and exercise pulmonary hemodynamics with a higher pulmonary vascular resistance of about 10% in upright versus supine position at rest and end-exercise, and should be considered and reported when assessing PH.

Keywords: body position; exercise; hemodynamic; pulmonary hypertension; right heart catheterization.

Figure 1. Differences of resting hemodynamic in upright (45°) vs supine position in patients undergoing right heart catheterization because of suspected pulmonary hypertension.

Mean differences with 95% CIs of main resting hemodynamic measures assessed by right heart catheterization in upright vs supine position within patients of the entire main cohort (all groups together) and within patients of the different hemodynamic subgroups. Differences are negative if values in upright position are lower than in supine position. Cardiac index, L/min per m²; mPAP, mean pulmonary artery pressure, mm Hg; PAWP, pulmonary artery wedge pressure, mm Hg; PH, pulmonary hypertension; and PVR, pulmonary vascular resistance.

Figure 2. Hemodynamic measures in upright (45°) and supine position at baseline rest, at 50% and 100% of individual work rate.

Means and SD of main hemodynamic measures assessed by right heart catheterization in upright (main cohort, n=217, black diamonds) and supine position (historical cohort, n=270, white squares) at baseline, and at 50% and 100% of individual end‐exercise work rate. *P<0.05 between groups in the adjusted regression analyses. A, Mean pulmonary artery pressure. B, Pulmonary artery wedge pressure. C, Cardiac index. D, Pulmonary vascular resistance. mPAP, mean pulmonary artery pressure; PAWP, pulmonary artery wedge pressure; PH, pulmonary hypertension; PVR, pulmonary vascular resistance; and WU, Wood units.

Figure 3. Differences of hemodynamic measures at the end of exercise in upright (45°) vs supine position unadjusted and adjusted for baseline values and end‐exercise work rate.

Mean differences with 95% CIs of main hemodynamic parameters assessed by right heart catheterization at the end of cycle exercise in upright (main cohort, n=217) vs supine position (historical cohort, n=270). Open circles represent unadjusted differences and filled circles represent differences adjusted for baseline values and end‐exercise work rate. Data from all patients and from patients of the different hemodynamic subgroups are displayed in separate panels. Differences are negative if values in upright position are lower than in supine position. Cardiac index, L/min per m²; mPAP, mean pulmonary artery pressure, mm Hg; PAWP, pulmonary artery wedge pressure, mm Hg; PH, pulmonary hypertension; and PVR, pulmonary vascular resistance.