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To compare the characteristics of exercise capacity and ventilatory efficiency between patients with severe pulmonary hypertension (SPH group) and with mild-moderate pulmonary hypertension (MMPH group), and to aid in providing the evidence for clinical diagnosis.
We retrospectively investigated the symptom-limited cardiopulmonary exercise test (CPET) with gas exchange measurements in totally 23 patients with confirmed PH. According to the results of right-heart catheterization, we divided patients into SPH group (n=15) and MMPH group (n=8). All subjects had also performed the 6-min walk test and the pulmonary function test (PFT). All data were computed with SPSS windows 13.0. Differences between two groups were compared using two independent samples t-test, with p less than 0.05 considered significant.
The two groups had similar demographics and pulmonary function at baseline. No adverse cardiac event occurred during the study. Only one patient with SPH failed to reach anaerobic threshold (AT). Exercise capacity was lower in SPH group than in MMPH group with a significant difference when measured by peak oxygen uptake per kilogram (peak VO2/kg, 16.12±2.96 ml·kg-1·min-1 vs 20.76±4.16 ml·kg-1·min-1, p=0.005), peak VO2/kg of pred%(44.2±13.3% vs 56.9±9.0%, p=0.026), VO2 @AT/kg (12.49±2.24 ml·kg-1·min-1 vs 15.86±2.74 ml·kg-1·min-1, p=0.005) and VO2 @AT/kg of pred% (34.7±10.8% vs 43.4±3.9%, p=0.014). But no significant difference was found in 6-minute walk distance (6MWD, 491.2±63.3m vs 532.9±77.5m, p = 0.178). Although being statistically insignificant, the lowest VE/VCO2 and VE/VCO2 slope (45.2±9.8 vs 40.0±13.0, 48.9±12.4 vs 39.0±17.0, respectively, both p > 0.1) in SPH group were slightly higher than those in MMPH group. In addition, Statistically significant differences between SPH group and MMPH group were observed in oxygen uptake efficiency slope (OUES), OUES of pred% and end-tidal carbon dioxide partial pressure at anaerobic threshold-PETCO2@AT(901.6±;306.6 ml/min/L/min vs 1304.1±356.47ml/min/L/min, p=0.01; 40.7±16.5% vs 62.6±16.8%, p=0.007; 26.5±4.2 mmHg vs 31.8±7.5 mmHg, p=0.047, respectively).
This study suggests that exercise capacity and ventilatory efficiency of patients with severe PH were more impaired than those of patients with mild-moderate pulmonary hypertension, approximately 50% of predicted normal. It is concluded that OUES and percentages of its predicted values are better physiological parameters in evaluating the gas exchange abnormality of patients with PH.
Key words: Pulmonary Hypertension; Exercise capacity; Ventilatory efficiency; Cardiopulmonary Exercise Testing