Abstract
BackgroundDecline in oxygen uptake efficiency (OUE), especially during exercise, is found in patients with chronic heart failure. In this study we aimed to test the validity and usefulness of OUE in evaluating gas exchange abnormality of patients with idiopathic pulmonary arterial hypertension (IPAH).MethodsWe retrospectively investigated the cardiopulmonary exercise test (CPET) with gas exchange measurements in 32 patients with confirmed IPAH. All patients also had resting hemodynamic measurements and pulmonary function test (PFT). Sixteen healthy subjects, matched by age, sex, and body size were used as controls, also had CPET and PFT measurements.ResultsIn IPAH patients, the magnitude of absolute and percentage of predicted (%pred) oxygen uptake efficiency slope (OUES) and oxygen uptake efficiency plateau (OUEP), as well as several other CPET parameters, were strikingly worse than healthy subjects (P<0.0001). Pattern of changes in OUE in patients is similar to that in controls, In IPAH patients, OUE values at rest, warming up, anaerobic threshold and peak exercise were all significantly lower than in normal (P<0.0001). OUEP%pred, better than OUES%pred, correlated significantly with New York Heart Association (NYHA) functional Class (r = −0.724, P<0.005), Total Pulmonary Vascular Resistance (TPVR) (r = −0.694, P<0.005), diffusing capacity for carbon monoxide (DLCO) (r = 0.577, P<0.05), and the lowest ventilation versus CO2 output ratio during exercise (LowestV˙E/V˙CO2) (r = −0.902, P<0.0001). In addition, the coefficient of variation (COV) of OUEP was lower (20.9%) markedly than OUES (34.3%) (P<0.0001).ConclusionsIn patients with IPAH, OUES and OUEP are both significantly lower than the healthy subjects. OUEP is a better physiological parameter than OUES in evaluating the gas exchange abnormality of patients with IPAH.
Highlights
Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and fatal disease caused by pulmonary vasculopathy [1,2]
We found that V O2/ventilatory response (V E) when plotted against time normally reached its highest and briefly stable values near the anaerobic threshold (AT), before declining due to hyperventilation stimulated by the metabolic acidosis [14]
The oxygen uptake efficiency slope (OUES) of idiopathic pulmonary arterial hypertension (IPAH) group was 1.0860.37 which was significantly lower than 1.9860.44 of control (p,0.0001)
Summary
Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and fatal disease caused by pulmonary vasculopathy [1,2]. The key CPET characteristics in these patients include a diminished aerobic capacity, an impaired ventilatory efficiency and a decreased minute O2 uptake versus heart rate at peak exercise (peak V O2/HR) etc [4,5,6,7,8]. These CPET parameters have been widely utilized to grade the severity of exercise limitation, to detect exercise-induced right-to-left shunting, to assess responses to therapy, and to predict prognosis in IPAH patients [5,6,7,8]. In this study we aimed to test the validity and usefulness of OUE in evaluating gas exchange abnormality of patients with idiopathic pulmonary arterial hypertension (IPAH)
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