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.

BACKGROUND: Exercise intolerance is the hallmark of COPD. Static lung hyperinflation and increased dynamic hyperinflation during exercise are associated with reduced functional capacity in COPD patients. Inspiratory capacity correction for the total lung capacity, defined as inspiratory fraction (IF), may be functionally more representative than other traditional indices in these patients. OBJECTIVE: To investigate the association between IF and exercise capacity in patients with stable, moderate to severe COPD. METHODS: Fifty COPD subjects and 34 healthy volunteers constituted the study cohort. Pulmonary function and cardiopulmonary exercise testing were performed, and ventilation and gas exchange parameters were measured. RESULTS: IF was significantly correlated with percent-of-predicted peak oxygen consumption (V O 2 ) in the subjects with COPD (r ‫؍‬ 0.52, P < .001). IF was an independent predictor of reduced exercise capacity in the COPD subjects, and was more sensitive and specific than percent-of-predicted FEV 1 . Statistical analysis generated the equation: percent-of-predicted peak V O 2 ‫؍‬ 65.9 IF ؉ 0.45 percent-of-predicted FEV 1 ؉ 35.8 (R C 2 ‫؍‬ 0.39, P < .001). The subjects with IF < 0.23 had more severe lung hyperinflation and less exercise capacity than the subjects with IF > 0.23. At peak exercise, the breathing frequencies of the 2 groups were similar, whereas the low-IF subjects had reduced peak minute ventilation and peak tidal volume, relative to the high-IF subjects. CONCLUSIONS: Compared to FEV 1 , IF is a robust factor to reflect lung hyperinflation and to estimate the exercise capacity of subjects with stable moderate to severe COPD.