This pilot study aimed to compare physiological responses between cycle cardiopulmonary exercise tests (CPETs) and 6-min walk tests (6MWTs) and to assess their prognostic value among patients with idiopathic pulmonary fibrosis (IPF).
Thirty-four patients with IPF (68 ± 8 yr) underwent CPETs and 6MWTs and were followed up for 40 mo. Differences, levels of agreement, and relative risks for mortality were analyzed between measured and estimated peak responses for the 2 tests.
Compared with the CPET, oxygen uptake (o2), heart rate (HR), and the nadir of SpO2 were lower during the 6MWT, whereas work rate (WR) was higher. Mean differences were as follows: o2 =−1.9 mL/kg/min, 95% CI, −1.1 to −2.7, P < .001; HR =−9 beats/min, 95% CI, −4 to −14, P = .002; SpO2 =−6%, 95% CI, −4 to −7, P < .001; and WR = 9 W/min, 95% CI, 3 to 16, P = .008. Interclass correlations ranged from 0.84 to 0.90 and both tests demonstrated prognostic value for mortality.
Significant differences and variation in peak physiological responses were observed between cycle CPETs and 6MWTs in patients with IPF. However, good agreement was evident, suggesting that both tests provide value for clinical and research settings. Future studies should compare the physiological responses between treadmill CPETs and 6MWTs for prognostic utility in IPF.