Am. J. Respir. Crit. Care Med., Volume 161, Number 2, February 2000, 487-492

Clinical Correlates and Prognostic Significance of Six-minute Walk Test in Patients with Primary Pulmonary Hypertension
Comparison with Cardiopulmonary Exercise Testing

SHOICHI MIYAMOTO, NORITOSHI NAGAYA, TORU SATOH, SHINGO KYOTANI, FUMIO SAKAMAKI, MASATOSHI FUJITA, NORIFUMI NAKANISHI, and KUNIO MIYATAKE

Division of Cardiology, Department of Medicine, National Cardiovascular Center, Osaka; and College of Medical Technology, Kyoto University, Kyoto, Japan

The six-minute walk test is a submaximal exercise test that can be performed even by a patient with heart failure not tolerating maximal exercise testing. To elucidate the clinical significance and prognostic value of the six-minute walk test in patients with primary pulmonary hypertension (PPH), we sought (1) to assess the relation between distance walked during the six-minute walk test and exercise capacity determined by maximal cardiopulmonary exercise testing, and (2) to investigate the prognostic value of the six-minute walk test in comparison with other noninvasive parameters. The six-minute walk test was performed in 43 patients with PPH, together with echocardiography, right heart catheterization, and measurement of plasma epinephrine and norepinephrine. Symptom-limited cardiopulmonary exercise testing was performed in a subsample of patients (n = 27). Distance walked in 6 min was significantly shorter in patients with PPH than in age- and sex-matched healthy subjects (297 ± 188 versus 655 ± 91 m, p < 0.001). The distance significantly decreased in proportion to the severity of New York Heart Association functional class. The distance walked correlated modestly with baseline cardiac output (r = 0.48, p < 0.05) and total pulmonary resistance (r = 0.49, p < 0.05), but not significantly with mean pulmonary arterial pressure. In contrast, the distance walked correlated strongly with peak O₂ (r = 0.70, p < 0.001), oxygen pulse (r = 0.57, p < 0.01), and E-VCO₂ slope (r = 0.66, p < 0.001) determined by cardiopulmonary exercise testing. During a mean follow-up period of 21 ± 16 mo, 12 patients died of cardiopulmonary causes. Among noninvasive parameters including clinical, echocardiographic, and neurohumoral parameters, only the distance walked in 6 min was independently related to mortality in PPH by multivariate analysis. Patients walking < 332 m had a significantly lower survival rate than those walking farther, assessed by Kaplan-Meier survival curves (log-rank test, p < 0.01). These results suggest that the six-minute walk test, a submaximal exercise test, reflects exercise capacity determined by maximal cardiopulmonary exercise testing in patients with PPH, and it is the distance walked in 6 min that has a strong, independent association with mortality. Miyamoto S, Nagaya N, Satoh T, Kyotani S, Sakamaki F, Fujita M, Nakanishi N, Miyatake K. Clinical correlates and prognostic significance of six-minute walk test in patients with primary pulmonary hypertension: comparison with cardiopulmonary exercise testing.