Distance and oxygen desaturation during the 6-min walk test as predictors of long-term mortality in patients with COPD.
BACKGROUND
The distance walked in the 6-min walk test (6MWT) predicts mortality in patients with severe COPD. Little is known about its prognostic value in patients with a wider range of COPD severity, living in different countries, and the potential additional impact of oxygen desaturation measured during the test.


METHODS
We enrolled 576 stable COPD outpatients in Spain and the United States and observed them for at least 3 years (median, 60 months). We measured FEV1, body mass index, Pao2, Charlson comorbidity score, 6-min walk distance (6MWD), and oxygen saturation by pulse oximetry (Spo2) during the 6MWT. Desaturation was defined as a fall in Spo2 > or = 4% or Spo2 < 90%. Regression analysis helped determine the association between these variables and all-cause and respiratory mortality.


RESULTS
The 6MWD was a good predictor of all-cause and respiratory mortality primarily in patients with FEV1 < 50% of predicted (p < 0.001) after adjusting for all covariates. Patients with desaturation during the 6MWT had a higher mortality rate than patients without desaturation (67% vs 38%, p < 0.001). Oxygen desaturation predicted mortality (relative risk, 2.63; 95% confidence interval, 1.53 to 4.51; p < 0.001) but with less power than Pao2 at rest.


CONCLUSIONS
The 6MWD helps predict mortality primarily in patients with severe COPD. Although the oxygen desaturation profile during the 6MWT improves the predictive ability of the 6MWD, it appears to be of less relevance than in other lung diseases and than the resting Pao2.
Casanova
Ciro
C
Pulmonary Department, Hospital La Candelaria, Tenerife. Electronic address: ccasanova@canarias.org.
Cote
Claudia
C
Pulmonary Division, Bay Pines VA Medical Center, St. Petersburg, FL.
Marin
José M
JM
Research Unit, Hospital La Candelaria, Tenerife.
Pinto-Plata
Víctor
V
Pulmonary Division. Caritas-St. Elizabeth's Medical Center, Boston, MA.
de Torres
Juan P
JP
Pulmonary Department, Hospital Miguel Servet, Zaragoza, Spain.
Aguirre-Jaíme
Armando
A
Research Unit, Hospital La Candelaria, Tenerife.
Vassaux
Carlos
C
Pulmonary Division. Caritas-St. Elizabeth's Medical Center, Boston, MA.
Celli
Bartolome R
BR
Pulmonary Division. Caritas-St. Elizabeth's Medical Center, Boston, MA.
D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism / Q000401:mortality* / Q000503:physiopathology*; D012720:Severity of Illness Index; D013030:Spain; D015996:Survival Rate; D014481:United States; D016138:Walking / Q000502:physiology*