Shorter Distance on Six-Minute Walk Test Points Up a Greater Risk of Death
For idiopathic pulmonary fibrosis (IPF) patients awaiting lung transplantation, a simple walk test can predict mortality rates. A new study found that individuals with IPF who can cover less than 680 feet during the six-minute test are four times more likely to die than those who can walk greater distances.
The research appears in the second issue for September 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
David J. Lederer, M.D., of the Division of Pulmonary, Allergy and Critical Care Medicine at Columbia University College of Physicians and Surgeons in New York City, and five associates examined the records of 454 adult IPF patients on U.S. transplantation waiting lists.
In IPF, lung tissue is damaged by an unknown cause. The walls of the air sacs become inflamed, which leads to scarring or fibrosis. As a result, patients with IPF frequently suffer from progressive respiratory failure. Eventually, the scarring causes permanent loss of the lungs' ability to transport oxygen.
To date, lung transplantation is the only medical therapy that has been shown to improve survival. Twenty-percent of all lung transplant procedures performed worldwide involve patients with IPF.
The investigators call the six-minute walk test a "simple, safe, reliable and inexpensive" way to assess the self-paced exercise capacity of IPF patients. It varies little when repeated on the same person over a short period of time.
"A total of 209 patients had a six-month follow-up without undergoing lung transplantation," said Dr. Lederer. "Forty-nine of these patients, 23 percent, died during that time period. The six-minute walk test's ability to separate those alive at six months from those who died was not only significantly better than chance, but also superior to the forced vital capacity percent (FVC%) predicted test."
The authors noted that a lower six-minute walking distance was associated with more severe lung disease, status as a minority and lower educational attainment in a nationwide cohort of patients with IPF who were listed for lung transplantation.
The test also predicted waitlist mortality independently of age, sex, race, lung function indices, presence of pulmonary hypertension and other potential confounders.
According to the investigators, the six-minute walk test has at least four advantages over other tests:
1) it is less costly than other tools;
2) it can be performed on patients with severe hypoxemia (inadequate amounts of oxygen in the blood) who require continuous high-flow oxygen;
3) it can be performed in any sufficiently long hallway by appropriately trained personnel; and
4) it does not require specialized equipment and expertise found only in established pulmonary function laboratories.
The authors concluded that a test like FVC% predicted might not be valid for gauging survival in patients with IPF who have been listed for lung transplantation because of the serious nature of their illness.