Two consecutive six-minute walk tests (6MWT) — which measure the distance a patient can walk in that time to assess their exercise capacity — with the recommended rest interval of one hour lead to reproducible results in adults with non-cystic fibrosis bronchiectasis (NCFB), according to a small study.
However, patients, particularly those older than 60 and women, walked a significantly shorter distance in the second test. Notably, this reduction was associated with higher blood pressure and breathing rate. Patients with more severe disease also walked significantly less distance.
These findings suggest that people with NCFB may need longer than the recommended rest interval between tests, and that vital signs, age, sex, and disease severity should be considered to determine whether the patient is fully recovered to perform the second test, researchers said.
The study, “Repeatability of the 6-min walk test in non-cystic fibrosis bronchiectasis,” was published in the journal Scientific Reports.
NCFB is a chronic and progressive lung disorder characterized by irreversible expansion, inflammation, and scarring of the bronchi — the small airways of the lungs — along with persistent cough, excessive sputum production, and recurrent lung infections.
One of the most widely used tests to measure a person’s exercise and cardiopulmonary functional capacity, including in people with lung diseases, is the 6MWT, which records the distance that a person can walk on a flat, hard surface in six minutes.
This test is particularly beneficial as it is easy to implement, inexpensive, well-tolerated, and highly representative of a person’s ability to perform everyday activities.
The European Respiratory Society and American Thoracic Society recommend that two consecutive 6MWTs with a one-hour interval be performed to minimize potential variability. Also, patients are thought to perform better in the second test due to improved stride length and coordination, as well as less anxiety.
However, data on the test’s repeatability in NCFB patients are limited. Repeatability, or test-retest reliability, is the closeness of agreement between results of successive tests carried out under the same conditions.
In the new study, researchers at the Federal University of Rio Grande do Sul, in Brazil, evaluated the repeatability of the 6MWT in 66 adults (45 women and 21 men) with NCFB.
Participants’ mean age was 54.8 years (range was 18–81) and most showed moderate (29%) to severe (44%) disease, as assessed with the Bronchiectasis Severity Index.
Each patient underwent two tests separated by one hour of rest at the Hospital de Clínicas de Porto Alegre, a large, tertiary care, university-affiliated hospital in Southern Brazil. In addition to the distance that patients could walk during each test, several parameters before and immediately after each test were assessed, including heart rate, blood pressure, breathing rate, shortness of breath, and leg fatigue.
Results showed a 9.4% variation between the results of the two consecutive tests and a considerably high test-retest reliability, or repeatability.
However, patients walked a significantly shorter distance (mean of 16.6 meters less) in the second test, and this reduction was only statistically significant in those older than 60 and in women.
Notably, participants’ blood pressure and breathing rate were significantly higher before starting the second 6MWT than before the first test, “suggesting that the participants were not fully recovered,” the researchers wrote. In agreement, the participants also showed a significant increase in blood pressure at the end of the second test.
The mean walked distance was significantly associated with sex, age, and disease severity, with women, patients older than 60, and those with more severe disease walking significantly shorter distances. Notably, bronchiectasis is known to be more severe in women than in men.
These findings suggest that 6MWT is reproducible in adults with NCFB, but a one-hour rest interval between the two tests may not be “enough to allow a patient with NCFB to return to their basal state, which could be due to [the underlying features] of the disease,” the scientists wrote.
“Vital sign verification should be attentively checked to assess if the patient is fully recovered to perform a second test, as well as the disease severity score,” they added.
The investigators said, however, that future studies including a greater number of NCFB patients and with a narrow age range are needed to confirm these results.
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