Factors related to pulmonary and physical activity could serve as predictors for how long patients with chronic obstructive pulmonary disease (COPD) can tolerate during an endurance walk test, potentially leading to more accurate analyses on the effectiveness of interventions.
A recent study found that measurements of pulmonary function, physical capacity, and physical activity are independent predictors for the time length that a patient with chronic obstructive pulmonary disease (COPD) could tolerate during an endurance shuttle walk test (ESWT).
The results, published in PLOS ONE, suggested that ESWTs should be adjusted based on individual needs to allow for better assessment of whether interventions are working.
The adjustments may include conducting multiple ESWTs at different intensities or requiring patients with low tolerated duration (a measure known as Tlim) to take a second ESWT at a lower fixed percentage.
ESWTs are used to evaluate the effectiveness of interventions and exercise endurance in patients with COPD. They are usually conducted by having patients walk at a fixed percentage, generally 85%, of their maximum walking pace for as long as they can.
“It appears that patients with more severe airway obstruction should be set at paces slower than 85% of maximal pace and patients with higher physical capacity and activity levels at paces faster than 85% of maximal pace,” wrote the investigators.
The pace used in ESWTs is pre-determined based on results from an incremental shuttle walk test (ISWT). Because pre-intervention values are needed to assess the impact of interventions, large variability among patients can result in complications with statistical analyses and an increase in the number of patients needed in clinical trials to get an accurate result.
Previous studies have shown considerable variability in Tlim. In the present study, 67% of patients with COPD could not tolerate more than 8 minutes of walking during an ESWT, showing high interindividual variability.
It is unknown why some patients’ Tlim falls outside of the recommended timeframe of 3 to 8 minutes. However, exercise intolerance can be influenced by multiple different factors. The present study is the first to examine possible predictors of Tlim in patients with COPD during ESWTs.
During the investigation, the researchers retrospectively analyzed an anonymized dataset collected from the Dekkerswalk-Radboudumc hospital in Nijnegen, The Netherlands between September 2016 and December 2019.
Out of 306 detected patients, 245 met the inclusion criteria by having a primary diagnosis of COPD as determined by the Global Initiative for Chronic Obstructive Lung Disease criteria and data available regarding ISWT and ESWT speed and time results.
The mean (SD) age of the included patients was 61.4 (7.8 years) and their median forced expiratory volume (FEV1) was 38% predicted. Male patients made up 47% of the cohort and the median ESWT Tlim was 6.0 minutes.
The patients were split into 3 group based on their ESWT Tlim:
In addition, group 3 contained 42 (17% of the total dataset) patients who reached the maximum test duration of 20 minutes, suggesting that they likely could have walked longer.
Group 3 had less severe dyspnea, as reflected by the Modified Medical Research Council dyspnea scale, (median, 2; mean (SD), 1.8 [1.2]) than group 2 (median, 2; mean (SD), 2.2 [1.2]; P = .006).
The patients’ pulmonary function was similar among the groups. However, group 1 had a lower forced expiratory volume in 1 second (FEV1) than group 2 (P < .001). Group 3 had a better physical capacity, determined their maximal workload and oxygen uptake (VO2max), and were more physically active, characterized by a higher daily step count and average physical activity level (PAL), than group 2 (P < .001).
Patients with a shorter ESWT Tlim desaturated more frequently during the ISWT than patients with a longer Tlim (P < .001). Additionally, patients in group 1 had a higher rest and maximal dyspnea Borg score compared with group 2. “This might suggest that patients who desaturate more during the ISWT should perform the ESWT at a lower relative load than 85%,” wrote the investigators.
The investigators found that patients in group 3 had a higher maximum oxygen saturation and higher resting and maximal dyspnea Borg score during the ESWT compared with group 2 (P < .001).
The multivariate linear regression analysis found that body mass index, VO2max, endurance time on a constant work rate cycle exercise test, average PAL, ISWT speed, dyspnea Borg score at rest, and increase of leg fatigue Borg score during ISWT were independent predictors of ESWT Tlim.
However, the model explained only about 30% of the Tlim variability (R2 = 0.297; P < .001), suggesting that future studies are needed to establish additional factors to better adjust individual ESWT pace and reduce variability.
Stoffels AAF, van den Borst B, Peters JB, et al. Correlates of variability in endurance shuttle walk test time in patients with chronic obstructive pulmonary disease. PLOS ONE. Published online April 21, 2021. doi: 10.1371/journal.pone.0249786