Measurement of Dynamic Hyperinflation During the 6-Minute Walk Test Using a Mobile Device

BACKGROUND: Dynamic hyperinflation is a major cause of dyspnea in patients with COPD. Dynamic hyperinflation is usually measured with cardiopulmonary exercise testing, but this test requires maximal effort from the patient, and inspiratory capacity (IC) measurements may influence test results. This study investigated another approach by measuring dynamic hyperinflation during the more natural and better-tolerated 6-min walk test (6MWT), using a mobile system for IC measurements. METHODS: Twenty subjects were studied, including 10 healthy subjects and 10 subjects with COPD. Each subject performed a pair of 6MWTs. RESULTS: The study showed that test-retest reliability in healthy subjects was excellent (intraclass correlation coefficient 0.995). In addition, mean resting IC in healthy subjects (3.27 ± 0.77 L) was not affected at the end of the 6MWT, whereas mean resting IC in subjects with COPD (2.45 ± 0.90 L) decreased to 1.93 L ± 0.68 L at the end of the 6MWT (P = .004). The tolerability of the device for subjects with COPD appeared to be only slightly hampered by an increased sense of dyspnea attributed to wearing a mask. CONCLUSIONS: This study provides a proof of principle for mobile IC measurements during the 6MWT, demonstrating good test performance, reasonable tolerability, and a power to differentiate normal from pathologic conditions.