Peak Oxygen Uptake During the Six-minute Walk Test in Diffuse Interstitial Lung Disease and Pulmonary Hypertension

Abstract

IntroductionThe six-minute walk test (6MWT) is widely used in evaluating diffuse interstitial lung disease (ILD) and pulmonary hypertension (PH). However, their physiological determining factors have not been well defined. ObjectiveTo evaluate the physiological changes that occur in ILD and PH during the 6MWT, and compare them with the cardiopulmonary exercise test (CPET). Material and MethodsThirteen patients with ILD and 14 with PH were studied using the 6MWT and CPET on an ergometer cycle. The respiratory variables were recorded by means of telemetry during the 6MWT. ResultsOxygen consumption (VO2), respiratory and heart rate reached a plateau from minute 3 of the 6MWT in both diseases. The VO2 did not differ from the peak value in the CPET (14±2 and 15±2ml/kg/min, respectively, in ILD; 16±6 and 16±6ml/kg/min, in PH). The arterial oxygen saturation decreased in both diseases, although it was more marked in ILD (−12±5%, P<.01). The ventilatory equivalent for CO2 (VE/VCO2) in PH during the 6MWT was strongly associated with functional class (FC) (85±14 in FC III-IV, 44±6 in FC I-II; P<.001). ConclusionsThe 6MWT in ILD and PH behaves like a maximal effort test, with similar VO2 to the CPET, demonstrating a limit in oxygen transport capacity. Monitoring using telemetry during the 6MWT may be useful for the clinical evaluation of patients with ILD or PH.