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Canadian Health&Care Mall: The Effects of Helium-Hyperoxia on 6-min Walking Distance in COPD

Tags: COPD, exercise

pulmonary function

Subjects

Sixteen stable COPD subjects, who were participants in an outpatient pulmonary rehabilitation maintenance program (three times per week), volunteered for the study. All subjects had exertional dyspnea and activity limitation despite their participation. None of the subjects had recent (ie, > 4 weeks) exacerbations, and patients continued receiving their usual medications during the study. Subjects receiving supplemental O2, or having significant cardiovascular or musculoskeletal abnormalities were excluded. The study was approved by research ethics committees, and all subjects provided written informed consent.

Study Design

The study was a blinded, randomized (in blocks of four subjects) crossover design requiring three visits. Visit 1 consisted of assessing pulmonary function, incremental cardiopulmonary exercise testing (CPET), and a practice 6MWT (each conducted while patients breathed RA). Exercise tests were separated by a 60-min rest period. During visits 2 and 3, two 6MWTs were performed at each visit in random order (separated by 60 min) to assess the effects of the study gases used (see next section) on walking distance and symptoms. Testing was undertaken at the same time of day for each subject.

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Study Gases

The following three different gases mixtures were utilized: RA (21% O2 and 79% N2); O2 (100% O2); and HeO2 (70% He and 30% O2). All gases were delivered from large-capacity cylinders (Medigas; Edmonton, AB, Canada) with individually calibrated gas-specific flowmeters. Subjects inspired each gas from either a mask (Pulmanex Hi-Ox mask; Viasys MedSystems; Wheeling, IL) at a flow of 15 L/min or from nasal prongs at a flow of 8 L/min (ie, the nasal O2 study).

The four arms of the study were as follows: RA with a mask (Hi-Ox mask; Viasys MedSystems) [the RA group]; O2 with a mask (Hi-Ox mask) [the mask O2 group); O2 with nasal prongs (the Nasal O2 group); and HeO2 with a mask (Hi-Ox mask) [the HeO2 group]. Subjects were seated and breathed the gas for 5 min before each 6MWT. The individual providing instructions and all subjects were blinded to the gas used, and subjects refrained from talking while breathing the gas prior to walking, during testing, and for 1 min following the test to avoid detecting any change in voice resonance.

Study Procedures

Spirometry, plethysmographic lung volumes (6200 Autobox; SensorMedics; Yorba Linda, CA), and single-breath diffusing capacity of the lung for carbon monoxide (Dlco) were measured at visit 1. Spirometry and Dlco were compared to the reported norms of Crapo et al, and lung volumes were compared to the norms of Goldman and Becklake.

A symptom-limited CPET on a treadmill was performed while subjects breathed RA. Exercise test measurements included respiratory gas exchange (Vmax229d; SensorMedics), intensity of dyspnea and leg fatigue using the modified Borg scale, and reasons for discontinuing exercise. 6MWTs were performed following accepted guidelines, using a 30-m course. Subjects rested for 10 min, and were provided consistent instruction by the same supervisor prior to testing and at each minute of walking. Heart rate (HR), Spo2, and Borg scores for dyspnea and leg fatigue were measured before and at the end of each 6MWT.

The practice 6MWT (visit 1) was performed with patients breathing RA. On visits 2 and 3, 6MWTs were performed while subjects breathed the randomized study gas delivered via 20 m of tubing from the blinded gas cylinder that was positioned to the side and at the midpoint of the walking course. The flowmeters were calibrated with the tubing in place for each of the gases.

Statistical Analysis

A one-way repeated measure of analysis of variance assessed statistical significance (GraphPad; GraphPad Software Inc; San Diego, CA). When the analysis of variance detected a significant effect, Bonferroni post hoc multiple comparison testing was performed. A one-way unpaired t test was used for the post hoc analysis of the effect of O2 desaturation and ventilatory reserve on walking distance. An a of 0.05 was considered to be significant.