Chest
Volume 128, Issue 1, July 2005, Pages 55-61
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Clinical Investigations
Copd
Encouraged 6-min Walking Test Indicates Maximum Sustainable Exercise in COPD Patients

https://doi.org/10.1378/chest.128.1.55Get rights and content

Study objectives

In patients with moderate-to-severe COPD, an encouraged 6-min walking test (6MWT) is a high-intensity submaximal exercise protocol that shows an oxygen uptake ( V˙o2) plateau after the third minute of the test. This last feature prompted the hypothesis that self-paced walking speed is set to achieve “maximal” sustainable V˙o2, namely “critical power” or “critical speed.”

Patents and methods

Eight patients with moderate-to-severe COPD (mean age, 68 ± 7 years [± SD]; FEV1, 50 ± 13% predicted; Pao2, 69 ± 8 mm Hg) underwent the following tests on different days in order: (1) encouraged 6MWT; (2) standard incremental shuttle test to identify peak walking speed; (3) four different high-intensity, constant walking speed tests to exhaustion to calculate critical walking speed; and (4) timed walking test at critical walking speed (CWS) to examine sustainability of the exercise.

Results

6MWT and CWS showed similar results (mean of last 3 min): V˙o2 (1,605 ± 304 mL/min vs 1,584 ± 319 mL/min), minute ventilation (47 ± 12 L/min vs 48 ± 11 L/min), respiratory exchange ratio (0.89 ± 0.1 vs 0.90 ± 0.1), heart rate (130 ± 18 beats/min vs 131 ± 16 beats/min), Borg dyspnea score (5.4 ± 1.3 vs 5.5 ± 2.4), and walking speed (1.49 ± 0.1 m/s vs 1.44 ± 0.1 m/s, respectively).

Conclusion

This study supports that 6MWT indicates maximum sustainable exercise that might be related with its predictive value in COPD patients.

Section snippets

Materials and Methods

Eight men with clinically stable COPD were recruited for the study. All of the men had a lack of exacerbations in the preceding 6 weeks. Oxyhemoglobin desaturation during exercise was an exclusion criteria. All patients were receiving inhaled, long-acting β2-agonists and ipratropium bromide. Five of patients were regularly treated with inhaled steroids, but none of the eight patients had received systemic steroids in the last 3 months prior to the study. The study design included two phases:

Results

The study group (mean age, 68 ± 7 years; range, 57 to 77 years) showed moderate-to-severe ventilatory dysfunction (FEV1, 1.63 ± 0.33 L; 50 ± 13% predicted; range, 32 to 67% predicted). Four patients were classified as Global Initiative for Chronic Obstructive Lung Disease (GOLD) type 2, three patients were GOLD type 3, and one patient was GOLD type 4.8 Seven of the eight patients showed air trapping (residual volume, 137 ± 26% predicted; range, 80 to 169%). On average, they presented moderate

Discussion

The current study showed similar physiologic responses between encouraged 6MWT-10 and walking at CWS, which indicates that patients with moderate-to-severe COPD set their walking speed during the test in order to achieve critical V˙o2. The level of V˙o2 achieved at CWS may indicate the integrated response of the systems involved in O2 transport/O2 utilization that ultimately determine the highest sustainable level of exercise. These results might constitute the underlying explanation

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      For example, Annegarn et al. [109] reported cadences in excess of 100 steps/min during a 6MWT for patients at all stages of COPD. Similarly, in three other studies [110–112], participants with COPD completed the 6MWT at speeds typically corresponding to cadences over 100 steps/min (based on prior evidence of the speed/cadence relationship [91]). We identify two bout intervals as the duration of 5 min may not be achievable by all patients, this longer bout measuring greater endurance in patients with higher fitness levels.

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    Alejandro Casas was a Pre-doctoral Research Fellow from Fundación Neumológica Colombiana (Colombia) supported by CHRONIC (IST-1999/12158) from the European Union; and, Anamaria Mayer was a Research Fellow from Federal University of Sao Paulo (Brasil) supported by CAPES and E-Remedy (IST-2000/25146).

    Supported by grants FIS 00/0281 from the Fondo de Investigaciones Sanitarias; and Comissionat per a Universitats i Recerca de la Generalitat de Catalunya (1999 SGR 00228); and Red Respira C03/11.

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