Detecting oxygen desaturation in patients with COPD: incremental versus endurance shuttle walking

There has been no direct comparison between an incremental and endurance walking test to detect the relative oxygen desaturation in patients with chronic obstructive pulmonary disease (COPD). This is of some importance as current guidelines have suggested that ambulatory oxygen should only be prescribed after a standard assessment and desaturation documented. No clear advice about the nature of the required exercise task is given. This study therefore compared the relative desaturation between the incremental shuttle walking test (ISWT) and the constant speed walking test (ESWT) and response to ambulatory oxygen.

Forty-one patients (29 male), mean (SD), age 71.18 (7.48) yrs, FEV(1) 0.85 (0.29) l with stable COPD were recruited after completion of a 7-week pulmonary rehabilitation programme. Patients completed a baseline (without carrying a cylinder) ISWT and ESWT and then, in random order in double blind fashion, completed the walk tests with a cylinder of air or a cylinder of oxygen. Measurements included distance walked, oxygen saturation, heart rate, perceived breathlessness and exertion (Borg scale).

All patients desaturated (<4% below 90%). There was no significant difference in desaturation between the ISWT and the ESWT. There was a significant improvement in performance with supplementary oxygen compared to cylinder air (p<0.05) for both tests. However, compared to the baseline walk, supplementary oxygen did not enhance the distance walked for either test. There was a significant decrease in walking performance on both the ISWT and the ESWT when carrying an air cylinder compared with the control walk. When comparing the percentage difference between oxygen and air for responders (i.e. those that achieve a 10% or more increase), the ESWT showed a greater percentage change 42.1% compared to 26.1% for the ISWT.

This study identifies that incremental and endurance walking provokes significant desaturation and that there is a short-term benefit of oxygen versus air in enhancing exercise performance. There was no significant difference in the level of desaturation between tests. Therefore the ISWT is a suitable exercise test that can be used to evaluate desaturation and is practically more realistic.