Validation of externally paced walking tests

Performance in an incremental treadmill test relates strongly to performance in the ISWT, measured as oxygen uptake (VO2; r=0.88; r=0.88 [54]; r=0.81 [55]). Detailed ventilatory and metabolic responses to the ISWT were compared, by Palange et al. [56], to those from a conventional incremental cycle-ergometry cardiopulmonary exercise test in patients with moderate-to-severe stable COPD, using a portable telemetric monitoring system. There were no significant differences in test duration, VO2,peak, PE,peak, peak respiratory frequency or peak fc; fc reserve and breathing reserve were also similar. However, like the results of Baarends et al. [28] and Troosters et al. [29], this study found that the ISWT evoked a lower Pco2,peak and blood lactate concentration than the incremental test, suggesting a reduced contribution from nonaerobic metabolism to energy production, influenced largely by the different muscle groups employed for the two activities. By contrast, the rate of increase in the ventilatory equivalent for carbon dioxide (Pe/Pco2) and oxygen pulse fC/Vo2) were higher in the IWST, as was perceived breathlessness. Thus, as the ventilatory demands of walking are greater than those of cycling, a cycling test may not represent the metabolic requirements of walking and daily activity well. The ISWT appears to provoke a maximal response that may be more appropriate for the evaluation of functional capacity. Performance in the ISWT has also been compared with Po2,peak in CHF [57] and in patients with severe CHF awaiting heart transplantation [58].

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