From the authors:
We are greatly honoured by the interest shown by M. Cesari and S. Scarlata in our recent publications on the 4-m gait speed (4MGS) in patients with chronic obstructive pulmonary disease (COPD) [1, 2]. We strongly agree with their view that the 4MGS has value as a “vital sign”, a “marker of global well-being” and reflects biological (rather than chronological) age. Gait speed has been shown to be a strong and consistent risk factor for adverse outcomes including disability, nursing home admission, falls and mortality in community dwelling older persons [3, 4]. The intention of our studies was to draw the attention of the respiratory fraternity to the 4MGS, as we believe that the 4MGS may have a future role in stratifying patients with COPD. Although forced expiratory volume in 1 s is the most commonly used surrogate marker of disease severity, it does not reflect extrapulmonary manifestations of COPD [5]. We believe that the 4MGS provides additional information to the clinician and, given its simplicity, could be implemented widely in most clinical settings [6]. As a leading authority, M. Cesari will be aware that the 4MGS is already used to screen for sarcopenia and frailty in older adults [7, 8].
M. Cesari and S. Scarlata erroneously believe that our studies were proposing the 4MGS as a simpler alternative to more established field walking tests used in patients with COPD, such as the incremental shuttle walk test (ISWT) or 6-min walk distance (6MWD). This was not our intention, and indeed we clearly expressed that the 4MGS was not a measure of exercise capacity. The first study demonstrated that the 4MGS was a reliable and robust measure, and correlated with measures of exercise capacity, health-related quality of life and dyspnoea [1]. In the second study, we demonstrated the 4MGS was responsive to pulmonary rehabilitation, and used external anchors (including, but not exclusively, the ISWT) to estimate a minimal clinically important difference [2]. In both studies we concluded that the 4MGS had potential as a simple assessment tool. The 4MGS appeared to be particularly responsive in those with poor exercise capacity levels. Although further work is required to confirm this, we believe that the 4MGS may be a useful functional assessment tool in specific settings; for example, patients with COPD recovering from hospitalisation or critical care. In these patients, walking 4 m at their usual speed may indeed be “pushing to the limit of the physiological reserves of the individual”.
It is worth reviewing why field walking tests, such as the ISWT and 6MWD, are used in patients with COPD. First, they are used as outcome measures to determine the benefits of interventions, typically pulmonary rehabilitation. Secondly, they are used by clinicians as a surrogate marker of the patient’s day-to-day physical functioning. Finally, they reflect disease severity, and both the ISWT and 6MWD have been shown to predict mortality in patients with COPD [9, 10]. Although the 4MGS is not a measure of exercise capacity, we believe our two studies in the European Respiratory Journal, coupled with the existing literature in other disease populations, provide some evidence that the 4MGS may provide similar information to the clinician.
Going forward, I am sure M. Cesari and S. Scarlata would agree that our initial findings might encourage the respiratory community to further evaluate the utility of the 4MGS in older chronic respiratory disease populations.
Footnotes
Conflict of interest: Disclosures can be found alongside the online version of this article at erj.ersjournals.com
- Received December 19, 2013.
- Accepted December 20, 2013.
- ©ERS 2014