Investigating the prognostic value of digital mobility outcomes in patients with chronic obstructive pulmonary disease: a systematic literature review and meta-analysis

Background: Reduced mobility is a central feature of COPD. Assessment of mobility outcomes that can be measured digitally (digital mobility outcomes (DMOs)) in daily life such as gait speed and steps per day is increasingly possible using devices such as pedometers and accelerometers, but the predictive value of these measures remains unclear in relation to key outcomes such as hospital admission and survival. Methods: We conducted a systematic review, nested within a larger scoping review by the MOBILISE-D consortium, addressing DMOs in a range of chronic conditions. Qualitative and quantitative analysis considering steps per day and gait speed and their association with clinical outcomes in COPD patients was performed. Results: 21 studies (6076 participants) were included. Nine studies evaluated steps per day and 11 evaluated a measure reflecting gait speed in daily life. Negative associations were demonstrated between mortality risk and steps per day (per 1000 steps) (hazard ratio (HR) 0.81, 95% CI 0.75–0.88, p<0.001), gait speed (<0.80 m·s⁻¹) (HR 3.55, 95% CI 1.72–7.36, p<0.001) and gait speed (per 1.0 m·s⁻¹) (HR 7.55, 95% CI 1.11–51.3, p=0.04). Fewer steps per day (per 1000) and slow gait speed (<0.80 m·s⁻¹) were also associated with increased healthcare utilisation (HR 0.80, 95% CI 0.72–0.88, p<0.001; OR 3.36, 95% CI 1.42–7.94, p=0.01, respectively). Available evidence was of low-moderate quality with few studies eligible for meta-analysis. Conclusion: Daily step count and gait speed are negatively associated with mortality risk and other important outcomes in people with COPD and therefore may have value as prognostic indicators in clinical trials, but the quantity and quality of evidence is limited. Larger studies with consistent methodologies are called for.