Wrist-Worn Step Trackers Shown to Accurately Predict Patient Health Outcomes

Use of wrist-worn step trackers, such as Fitbits and Apple Watches, were shown to accurately estimate exercise capacity and determine the health status of patients with COPD and cardiovascular diseases, indicating a possible transition from the standardized 6-minute walk distance test (6MWD) conducted in a clinical setting.

Study results were presented at the 2019 European Respiratory Society Congress (ERS) in Madrid, Spain, which ran from September 28 to October 2.

The 6MWD has served as a vital standard for physicians in predicting health outcomes and mortality for patients with chronic obstructive pulmonary disease (COPD) and respiratory diseases. The assessment, which measures a patient’s exercise capacity through their covered walking meters after 6 minutes, is conducted in clinical settings once every few months or in some cases, once a year. This limitation can inhibit a physician’s knowledge of fluctuations in the 6MWD step count that attributes to a patient’s current health status.

The use of wrist accelerometers would allow physicians to monitor patient progress and disease management on a daily basis, and further provide patients with a convenient alternative to the 6MWD assessment administered in clinics. Researchers sought to investigate the accuracy of wrist-worn step trackers in relation to estimated 6MWD step counts.

A 12-week, blinded, randomized, cross-over trial was conducted on 52 adult patients with a history of respiratory issues during periods of elevated air pollution to examine wrist accelerometer efficacy. Chief goals of the study were to determine whether estimated 6MWD step counts, derived from the wrist accelerometers, correlated with measured 6MWD, and additionally whether estimated 6MWD using the devices were comparable with respiratory symptoms:

• Daily step counts used to obtain estimated 6MWD through the maximum weekly distance walked in 6 minutes for each patient in each week
• Respiratory symptoms measured by the St. George Respiratory Questionnaire tailored for patients with COPD (SGRQ-C scores)
• Estimated 6MWD using wrist accelerometer step counts were compared to the clinically measured 6MWD for each patient during each week
• Weekly estimated wrist accelerometer step count 6MWD measures were preferentially paired with symptom ratings from the same week, the prior week, or following week

Of the study group, 20 patients had adequate data for analysis (>1000 step derived 6MWD and >0 measured 6MWD). The available data attributed to 1,237,459 steps derived 6MWDs, 54 measured 6MWD, and 30 paired measured 6MWD. Step derived 6MWD was shown to be correlated with, and additionally lower than, the measured 6MWD (correlation coefficient (r_s)=0.74, CI, 0.52-0.57).

Step derived 6MWD was correlated with SGRQ-C scores and provided similarly lower estimates to that of measured 6MWD:

• SGRQ-C activity score: measured 6MWD (r_s=-0.65; CI, -0.81 to -0.40), step derived 6MWD (r_s=-0.63; CI, -0.73 to -0.50)
• SGRQ-C impacts score: measured 6MWD (r_s=-0.29; CI, -0.57 to 0.005), step derived 6MWD (r_s=-0.53; CI, -0.66 to 0.38)
• SGRQ-C symptom score: measured 6MWD (r_s=-0.15; CI, -0.46 to 0.2), step derived 6MWD (r_s=-0.38; CI, -0.53 to -0.20)
• SGRQ-C total score: measured 6MWD (r_s=-0.44; CI, -0.68 to -0.12), step derived 6MWD (r_s=-0.58; CI, -0.70 to -0.44)

Higher 6MWD was correlated with fewer symptoms, more activity, lower disease impact, and an improved overall score. The step count derived 6MWD was found to be correlated with measured 6MWD and SGRQ-C scores in the study which stresses a wrist accelerometers potential in clinical care and disease monitoring.

Lead investigator of the study Denitza Blagev, MD, pulmonary and critical care physician at Intermountain Healthcare, highlighted the potential of wrist-worn step trackers in tracking disease progress more frequently and in a way that is “less expensive and more convenient than current standardized testing,” said Blagev. Blagev noted that this new finding could be the first step in managing healthcare and detecting deterioration in patients earlier.

“Normally, the 6MWD test is done every few months or once a year. Now we may be able to measure patients on a regular basis and know if we need to intervene if their estimated 6MWD by step count changes,” said Blagev.

Reference

Blagev DP, Bride DL, Mendoza DL, et al. Correlation between clinically measured and wrist accelerometer derived 6 minute walk distance. Presented at the 2019 European Respiratory Society International Congress on September 29, 2019.