Test-retest Reliability of GPS derived Measurements in Patients with Claudication

In patients with peripheral artery disease (PAD), the different distances between stops and the stop durations recorded with Global Positioning System (GPS) during a 1 hour stroll in the community are highly variable. Nevertheless, the reliability of the greatest community walk distance (greatest distance), the average of walking speeds (average speed) and the durations of stops (average stop durations) have not been studied.

Seventeen PAD patients performed two series of evaluations (T1 and T2) within a 1 month period.

Each series included: a 1 hour stroll in the community with the calculation of the walking impairment questionnaire (WIQ) scores, the measurement of maximal walking distance on a treadmill (MWD on treadmill) and a 1 hour stroll in the community with GPS. The Garmin GPS-60 (Garmin Ltd, Olathe, Kan) receiver was used for all patients. Test-retest reliability of MWD on treadmill, WIQ, and GPS parameters were assessed with intraclass coefficient of correlation (ICC).

ICCs are almost perfect between T1 and T2 for greatest distance (ICC = 0.911), average speed (ICC = 0.905), and MWD on treadmill (ICC = 0.992), and substantial for the average WIQ (ICC = 0.794). Correlation of average stop durations was considered substantial (ICC = 0.691).

Despite the previously reported "within stroll" variability of walking bouts for distances, speeds, and stop durations, GPS derived greatest distance and average speed are reliable in PAD patients in test-retest experiments. The GPS appears to be a new tool to assess walking limitation and allows objective clinical investigation.