gms | German Medical Science

Objective: The goal of the study was to evaluate the suitability of a smartphone-based positioning infrastructure for quantitative monitoring of patient outdoor mobility.

Method: An inexpensive, compact Android smartphone equipped with a global positioning system (GPS) receiver and wireless local connectivity (WiFi) was used for mobility measurement. The patients received the smartphone per mail a week before surgery and about 3 months later, for follow-up. They were instructed to carry the smartphone whenever they leave their homes and recharge it every evening. No further action was required. The measurement was automatically performed daily between 6 AM and 10 PM. All data were stored on the smartphone and evaluated after it had been returned. We calculated the average walking distance (s), speed (v), and duration (t) per day. For validation, the patients were also asked to provide their subjective judgment of the said three parameters and of pain according to a VAS.

Results: So far, 61 patients have entered the study and for 24 (15 M, 9 F, aged 42-86) all measurements have been completed and the data evaluated. We collected 1874 positions based on GPS and 82 on mobile network and WiFi per patient and day (median). The median spatial accuracy was 15 m for the GPS and 30 m for WiFi. The temporal resolution was 1 s for the GPS and 45 s otherwise. The median covered distance per patient and day was 917 m.

Of the above 24 patients, 7 (29%) worsened in all measured values. Twelve (50%) improved in speed, 10 (41%) in distance, and 5 (21%) in all values. All patients improved on the pain VAS. For 21 patients we could compare the measured values with the self-reported ones and noticed differences in 13 cases. Possible reasons are:

1.

patients’ error in judgment,

2.

technical error in the measurement,

3.

secondary illness, or

4.

incomplete compliance.

We have also experienced technical problems caused by an update of the operating system and which, in turn, required updating the measurement software.

In the course of two-and-half years two smartphones were lost (total worth: ~150 €). The mobile service provider costs amounted to about 5 € per smartphone and month. A misuse of SIM cards hasn’t been observed.

Conclusions: GPS-equipped smartphones allow for low-cost objective measurement of patient outdoor mobility and an assessment of the therapy outcome. The analysis and measurement itself proved to be more difficult than expected.