OBJECTIVES: We have developed an Android mobile application that can sample from any on-board smartphone sensor. This is intended to enable objective performance outcome (PerfO) measures to be developed for remote assessments in clinical trials. This study aimed to assess the suitability of the smartphone barometer in detecting and measuring height changes that could have application in instrumenting an at-home stair-climbing PerfO using a smartphone.

METHODS: The stability of atmospheric pressure (AP) measurements was assessed in 3 conditions: indoor with windows closed (INWC), indoor with windows open (INWO) and outdoors (OUT) by measuring AP for 60 s (3 repetitions). The ability to detect height transitions was assessed by holding the smartphone at a constant height for 20 s, moving vertically for 0.6 m, and retaining the new height for 20 s (8 repetitions per condition). AP data were smoothed using a Savitzky-Golay filter and converted to altitude heights using the barometric formula. Height gain was estimated by algorithmic detection of the height transition event and estimating the mean AP before and after transition.

RESULTS: AP measurements were symmetrically distributed. Fluctuations from the mean were greater for INWO and OUT. Height transition was successfully detected in all repetitions for each condition. Mean [SD] estimates of height gain were 0.65 [0.13] m, 0.66 [0.16] m and 0.81 [0.15] m for INWC, INWO and OUT respectively. OUT estimates were significantly different to the true value of 0.6 m (p=0.016).

CONCLUSIONS: Smartphone barometer data is able to adequately detect height transitions of 0.6 m, especially in indoor conditions. 0.6 m corresponds to an elevation of approximately 3 stairs within a standard staircase, meaning that the barometer may be useful in helping to instrument an at-home stair-climbing PerfO when combined with a timer using a smartphone app.