iPhysioMeter: a smartphone photoplethysmograph for measuring various physiological indices.

iPhysioMeter is a new smartphone application ("App") for the Apple iPhone and iPod touch that allows photoplethysmography (PPG) to be implemented without the need for any additional devices. The resulting signal, the photoplethysmogram, allows the calculation of basic but valuable and frequently used physiological indices such as heart rate (HR) and pulse volume (PV). The design of iPhysioMeter has very much been influenced by a consideration of usability, as is immediately evident from ones first experience with it. However, its apparent simplicity in use should not disguise the need for correct operation, which otherwise might lead to collection of invalid or inaccurate data. There are several unexpected pitfalls that might not only produce inaccurate values, but, under some circumstances, could also damage the device or present a hazard to the user or subject. We therefore describe here, firstly, the core technology that makes it possible to perform PPG and to calculate HR and normalized PV (NPV) from the photoplethysmogram using only a smartphone, secondly, the correct and optimum methods and procedures for using iPhysioMeter that will help to ensure safety and the derivation of valid data under real operational conditions. We hope that these descriptions will help facilitate any activities related to physiological measurement when using only a smartphone.