Medical monitoring gets personal, goes mobile

The smartphone opens another avenue

The soon-to-be-ubiquitous smart phone is potentially rich with apps that use native sensors to determine vital parameters such as activity levels or sleep patterns, with the built-in accelerometer used to detect heart rate via the image sensor.

But there is additional potential beyond the smart phone becoming the communications link between vital-signs monitor and health service provider. It may also become the vital -signs monitor itself.

For example, a front-end loaded with sensors can be used in conjunction with the handset, directly reporting data to the phone. Alternatively, the handset can have embedded sensors which can be used to determine heart rate or, in a more advanced design, the level of oxygen in the blood (pulse oximetry). (Figure 4)

The pulse oximeter is a spin-off from the long-established technology for assessing patient's blood-oxygen saturation level (SpO2—the ratio of oxyhemoglobin to the total concentration of hemoglobin present in the blood) and pulse rate non-invasively, in real time, by using photometric techniques. The method uses measurement of the transmission of both red and infrared wavelengths through the skin and blood vessels, and then uses an algorithm to calculate SpO2. (Figure 5)



It is even feasible for additional sensors to be embedded within the smartphone and on its case exterior. In addition to motion sensors in the phone, the periphery could have contact temperature sensors, as well as contact electrodes for measuring skin conductance and even bio-potential signals to capture heart rate and electrocardiogram (ECG/EKG) waveform data.

Here, as with the steering wheel or gym handles, engineers will need innovative thinking in enclosure design and materials, since the smartphone will need electrically conductive sensors on its periphery, and users will need to hold the phone with both hands for the HRM reading.