Development of a compact home health monitor for telemedicine.

A compact and easy-to-use home health monitor was developed. A palm-size health monitor contained a finger probe as sensor unit. In the finger probe, light from a light emitting diode (LED) array was illuminated on a finger nail bed, and transmitted light was measured to obtain photoplethysmography (PPG) signals. Hematocrit, pulse, respiration rate, and saturated oxygen in arterial blood (SpO(2)) were measured simultaneously from PPGs using five different wavelengths: 569, 660, 805, 904, and 975 nm. To predict hematocrit, a dedicated algorithm was used based on scattering theory of red blood cells using these wavelengths. Preliminary clinical tests showed that the achieved percent errors were +/- 8.2% for hematocrit when tested with 549 persons (N = 549). Digital filtering techniques were used to extract respiratory information from a single PPG signal. SpO(2) was predicted on the basis of the ratio of the wavelengths 660 nm and 940 nm. The accuracies were within clinically acceptable errors. In addition, the compact home health monitor included a blood pressure monitoring unit. For convenient and simultaneous measurement with the other previously mentioned signals, blood pressure was measured on a finger. An air cuff was installed on the same finger where PPGs were measured. Achieved mean differences were +/- 3.8 mmHg for systole and +/- 5.1 mmHg for diastole. One can use the palm-size monitor simply by inserting a finger into the home health monitor that is suitable for telemedicine.