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.

Noninvasive total hemoglobin measurement.

Wavelength selection and prediction algorithm for determining total hemoglobin concentration are investigated. A model based on the difference in optical density induced by the pulsation of the heart beat is developed by taking an approximation of Twersky's theory on the assumption that the variation of blood vessel size is small during arterial pulsing. A device is constructed with a five-wavelength light emitting diode array as the light source. The selected wavelengths are two isobestic points and three in compensation for tissue scattering. Data are collected from 129 outpatients who are randomly grouped as calibration and prediction sets. The ratio of the variations of optical density between systole and diastole at two different wavelengths is used as a variable. We selected several such variables that show high reproducibility among all variables. Multiple linear regression analysis is made in order to predict total hemoglobin concentration. The correlation coefficient is 0.804 and the standard deviation is 0.864 g/dL for the calibration set. The relative percent error and standard deviation of the prediction set are 8.5% and 1.142 g/dL, respectively. We successfully demonstrate the possibility of noninvasive hemoglobin measurement, particularly, using the wavelengths below 1000 nm.