A new portable device for the indirect measurement of ambulatory blood pressure in the finger was successfully applied to normotensive and hypertensive subjects in and outside a ward setting. The device uses the volume-oscillometric technique and, equipped with a microprocessor, permits long-term ambulatory monitoring of indirect systolic and mean blood pressure at desired intervals (once every 1-10 min). Systolic and mean blood pressures obtained by this method were well correlated with those measured by the direct (Oxford) and arm-cuff methods. Systolic and diastolic blood pressure obtained by the volume-oscillometric device were almost identical with those recorded by an arm-cuff. Systolic blood pressure obtained by the volume oscillometric method was, however, significantly lower than that measured by the direct method. The new device has also been used to measure blood pressure during treadmill exercise and ice-water immersion. Mean values of blood pressure and the SD of these averaged for 24 hours, or for every hour, were reproducible when the measurements were repeated under the same condition. The present device is portable, causes minimal noise, can detect rapid change in blood pressure and causes less discomfort when compared to the conventional arm-cuff method. Regular measurements can be made with minimal sleep disturbance. This fully automatic volume-oscillometric device allows reliable 24-hour monitoring of ambulatory blood pressure not only in but also outside a ward setting, and as such is useful for studies of hypertension.

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We describe further development of a novel method for non-invasive measurement of blood glucose concentration (BGL), named Pulse Glucometry, based on differential near infrared spectrophotometry. Sequential temporal differences of infrared transmittance spectra from the radiation intensity (I(lambda)) emerging from a fingertip containing an arterial pulse component (DeltaI(lambda)) are analysed. To perform the measurements we developed a new high-speed spectrophotometer, covering the wavelength range from 900 to 1700 nm, scanning at a maximum spectral rate of 1800 spectra/s, with a minimum exposure time of 20 micros. Spectra related only to the pulsatile blood component are derived, thus minimising influences of basal components such as resting blood volume, skin, muscle and bone. We have now improved the performance of the spectrophotometer and in the present paper we describe new in vivo measurements carried out in 23 healthy volunteers undergoing glucose tolerance tests. Blood samples were collected from the cephalic vein simultaneously with radiation intensity measurements in the fingertip every 10 min before and after oral administration of glucose solution for 120 min. BGL values were then predicted using a PLS calibration model and compared with blood values determined by colorimetric assay. The precision and accuracy of the non-invasive determinations are encouraging.

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The aim of this study was to discover a simple/convenient geometrical arrangement of radiation sources and detector to acquire finger-photoplethysmograms (PPGs) with wavelength regions of blood glucose (BGL) absorption, toward practical noninvasive BGL measurement. First, we compared PPGs with three wavelengths: 808 nm (without water absorption), 1160 nm (with weak water absorption), and 1600 nm (with nearly peak BGL absorption and strong water absorption), while the source-detector spacing was successively increased circumferentially around a fingertip. In 10 healthy subjects, we observed clear cardiac-related pulsatile components of PPG signals at 808 and 1160 nm in any incident positions with more than 15 dB of signal-to-noise ratio ( S / N ), but reliable PPG detections at 1600 nm with more than 10 dB of S / N was only possible when the source-detector distance was less than 3 mm around the fingertip circumference. Second, with this arrangement, an experiment was performed using six wavelengths to cover glucose absorption bands (from 1550 to 1749 nm), obtaining pulsatile PPG signals with more or less 15 dB of S / N . Through the present experiments, this orthogonal arrangement of the source and detector to detect forward- and side-scattered radiation through the tissue is appropriate for PPG measurements with wavelength regions where there is potential for BGL measurement.