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Noninvasive monitoring with strongly absorbed light

McEwen M P, Reynoldsk J

Optica Applicata

2014

Vol. 44, nr 2

177--190

The transmission of light through tissue is used in noninvasive monitoring, in particular photoplethysmography. Investigations involving the transmission of wavelengths absorbed by bilirubin (short wavelength visible light) have been limited, due to strong absorption by haemoglobin. Achieving transmission of these wavelengths through tissue may advance noninvasive monitoring of substances like bilirubin. This work investigates the use of high power light sources together with improvements in signal-to-noise ratio as a means of enabling the transmission of strongly absorbed light through tissue. A custom device using multiple high-power short-wavelength visible light sources together with low power red and infrared sources, and background light cancellation – to improve signal-to-noise ratio, was constructed. Transmission of 454–1200 nm light through tissue was achieved, with pulsations present in measured signals. The transmission through tissue of multiple wavelengths of strongly absorbed light can be achieved by using high power light sources in conjunction with cancelling the effect of background light. Use of these techniques may allow investigations into the noninvasive monitoring of substances such as bilirubin using photoplethysmography.

Accuracy Comparison of Oscillometric and Electronic Palpation Blood Pressure Measuring Methods Using Intra-Arterial Method as a Reference

Sorvoja H., Myllylä R., Kärjä-Koskenkari P., Koskenkari J., Lilja M., Antero Kesäniemi Y.

Molecular and Quantum Acoustics

2005

Vol. 26

235-260

This paper evaluates blood pressure measurements by the electronic palpation method (EP) and compares their accuracy to that of the oscillometric method (OSC) using average intra-arterial (IA) blood pressure as a reference. All of these three measurements were made simultaneously for each patient. The EP method, based on noninvasively detecting the amplitude of pressure pulsations in the radial artery, differs from the ordinary palpation method by allowing also diastolic pressure to be determined from the pulse delay produced by cuff pressure. In one test group, measurements were conducted on healthy volunteers in sitting and supine position during increasing and decreasing cuff pressure. Another group, comprising older, cardiac patients, was measured only in the supine position during cuff inflation. The results showed that the EP method was approximately as accurate as the OSC method with the healthy subjects and slightly more accurate with the cardiac patient group. The advantage of the EP method is that also the wave shape and velocity of arterial pressure pulses is available for further analysis like the assessment of arterial stiffness. Keywords: noninvasive, blood pressure, cuff, pulse transit time, pulse wave velocity