Yuzo Nakase

Study of an algorithm based on model experiments and diffusion theory for a portable tissue oximeter.

A portable tissue oximeter that uses light-emitting diodes and two-wavelength near infrared spectroscopy has been developed. The tissue oximeter is compact enough to be portable and it is therefore expected to make better use of the advantages of NIRS-based oximetry and to expand the scope of applications of monitoring tissue oxygen. The algorithm for this instrument was deduced through systematic experiments by varying blood volume and scattering intensity in a tissuelike phantom. The experimental results were compared with theoretical results obtained from diffusion theory. Experimentally determined coefficients of the algorithm were in close agreement with the theoretically derived coefficients. From evaluation tests of the algorithm applied to in vitro and in vivo measurements, it was confirmed that a good linear response to the concentration of oxygenated and deoxygenated blood can be obtained by this algorithm within a range of about a 50% change in concentration from an initial state.

Development of a portable tissue oximeter using near infra-red spectroscopy

NON-INVASIVE AND continuous monitoring of physiological conditions during cxcrcise is very important for clinical diagnosis, sports medicine, healthcare monitoring etc. For the continuous monitoring of cardiovascular conditions, several types of instruments have been developed, such as the Holter ECG (HOLTER, 1961; ISHn3A et al., 1990) and ambulatory blood pressure monitors (YAMAKOSHI, 1991); these instruments are now widely accepted for clinical and research use. On the other hand, for monitoring metabolic conditions which also provide important physiological information, only a few methods have been developed, such as MRS (WANG et al., 1990; ZATINA et al., 1986); they are expensive and complicated systems, and are not appropriate for use during exercise. The optical method is more convenient to use and is capable of detecting tissue metabolism, as has been shown in previous work (CHANCE et al., 1992). Therefore, this method may be useful as a portable monitor of metabolic conditions during exercise. Many attempts have been made to use this method for research. Study by the optical method began with the work of Kramer and Millikan, followed by the work of Chance and Weber on isolated tissue metabolism monitoring (KR~IER, 1935; MmLm~aq, 1937; CHANGE and WEBER, 1963). Jobsis first showed that near infra-red (NIR) region light has the characteristic of excellent penetration through biological tissues (JOBStS; 1977) after this the NIR method then attracted attention. Cope and Delpy and Rolfe et aL applied the multiwavelength NIR method to neonates, and Chance et al. applied simple ~jal wavelength spectroscopy for muscle studies (COPE and DELPY, 1988; ROLFE et aL, 1991; CHANCE et al., 1992). In recent years, Chance et. al. have developed quantitative noninvasive methods by using timeand frequency-resolved spectroscopy to determine the optical path length (CHANCE et aL, 1988; 1990). By using time-resolved spectroscopy, Delpy et al. esftmated the optical path length through tissue, and 9 Ferrari et a/. examined the spectral properties of muscle tissue (DELPY et al., 1988; FEBRARI et aL, 1992). However, many of these instruments, which have complex