A portable infrared spectrometer for in-vivo measurements of limb oxygenation

Near Infrared Spectroscopy (NIRS) can be employed to noninvasively and continuously measure in-vivo local changes in haemodynamics and oxygenation of human tissues. To this respect, the availability of a portable NIRS spectrometer would be highly desirable, as it could be of major interest for the monitoring of peripheral vascular diseases during unattended patient activities. We present a portable NIRS acquisition system prototype, which can be employed during unattended exercise or everyday life. The prototype is able to control four LED sources and a detector. Such a number of sources is theoretically sufficient for multi-wavelength spectroscopy of tissue constituents other than oxygen, such as cytochrome aa3. The LEDs and the detector are carried by separate probes, which carry also the relevant miniaturized drivers and preamplifiers. The probes can be non-invasively attached to the patient. A single-chip mixed-signal RISC microcontroller performs all the data sampling and acquisition functions using either a time-multiplexing scheme or a digital correlation technique. The acquired data are stored on an on-board 64 Kb EEPROM bank that allows for a few hours of continuous recording. The recorded signals can be subsequently uploaded to a handheld data logger or to a personal computer for storage, visualization and postanalysis. The resulting instrument is compact and lightweight. The probes are sufficiently small to avoid hindrance to movement and exercise. A test of the instrument performance during everyday activities is presented and discussed.