Monitoring tissue oxygen availability with near infrared spectroscopy (NIRS) in health and disease

Near infrared spectroscopy (NIRS) is becoming a widely used research instru ment to measure tissue oxygen (Oz) status non-invasively, Continuous-wave s pectrometers are the most commonly used devices, which provide semiquantita tive changes in oxygenated and deoxygenated hemoglobin in small blood vesse ls (arterioles, capillaries and venules), Refinement of NIRS hardware and t he algorithms used to deconvolute the light absorption signal have improved the resolution and validity of cytochrome oxidase measurements. NIRS has b een applied to measure oxygenation in a variety of tissues including muscle , brain and connective tissue, and more recently it has been used in the cl inical setting to assess circulatory and metabolic abnormalities. Quantitat ive measures of blood flow are also possible using NIRS and a light-absorbi ng tracer, which can be applied to evaluate circulatory responses to exerci se along with the assessment of tissue O-2 saturation. The venular O-2 satu ration can be estimated with NIRS by applying venous occlusion and measurin g changes in oxygenated vs. total hemoglobin. These various measurements pr ovide the opportunity to evaluate several important metabolic and circulato ry patterns in very localized regions of tissue and may be fruitful in the study of occupational syndromes and a variety of diseases.