MEASUREMENT OF CHANGES IN OPTICAL PATHLENGTH THROUGH HUMAN MUSCLE DURING CUFF OCCLUSION ON THE ARM

Concentration changes of haemoglobin and cytochromes indicative of tis sue perfusion and oxygenation can be quantitatively evaluated from nea r-infrared (NIR) measurements of absorption and optical pathlength thr ough tissue. The accuracy of such measurements is limited as current b edside instrumentation cannot measure optical pathlength. Using a rece ntly developed phase-resolved spectroscopic technique we can produce c ontinuous and simultaneous measurements of changes in both attenuation and optical pathlength at four wavelengths in the NIR in a bedside in strument. The change in optical pathlength through arm muscle during a cuff occlusion is compared with the absolute pathlength estimated fro m time resolved spectroscopy measurements in the laboratory. These sho w that the pathlength varies by 4-10% during the occlusion, demonstrat ing the need for continuous measurements of optical pathlength.