NIR spectroscopy measures blood flow

Peripheral vascular disease, common among the elderly, results in reduced blood flow to the lower limbs. Currently, the severity of this disease is evaluated by taking blood pressure measurements at the brachial artery in the arm and at arteries in the foot. However, this method provides only an indirect estimate of blood flow, whereas NIR spectroscopy can directly measure the levels of oxygenated and deoxygenated hemoglobin in blood vessels.

Dr. Moshe Vardi from Carmel Medical Center in Haifa and Dr. Asaph Nini from Sheba Medical Center in Hashomer, both in Israel, have reviewed 21 clinical studies that evaluated NIR spectroscopy for detecting peripheral vascular disease. They noted that one study with a large number of subjects indicated that the technique has high sensitivity and specificity for this purpose. In another investigation, subjects underwent a common test for peripheral vascular disease called postocclusive reactive hyperemia. This study also found a significant spectral difference between subjects who have the disease and those who do not.

Some exercise tests demonstrated that the technique indeed shows a significant difference in oxygen recovery time between healthy patients and those who have the illness. Patients with co-occurring diabetes had reduced blood volume but the same oxygenation levels as others with peripheral vascular disease. These exercise tests also revealed that measurement at the calf muscle was reliable but that measurement at the back of the foot was not.

Magnetic resonance spectroscopy also proved useful for evaluating the level of oxygenation, but the authors noted that the technique is much more costly and much less available than NIR spectroscopy. Recent studies of peripheral vascular disease have employed various NIR spectroscopy methods, including spatially resolved spectroscopy, spectral mapping, diffuse correlation spectroscopy and diffuse reflectance spectroscopy. The doctors commented that these methods may become clinically useful, although none are currently. (European Journal of Vascular & Endovascular Surgery, January 2008, pp. 68-74.)