Near-infrared spectroscopy and the tilting table protocol: a novel method to study the blood flow and the oxygen consumption in tissues

We present a novel technique based on tilting the bed where the subject is lying, to non-invasively measure the tissue blood flow (BF) and oxygen consumption (OC) with near-infrared (NIR) spectroscopy. We used a NIR, frequency domain spectrometer to measure the concentrations of oxy-hemoglobin ([HbO2]), deoxy-hemoglobin ([Hb]) and total hemoglobin (THC) in the calf muscle of human subjects. The subject was lying horizontally, and after a baseline acquisition, the bed was tilted by 10 degrees (feet down, head up). This position was kept for 1 min, then the subject was brought back to the horizontal position. This tilting procedure caused variations in the calf [Hb02], [Hb], and THC similar to those observed during a pneumatic-cuff-induced venous occlusion. The increasing rate of THC and [Hb] caused by tilting allowed the calculation of blood flow and oxygen consumption. We found a quantitative agreement between the values of BF (OC) measured with the tilting table and with the venous occlusion protocols. On the 26 subjects examined with the tilting table protocol, we found population average values of BF = 1.51 ml (100ml)-1-min-1 and OC = 6.10 ?mol( 100ml)-1 min-1.