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 [HbO2], [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 μmol·(100ml)-1·min-1.

We present non-invasive measurements of the calf muscle blood flow (BF) and oxygen consumption (OC) by near-infrared spectroscopy. We used a frequency domain tissue oximeter (modulation frequency: 110 MHz, wavelengths: 758 and 830 nm) to measure in real time (acquisition time: 0.64 s) the hemoglobin concentration and saturation. After 1-min of baseline acquisition, we achieved venous occlusion by inflating a pneumatic cuff on the subject's thigh to a pressure of 60 mmHg. The cuff was released after 1 min. The baseline/inflation/release procedure was repeated 3 times to verify reproducibility. We calculated the BF and OC from the initial rate of increase of the total hemoglobin and deoxy-hemoglobin concentration immediately after the onset of venous occlusion. We examined 8 healthy subjects and 18 patients affected by peripheral vascular disease (PVD) in 1 or 2 legs to investigate whether muscle BF and OC at rest can be useful indicators of vascular insufficiency. In healthy legs, we obtained average values of BF=0.73 ml/(100ml)/min and OC=0.10 ml/(100g)/min. The corresponding average values found in legs affected by PVD are BF=1.39 ml/(100ml)/min and OC=0.16 ml/(100g)/min. The ranges of values of BF and OC measured in the healthy legs broadly overlap with the corresponding ranges measured in the PVD legs.