Near-infrared monitoring of tissue oxygenation during application of lowerbody pressure at rest and during dynamical exercise in humans

During the application of a wide range of graded lower body pressures (LBP) (-50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used ne ar-infrared spectroscopy (NIRS) to measure the changes induced by LBP in to tal Hb content and Hb oxygenation in seven subjects. At rest total Hb incre ased and Hb oxygenation decreased in the thigh muscles during -25 and -50 m mHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was th e reverse of that in the thigh. Measurements from the forehead showed chang es only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower par ts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above -25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. Th ese results suggest that during dynamical exercise ii) LBP at +25 mmHg or m ore causes a graded decline in blood volume and/or flow in the thigh muscle s. and (ii) especially at +50 mmHg LBP, the O-2 content may decrease marked ly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurri ng in human skeletal muscles and head during the graded changes in blood fl ow and/or volume caused by changes in external pressure and secondary refle xes both at rest and during dynamical exercise.