The cardiovascular system is designed to deliver oxygen to every cell in the body through the microcirculation. Optical
Reflectance Spectroscopy (ORS) is a powerful tool used to study oxygen delivery through vessels less than 50 &mgr;m in
diameter. Depth analysis can be achieved by varying the geometry of the incident light source and the detector of the
back-scattered light. A fibre optic probe has been designed with spacings to study the capillary loops and microvessels of
the skin. Similarly, Near Infrared Spectroscopy (NIRS) can directly measure haemodynamics in muscle. A combined
study of ORS and NIRS is currently investigating the relationship of vasomotion in the skin and underlying muscle.
Vasomotion is usually defined as rhythmic changes in the diameter of the small blood vessels and has been linked to
both endothelial and sympathetic activity. It has been suggested that vasomotion in the muscle preserves nutritive
perfusion not only in the muscle itself but also to neighbouring tissue i.e. skin. ORS and NIRS can provide a direct
measure of these changes in blood volume. At frequencies linked with endothelial and sympathetic activity, rhythmical
oscillations in blood volume of the same magnitude, were demonstrated in both skin and muscle, 15.3(4.0)% skin vs
16.3(5.3)% muscle for endothelial frequencies, (mean(SD), t-test, p=0.633) and 10.9(3.8)% skin and 12.4(5.5)% muscle
for sympathetic frequencies (p=0.354). These data demonstrate the potential of these optical techniques to enable
simultaneous examination of microvascular haemodynamics in two tissue types.
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