Acta physiologica Scandinavica
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Acta Physiol. Scand. · Apr 2000
ReviewOxygen supply to contracting skeletal muscle at the microcirculatory level: diffusion vs. convection.
An adequate supply of oxygen is essential for the normal function of all cells. Because skeletal muscle cells have the ability to vary their oxygen demand by over an order of magnitude on going from rest to vigorous contraction, it is important that mechanisms be in place to ensure that the supply of oxygen is maintained at sufficient levels. Microcirculation plays a critical role in this process, as the terminal branches of this intricate network of blood vessels determine the distribution of perfusion, as well as the structural framework for diffusion. ⋯ Diffusive interactions among neighbouring capillaries have also been observed. In contracting muscles, microvessels observed immediately following the period of stimulation exhibit enhancements of both convective (increased flow of red blood cells) and diffusive (increased perfused capillary surface area) transport. The use of computational models in the interpretation of experimental studies is leading to an increased understanding of the processes that underlie the oxygen transport system in skeletal muscle.
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Acta Physiol. Scand. · Apr 2000
ReviewNear-infrared spectroscopy for monitoring muscle oxygenation.
Near-infrared spectroscopy (NIRS) is a non-invasive method for monitoring oxygen availability and utilization by the tissues. In intact skeletal muscle, NIRS allows semi-quantitative measurements of haemoglobin plus myoglobin oxygenation (tissue O2 stores) and the haemoglobin volume. Specialized algorithms allow assessment of the oxidation-reduction (redox) state of the copper moiety (CuA) of mitochondrial cytochrome c oxidase and, with the use of specific tracers, accurate assessment of regional blood flow. ⋯ During work, the extent to which skeletal muscles deoxygenate varies according to the type of muscle, type of exercise and blood flow response. In some instances, a strong concordance is demonstrated between the fall in O2 stores with incremental work and a decrease in CuA oxidation state. Under some pathological conditions, however, the changes in O2 stores and redox state may diverge substantially.