Acta physiologica Scandinavica
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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.
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Acta Physiol. Scand. · Mar 2000
No apparent effect of nitric oxide on the local matching of pulmonary perfusion and ventilation in awake sheep.
The respiratory tissue in the lung receives nitric oxide (NO) from two sources; NO produced in upper airways, and NO produced in lung parenchyma. It has been hypothesized that optimal local matching of ventilation and perfusion (which is necessary for effective gas exchange) is ensured because well-ventilated lung tissue has a higher concentration of NO and thereby higher blood flow owing to the vasodilatory effect of NO. To test this hypothesis, we simultaneously measured the distributions of local (regions of approximately 1.5 cm3) blood flow (radioactive microspheres) and local ventilation (fluorescent aerosol) in five tracheostomized, awake and standing sheep. ⋯ These changes in vertical distribution of perfusion can be explained by the effect of variable NO concentrations on pulmonary arterial pressure and cardiac output. Variable access to NO had no effect on arterial blood gases. We conclude that NO is important for the vertical distribution of pulmonary perfusion, but has no apparent effect on the local matching of ventilation and perfusion within horizontal layers of the lung.
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Acta Physiol. Scand. · Aug 1999
Clinical TrialHyperoxia does not increase peak muscle oxygen uptake in small muscle group exercise.
We examined the influence of hyperoxia on peak oxygen uptake (VO2peak) and peripheral gas exchange during exercise with the quadriceps femoris muscle. Young, trained men (n=5) and women (n=3) performed single-leg knee-extension exercise at 70% and 100% of maximum while inspiring normal air (NOX) or 60% O2 (HiOX). Blood was sampled from the femoral vein of the exercising limb and from the contralateral artery. ⋯ The VO2peak-to-PvO2 ratio was lower (P < 0.05) in HiOX than in NOX suggesting a lower O2 conductance. We conclude that the similar VO2peak values despite higher O2 driving pressure in HiOX indicates a peripheral limitation for VO2peak. This may relate to saturation of the rate of O2 turnover in the mitochondria during exercise with a small muscle group but can also be caused by tissue diffusion limitation related to lower O2 conductance.
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Acta Physiol. Scand. · Jun 1999
Near-infrared monitoring of tissue oxygenation during application of lower body 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 near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during -25 and -50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. ⋯ 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. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O2 content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.
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Acta Physiol. Scand. · May 1999
Clinical Trial Controlled Clinical TrialIsotonic and hypertonic sodium loading in supine humans.
The hypothesis that hypertonic saline infusion induces a greater natriuresis than infusion of the same amount of sodium as isotonic saline was tested in 8 supine subjects on fixed sodium intake of 150 mmol NaCl day(-1). Sodium loads equivalent to the amount of sodium contained in 10% of measured extracellular volume were administered intravenously over 90 min either as isotonic saline or as hypertonic saline (850 mmol L(-1)). A third series without saline infusion served as time control. ⋯ In conclusion, hypertonic saline did not produce excess natriuresis. However, as the two loading procedures induced similar natriureses during different volumetric stimuli, part of the natriuresis elicited by hypertonic saline could be mediated by stimulation of osmoreceptors involved in renal sodium excretion. The supine position does not provide stable time control conditions with regard to renal excretory function.