Acta physiologica Scandinavica
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The discovery of the Bainbridge reflex 70 years ago, of a tachycardic response to a rise in central venous pressure, stimulated a lot of interest in this and other cardiovascular reflexes. The mechanoreceptors that elicit the reflex are located at the junction of the right atrium and caval veins or at the junctions of the pulmonary veins and the left atrium. The Bainbridge reflex is controversial, however, because its existence cannot always be demonstrated. ⋯ This paper reviews the history of the studies associated with the reflex. Results are reported, which demonstrate that the chronotropic response to i.v. infusions depends upon the resulting change in aortic diameter; bradycardia is evoked by infusions leading to a rise in aortic baroreceptor activity through increases in aortic diameter, volume or pressure; tachycardia follows whenever the infusion fails to trigger the baroreflex. The importance of the Bainbridge reflex as a counterbalance to the baroreceptor reflex is discussed.
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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. · Nov 2004
Partial reversal of conduction slowing during repetitive stimulation of single sympathetic efferents in human skin.
To describe and identify the function of a class of human C fibre with an unusual response to repetitive electrical stimulation. Other C fibres slow progressively at 2 Hz (type 1), reach a latency plateau (type 2) or hardly slow at all (type 3). ⋯ The distinctive activity-dependent slowing profiles of these type-4 sympathetic C units may help identification in vitro, and suggest that hyperpolarization-activated channels have a particularly prominent role in the axonal membrane.
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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. · 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.