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      Evaluation of the Time Course of Vascular Responses to Venous Congestion in the Human Lower Limb

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          Abstract

          This study examined the time course of changes in blood flow to the lower leg in response to venous distension – the veni-arteriolar vasoconstrictor response – in 31 healthy males. During a 5-min period of venous distension (thigh cuff pressure 50 mm Hg), calf blood flow (venous occlusion plethysmography) decreased more rapidly (within 30 s) compared to skin perfusion (after 2 min, Laser Doppler flowmetry), consistent with disparate filling times of superficial and deeper veins and a greater increase in deep vein volume. On completion of venous filling, vascular resistance in the skin was unchanged from baseline, implying that the reduction in perfusion was solely the result of reduced perfusion pressure. For the whole calf, vascular resistance was unchanged after 1 min but decreased thereafter by 35–45% from baseline, indicating adjustment of pre- or post-capillary resistances to maintain flow. Repeated plethysmographic flow measurements assisted the decrease in resistance, most likely by intermittent compression of the thigh cuff acting to displace blood volume centrally and alleviate congestion. These findings do not support an active veni-arteriolar vasoconstrictor mechanism in response to venous distension alone in the lower leg, and provide evidence of dynamic flow adjustments that should be acknowledged during procedures that involve prolonged periods of venous congestion.

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          Most cited references13

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          Local reflex in microcirculation in human skeletal muscle.

          The effect of venous stasis of 40 mmHg upon blood flow in human skeletal muscle was studied in four normal subjects and in two chronically sympathectomized patients. Blood flow in skeletal muscle was measured by the local 133Xenon washout technique. Blood flow decreased about 30 per cent during venous stasis of 40 mmHg. In a "passive vascular bed" induced by means of histamine, blood flow decreased only by 16 per cent, indicating that the decrease in blood flow is due to a vasoconstrictor response to increase in vascular transmural pressure. The vasoconstrictor response was unaffected by a spinal sympathetic blockade, but was blocked in areas infiltrated with lidocaine or with phentolamine. The vasoconstrictor response was present in the nonoperated limbs used as a control, but abolished in the denervated arms in the two chronically sympathectomized patients. The findings strongly suggest that the vasoconstrictor response in skeletal muscle is due to a local nervous mechanism involving adrenergic fibres. Thus a local reflex mechanism, most likely a sympathetic axon reflex, seems to be present in human skeletal muscle as in cutaneous and subcutaneous tissue. This indicates that about 45 per cent of the change in total vascular conductance, when a person changes from supine to upright position, is due to this local reflex mechanism operating independently of the central nervous system.
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            Assessment of venous capacitance. Radionuclide plethysmography: methodology and research applications.

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              Deep venous contribution to hydrostatic blood volume change in the human leg.

              The causes of orthostatic intolerance following prolonged bed rest, head-down tilt or exposure to zero gravity are not completely understood. One possible contributing mechanism is increased venous compliance and peripheral venous pooling. The present study attempted to determine what proportion of the increased calf volume during progressive venous occlusion is due to deep venous filling. Deep veins in the leg have little sympathetic innervation and scant vascular smooth muscle, so their compliance may be determined primarily by the surrounding skeletal muscle. If deep veins make a large contribution to total leg venous compliance, then disuse-related changes in skeletal muscle mass and tone could increase leg compliance and lead to decreased orthostatic tolerance. The increase in deep venous volume during progressive venous occlusion at the knee was measured in 6 normal subjects using calf cross-sectional images obtained with magnetic resonance imaging. Conventional plethysmography was used simultaneously to give an independent second measurement of leg volume and monitor the time course of the volume changes. Most of the volume change at all occlusion levels (20, 40, 60, 80 and 100 mm Hg) could be attributed to deep venous filling (90.2% at 40 mm Hg and 50.6% at 100 mm Hg). It is concluded that a large fraction of the calf volume change during venous occlusion is attributable to filling of the deep venous spaces. This finding supports theories postulating an important role for physiological mechanisms controlling skeletal muscle tone during orthostatic stress.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2006
                February 2006
                16 February 2006
                : 43
                : 2
                : 166-174
                Affiliations
                School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UK
                Article
                90946 J Vasc Res 2006;43:166–174
                10.1159/000090946
                16407662
                7b73fa08-e1e6-4a07-90f6-69f25a2a075b
                © 2006 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                History
                : 06 July 2005
                : 15 October 2005
                Page count
                Figures: 5, Tables: 1, References: 35, Pages: 9
                Categories
                Research Paper

                General medicine,Neurology,Cardiovascular Medicine,Internal medicine,Nephrology
                Laser Doppler flowmetry,Venous distension,Veni-arteriolar response,Plethysmography,Human calf

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