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      Volume and its relationship to cardiac output and venous return

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          Abstract

          Volume infusions are one of the commonest clinical interventions in critically ill patients yet the relationship of volume to cardiac output is not well understood. Blood volume has a stressed and unstressed component but only the stressed component determines flow. It is usually about 30 % of total volume. Stressed volume is relatively constant under steady state conditions. It creates an elastic recoil pressure that is an important factor in the generation of blood flow. The heart creates circulatory flow by lowering the right atrial pressure and allowing the recoil pressure in veins and venules to drain blood back to the heart. The heart then puts the volume back into the systemic circulation so that stroke return equals stroke volume. The heart cannot pump out more volume than comes back. Changes in cardiac output without changes in stressed volume occur because of changes in arterial and venous resistances which redistribute blood volume and change pressure gradients throughout the vasculature. Stressed volume also can be increased by decreasing vascular capacitance, which means recruiting unstressed volume into stressed volume. This is the equivalent of an auto-transfusion. It is worth noting that during exercise in normal young males, cardiac output can increase five-fold with only small changes in stressed blood volume. The mechanical characteristics of the cardiac chambers and the circulation thus ultimately determine the relationship between volume and cardiac output and are the subject of this review.

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          Most cited references 48

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          On the mechanical factors which determine the output of the ventricles.

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            Determination of cardiac output by equating venous return curves with cardiac response curves.

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              Venous return at various right atrial pressures and the normal venous return curve.

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                Author and article information

                Contributors
                sheldon.magder@muhc.mcgill.ca
                Journal
                Crit Care
                Critical Care
                BioMed Central (London )
                1364-8535
                1466-609X
                10 September 2016
                10 September 2016
                2016
                : 20
                : 1
                Affiliations
                Department of Critical Care, McGill University Health Centre, 1001 Decarie Blvd., Montreal, Quebec H4A 3J1 Canada
                1438
                10.1186/s13054-016-1438-7
                5018186
                27613307
                © Magder. 2016

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                Funding
                Funded by: none
                Categories
                Review
                Custom metadata
                © The Author(s) 2016

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