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In [[medicine]], the '''mean systemic pressure''' ('''mean systemic filling pressure''' (MSFP), or '''mean circulatory filling pressure''', (MCFP)) is defined as the [[arithmetic mean|mean]] [[pressure]] that exists in the [[circulatory system]] when there is no blood motion. The value of MSP in animal experimental models is approximately 7&nbsp;mm Hg. It is an indicator of how full the circulatory system is (i.e. the [[Blood volume|volume of blood]] in the system compared to the capacity of the system), and is influenced by the volume of circulating blood and the [[smooth muscle]] [[Muscle tone|tone]] in the walls of the [[Vein|venous system]] (which determines the capacity of the system).<ref name="rothe">{{cite journal|last=Rothe|first=CF|date=Feb 1993|title=Mean circulatory filling pressure: its meaning and measurement.|journal=J Appl Physiol|volume=74|issue=2|pages=499–509|doi=10.1152/jappl.1993.74.2.499|pmid=8458763}}</ref>
<ref name="tabrizchi">{{cite journal |last=Tabrizchi |first=R |author2=Pang CC |date= May 1992|title=Effects of drugs on body venous tone, as reflected by mean circulatory filling pressure. |journal=Cardiovasc. Res. |volume=26 |issue=5 |pages=443–8 |pmid=1446314 |doi= 10.1093/cvr/26.5.443}}</ref>

MSP is measured in two ways experimentally, and as a result has two alternative naming conventions. MSFP is measured after clamping the aortic root and the great veins at point of entry to right atrium.<ref>{{cite book|title=Medical Physiology|author=Boron and Boulpaep|edition=2nd|date=2009}}</ref> On the other hand, MCFP is measured experimentally by briefly inducing [[cardiac arrest]] or naturally during [[cardiac arrest]] once the blood redistributes.  It may also be estimated ''in vivo'' using a series of inspiratory holds when a patient is on a mechanical ventilator.<ref>{{cite journal |last=Kenny |first=JE |date= June 2017|title=ICU Physiology in 1000 Words: The Mean Systemic Filling Pressure – Part 2. |journal=PulmCCM |url= https://pulmccm.org/cardiovascular-disease-review/icu-physiology-1000-words-mean-systemic-filling-pressure-part-2/}}</ref> It can be used to demonstrate effects of [[Pharmaceutical drug|drugs]] on the venous tone while the circulating blood volume remains constant,<ref>{{cite journal |last=Hoka |first=S |author2=Yamaura K |author3=TAkenaka T |author4=Takahashi S  |date= Dec 1998|title=Propofol-induced increase in vascular capacitance is due to inhibition of sympathetic vasoconstrictive activity. |journal=Anesthesiology |volume=89 |issue=6 |pages=1495–1500 |pmid=9856725 |doi= 10.1097/00000542-199812000-00028}}</ref> or to measure [[Haemodynamic response|haemodynamic changes]] during [[Bleeding|haemorrhage]].<ref>{{cite journal |last=Rothe CF |author2=Maass-Moreno R |date= Mar 1994|title=Gastrointestinal hemodynamics during compensation for hemorrhage and measurement of P<sub>mcf</sub>. |journal=Am J Physiol |volume=266 |issue=3 pt 2 |pages=H1242–50 |pmid=8160829 |doi= 10.1152/ajpheart.1994.266.3.H1242|first1=CF}}</ref>

Mean systemic pressure increases if there is an increase in blood volume or if there is a decrease in venous compliance (where blood is shifted from the veins to the arteries). An increase in mean systemic pressure is reflected in a shift of the vascular function curve to the right. Mean systemic pressure is decreased by a decrease in blood volume or by an increase in venous compliance (where blood is shifted from the arteries to the veins). A decrease in mean systemic pressure is reflected in a shift of the vascular function curve to the left.

== Calculations involving MSP ==
Mean systemic pressure is defined by the stressed volume in the cardiovascular system and the overall systemic capacitance:

:<math>MSP = \frac{Vs}{Csys}</math>

Mean systemic pressure is involved in the following calculations:

:<math>VR \simeq MSP - RAP</math>

* VR = [[Venous return]]
* MSP = Mean systemic pressure
* RAP = [[Right atrial pressure]]

:<math>SVR = \frac{MSP - RAP}{CO}</math>

* SVR = [[Systemic vascular resistance]]
* MSP = Mean systemic pressure
* RAP = [[Right atrial pressure]]
* CO = [[Cardiac output]]

== See also ==
*[[Mean arterial pressure]]
*[[Central venous pressure]]

== References ==
{{Reflist}}

{{DEFAULTSORT:Mean Systemic Pressure}}
[[Category:Physiology]]


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