Mean arterial pressure

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Mean arterial pressure
Arterial-blood-pressure-curve.svg
Representation of the arterial pressure waveform over one cardiac cycle. The notch in the curve is associated with closing of the aortic valve.
MeSH D062186

In medicine, the mean arterial pressure (MAP) is an average calculated blood pressure in an individual during a single cardiac cycle. [1] Although methods of estimating MAP vary, a common calculation is to take one-third of the pulse pressure (the difference between the systolic and diastolic pressures), and add that amount to the diastolic pressure. [2] [3] A normal MAP is about 90 mmHg. [4]

Contents

Mean arterial pressure = diastolic blood pressure + (systolic blood pressure - diastolic blood pressure)/3

MAP is altered by cardiac output and systemic vascular resistance. [5] It is used clinically to estimate the risk of cardiovascular diseases, where a MAP of 90 mmHg or less is low risk, and a MAP of greater than 96 mmHg represents "stage one hypertension" with increased risk. [3] [4]

Testing

Arterial line Arterial-line-shaded.png
Arterial line

Mean arterial pressure can be measured directly or estimate from systolic and diastolic blood pressure by using a formula. [5] The least invasive method is the use of a blood pressure cuff which gives the values to calculate an estimate of the mean pressure. A similar method is to use a oscillometric blood pressure device that works by a cuff only method where a microprocessor determines the systolic and diastolic blood pressure. [6] Invasively, an arterial catheter with a transducer is placed and the mean pressure is determined by the subsequent waveform.

Estimating MAP

Mean arterial pressure in relation to systolic and diastolic pressure in blood vessels 2109 Systemic Blood Pressure.jpg
Mean arterial pressure in relation to systolic and diastolic pressure in blood vessels

While MAP can only be measured directly by invasive monitoring, it can be estimated by using a formula in which the lower (diastolic) blood pressure is doubled and added to the higher (systolic) blood pressure and that composite sum then is divided by 3 to estimate MAP. [2]

Thus, a common way to estimate mean arterial pressure is to take one-third of the pulse pressure added to the diastolic pressure: [2] [3] [7]

where:

Systolic pressure minus diastolic pressure equals the pulse pressure which may be substituted in. [5]

Blood pressure cuff Blood pressure measurement.JPG
Blood pressure cuff

Another way to find the MAP is to use the systemic vascular resistance equated (), which is represented mathematically by the formula

where is the change in pressure across the systemic circulation from its beginning to its end and is the flow through the vasculature (equal to cardiac output).

In other words:

Therefore, MAP can be determined by rearranging the equation to:

where:

This is only valid at normal resting heart rates during which can be approximated using the measured systolic () and diastolic () blood pressures: [9] [10]

Elevated heart rate

At high heart rates is more closely approximated by the arithmetic mean of systolic and diastolic pressures because of the change in shape of the arterial pressure pulse.

For a more accurate formula of for elevated heart rates use:

Where

Most accurate

The version of the MAP equation multiplying 0.412 by pulse pressure and adding diastolic blood is indicated to correlate better than other versions of the equation with left ventricular hypertrophy, carotid wall thickness and aortic stiffness. [12] It is expressed:

where:

Young patients

For young patients with congenital heart disease a slight alteration to the factor used found to be more precise. This was written as:

where:

This added precision means cerebral blood flow can be more accurately maintained in uncontrolled hypertension. [13]

Neonates

For neonates, because of their altered physiology, a different formula has been proposed for a more precise reading:

where:

It has also been suggested that when getting readings from a neonates radial arterial line, mean arterial pressure can be approximated by averaging the systolic and diastolic pressure. [14]

Other formula versions

Other formulas used to estimate mean arterial pressure are:

[15]

or

[16]

or

[17]

or

[18]

Clinical significance

Thresholds for 24 hr. mean arterial pressure (MAP) [3]
24 hr. MAP category24 hr. MAP
Normal< 90 mmHg
Elevated blood pressure90 to < 92 mmHg
Stage 1 hypertension92 to < 96 mmHg
Stage 2 hypertension> 96 mmHg

Mean arterial pressure is a major determinant of the perfusion pressure seen by organs in the body. MAP levels greater than 90 mmHg increase the risk stepwise of having higher risk of cardiovascular diseases, such as stroke, and mortality. [3]

Hypotension

When assessing hypotension, the context of the baseline blood pressure needs to be considered. Acute decreases in mean arterial pressure of around 25% put people at increased risk for organ damage and potential mortality. [19] Even one minute at a MAP of 50 mmHg, or accumulative effects over short periods, increases the risk of mortality by 5%, and can result in organ failure or complications. [20] [21]

In people hospitalized with shock, a MAP of 65 mmHg lasting for more than two hours was associated with higher mortality. [22] In people with sepsis, the vasopressor dosage may be titrated on the basis of estimated MAP. [2]

MAP may be used like systolic blood pressure in monitoring and treating target blood pressure. Both are used as targets for assessing sepsis, major trauma, stroke, and intracranial bleeding. [23]

Hypertension

In younger people, elevated MAP is used more commonly than pulse pressure in the prediction of stroke. However in older people, MAP is less predictive of stroke and a better predictor of cardiovascular disease. [24] [25]

See also

Related Research Articles

<span class="mw-page-title-main">Artery</span> Blood vessels that carry blood away from the heart

An artery is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in the pulmonary circulation that carry blood to the lungs for oxygenation, and the umbilical arteries in the fetal circulation that carry deoxygenated blood to the placenta. It consists of a multi-layered artery wall wrapped into a tube-shaped channel.

<span class="mw-page-title-main">Blood pressure</span> Pressure exerted by circulating blood upon the walls of arteries

Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" refers to the pressure in a brachial artery, where it is most commonly measured. Blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure in the cardiac cycle. It is measured in millimeters of mercury (mmHg) above the surrounding atmospheric pressure, or in kilopascals (kPa). The difference between the systolic and diastolic pressures is known as pulse pressure, while the average pressure during a cardiac cycle is known as mean arterial pressure.

<span class="mw-page-title-main">Hypertension</span> Long-term high blood pressure in the arteries

Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms itself. It is, however, a major risk factor for stroke, coronary artery disease, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia. Hypertension is a major cause of premature death worldwide.

Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when standing up or sitting down. Primary orthostatic hypotension is also often referred to as neurogenic orthostatic hypotension. The drop in blood pressure may be sudden, within 3 minutes or gradual. It is defined as a fall in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg after 3 minutes of standing. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain adequate blood pressure when changing the position to standing. As a result, blood pools in the blood vessels of the legs for a longer period, and less is returned to the heart, thereby leading to a reduced cardiac output and inadequate blood flow to the brain.

<span class="mw-page-title-main">Heart murmur</span> Medical condition

Heart murmurs are unique heart sounds produced when blood flows across a heart valve or blood vessel. This occurs when turbulent blood flow creates a sound loud enough to hear with a stethoscope. The sound differs from normal heart sounds by their characteristics. For example, heart murmurs may have a distinct pitch, duration and timing. The major way health care providers examine the heart on physical exam is heart auscultation; another clinical technique is palpation, which can detect by touch when such turbulence causes the vibrations called cardiac thrill. A murmur is a sign found during the cardiac exam. Murmurs are of various types and are important in the detection of cardiac and valvular pathologies.

<span class="mw-page-title-main">Cardiac output</span> Measurement of blood pumped by the heart

In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols , , or , is the volumetric flow rate of the heart's pumping output: that is, the volume of blood being pumped by a single ventricle of the heart, per unit time. Cardiac output (CO) is the product of the heart rate (HR), i.e. the number of heartbeats per minute (bpm), and the stroke volume (SV), which is the volume of blood pumped from the left ventricle per beat; thus giving the formula:

<span class="mw-page-title-main">Ventricle (heart)</span> Chamber of the heart

A ventricle is one of two large chambers located toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper heart that is smaller than a ventricle. Interventricular means between the ventricles, while intraventricular means within one ventricle.

Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously monitors and adjusts to conditions in the body and its environment. Hemodynamics explains the physical laws that govern the flow of blood in the blood vessels.

In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood in the ventricle at the end of a beat from the volume of blood just prior to the beat. The term stroke volume can apply to each of the two ventricles of the heart, although when not explicitly stated it refers to the left ventricle and should therefore be referred to as left stroke volume (LSV). The stroke volumes for each ventricle are generally equal, both being approximately 90 mL in a healthy 70-kg man. Any persistent difference between the two stroke volumes, no matter how small, would inevitably lead to venous congestion of and/or shunt between the systemic and the pulmonary circulation.

<span class="mw-page-title-main">Sphygmomanometer</span> Instrument for measuring blood pressure

A sphygmomanometer, also known as a blood pressure monitor, or blood pressure gauge, is a device used to measure blood pressure, composed of an inflatable cuff to collapse and then release the artery under the cuff in a controlled manner, and a mercury or aneroid manometer to measure the pressure. Manual sphygmomanometers are used with a stethoscope when using the auscultatory technique.

<span class="mw-page-title-main">Pulse pressure</span> Difference between systolic and diastolic blood pressure

Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Healthy pulse pressure is around 40 mmHg. A pulse pressure that is consistently 60 mmHg or greater is likely to be associated with disease, and a pulse pressure of 50 mmHg or more increases the risk of cardiovascular disease. Pulse pressure is considered low if it is less than 25% of the systolic. A very low pulse pressure can be a symptom of disorders such as congestive heart failure.

<span class="mw-page-title-main">Afterload</span> Pressure in the wall of the left ventricle during ejection

Afterload is the pressure that the heart must work against to eject blood during systole. Afterload is proportional to the average arterial pressure. As aortic and pulmonary pressures increase, the afterload increases on the left and right ventricles respectively. Afterload changes to adapt to the continually changing demands on an animal's cardiovascular system. Afterload is proportional to mean systolic blood pressure and is measured in millimeters of mercury.

<span class="mw-page-title-main">Aortic regurgitation</span> Medical condition

Aortic regurgitation (AR), also known as aortic insufficiency (AI), is the leaking of the aortic valve of the heart that causes blood to flow in the reverse direction during ventricular diastole, from the aorta into the left ventricle. As a consequence, the cardiac muscle is forced to work harder than normal.

Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system. The resistance offered by the systemic circulation is known as the systemic vascular resistance (SVR) or may sometimes be called by the older term total peripheral resistance (TPR), while the resistance offered by the pulmonary circulation is known as the pulmonary vascular resistance (PVR). Systemic vascular resistance is used in calculations of blood pressure, blood flow, and cardiac function. Vasoconstriction increases SVR, whereas vasodilation decreases SVR.

<span class="mw-page-title-main">Hypertensive emergency</span> Very high blood pressure and signs of organ damage

A hypertensive emergency is very high blood pressure with potentially life-threatening symptoms and signs of acute damage to one or more organ systems. It is different from a hypertensive urgency by this additional evidence for impending irreversible hypertension-mediated organ damage (HMOD). Blood pressure is often above 200/120 mmHg, however there are no universally accepted cutoff values.

Cardiovascular physiology is the study of the cardiovascular system, specifically addressing the physiology of the heart ("cardio") and blood vessels ("vascular").

In medicine, systolic hypertension is defined as an elevated systolic blood pressure (SBP). If the systolic blood pressure is elevated (>140) with a normal (<90) diastolic blood pressure (DBP), it is called isolated systolic hypertension. Eighty percent of people with systolic hypertension are over the age of 65 years old. Isolated systolic hypertension is a specific type of widened pulse pressure.

A plot of a system's pressure versus volume has long been used to measure the work done by the system and its efficiency. This analysis can be applied to heat engines and pumps, including the heart. A considerable amount of information on cardiac performance can be determined from the pressure vs. volume plot. A number of methods have been determined for measuring PV-loop values experimentally.

<span class="mw-page-title-main">Orthostatic hypertension</span> Medical condition

Orthostatic hypertension is a medical condition consisting of a sudden and abrupt increase in blood pressure (BP) when a person stands up. Orthostatic hypertension is diagnosed by a rise in systolic BP of 20 mmHg or more when standing. Orthostatic diastolic hypertension is a condition in which the diastolic BP raises to 98 mmHg or over in response to standing, but this definition currently lacks clear medical consensus, so is subject to change. Orthostatic hypertension involving the systolic BP is known as systolic orthostatic hypertension.

<span class="mw-page-title-main">Blood pressure measurement</span> Techniques for determining blood pressure

Arterial blood pressure is most commonly measured via a sphygmomanometer, which historically used the height of a column of mercury to reflect the circulating pressure. Blood pressure values are generally reported in millimetres of mercury (mmHg), though modern aneroid and electronic devices do not contain mercury.

References

  1. Zheng L, Sun Z, Li J, Zhang R, Zhang X, Liu S, et al. (July 2008). "Pulse pressure and mean arterial pressure in relation to ischemic stroke among patients with uncontrolled hypertension in rural areas of China". Stroke. 39 (7): 1932–1937. doi: 10.1161/STROKEAHA.107.510677 . PMID   18451345.
  2. 1 2 3 4 "Calculating the mean arterial pressure (MAP)". Nursing Center. 8 December 2011.
  3. 1 2 3 4 5 Melgarejo JD, Yang WY, Thijs L, et al. (January 2021). "Association of Fatal and Nonfatal Cardiovascular Outcomes With 24-Hour Mean Arterial Pressure". Hypertension. 77 (1): 39–48. doi:10.1161/HYPERTENSIONAHA.120.14929. PMC   7720872 . PMID   33296250.
  4. 1 2 "Understanding Blood Pressure Readings". American Heart Association. 2023. Retrieved 3 June 2023.
  5. 1 2 3 DeMers D, Wachs D (2022). "Physiology, Mean Arterial Pressure". StatPearls. Treasure Island (FL): StatPearls Publishing. PMID   30855814 . Retrieved 2022-05-22.
  6. Lewis PS (May 2019). "Oscillometric measurement of blood pressure: a simplified explanation. A technical note on behalf of the British and Irish Hypertension Society". Journal of Human Hypertension. 33 (5): 349–351. doi:10.1038/s41371-019-0196-9. PMC   8076036 . PMID   30926901.
  7. "Mean arterial pressure calculator". PhysiologyWeb. 2023. Retrieved 3 June 2023.
  8. Klabunde RE. "Mean Arterial Pressure". Cardiovascular Physiology Concepts. Marian University College of Osteopathic Medicine.
  9. Nosek TM. "Section 3/3ch7/s3ch7_4". Essentials of Human Physiology. Archived from the original on 2016-03-24.
  10. "Cardiovascular Physiology (page 3)". World of Anesthesia. Nuffield Dept.of Anaesthetics, University of Oxford. 12 September 2006. Archived from the original on 2006-12-11.
  11. Moran D, Epstein Y, Keren G, Laor A, Sherez J, Shapiro Y (November 1995). "Calculation of mean arterial pressure during exercise as a function of heart rate". Applied Human Science. 14 (6): 293–295. doi: 10.2114/ahs.14.293 . PMID   8591100.
  12. Papaioannou TG, Protogerou AD, Vrachatis D, et al. (September 2016). "Mean arterial pressure values calculated using seven different methods and their associations with target organ deterioration in a single-center study of 1878 individuals". Hypertension Research. 39 (9): 640–647. doi: 10.1038/hr.2016.41 . PMID   27194570. S2CID   11382793.
  13. Meaney E, Alva F, Moguel R, Meaney A, Alva J, Webel R (July 2000). "Formula and nomogram for the sphygmomanometric calculation of the mean arterial pressure". Heart. 84 (1): 64. doi:10.1136/heart.84.1.64. PMC   1729401 . PMID   10862592.
  14. Gevers M, Hack WW, Ree EF, Lafeber HN, Westerhof N (1993). "Calculated mean arterial blood pressure in critically ill neonates". Basic Research in Cardiology. 88 (1): 80–85. doi:10.1007/BF00788533. PMID   8471006. S2CID   27547225.
  15. Chemla D, Hébert JL, Zamani K, Coirault C, Lecarpentier Y (August 1999). "Estimation of mean aortic pressure". Lancet. 354 (9178): 596. doi: 10.1016/S0140-6736(05)77948-4 . PMID   10470724. S2CID   20720814.
  16. Razminia M, Trivedi A, Molnar J, Elbzour M, Guerrero M, Salem Y, et al. (December 2004). "Validation of a new formula for mean arterial pressure calculation: the new formula is superior to the standard formula". Catheterization and Cardiovascular Interventions. 63 (4): 419–425. doi:10.1002/ccd.20217. PMID   15558774. S2CID   25022922.
  17. Chemla D, Nitenberg A (June 2005). "A call for improving mean aortic pressure estimation". American Journal of Hypertension. 18 (6): 891. doi: 10.1016/j.amjhyper.2004.10.025 . PMID   15925755.
  18. Chemla D, Hébert JL, Aptecar E, Mazoit JX, Zamani K, Frank R, et al. (July 2002). "Empirical estimates of mean aortic pressure: advantages, drawbacks and implications for pressure redundancy". Clinical Science. 103 (1): 7–13. doi:10.1042/cs1030007. PMID   12095398.
  19. Jones D, Francesco L (2017). "Hypotension". In McKean SC, Ross JJ, Dressler DD, Scheurer DB (eds.). Principles and Practice of Hospital Medicine (2nd ed.). McGraw Hill. ISBN   978-0-07-184313-3.
  20. Nicklas JY, Beckmann D, Killat J, Petzoldt M, Reuter DA, Rösch T, Saugel B (February 2019). "Continuous noninvasive arterial blood pressure monitoring using the vascular unloading technology during complex gastrointestinal endoscopy: a prospective observational study". Journal of Clinical Monitoring and Computing. 33 (1): 25–30. doi:10.1007/s10877-018-0131-6. PMID   29556885. S2CID   4025532.
  21. Maheshwari K, Khanna S, Bajracharya GR, Makarova N, Riter Q, Raza S, Cywinski JB, Argalious M, Kurz A, Sessler DI (August 2018). "A Randomized Trial of Continuous Noninvasive Blood Pressure Monitoring During Noncardiac Surgery". Anesthesia and Analgesia. 127 (2): 424–431. doi:10.1213/ANE.0000000000003482. PMC   6072385 . PMID   29916861.
  22. Vincent, Jean-Louis; Nielsen, Nathan D.; Shapiro, Nathan I.; et al. (2018-11-08). "Mean arterial pressure and mortality in patients with distributive shock: a retrospective analysis of the MIMIC-III database". Annals of Intensive Care. 8 (1): 107. doi: 10.1186/s13613-018-0448-9 . ISSN   2110-5820. PMC   6223403 . PMID   30411243.
  23. Magder SA (May 2014). "The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock". Critical Care Medicine. 42 (5): 1241–1251. doi:10.1097/ccm.0000000000000324. PMID   24736333. S2CID   39745357.
  24. Wong ND, Franklin SS (2017). "Epidemiology of hypertension.". In Fuster V, Harrington RA, Narula J, Eapen ZJ (eds.). Hurst's The Heart (14th ed.). McGraw Hill. ISBN   978-0-07-184324-9.
  25. Verdecchia P, Schillaci G, Reboldi G, Franklin SS, Porcellati C (May 2001). "Different prognostic impact of 24-hour mean blood pressure and pulse pressure on stroke and coronary artery disease in essential hypertension". Circulation. 103 (21): 2579–84. doi: 10.1161/01.cir.103.21.2579 . PMID   11382727. S2CID   13521935.