Editing Cardiac output (section)

{{short description|Measurement of blood pumped by the heart}}
{{Use British English|date = May 2015}}
{{Use dmy dates|date=July 2021}}

[[File:2031 Factors in Cardiac Output.jpg|thumb|Major factors influencing cardiac output – heart rate and stroke volume, both of which are variable.<ref name="CNX2014">{{cite book|last1=Betts|first1=J. Gordon|name-list-style=vanc|title=Anatomy & physiology|date=2013|isbn=978-1938168130|url=https://cnx.org/content/m46676/latest/?collection=col11496/latest|access-date=11 August 2014|pages=787–846|publisher=OpenStax College, Rice University |archive-date=23 February 2022|archive-url=https://web.archive.org/web/20220223063018/https://openstax.org/books/anatomy-and-physiology/pages/19-1-heart-anatomy|url-status=live}}</ref>|330x330px]]

In [[cardiac physiology]], '''cardiac output''' ('''CO'''), also known as '''heart output''' and often denoted by the symbols <math>Q</math>, <math> \dot Q</math>, or <math> \dot Q_{c} </math>,<ref name="Williams Kenyon Adamson 2010 pp. 173–230">{{cite book|last1=Kenyon|first1=Anna|url=https://books.google.com/books?id=_DdNPgAACAAJ|title=Basic Science in Obstetrics and Gynaecology|last2=Williams|first2=David|last3=Adamson|first3=Dawn|date=10 June 2010|publisher=Elsevier|isbn=978-0-443-10281-3|pages=173–230|chapter=Physiology|doi=10.1016/b978-0-443-10281-3.00014-2|oclc=1023146175|access-date=23 February 2022|archive-date=30 June 2022|archive-url=https://web.archive.org/web/20220630073505/https://www.google.co.in/books/edition/Basic_Science_in_Obstetrics_and_Gynaecol/_DdNPgAACAAJ?hl=en|url-status=live}} edited by Catherine E. Williamson, Phillip Bennett</ref> is the [[volumetric flow rate]] of the [[heart]]'s pumping output: that is, the volume of [[blood]] being pumped by a single [[Ventricle (heart)|ventricle]] of the heart, per unit time (usually measured per minute). 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:
:<math>CO = HR \times SV</math><ref name="OpenStax 2013">{{cite web|author=OpenStax|title=Cardiac Physiology|website=BC Open Textbooks – Open Textbooks Adapted and Created by BC Faculty|date=6 March 2013| url=https://opentextbc.ca/anatomyandphysiology/chapter/19-4-cardiac-physiology/|url-status=live|archive-url=https://web.archive.org/web/20211106112910/https://openstax.org/books/anatomy-and-physiology/pages/19-4-cardiac-physiology|archive-date=6 November 2021|access-date=2020-04-07}}</ref>
Values for cardiac output are usually denoted as L/min. For a healthy individual weighing 70&nbsp;kg, the cardiac output at rest averages about 5 L/min; assuming a heart rate of 70 beats/min, the stroke volume would be approximately 70 mL.

Because cardiac output is related to the quantity of blood delivered to various parts of the body, it is an important component of how efficiently the heart can meet the body's demands for the maintenance of adequate tissue [[perfusion]]. [[Tissue (biology)|Body tissues]] require continuous oxygen delivery which requires the sustained transport of oxygen to the tissues by [[Circulatory system#Structure|systemic circulation]] of oxygenated blood at an adequate pressure from the left ventricle of the heart via the aorta and arteries. Oxygen delivery (DO<sub>2</sub> mL/min) is the resultant of blood flow (cardiac output CO) times the blood oxygen content (CaO<sub>2</sub>). Mathematically this is calculated as follows: oxygen delivery = cardiac output × arterial oxygen content, giving the formula:
:<math>D_{O2} = CO \times C_aO2</math><ref>{{Cite journal|last1=Dunn|first1=J.-Oc|last2=Mythen|first2=M. G.|last3=Grocott|first3=M. P.|date=1 October 2016|title=Physiology of Oxygen Transport|url=https://bjaed.org/article/S2058-5349(17)30035-5/abstract|journal=BJA Education|url-status=live|archive-url=https://web.archive.org/web/20220223063020/https://www.bjaed.org/article/S2058-5349%2817%2930035-5/fulltext|archive-date=23 February 2022|language=en|volume=16|issue=10|pages=341–48|doi=10.1093/bjaed/mkw012|issn=2058-5349|doi-access=free}}</ref>
With a resting cardiac output of 5 L/min, a 'normal' oxygen delivery is around 1 L/min. The amount/percentage of the circulated oxygen consumed (VO<sub>2</sub>) per minute through metabolism varies depending on the activity level but at rest is circa 25% of the DO<sub>2</sub>. Physical exercise requires a higher than resting-level of oxygen consumption to support increased muscle activity. Regular aerobic exercise can induce physiological adaptations such as improved stroke volume and myocardial efficiency that increase cardiac output.<ref>{{cite journal | url=https://journals.physiology.org/doi/full/10.1152/jappl.1997.83.6.1900 | doi=10.1152/jappl.1997.83.6.1900 | title=Cardiovascular adaptations to 10 days of cycle exercise | date=1997 | last1=Mier | first1=Constance M. | last2=Turner | first2=Michael J. | last3=Ehsani | first3=Ali A. | last4=Spina | first4=Robert J. | journal=Journal of Applied Physiology | volume=83 | issue=6 | pages=1900–1906 | url-access=subscription }}</ref> In the case of [[heart failure]], actual CO may be insufficient to support even simple activities of daily living; nor can it increase sufficiently to meet the higher metabolic demands stemming from even moderate exercise.

Cardiac output is a global blood flow parameter of interest in [[hemodynamics]], the study of the flow of blood. The factors affecting stroke volume and heart rate also affect cardiac output. The figure at the right margin illustrates this dependency and lists some of these factors. A detailed hierarchical illustration is provided in [[Cardiac output#Factors influencing cardiac output|a subsequent figure]].

There are many methods of measuring CO, both invasively and non-invasively; each has advantages and drawbacks as described below.

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[[File:Vascular function curve.png|thumb|350px|Trend of [[central venous pressure]] as a ''consequence'' of variations in cardiac output. The three functions indicate the trend in physiological conditions (in the centre), in those of decreased [[Preload (cardiology)|preload]] (e.g. in [[hemorrhage]], bottom curve) and in those of increased preload (e.g. following [[Blood transfusion|transfusion]], top curve).]]