{{short description|Ability of a biological organ to distend}}'''Compliance''' is the ability of a hollow organ (vessel) to distend and increase volume with increasing transmural pressure or the tendency of a hollow organ to resist recoil toward its original dimensions on application of a distending or compressing force. The reciprocal of compliance is '''elastance''', a measure of the tendency of a hollow organ to recoil toward its original dimensions upon removal of a distending or compressing force.
==Blood vessels== The terms elastance and compliance are of particular significance in [[cardiovascular physiology]] and [[respiratory physiology]]. In compliance, an increase in volume occurs in a vessel when the pressure in that vessel is increased. The tendency of the [[arteries]] and [[veins]] to stretch in response to pressure has a large effect on perfusion and blood pressure. This physically means that blood vessels with a higher compliance deform easier than lower compliance blood vessels under the same pressure and volume conditions.<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 3/3ch7/s3ch7_10 |chapter-url=http://humanphysiology.tuars.com/program/section3/3ch7/s3ch7_10.htm }}{{dead link|date=August 2020|bot=medic}}{{cbignore|bot=medic}}</ref> Venous compliance is approximately 30 times larger than arterial compliance.<ref name = "Gelman 2008">{{cite journal |doi=10.1097/ALN.0b013e3181672607 |title=Venous Function and Central Venous Pressure |year=2008 |last1=Gelman |first1=Simon |journal=Anesthesiology |volume=108 |issue=4 |pages=735–48 |pmid=18362606|doi-access=free }}</ref> Compliance is calculated using the following equation, where <math>\Delta V</math> is the change in volume (mL), and <math>\Delta P</math> is the change in pressure ([[Millimeter of mercury|mmHg]]):<ref>[http://www.cvphysiology.com/Blood%20Pressure/BP004.htm Vascular compliance<!-- Bot generated title -->]</ref> :<math>C = \frac{ \Delta V}{ \Delta P} </math>
Physiologic compliance is generally in agreement with the above and adds ''<math display="inline">\tfrac{dP}{dt}</math>'' as a common academic physiologic measurement of both pulmonary and cardiac tissues. Adaptation of equations initially applied to [[rubber]] and [[latex]] allow modeling of the dynamics of pulmonary and cardiac tissue compliance. Veins have a much higher compliance than arteries (largely due to their thinner walls.) Veins which are abnormally compliant can be associated with [[edema]]. [[Compression stockings|Pressure stockings]] are sometimes used to externally reduce compliance, and thus keep blood from pooling in the legs.
{{Anchor|Complexity of hemodynamic response}} [[Vasodilation]] and [[vasoconstriction]] are complex phenomena; they are functions not merely of the [[fluid mechanics]] of pressure and tissue [[elasticity (physics)|elasticity]] but also of active [[homeostasis|homeostatic]] regulation with [[hormone]]s and [[cell signaling]], in which the body produces [[endogeny (biology)|endogenous]] vasodilators and vasoconstrictors to modify its vessels' compliance. For example, the [[muscle tone]] of the [[smooth muscle tissue]] of the [[tunica media]] can be adjusted by the [[renin–angiotensin system]]. In patients whose endogenous homeostatic regulation is not working well, dozens of [[pharmaceutical drug]]s that are also [[vasoactive]] can be added. The response of vessels to such vasoactive substances is called vasoactivity (or sometimes vasoreactivity). Vasoactivity can vary between persons because of [[genetics|genetic]] and [[epigenetics|epigenetic]] differences, and it can be impaired by pathosis and by age. This makes the topic of [[haemodynamic response]] (including vascular compliance and [[vascular resistance]]) a matter of medical and [[pharmacology|pharmacologic]] complexity beyond mere [[hydraulics|hydraulic]] considerations (which are complex enough by themselves).
The relationship between vascular compliance, pressure, and flow rate is:<math display="block">Q=C\frac{\mathrm{d}P}{\mathrm{d}t}=\mathrm{(flow rate)(cm^3/sec)}</math>
===Arterial compliance===
The classic definition by MP Spencer and AB Denison of compliance (<math>C</math>) is the change in arterial blood volume (<math>\Delta V</math>) due to a given change in [[arterial blood pressure]] (<math>\Delta P</math>). They wrote this in the "Handbook of Physiology" in 1963 in work entitled "Pulsatile Flow in the Vascular System". So, <math>C=\frac{\Delta V}{\Delta P}</math>.<ref>{{cite journal |first1=Piergiorgio |last1=Tozzi |first2=Antonio |last2=Corno |first3=Daniel |last3=Hayoz |title=Definition of arterial compliance |journal=American Journal of Physiology |pmid=10787279 |url=http://ajpheart.physiology.org/cgi/pmidlookup?view=long&pmid=10787279 |year=2000 |volume=278 |issue=4 |article-number=H1407|doi=10.1152/ajpheart.2000.278.4.H1407 |url-access=subscription }}</ref>
Arterial compliance is an index of the [[Elasticity (physics)|elasticity]] of large arteries such as the [[thoracic aorta]]. Arterial compliance is an important cardiovascular risk factor. Compliance diminishes with age and menopause. Arterial compliance is measured by [[ultrasound]] as a pressure ([[carotid artery]]) and volume (outflow into [[aorta]]) relationship.<ref name="Pmid">{{cite journal |doi=10.1210/jcem.84.3.5561 |title=Isoflavones from Red Clover Improve Systemic Arterial Compliance but Not Plasma Lipids in Menopausal Women |year=1999 |last1=Nestel |first1=P. J. |journal=Journal of Clinical Endocrinology & Metabolism |volume=84 |issue=3 |pmid=10084567 |pages=895–8 |last2=Pomeroy |first2=S |last3=Kay |first3=S |last4=Komesaroff |first4=P |last5=Behrsing |first5=J |last6=Cameron |first6=JD |last7=West |first7=L|doi-access=free }}</ref>
Compliance, in simple terms, is the degree to which a container experiences pressure or force without disruption. It is used as an indication of [[arterial stiffness]]. An increase in the age and also in the systolic [[blood pressure]] (SBP) is accompanied with decrease on arterial compliance.<ref>{{Cite web | title= Arterial Compliance Experts | url = http://www2.intota.com/experts.asp?strSearchType=all&strQuery=arterial+compliance | access-date = 2011-11-09 }} </ref>
Endothelial dysfunction results in reduced compliance (increased arterial stiffness), especially in the smaller arteries. This is characteristic of patients with [[hypertension]]. However, it may be seen in normotensive patients (with normal blood pressure) before the appearance of clinical hypertension. Reduced arterial compliance is also seen in patients with [[diabetes]] and also in smokers. It is actually a part of a vicious cycle that further elevates blood pressure, aggravates [[atherosclerosis]] (hardening of the arteries), and leads to increased cardiovascular risk. Arterial compliance can be measured by several techniques. Most of them are invasive and are not clinically appropriate. [[Pulse contour analysis]] is a non-invasive method that allows easy measurement of arterial elasticity to identify patients at risk for cardiovascular events.<ref>{{cite journal |doi=10.1016/S0895-7061(01)02154-9 |title=Arterial compliance to stratify cardiovascular risk: More precision in therapeutic decision making |year=2001 |last1=Cohn |first1=J |journal=American Journal of Hypertension |volume=14 |issue=8 |pages=S258–S263|pmid=11497206 |doi-access= }}</ref>
==See also== * [[Cardiovascular System Dynamics Society]] * [[Windkessel effect]]
==References== {{reflist|30em}}
==External links== * {{MeshName|Compliance}}
{{Cardiovascular physiology}}
[[Category:Respiratory physiology]] [[Category:Cardiovascular physiology]]