by the blood vessels. mean blood pressure decreases as the circulating blood moves away from the heart through arteries and capillaries due to viscous losses of energy. mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles. gravity affects blood pressure via hydrostatic forces (e.g., during standing), and valves in veins, breathing, and pumping from contraction of skeletal muscles also influence blood pressure in veins. the relationship between pressure, flow, and resistance is expressed in the following equation: f l o w = p r e s s u r e / r e s i s t a n c e when applied to the circulatory system, we get: c o = ( m a p − r a p ) / t p r where co = cardiac output (in l/min) map = mean arterial pressure (in mmhg), the average pressure of blood as it leaves the heart rap = right atrial pressure (in mmhg), the average pressure of blood as it returns to the heart tpr = total peripheral resistance (in mmhg * min/l) a simplified form of this equation assumes right atrial pressure is approximately 0: c o ≈ m a p / t p r the ideal blood pressure in the brachial artery, where standard blood pressure cuffs measure pressure, is <120/80 mmhg. other major arteries have similar levels of blood pressure recordings indicating very low disparities among major arteries. in the innominate artery, the average reading is 110/70 mmhg, the right subclavian artery averages 120/80 and the abdominal aorta is 110/70 mmhg. the relatively uniform pressure in the arteries indicate that these blood vessels act as a pressure reservoir for fluids that are transported within them. pressure drops gradually as blood flows from the major arteries, through the arterioles, the capillaries until blood is pushed up back into the heart via the venules, the veins through the vena cava with the help of the muscles. at any given pressure drop, the flow rate is determined by the resistance to the blood flow. in the arteries, with the absence of diseases, there is very little or no resistance to blood. the vessel diameter is the most principal determinant to control resistance. compared to other smaller vessels in the body, the artery has a much bigger diameter (4 mm), therefore the resistance is low. the arm–leg (blood pressure) gradient is the difference between the blood pressure measured in the arms and that measured in the legs. it is normally less than 10 mm hg, but may be increased in e.g. coarctation of the aorta. clinical significance pressure monitoring an anesthetic machine with integrated systems for monitoring of several hemodynamic parameters, including blood pressure and heart rate hemodynamic monitoring is the observation of hemodynamic parameters over time, such as blood pressure and heart rate. blood pressure can be monitored either invasively through an inserted blood pressure transducer assembly (providing continuous monitoring), or noninvasively by repeatedly measuring the blood pressure with an inflatable blood pressure cuff. hypertension is diagnosed by the presence of arterial blood pressures of 140/90 or greater for two clinical visits. pulmonary artery wedge pressure can show if there is congestive heart failure, mitral and aortic valve disorders, hypervolemia, shunts, or cardiac tamponade. remote, indirect monitoring of blood flow by laser doppler laser doppler imaging reveals retinal blood flow noninvasive hemodynamic monitoring of eye fundus vessels can be performed by laser doppler holography, with near infrared light. the eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. laser doppler imaging by digital holography can measure blood flow in the retina and choroid, whose doppler responses exhibit a pulse-shaped profile with time this technique enables non invasive functional microangiography by high-contrast measurement of doppler responses from endoluminal blood flow profiles in vessels in the posterior segment of the eye. differences in blood pressure drive the flow of blood throughout the circulation. the rate of mean blood flow depends on both blood pressure and the hemodynamic resistance to flow presented by the blood vessels. glossary anhacute normovolemic hemodilution anhunumber of units during anh blhmaximum blood loss possible when anh is used before homologous blood transfusion is needed bliincremental blood loss possible with anh.(blh – bls) blsmaximum blood loss without anh before homologous blood transfusion is required ebvestimated blood volume(70 ml/kg) hcthaematocrit always expressed here as a fraction hiinitial haematocrit hmminimum safe haematocrit prbcpacked red blood cell equivalent saved by anh rcmred cell mass. rcmhcell mass available for transfusion after anh rcmired cell mass saved by anh sblsurgical blood loss etymology and pronunciation the word hemodynamics (/ˌhiːmədaɪˈnæmɪks, -moʊ-/) uses combining forms of hemo- (which comes from the ancient greek haima, meaning blood) and dynamics, thus "the dynamics of blood". the vowel of the hemo- syllable is variously written according to the ae/e variation. blood hammer blood pressure cardiac output cardiovascular system dynamics society electrical cardiometry esophogeal doppler hemodynamics of the aorta impedance cardiography photoplethysmogram laser doppler imaging windkessel effect functional near-infrared spectroscopy notes and references tortora, gerard j.; derrickson, bryan (2012). 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