به نام خدا Blood Circulation 2 Dr. Radmanesh

Distensibility distensibility Vascular distensibility: Increase in volume/Increase in pressure* Original volume distensibility is related to a vessel’s ability to distend with increase in pressure

Difference in distensibility of the arteries and the veins. the walls of the arteries are far stronger than those of the veins. the arteries, on average, are about eight times less distensible than the veins.

In the pulmonary circulation the pulmonary arteries under pressures about one sixth of those in the systemic arterial their distensibilities are about six times the distensibility of systemic arteries

Compliance Definition of vascular compliance (capacitance) Compliance VC = increase in volume / increase in pressure Or VC = VD X original volume Compliance and distensibility are quite different Compliance is related to the total amount of blood that can be stored in a vessel with increasing pressure

Compliance and distensibility are quite different Veins are 8 times more distensible, it has a volume about 3 times as great Veins 24 times more compliant than arteries (8*3 = 24)

Volume - Pressure Curves Downloaded from: StudentConsult (on 14 June 2006 12:20 PM) © 2005 Elsevier

(stress-relaxation) of vessels Delayed compliance (stress-relaxation) of vessels Effect on the intravascular pressure of injecting a volume of blood into a venous segment and later removing the excess blood, demonstrating the principle of delayed compliance. Downloaded from: StudentConsult (on 14 June 2006 12:20 PM) © 2005 Elsevier

Pressure Pulse Systolic pressure – diastolic pressure PP is proportional to stroke volume / AC AC: compliance of the arterial tree .

Abnormal Pressure Pulse Contours Downloaded from: StudentConsult (on 14 June 2006 12:20 PM) © 2005 Elsevier

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Veins and their Functions

Right Atrial Pressure (Central Venous Pressure) (-3 to-5, 20-30mmHg) regulated by a balance between (1) the tendency for blood to flow from the peripheral veins into the right atrium. (2) the ability of the heart to pump blood out of the right atrium and ventricle into the lungs

Factors that increase venous return Increased blood volume Increased large venous tone Dilation of arterioles (decrease resistance)

Venous Resistance the veins from the arms are compressed by their sharp angulations over the first rib. the pressure in the neck veins veins coursing through the abdomen

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Peripheral venous pressure Effect of Intra-abdominal pressure When increased, it increases venous pressure in the legs Intra-abdominal pressure may increase: Due to pregnancy Abdominal tumors Ascites (excessive fluid in the peritoneal cavity)

Effect of gravitational pressure Venous pressure above the heart is less than 0 mm Hg Venous pressure below the heart is greater than 0 mm Hg the pressure in the veins of the feet is about +90 mm Hg

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Veins and their Functions Valves ensure one-way movement of blood Muscle pump Thoracic pump

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Downloaded from: StudentConsult (on 14 June 2006 12:20 PM) © 2005 Elsevier