The document discusses vascular distensibility and compliance. It defines distensibility as the fractional increase in volume per mmHg pressure rise. Compliance refers to the total blood volume change per pressure rise. Veins are the most distensible vessels and provide a reservoir function. The pulmonary arteries have greater distensibility than systemic arteries due to lower operating pressures. Sympathetic stimulation increases vessel pressure at each volume, while inhibition decreases it. Pulse pressure is affected by stroke volume and arterial compliance. It rises with reduced compliance as in arteriosclerosis.

1. Vascular Distensibility A valuable characteristic of the vascular system is that all blood vessels are distensible The most distensible of all the vessels are the veins The veins provide a reservoir functionfor storing large quantities of extra blood

2. Units of Vascular Distensibility Vascular distensibility normally is expressed as the fractional increase in volume for each millimeter of mercury rise in pressure, in accordance with the following formula: Vascular distensibility = Increase in Volume/Increase in pressure X original volumeThat is, if 1 mm Hg causes a vessel that originally contained 10 millimeters of blood to increase its volume by 1 milliliter, the distensibility would be 0.1 per mm Hg

3. In the pulmonary circulation, the pulmonary vein distensibilities are similar to those of the systemic circulation The pulmonary arteries normally operate under pressures about one sixth of those in the systemic arterial system, and their distensibilities are correspondingly greater, about six times the distensibility of systemic arteries

4. Vascular Compliance (or Vascular Capacitance) To know the total quantity of blood that can be stored in a given portion of the circulation for each millimeter of mercury pressure rise. This value is called the compliance or capacitance of the respective vascular bed Vascular compliance = increase in volume/increase in pressure

5. compliance is equal to distensibility times volume The compliance of a systemic vein is about 24 times that of its corresponding artery because it is about 8 times as distensible and it has a volume about 3 times as great (8 × 3 = 24).

6. Volume-pressure Relationships in Circulation Any given change in volume within the arterial results in larger increases in pressure than in veins When veins are constricted, large quantities of blood are transferred to the heart, thereby increasing cardiac output

7. when the arterial system is filled with about 700 milliliters of blood, the mean arterial pressure is 100 mm Hg, but when it is filled with only 400 milliliters of blood, the pressure falls to zero Volume-pressure curves

8. In the entire systemic venous system, the volume normally ranges from 2000 to 3500 milliliters, and a change of several hundred millimeters in this volume is required to change the venous pressure only 3 to 5 mm Hg Volume-pressure curves

9. Increase in sympathetic stimulation increases the pressure at each volume of the arteries or veins, whereas sympathetic inhibition decreases the pressure at each volume Effect of Sympathetic Stimulation or Sympathetic Inhibition on the Volume-Pressure Relations of the Arterial and Venous Systems

10. In the healthy young adult, the pressure at the top of each pulse, called the systolic pressure, is about 120 mm Hg. At the lowest point of each pulse, called the diastolic pressure, it is about 80 mm Hg. The difference between these two pressures, about 40 mm Hg, is called the pulse pressure Arterial Pressure Pulsations

11. Factors Affecting Pulse Pressure Stroke volume output of the heart—increases in stroke volume increase pulse pressure, conversely decreases in stroke volume decrease pulse pressure. Arterial compliance (total distensibility)—decreases in compliance increases pulse pressure; increases in compliance decrease pulse pressure Any condition of the circulation that affects either of these two factors also affects the pulse pressure

12. Age related changes in arterial pressure Progressive increase in arterial pressure due to: Age related changes in kidneys Hardening of arteries due to atherosclerosis The mean arterial pressure is determined about 60 per cent by the diastolic pressure and 40 per cent by the systolic pressure

13. Arterial Pressure pulsation Stroke volume Cardiac output Systolic Pressure } Pulse Pressure Mean Pressure Diastolic Pressure Arterial compliance Peripheral resistance Pressure Time

14. In arteriosclerosisthe pulse pressure rises , because the arteries have become hardened with and therefore are relatively noncompliant In aortic stenosis, the diameter of the aortic valve opening is reduced significantly, and the aortic pressure pulse is decreased significantly In patent ductus arteriosus, one half or more of the blood pumped into the aorta by the left ventricle flows immediately backward through the wide-open ductus into the pulmonary artery and lung blood vessels, thus allowing the diastolic pressure to fall very low before the next heartbeat In aortic regurgitation, the aortic valve is absent or will not close completely. Therefore, after each heartbeat, the blood that has just been pumped into the aorta flows immediately backward into the left ventricle. Significant fall of diastolic pressure and no incisura Abnormal Pressure Pulse Contours

15. Damping of the Pressure Pulses in the Smaller Arteries, Arterioles, and Capillaries The progressive diminution of the pulsations in the periphery is called damping of the pressure pulses The intensity of pulsations becomes progressively less in the smaller arteries The degree of damping is proportional to the resistance of small vessels and arterioles and the compliance of the larger vessels