Systemic Arterial Function PDF

Systemic Arterial Function COSTANZO :7TH edition : Pg 130-134 Guyton : 14th edition Pg 182-184 Introduction to Dr. Shahenaz Satti [email protected] cardiovascular physiology ...

Systemic Arterial Function COSTANZO :7TH edition : Pg 130-134 Guyton : 14th edition Pg 182-184 Introduction to Dr. Shahenaz Satti [email protected] cardiovascular physiology  LEARNER'S OBJECTIVES 1. Define vascular distensibility and vascular compliance 2. Differentiate vascular distensibility of arteries and veins 3. Elaborate factors effecting vascular compliance 4. Describe the role of large artery distension and recoil on arterial function 5. Define systolic, diastolic and mean arterial pressure and pulse pressure. 6. Understand the significance of stroke volume and arterial compliance and their influence on pulse pressure 7. Describe the cyclical pressure changes in the aorta and in other arteries 8. Describe the aortic pulse pressure wave and its transmission along the arterial tree  Arterial Pressure Blood pressure means the force exerted by the blood against any unit area of the vessel wall. Blood pressure is measured in millimeters of mercury (mmHg) some times we use (cm H2O) Mercury manometer has been used as the standard reference for measuring pressure since its invention in 1846 by Poiseuille.  Capacitance (compliance) Compliance describes how the volume of blood contained in a vessel changes for a given change in pressure (ΔV/ΔP). is inversely related to elastance, or stiffness. The greater the amount of elastic tissue there is in a blood vessel the higher the elastance is ,the lower the compliance.  Compliance of the arteries is much lower than that of the veins; the arteries hold much less blood than the veins, and they do so at high pressure. The veins are most compliant and contain the unstressed volume (large volume under low pressure). The arteries are much less compliant and contain the stressed volume (low volume under high pressure).  Vascular Distensibility All the blood vessels are distensible. The distensible nature of the arteries allows them to accommodate the pulsatile output of the heart and to average out the pressure pulsations. The most distensible by far of all the vessels are the veins. Even slight increases in venous pressure cause the veins to store 0.5 to 1.0 liter of extra blood.  If 1 mm Hg causes a vessel that originally contained 10 ml of blood to increase its volume by 1 ml, the distensibility would be 0.1 per mm Hg, or 10% per mm Hg. The fractional increase in volume for each mmHg rise in pressure  Veins are 8 times more distensible than arteries 0 mmHg 100 mmHg Artery 100 ml Vein 800 ml  What is the difference between Distensibility and Compliance?  A highly distensible vessel that has a small volume may have far less compliance than a much less distensible vessel that has a large volume b/c compliance is equal to distensibility times volume.  The compliance of veins is 24 times that of arteries b/c it is about 8 times as distensible and has a volume about 3 times as great (8 X 3 = 24).  Distension and Recoil of Elastic Arteries  Distension - Results in energy transfer from blood to arterial wall  Prevents very steep pressure rise during ejection  Recoil (energy transfer reversed)  Prevents steep fall in pressure during diastole  Volume-pressure Relationships in Circulation  Any given change in volume within the arterial tree results in larger increases in pressure than in veins.  A given volume causes greater pressure when compliance of the vessel is low.  When veins are constricted, large quantities of blood are transferred to the heart, thereby increasing cardiac output.  Inflow into the Arteries  Inflow (Stroke output/Cardiac output)  Depends on pump efficiency  Contractile efficiency (Ejection Fraction)  Heart rate  Stroke output mainly influences peak systolic pressure  Outflow from the Arteries Outflow (through resistance vessels)Continuous, in both systole & diastole Depends on arteriolar resistance  Mainly influences diastolic pressure  Pressures in the Cardiovascular System  Blood pressures are not equal throughout the cardiovascular system. If they were equal, blood would not flow, since flow requires a driving force (i.e., a pressure difference).  The pressure differences that exist between the heart and blood vessels are the driving force for blood flow.  The pressure remains high in the large arteries, which branch off the aorta, because of the high elastic recoil of the arterial walls.  Thus little energy is lost as blood flows from the aorta through the arterial tree.  Arterial Pressures  Systolic pressure Defined  Maximum arterial pressure during systole  Diastolic pressure  Minimum arterial pressure during diastolic  Mean Arterial Pressure  Average pressure in a complete cardiac cycle  Diastolic pressure + 1/3 of pulse pressure  Main Determinants of Arterial Systolic Pressure  Stroke Volume  Increases with increase in force of contraction  Arterial Distension  Behaves like a shock absorber during ejection  Blood Volume and its distribution  Determines basic ‘fullness’ of arteries  Main Determinants of Arterial Diastolic Pressure  No inflow in this phase  Total Peripheral Resistance  Outflow determines diastolic drop in pressure  Arterial Recoil  Reinforces pressure during diastole  Blood Volume and its distribution  Determines basic ‘fullness’ of arteries  Arterial Pulse  The alternate expansion and recoil of elastic arteries after each systole of the left ventricle creating a traveling pressure wave that is called the pulse.  Aorta expands to accommodate the ejected blood volume, when it expands it has got elastic recoil, so it shortens back.  This causes pressure wave which leads to expansion of arterial wall which can be palpated as arterial pulse.  Pulse Pressure  Pulse Pressure is the difference between systolic & diastolic pressure.  If all other factors are equal, the magnitude of the pulse pressure reflects the volume of blood ejected from the left ventricle on a single beat, or the stroke volume.  Depends upon  Stroke volume  Arterial stiffness, which depends on  Aortic smooth muscle tone, Mean blood pressure and rate of ventricular ejection Blood Pressure Profile in the Circulatory System