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Physiology II
Cardiovascular Physiology

ARTERIAL AND VENOUS SYSTEMS

key words:

hydraulic filter:  Pressure from large elastic artery vessels.

compliance (dV/dP):  The total quantity of blood that can be stored in a given portion of the circulation for each millimeter of mercury pressure rise. Compliance is equal to distensibility times volume.  Compliance of a 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 X 3 = 24)   Guyton pg. 171-172

elasticity (distensibility ?):  arterial vessels ability to accommodate the pulsatile output of the heart and to average out the pressure pulsations.  This provides an almost completely smooth, continuous flow of blood through the very small blood vessels of the tissues.

mean arterial pressure:  The average of all the pressures measured millisecond by millisecond over a period of time.  It is about 60% diastolic and 40% systolic.  

systolic pressure:  The peak pressure in the arteries during systole.

diastolic pressure:    The lowest pressure in the arteries during diastole.

pulse pressure:  The difference between the systolic pressure and diastolic pressure.  (SBP - DBP)

hypertension:  The mean arterial pressure is greater than the upper range of accepted normality.  A mean arterial pressure greater than 110 mm Hg (normal is about 90 mm Hg) under resting conditions usually is considered to be hypertensive .. this level occurs when the diastolic blood pressure is greater than 90 mm Hg and the systolic pressure greater tahn about 135 to 140 mm Hg.  Guyton pg. 225

direct arterial pressure measurement:  Insertion of  a catheter into an artery and recording the pressures.

indirect arterial pressure measurement:  Using a cuff around a peripheral limb to attain the arterial pressures.

palpatory method:  Use a cuff around a limb (upper arms are most common), fill with air to create enough pressure to stop the flow of blood past the cuff.  Slowly let out the pressure and feel for an arterial pulse (radial artery works great).  When you first feel a pulse, take note of the pressure and it is used as the Systolic Blood Pressure.  You cannot get a diastolic pressure by this method.

auscultatory method:  Use a cuff around a limb (upper arms are most common), fill with air to create enough pressure to stop the flow of blood past the cuff.  Slowly let out the pressure and listen for a "tapping" sound with a stethoscope on the antecubital area.  Once you hear a tapping sound take note of the pressure and it is used as the Systolic Blood Pressure.  Keep listening and when the tapping sounds disappear, take note of that pressure.  It is considered the diastolic pressure.

sphygmomanometer:  A pressure gage used most frequently with BP cuffs.

Korotkoff sounds:  Sounds heard when listening for the BP using the auscultatory method.  It is debated exactly what these sounds are but they are most likely the sound of blood jetting through partly closed vessels.

right atrial (central venous) pressure:  The pressure in the veins at the right atrium.  Measurement is taken by inserting a catheter into or just before the right atrium.

hydrostatic pressure:  The pressure that results from the weight of water in the body.

venous return:  The flow of blood from the capillaries back to the heart.

venous valves:  Valves in the veins that prevent the blood from flowing back down with gravity.  If it were not for the valves, the the venous pressure in the feet would always be about +90 mm Hg...because of the valves, the pressure in a normal adult is about 25 mm Hg.  Guyton pg. 178

capacitance vessels:  See compliance above.  More than 60 % of the total amount of blood is found in the veins at any one time.

reservoir function:  Because more than 60% of the body's blood is found in the veins at any one time, the veins are considered the body's blood reservoir.

venous pooling:  The compliance of the veins increases so that a larger than normal amount of blood is within the venous system.

varicose veins:  (from class)  The pressure within the veins may be so great that the pressure of the blood can destroy the valves.  The valves are usually destroyed from top to bottom.  When a valve is destroyed, the pressure is then put on the next available valve down the system.  These veins with destroyed valves can bulge.

learning objectives:

describe using words and/or diagrams how large elastic arteries act as an hydraulic filter to convert a discontinuous ventricular output into a continuous microcirculatory flow:  When the pressure in the arterioles is increased, this dilates the arterioles and therefore decreases their resistance.  The result is increased blood flow not only because of increased pressure but also because of decreased resistance, usually giving at least twice as much flow increase as one might expect.  The distensible nature of the arteries allows them to accommodate the pulsatile output of the heart and to average out the pressure pulsations.  This provides an almost completely smooth, continuous flow of blood through the very small blood vessels of the tissues.

describe, in words and using a simple mathematical expression, the relationships among transmural pressure, blood vessel wall tension, vessel wall thickness and vessel radius (the law of LaPlace):  Law of LaPlace is Tension = Pressure X Radius  t=Pr.  

describe the structural bases for active and passive blood vessel wall tension:  

identify the following on a tracing of arterial pressures fluctuations in a healthy adult human subject: Use the diagram below.
    systolic pressure:
  The highest point on the dotted curve, about C/D line
    pulse pressure: 
The difference between the highest point on the dotted line and the lowest point on the dotted line.
    diastolic pressure:
  The lowest point on the dotted line
    mean arterial pressure: 
60% of the diastolic pressure plus 40% of the systolic pressure.
    incisura or dicrotic notch:  
It appears about on the D/E line.

compare and contrast the physiological determinants of mean systemic arterial pressure and arterial pulse pressure:  See definitions above.

describe the structure and function of the small muscular arterioles and indicate an understanding of the importance of this portion of the arterial system in the overall regulation of mean systemic arterial pressure and tissue blood flow distribution

describe the basic physiological principles underlying the indirect measurement of arterial pressure with a sphygmomanometer:  Already covered...see keywords above.

 compare and contrast the compliance of the large elastic arteries and the large veins:  See above and below

   Large Elastic Arteries Small Muscular Arterioles Large Veins
Components of wall:  Elastic tissue ++++ + ++
Components of wall:  VSM + ++++ ++
Diameter of segment Large Small Large
Effect of VSM contraction in segment small decrease radius.
small decrease resistance
small decrease compliance
large decrease radius
small decrease compliance
small decrease radius
Large decrease compliance
Net effect of VSM contraction Increase resistance = Increased Pressure decreased compliance = increased pressure

list at least four factors that aid in returning venous blood to the heart

distinguish clearly between the terms arterial diastolic pressure and diastolic filling pressure:  Arterial diastolic pressure is the lowest pressure in the arteries.  Diastolic filling pressure is the pressure in the veins that flows blood into the right atrium.

 


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