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34 Cards in this Set
- Front
- Back
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Formula for vascular distensibility:
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Vascular distensibility= Increase in volume/ Increase in pressure x Original volume
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Difference in distensibility of arteries and veins due to stronger arterial walls:
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A given increase in pressure causes 8 times as much increase in blood in veins as in arteries.
There are 6 times more distensibility in systemic arteries then in pulmonary arteries |
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Significants of sympathetic stimulation of vascular tone:
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Increase in vascular tone can re- distribute blood to maintain a almost normal circulation even after a 25 % blood volume loss in hemorrhage
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Delayed compliance (Stress- Relaxation):
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Increased volume first leads to a increase in pressure, but then the smooth mm. gradually stretch and the pressure normalize
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Pulse pressure:
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Difference between systolic and diastolic pressure
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Two factors that affect pulse pressure:
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1. Stroke volume of heart
2. Compliance (total distensibility) of arterial tree |
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Why is there increased pulse pressure in old aged persons:
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Because arteriosclerosis hardens and make the vessel noncompliant
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Formula for pulse pressure:
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Stroke volume/ arterial compliance
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Effect of stroke volume and arterial compliance on pulse pressure:
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Reduced stroke volume narrows pulse pressure while reduced arterial compliance (noncompliance due to arteriosclerosis) widens pulse pressure
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Aortic valve stenosis effect on pressure pulse contours:
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Aortic pressure pulse is decreased because of diminished flow through the stenotic valve.
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Patent ductus arteriosus effect on pressure pulse contours:
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More then half of the blood flow through the aorta flow back to the pulmonary trunk through ductus arteriosus--> reducing diastolic pressure (widened pulse pressure)
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Aortic regurgitation effect on pressure pulse contours:
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Aortic diastolic pressure can fall to zero, widened pulse pressure. No incisura in the aortic pulse contour because there is "no" aortic valve to close
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Velocity of transmission of the pressure pulse:
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Aorta: 3 to 5 m/sec
Large arterial branches: 7-10 m/sec Small arteries: 15 to 35 m/sec |
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Why is there slower transmission of pulse pressure in aorta then small arteries:
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Because transmission is slower in compliant blood vessels such as aorta
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Damping of pressure pulse:
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Diminished pulsations in the periphery due to resistance to blood movement in the vessel and compliance of the vessel.
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Korotkoff sound is cause by:
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Blood jetting through a partly occluded vessel and by vibrations of the vessel wall. The jet causes turbulence in the vessel beyond the cuff, and this sets up the vibrations heard through the stethoscope.
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MAP:
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Diastolic pressure + 1/3 of pulse pressure
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Central venous pressure:
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Pressur in right atrium
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Central venous pressure is regulated by a balance between:
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1. The ability of the heart to pump blood out of the right atrium and ventricle into the lungs.
2. The tendency of blood to flow from the peripheral veins into the right atrium |
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Factors increasing venous return:
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1. Increased blood volume
2. Increased large vessel tone which increases peripheral venous pressure 3. Dilatations of arterioles which decreases peripheral resistance and allows rapid flow of blood from arteries into the veins |
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Normal central venous pressure:
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0 mmHg
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Central venous pressure can increase to 20- 30 mmHg under abnormal conditions:
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1. Serious heart failure
2. Massive transfusions |
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Lowest values of central venous pressure:
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-3 to - 5 mmHg (same as chest cavity)
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Why is the pressure in more peripheral small veins +4 to + 6 mmHg higher then the central venous pressure:
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Because pressure in e.g. abdominal cavity tends to "collapse" veins which then offer the large veins some resistance.
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Can veins of the skull collapse?
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No because they are in a non- collapsable cavity (the skull cavity)
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Venous pressure in saggital sinus:
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- 10 due to sucking force of the hydrostatic pressure because it is at a higher level then the heart
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Venous pressure in feet of a standing man due to hydrostatic pressure of blood:
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+ 90 mmHg
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Effect of muscle- venous pump on peripheral venous pressure:
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Pumps blood towards the heart and reduces the pressure in a walking mans feet to less then + 20 mmHg
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How much of the circulatory blood volume do you loose to interstitial fluid from 15- 30 min standing absolutely still:
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Up to 20 %
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Mechanism of developing varicose veins:
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Excess venous pressure lasting for weeks- months increases cross sectional diameter of veins but valves do not increase in size--> insufficiencies---->increased pressure in veins of feet---> destruction of valves---> Constant edemas in legs
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How high must the central venous pressure be for the veins of the neck to be distended:
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Over + 10 mmHg the lower veins of neck becomes distended
Over + 15 mmHg all the veins of the neck become distended |
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Reference level for pressure measurement:
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Level of the tricuspid valve.
--> a point in the circulatory system at which gravitational pressure factors caused by changes in body position of a healthy person usually do not affect pressure measurements more then 1- 2 mmHg |
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Specific blood reservoirs:
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1. Spleen: Can shrink and release 100 ml blood
2. Liver: The sinuses can release several hundred ml blood 3. Large abdominal veins: Can release 300 ml blood 4. Venous plexus beneath the skin: Can release several hundred ml. 5. Heart: Can shrink during sympathetic activation and release 50- 100 ml 6. Lungs: Can release up to 200 ml blood with low pulmonary pressure values |
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Red pulp of spleen can release:
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50 ml concentrated RBC, increasing hematocrit 2 %
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