Chapter 15: VASCULAR DISTENSIBILITY AND FUBCTIONS OF THE ARTERIAL AND VENOUS SYSTEMS

Question 1

How is vascular distensibility calculated ?

Answer 1

Vascular distensibility = increase in volume/ increase in pressure X original volume.

Question 2

The veins are _____times distensible than the arteries of same caliber at a given increase in pressure.

Answer 2

8 times

Question 3

Pulmonary arteries operate at low pressure than the systemic arteries, therefore, their distensibility is ___ times greater than the systemic arteries.

Answer 3

6 times

Question 4

How to calculate the vascular compliance or capacitance of a vascular bed?

Answer 4

Vascular compliance= increase in volume/ increase in pressure.

Question 5

What is the compliance and distensibility of a systematic vein as compared to an artery of similar caliber?

Answer 5

The compliance is 24 times more than the artery and has 8 times more distensibility and has 3 times greater volume than the artery.

Question 6

The average blood volume of the adult arterial system?

Answer 6

700 mL

Question 7

The mean arterial pressure of an adult?

Answer 7

100 mmHg

Question 8

A ____ mL reduction in arterial volume will bring the arterial blood pressure to zero.

Answer 8

300 mL.

Question 9

The mean venous blood volume of an adult?

Answer 9

2000-3500 mL and a drop in several 100 ML is required to cause 2 to 3 mmHg of venous pressure reduction.

Question 10

What is one of the principal mechanisms of the body to increase cardiac output when needed?

Answer 10

Increasing systemic vascular tone to shift blood into the heart.

Question 11

What is the significance of sympathetic control of vascular capacitance of the veins during hemorrhage?

Answer 11

It will ensure adequate cardiac output, volume, and pressure in the arteries even if there is 25% arterial blood volume lose.

Question 12

Delayed complaince or stress relaxation of blood vessels?

Answer 12

When the vascular volume increase as in blood transfusion. The venous pressure also increases. However, within min, even if the volume is not changed the pressure within the vein decreases as a function of the stretching of venous vascular smooth muscles.

Question 13

What is called pulse pressure?

Answer 13

It is the pressure difference between the SBP and DBP which is normally 40 mmHg.

Question 14

What are the factors that affect pulse pressure?

Answer 14

1) Stroke volume out put of the heart.
2) vascular compliance or distensibility of the arterial tree.
3) The character of systolic ejection from the heart.

Question 15

Pulse pressure is approximately equal to?

Answer 15

The ratio of cardiac output and arterial compliance.

Question 16

What are the conditions that cause abnormal pressure pulse contours ?

Answer 16

Aortic stenosis- the diameter of the aortic valve opening is reduced. Consequently, the aortic pressure pulse is decreased. Which on aortic pressure contours of the volume pressure curve manifested as low amplitude peaks and obliterated incisura.
Patent ductus arteriosus- 50% of the systolic ejection falls through the ductus into the pulmonary circulation, leading to significant drop in diastolic pressure on the volume pressure curve it is manifested as high amplitude pressure contours.
Aortic regurgitation- on contours of the volume pressure curve it is classically presented as the absence of incisura as in aortic regurgitation there is no closing of aortic valve occurs. In addition the contours will look sinusoids due to fall of diastolic blood pressure to zero between heat beats

Question 17

The velocity of pressure pulse transmission in the normal aorta?

Answer 17

3 to 5 m/sec.

Question 18

The velocity of pressure pulse transmission in the large arterial branches?

Answer 18

7 to 10 m/ sec

Question 19

The velocity of pressure pulse transmission in the small arteries?

Answer 19

15 to 35 m/sec

Question 20

The cause of slow transmission of pressure pulse in the aorta as compared to the small vessels?

Answer 20

It is because the Greater the compliance of the vessel the lesser the transmission velocity of pulse pressure.

Question 21

What may cause observable capillary pulsation?

Answer 21

The pathological observable capillary pulsation are seen or felt only when the aortic pulsation are extremely large or the arterioles are greatly dilated

Question 22

What are the causes of damping of the pressure pulse?

Answer 22

1) Resistance to blood movement in the vessel: A small amount of blood flow should occur to distend the next segment of the vessel in muscular arteries with high resistance this process becomes increasingly difficult.
2) compliance of the vessel: the greater the compliance of the vessel, the greater the quantity of blood required to increase the pressure within the vessel

Question 23

How does ageing affect the blood pressure mechanism?

Answer 23

Ageing will cause the blood pressure to increase due to arterial stiffening and atherosclerosis

Question 24

At normal heart rate a greater fraction of the cardiac cycle is spend in ____than _____?

Answer 24

Diastolic than systolic

Question 25

What is the relative contributions of diastolic and systolic pressure to mean arterial pressure?

Answer 25

60% diastolic pressure and 40% systolic pressure

Question 26

What is central venous pressure?

Answer 26

It is the pressure within the right atrium as it is to the right atrium the blood from all parts of the body flows.

Question 27

Regulation of central venous pressure or the right Atrial pressure?

Answer 27

It is regulated by a balance between the ability of right heart to pump blood into the lungs and the tendency of blood to flow from the peripheral veins to right atrium.

Question 28

What are the factors that can increase right Atrial pressure?

Answer 28

1) weakness of the heart.
2) hypervolemia
3) increase in peripheral venous pressure due to increase in large vessel tone.
4) arterioler dilation induced rapid blood flow to the venous system

Question 29

Normal right Atrial pressure?

Answer 29

0 mmHg

Question 30

The pathological maxim rage of increase in right atrial pressure?

Answer 30

20 to 30 mmHg

Question 31

The lower limit of right Atrial pressure?

Answer 31

-3 to -5 mmHg< atmospheric pressure which is the pressure in the chest cavity that surrounds the heart

Question 32

Why is peripheral venous pressure not noticably elevated in early stages of heart failure?

Answer 32

The heart function has to be significantly impaired to incur a 4 to 6 mmHg of increase in right Atrial pressure which is necessary to cause pooling of blood in the veins

Question 33

Normal intra-abdominal pressure?

Answer 33

6 mmHg

Question 34

What are the factors that can significantly increase intra-abdominal pressure ( 15 to 30 mmHg)?

Answer 34

Pregnancy, large tumors, abdominal obesity and ascites.

Question 35

What is hydrostatic pressure or gravitational pressure?

Answer 35

It is the pressure exerted by the weight of the blood on the vasculature. The venous pressure is maximum at the feet ( 90 mmHg), minimum at the brain( -10 mmHg)

Question 36

What is the risk of Opening the sagittal sinus during surgery?

Answer 36

The venous pressure within the sagittal sinus is only -10 mmHg. Therefore, opening the venous sinus can cause the air to be sucked into it and cause air embolism of the heart or lung leading to death.

Question 37

The mean arterial pressure is calculated at what level of the Arterial system?

Answer 37

It is calculated at the level of the heart. At the level of the feet it can be as high as 190 mmHg. The mean arterial pressure is a product of the gravitational factor too.

Question 38

What is the role of muscle pump or venous pump in venous pressure regulation?

Answer 38

The one way valves of the veins in conjunction with the contraction of the skeletal muscles pumps venous blood towards the heart. Therefore, during normal walking the venous blood pressure is down regulated from 90 mmHg to 20 mmHg

Question 39

What is the time required for the venous pressure at the feet to return to 90 mmHg when a person stands still?

Answer 39

30 seconds.

Question 40

A 15 to 30 min of standing still can cause 10 to 20% of reduction in Arterial blood volume. Why?

Answer 40

Increase in the hydrostatic pressure within the capillaries will increase Jv leading to the phenomenon of falling soldier who is in attention position for a long time

Question 41

What will be the atrial pressure when neck veins start to protrude and or become pulsatile?

Answer 41

It is when the right atrial pressure becomes 10 mmHg the lower neck veins protrude and when it reach close to 15 mmHg the all the veins will bulge

Question 42

What is the reference level of pressure measurement in the body and it’s approximate location?

Answer 42

It is a point in the circulatory system to which all pressure measurements are referred to be it arterial or venous. The anatomical location is at the level of tricuspid valve

Question 43

What is the mechanism behind keeping the tricuspid valve as the reference point for vascular pressure measurement?

Answer 43

The heart spontaneously prevents gravitational pressure changes at the level of the tricuspid valve by increasing the right ventricular systolic volume, if the pressure at the level of the tricuspid valve increases, thereby regulating the pressure closer to 0 mmHg. Conversely, if the pressure at the level of the tricuspid valve decreases the right ventricular diastolic volume will be reduced there by regulating the BP closer to 0 mmHg.

Question 44

What are the specific blood reservoirs ?

Answer 44

1) the spleen which can release as much as 100 ml of blood into the circulation by decreasing it’s size.
2) the liver: hepatic sinusoids can release several 100 MLs of blood when required.
3) the large abdominal veins which can release 300 mL when required.
4) Venus plexus beneath the skin: which can release several 100 mL
5) the heart and lungs: 100 and 100 to 200 ML

Question 45

What are the blood storage areas of the spleen?

Answer 45

The venous sinuses and the pulp

Question 46

The splenic capillary filtration physiology at the pulp ?

Answer 46

The steverman’s reflection co-efficient of the splenic capillary are very low. Therefore, the RBC’s ooze out into the trabecular mesh of the pulp, where they are stored. The plasma fluid then filtered from the trabeculum to the venous blood.

Question 47

Role of spleen in modulating hematocrit concentration?

Answer 47

When the splenic and splenic vascular constriction occurs due to sympathetic stimulation. The spleen release approximately 50 ml of concentrated red blood cells into the systemic circulation, raising the hematocrit concentration by 1 to 2%.

Question 48

What is the function of the splenic white pulp?

Answer 48

Its function is to produce lymphoid cells just like the ones manufactured by the lymph nodes.

Question 49

Blood cleaning function of the spleen?

Answer 49

The splenic pulp thoroughly sequences the blood before it goes to the sinuses. The old and fragile RBC’S are destroyed and the hemoglobin and the stroma of the RBC’S are digested by the reticuloendothelial cells of the spleen.

Question 50

What is the function of the reticuloendothelial cells of the spleen and liver?

Answer 50

They are integral parts of the blood cleansing and phagocytic system. When there is blood infection, these reticuloendothelial cells actively remove bacteria, parasites, debris. In many chronic infections splenomegaly occurs, just like lymphadenopathy as it works more intensily to remove the pathogens.