Blood pressure (L18)

Question 1

Laminar vs Turbulent flow

Answer 1

Laminar flow should be silent, when liquid is flowing in one direction.

Turbulent flow is not silent and layers are not moving in a homogenous direction, meaning there is a lot of mixing of layers. The way you would switch from laminar to turbulent flow is based on reynold’s number.

Question 2

What is reynold’s number?

Answer 2

A dimensionless number which will indicate the propensity of a liquid to switch to turbulent flow. Greater density, diameter, and velocity of liquid will tend to make to more likely to be turbulent,

however he more viscous a liquid is the less likely it will be to become turbulent.

Question 3

What are Korotkoff sounds?

Answer 3

The sound of mixing blood in turbulent flow

Question 4

What is the sound of mixing blood in turbulent flow?

Answer 4

Korotkoff sounds

Question 5

What is an example of a pathological situation you may hear turbulent flow in this way, and why?

Answer 5

Anemia.

This is because you have reduced hematocrit. Hematocrit is directly proportional to viscosity so by decreasing hematocrit you have decreased viscosity. This means that as you become anemic your reynold’s number is increasing making it more likely for turbulent flow to exist in a given vessel.

Question 6

What would the effect of anemia be on cardiac output?

Answer 6

Cardiac output would be positively affected by anemia because of a decreased resistance

Question 7

How does a blood pressure cuff work?

Answer 7

By measuring Korotkoff sounds.

Basically, you squeeze down the vessel by increasing pressure until it overcomes it. Then you slowly release the pressure. When you start hearing noise, this is turbulent flow (remember, the diameter of the vessel is small now but the pressure and velocity is extremely high). So you begin counting here. The laminar flow will continue until the diastolic pressure has also been passed because at this point the transmural pressure is not great enough to beat against the vessel. This is where you stop counting.

This happens because you have decreased diameter, but not velocity. Velocity is related to cross-sectional area, so the relative contribution of velocity has increased a lot (CSA would be calculated by pi*r^2). So you’re still doubling reynold’s number and propensity for turbulence.

Question 8

What subsystem of the circulation tube set contains the largest CSA space?

Answer 8

Capillaries

Question 9

What subsystem of the circulation tube set contains the most amount of blood

Answer 9

Veins (~64%) - remember these are capacitance vessels that act as partly filled sacks.

Question 10

Why is the relative volume in capillaries so small compared to veins when the cross-sectional area is huge?

Answer 10

This is because the capillaries are short and you want blood to be moving slowly and deliberately through it.

Question 11

Mean Arterial Pressure

Answer 11

Can be used to describe the overall pressure of the system, specifically looking at the aorta, and can be approximately calculated by 1/3 systolic pressure, 2/3 diastolic pressure.

Question 12

Pressure changes during the cardiac cycle: Where does the greatest pressure drop happen?

Answer 12

Due to the precapillary sphincters and the thick arterioles, this happens in the muscular arteries and arterioles.

Question 13

pressure in larger arteries is higher than that of aorta. Why is this?

Answer 13

The aorta is extremely compliant, more so than the subsequent arteries. This means i will have a comparatively lower higher systolic pressure (not stretchy) and a lower diastolic pressure (not storing energy, not bouncing back, not producing pressure in diastole), leading to a larger pulse pressure in these vessels.

Question 14

What two physiological parameters determine arterial pressure

Answer 14

Cardiac output and total peripheral resistance of the vascular system

Question 15

How does cardiac output influence arterial pressure?

Answer 15

If you increase the blood volume you eject you’re putting more pressure on the aorta.

Question 16

How does resistance of peripheral vascular system affect arterial pressure?

Answer 16

Total peripheral resistance is the summation of all resistance downstream of aorta and large arteries. Also, during diastole, the blood is flowing toward the periphery. So if you’re altering the resistance of the peripheral vascular system, you’re affecting diastolic BP.

Question 17

What two physical factors affect arterial pressure?

Answer 17

changes of arterial blood volume (can overstretch aorta)
Arterial compliance (compliance of a vessel affects systolic and diastolic bp)

Question 18

4 things that can alter the physiological and physical aspects of arterial pressure

Answer 18

Baroreceptor (affects both CO and peripheral resistance)
Metabolic activity (local changes can override CNS)
Exercise, systolic pressure increases and diastolic pressure drops or remains the same, widens pulse pressure and MAP goes up
Disease (CHF, for instance)

Question 19

SNS stimulation of heart and how it affects heart rate

Answer 19

SNS stimulation on the heart increases heart rate, which will increase cardiac output, which increases blood pressure

SNS stimulation of the heart also increases the contraction strength, which increases stroke volume (which is essentially an increase in volume being ejected), so this thus increases blood pressure

Question 20

SNS stimulation of veins and how it affects blood pressure and how it affects BP

Answer 20

SNS will stimulate veins to venoconstrict (squeeze blood like toothpaste) which will lead to increased venous return which leads to increased preload which increases stroke volume and leads to an increase in blood pressure

Question 21

SNS stimulation of arteries and arterioles and how it affects BP

Answer 21

Sns stimulation of arteries and arterioles leads to vasoconstriction of these vessels, subsequent increase in peripheral resistance will then lead to an increase in blood pressure

Question 22

PSNS activity on heart and how it affects BP

Answer 22

Decrease in heart rate leading to a decrease in cardiac output which means you have a decrease in overall blood pressure (less blood getting into aorta)

Question 23

What are the two things that primarily affect total peripheral resistance

Answer 23

Radius of the vessel (primary contributor)

Viscosity

Question 24

What are some ways the radius of a vessel can change?

Answer 24

Vasoconstriction and vasodilation from things like RAAS and NO