Unit 2 Lecture 7: Mean Arterial Pressure

Question 1

Using the cardiac output formula and rearranging it, what would the formula for MAP (mean arterial pressure) be?

Answer 1

MAP = CO x TPR

MAP is the pressure that the arteries feel & increasing CO increases blood flow which increases the pressure the arteries feel and increasing TPR increases resistance which therefore increases pressure too

Question 2

How is MAP important?

Answer 2

• # 1 Homeostatically regulated variable in the body
• Provides “driving force” to move blood through the circulation
• Contributes to the heart’s workload

Question 3

What is Low Blood Pressure characterized as? (numerically)

Answer 3

90/60 (Systolic/Diastolic)

• Impaired delivery of blood flow

Question 4

Symptoms of LBP?

Answer 4

Dizziness, fainting, fading vision, faitgue, nausea, trouble concentrating

Question 5

Causes of LBP?

Answer 5

Dehydration, pregnancy, heart failure, endocrine disorders, blood loss, anaemia

• Dehydration causes a decrease in CO (cardiac output) meaning not enough liquid moving
• Anaemia means not enough RBC so blood flow is obviously decreased

Question 6

Risk factors for LBP?

Answer 6

Age, certain medications, certain diseases (Parkinson’s, heart diseases, diabetes)

Parkinson’s can specifically cause problems to the autonomic system

Question 7

What are the different stages of high BP?

Answer 7

Stage 1: SBP/DBP = 130-139/80-89
Stage 2: ≥140/≥90
Hypertensive Crisis: >180/>120

Question 8

Symptoms of HBP?

Answer 8

Blindness, pregnancy complications, heart attack, heart failure, sexual dysfunction, pulmonary edema, sudden loss of kidney

Question 9

Symptoms of HBP are consequences of?

Answer 9

Increased blood flow

• Most of the times with symptoms start with LBP then as they progress it leads into HBP stages
• i.e., Heart failure early stage is LBP and then later critical stages BP is high

Question 10

Consequences of High BP is?

Answer 10

Damage to blood vessels

Blindness caused by blood vessels breaking in the retina
Sexual dysfunction cause by the blood vessels breaking not allowing for blood to flow to the tissue to cause vasodilation

Question 11

Causes of HBP?

Answer 11

Atherosclerosis, congenital heart defects, kidney disease, obstructive sleep apnea, thyroid problems

Question 12

Risk factors of HBP?

Answer 12

Age, ethnicity, genetics, physical inactivity, obesity, tobacco use/vaping, high sodium intake, low potassium levels, excessive alcohol consumption, stress, pregnancy

Question 13

Arteries are conduit vessels. What are the functions of conduit arteries?

Answer 13

Conduit arteries must take blood from the heart and distribute it to various tissues/organs without blood flow being impeded

Question 14

How can we make conduit arteries maintain flow?

Answer 14

1. Minimize the resistance to flow - Large Diameter, Low Contractility [Smooth muscle - active process], High distensibility (compliance)[elasticity - passive process]
2. Artery walls must be strong to withstand high systolic pressure

Question 15

Why is smooth muscle low contractility while the elastic fibres are high distensibility?

Answer 15

• If the smooth muscle had high contractility, that can put the blood vessel at risk of creating too much pressure and damaging it
• Elastic fibres because they are stretchable won’t easily damage which is why they are highly distensable

• Smooth muscle is active process because we can somewhat control it with SNS and PNS
• Passive process of elasticity due to the fact that we can’t control the elasticity; either high elasticity or low due to overuse

Question 16

The aorta is elastic in nature, how is that important when it comes to systolic BP and diastolic BP?

Answer 16

• In systole when blood moves through aorta, it can easily distend to minimize resistance to flow (Passively distends)
• In diastole, the same elastic-walled aorta passively recoils to maintain blood flow (not increase nor decrease BP)

Question 17

Major benefits of Compliance in the Aorta?

Answer 17

1. Low Systolic BP
2. Converts intermittent flow to continuous flow (Windkessel Effect)

Right picture: high compliance leads to continuous flow as the aorta distends

Question 18

Define the Windkessel Effect

Answer 18

Dampen the fluctuation in blood pressure (pulse pressure) over a cardiac cycle to maintain continuous blood flow when ventricular ejection ends (i.e. diastole)

Blood pressure is not too high or too low with the windkessel effect

Question 19

What gives the aorta its compliance?

Answer 19

Elastin = an extracellular matrix protein that surrounds the tissues/organs and gives them the ability to stretch

• The protein is coiled but in order to stretch it has to uncoil
• Outside the lumen of the aorta you can see multiple layers of elastin which uncoil upon stretching

Aorta is highly compliant (high pressure for a given volume)

Question 20

What is pulse pressure?

Answer 20

The difference in blood pressure
PP = SP-DP

Question 21

What is the MAP formula that is related to PP?

Answer 21

MAP = DP + 1/3(SP-DP)

• We use 1/3 of PP (SP-DP) because it is more accurate and looking at where the aortic valve closes (dicrotic notch) it is roughly around the time of 1/3 of systolic pressure

Question 22

PP is determined by (Modified)?

Answer 22

1. Stroke Volume (↑SV ⇒ ↑SBP ⇒ ↑PP)
2. Speed of ejection into the aorta (↑speed ⇒ ↑SBP ⇒ ↑PP)
3. Aortic compliance (↑ compliance ⇒ ↓SBP ⇒ ↓PP)

Increased aortic compliance causes the aorta to distend more but that makes SBP decrease and therefore PP decrease b/c difference of SP and DP is smaller

Question 23

How can we increase the speed of ejection into the aorta?

Answer 23

• Increasing HR which will cause the heart to pump more blood out quicker
• Increasing SV also increases speed of ejection

Question 24

Explain the effect of aging on pulse pressure

Answer 24

Diastolic pressure barely increases but we have a significant increase in systolic pressure because the aortic compliance decreases which leads to low compliant aorta and high systolic BP

Question 25

Why do we need an increase in SBP during exercise?

Answer 25

Need to deliver more blood to the muscles

Question 26

Explain the mechanism behind increase in SBP as weight lifted increases

Answer 26

Exercise pressor reflex: ↑SNS + ↓PNS ⇒ ↑SV + ↑Vasoconstriction ⇒ ↑SBP + ↑TPR

Metaboreceptors sense increases in Lactic acid which is built up from exercising and this activates the SNS but decreases the PNS which causes vasoconstriction and SV to increase and that allows for SBP to increase along with TPR