32 Integrated cardiovascular physiology

Question 1

What will happen to the MAP if a person stands up from a supine position?
What compensation mechanisms can be seen? (x2)

Answer 1

MAP will decrease as there is an increase pooling to peripheral veins, thus decrease venous return and CO

Compensation:
baroreceptors sense decrease in pressure, thus increases MAP by increasing CO

Cardiopulmonary reflex and sympathetic stimulation of RAAS - increases blood volume via increasing Na+ and water retention

Question 2

Which of the following regarding blood flow during dynamic exercise is correct?

A. Skeletal muscles have the greatest increase in blood flow

B. There is an increase in blood flow in the heart

C. There is a decrease in blood flow to the brain

D. There is a decrease in cutaneous blood flow

Answer 2

A and B only

C: increases marginally due to increased MAP

D: should be increase, thermoregulatory

Question 3

During exercise, cardiac output increases. Stroke volume or heart rate contributes more to the increased output?

Answer 3

Heart rate

stroke volume increase is limited when
heart rate is very high, shortening diastolic time and
thus filling

Question 4

What is the effect to TPR during dynamic exercises?

Answer 4

There will be increased CO2, H+, K+ and adenosine production, which causes active hyperemia. Vasodilation occurs, thus lowering TPR.

Question 5

Normally baroreceptors should have regulated the blood pressure (decrease MAP) during dynamic exercise. What does this not happen?

Answer 5

The normal MAP set point increased in cardiovascular centers.

Anticipation of exercise triggers central command.

Mechanoreceptors and chemoreceptors in exercising muscles also stimulate the medullary cardiovascular centres and alter pressure setpoint

> > to ensure sufficient perfusion to organs

Question 6

As the set point of baroreceptors are raised in dynamic exercise, why would not the MAP increase dramatically?

Answer 6

MAP = CO x TPR

CO is sustained,
but TPR will decrease due to vasodilation!

Question 7

What are the central command responses in dynamic exercise? (what nerve is stimulated?)

Answer 7

Stimulation of sympathetic activity.

• increased contractility
• increased CO
• venoconstriction > increases venous return
• arteriolar vasoconstriction at renal, splanchnic circulation
• cutaneous vessels respond
• inhibition of parasympathetic activity

#note: arteriolar vasoconstriction is not present at exercising muscles
and heart, these vessels dilated by active hyperaemia

Question 8

What are the 2 ways that hypothalamus respond to induced temperature increase?

Answer 8

1. decrease sympathetic activity to cutaneous blood vessels > vasodilation
2. increasing sweat production (mediated by Ach-releasing sympathetic fibers)

#increased sympathetic activity
also constricts cutaneous vessels initially, but this is subsequently overridden by heat-induced reflex responses

Question 9

What does it mean by static exercise?

Answer 9

isometric muscle contraction, such as weightlifting

Question 10

What cardiovascular response will static exercise induce?

Answer 10

Increase in central command, mechanoreceptor and chemoreceptor response from muscles > increased sympathetic activity

Question 11

Exercising muscles during static exercise will cause vasodilation. Why will there be an increase in MAP in the end?

Answer 11

There is a point where the contractility is so great that the muscles physically compress the vessels, TPR decreases greatly, large increase in MAP

Question 12

How will an increase in MAP affect the afterload?

Answer 12

Increase afterload,

may lead to ventricular hypertrophy in the long run

Question 13

How can circulatory shock happen?

Answer 13

When decrease in MAP cause all organs and tissues to be inadequately perfused, not receiving sufficient blood supply.

Question 14

How can a septic shock happen?

Bacterial endotoxins or lipoteichoic acid (LTA) triggers cascade of events leading to inducible _____ expression and _____ production, resulting in pronounced ___________ and increased membrane permeability, causing _______.

Answer 14

NOS
NO
vasodilation (> decreased TPR)
edema> decreases venous return and cardiac output

Question 15

In hemorrhage, MAP ______ due to decrease in ______.
Decompensatory mechanisms attempt to _____ MAP by causing widespread _______ that perfusion to organs may stop.

What is the worst case scenario of hemorrhage?

Answer 15

decreases; blood volume;
increase;
vasoconstriction;

multiple-organ failure > death

Question 16

Other than vasoconstriction, what is under sympathetic activity to increase MAP in hemorrhage conditions?

Answer 16

RAAS is activated, ADH release too.

AngII and ADH are potent vasoconstrictors

Question 17

What does it mean by decompensatory mechanisms to hemorrhage? Why it will happen?

Answer 17

Compensatory mechanisms causes further decrease of MAP

e.g. poor perfusion of organs cause damage, like myocardial infarction, which further reduces CO and MAP