Lecture 26: Control of the Cardiovascular System During Exercise

Question 1

What are the control pathways of the cardiovascular system during exercise?

Answer 1

Central Command
Exercise Pressor Reflex
Arterial Baroreceptor Reflex

Question 2

What is an efference copy and how does it activate the cardiovascular and respiratory systems?

Answer 2

A copy of a motor program issued by the cortex, that causes parallel signalling to the cardiovascular and respiratory systems

Question 3

What is curare?

Answer 3

A neuromuscular blocker (blocks central command)

Question 4

What physiological effect did curare have during an MVC?

Answer 4

Decreased heart rate

No change in MAP or SNS

Question 5

What is the role of central command at exercise onset?

Answer 5

To cause an increase in heart rate by stimulating vagus withdrawal (withdrawal of the parasympathetic nervous system)

Question 6

What sensory afferents do the mechanoreflex and metaboreflex consist of?

Answer 6

Mechanoreflex: unmyelinated (type 3)
Metaboreflex: myelinated (type 4)

Question 7

How does perfusion regulation by a perfusion cuff show effects of the metaboreflex?

Answer 7

Perfusion cuff pressure mechanically restricts blood flow reaching the exercising muscle
Causes a build up of metabolites (namely H+)
See an increase in sympathetic nerve activity which causes vasoconstriction, therefore increased blood pressure (higher rise during exercise)
This occurs during the recovery phase as well as during MVC, showing the metaboreflex is a powerful activator of sympathetic stimulation

Question 8

What physiological aspect is under the control of the metaboreflex?

Answer 8

SNS

Question 9

Why do we think acidosis is a stimulator of the metaboreflex?

Answer 9

Mcardles patients (no glycogen breakdown therefore no acidosis) had no increase in SNS activity

Question 10

What are the four factors influencing the magnitude of the metaboreflex?

Answer 10

Fibre type (type 2 has increased SNS/BP response due to greater metabolite production)
Training status of the muscle (muscles consistently producing large amounts of metabolite have a desensitised metaboreflex)
Blood flow obstruction (increases metaboreflex response due to a greater increase in metabolites) 
Blood volume (increased blood volume causes a decreased response as there is more blood to flush away metabolites)

Question 11

What is the role of the muscle mechanoreflex?

Answer 11

Increases heart rate via vagus withdrawal

Causes a slight increase in sympathetic stimulation of the heart

Question 12

What four factors influence the magnitude of the mechanoreflex response?

Answer 12

Degree of stretch
The force of the stretch
External pressure
Metabolite production (set the reflex sensitivity at a specific level)

Question 13

Injecting fentanyl opioids in unhealthy people has what effect on the exercise pressor reflex?

Answer 13

Causes attenuation of the EPR due to prevention of sensory feedback by the spine
This decreases minute ventilation
Which causes a decrease in BP and HR
This stimulates an ability to be able to exercise for longer in unhealthy individuals

Question 14

Injecting fentanyl opioids in healthy people has what effect on the pressor reflex?

Answer 14

Causes an inability to regulate exercise intensity as there is no feedback from the metaboreflex and the mechanoreflex

Question 15

Where are the arterial baroreceptors found?

Answer 15

In the carotid sinus and the aortic arch

Question 16

Give a brief description of what the baroreceptors respond to.

Answer 16

Respond to increased/decreased blood pressure by elevating/slowing heart rate

Question 17

When using a neck cuff, what effect does negative pressure production have on the arterial baroreceptors?

Answer 17

Negative pressure replicates acute hypertension
This fools the baroreceptors into thinking there is increased blood pressure
The result of this is signalling by the baroreceptors that causes decreased heart rate and SNA

Question 18

What has evidence suggested about the role of the arterial baroreceptor during exercise?

Answer 18

Despite both blood pressure and heart rate increasing during exercise, the baroreceptors are still in effect, but are simply working around a new set point
This was done via wearing a neck brace during exercise (even more blood pressure caused heart rate to decrease during exercise)

Question 19

What kind of curve does the BP-HR relationship give?

Answer 19

Sigmoidal

Question 20

What effect does exercise intensity have on the BP-HR curve?

Answer 20

At a higher exercise intensity, baroreceptors work at a higher set point
Therefore a much higher heart rate is needed to see a BP response
There is also less of a BP response to these increased heart rates