L15: Cardiovascular Respiratory Interactions

Question 1

What are the 2 types of interactions of respiratory system that influence the heart

Answer 1

Mechanical

Neural

Question 2

What does the mechanical interaction involve

Answer 2

• respiratory pump : increasing venous return back to heart

So stroke volume increases due to the starlings law

Question 3

What is the neural interaction

Answer 3

When we inspire the heart rate increases and when we breath out the heart rate decreases

Question 4

What is the increase in heart rate due to increase in breathing called

Answer 4

Sinus arrhythmia

Question 5

What is the central nervous mechanism? Describe it

Answer 5

1) inspiratory neurones in brain are active during inspiration and they increase the activity of the inspiratory motor neurone
2) inspiratory motor neurone increase the activity of the diaphragm and intercostal muscles
3) inspiratory neurones also send an inhibitory signal to the nucleus ambiguus and this decreases the PNS activity to the heart so Heart rate increases.

Question 6

How does a reflex become incorporated into the central nervous mechanism

Answer 6

1) increase in inpiratory motor neurones cause widening of airways and pulmonary stretch receptors are stretched in inspiration
2) vagus afferents from the pulmonary stretch receptors feed into the NTS
3) NTS sends an inhibitory signal to the nucleus ambiguus so the vagus tone of the heart decreases and the heart rate increases

Question 7

When can inspiration increase

Answer 7

Systemic hypoxia

Question 8

What is systemic hypoxia

Answer 8

A fall in arterial Po2 below 8kpa

Question 9

Which receptors detect a change in the arterial blood

Answer 9

Peripheral chemoreceptors

Question 10

Where are peripheral chemoreceptors found

Answer 10

In the carotid BODY

In the aortic arch

Question 11

What stimulates peripheral chemoreceptors

Answer 11

Decrease in oxygen
Increase in carbon dioxide
Decrease in arterial pH

Question 12

What are the afferent nerve fibres of the peripheral chemoreceptors in the carotid sinus

Answer 12

Glossopharyngeal nerve (CN9)

Question 13

What are the afferent nerve fibres of the peripheral chemoreceptors in the aortic arch

Answer 13

Vagus nerve (CN10)

Question 14

Which nucleus does the afferent nerves from the peripheral chemoreceptors feed into

Answer 14

NTS

Question 15

Describe what happens when the peripheral chemoreceptors are stimulated but respiration cannot increase

Answer 15

1) peripheral chemoreceptors detect hypoxia and increase activity in CN9/10 to NTS
2) NTS feeds into the vagus ambiguus so vagal activity of the heart increases and this leads to a decrease in HR
3) NTS also simulates the RVLM so sympathetic activity only to arterioles increase to give vasoconstriction
4) this results in bradycardia and vasoconstriction to conserve the oxygen .

Question 16

What happens when the peripheral chemoreceptors are stimulates and the respiration can increase

Answer 16

1) inspiration motor neurones cause increased inspiration so pulmonary receptors stretch and input into the NTS
2) NTS inhibits the nucleus ambiguus so vagal tone of the heart decreases and the heart rate increases
3) peripheral chemoreceptors which have detected hypoxia cause increase in nucleus ambiguus to give decreased heart and vasoconstriction
4) these 2 opposing effects has the pulmonary stretch receptor take action to overall the Heart rate increases
5) overall heart rate increases and vasoconstriction occurs

Question 17

When does systemic hypoxia occur when respiration cannot increase

Answer 17

Paralysed muscle
After spinal injury
Long dive under water
Severe respiratory disease

Question 18

When does systemic hypoxia occur when respiration can increase

Answer 18

Hypoxic atmosphere
High altitude
Less severe respiratory disease

Question 19

What is the diving reflex

Answer 19

When respiration decreases heart rate decreases

Question 20

Describe the diving reflex

Answer 20

1) trigeminal nerve is stimulated by cold water on the face and feeds into the NTS
2) NTS inhibits the inspiratory neurones so expiratory apnoea occurs (holding at expiration)
3) pulmonary stretch receptors decrease in activity as no inspiration occurs
4) this causes an increases vagal tone to the heart so hear rate decreases
5) vasoconstriction occurs