L15: Cardiovascular Respiratory Interactions Flashcards
What are the 2 types of interactions of respiratory system that influence the heart
Mechanical
Neural
What does the mechanical interaction involve
- respiratory pump : increasing venous return back to heart
So stroke volume increases due to the starlings law
What is the neural interaction
When we inspire the heart rate increases and when we breath out the heart rate decreases
What is the increase in heart rate due to increase in breathing called
Sinus arrhythmia
What is the central nervous mechanism? Describe it
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.
How does a reflex become incorporated into the central nervous mechanism
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
When can inspiration increase
Systemic hypoxia
What is systemic hypoxia
A fall in arterial Po2 below 8kpa
Which receptors detect a change in the arterial blood
Peripheral chemoreceptors
Where are peripheral chemoreceptors found
In the carotid BODY
In the aortic arch
What stimulates peripheral chemoreceptors
Decrease in oxygen
Increase in carbon dioxide
Decrease in arterial pH
What are the afferent nerve fibres of the peripheral chemoreceptors in the carotid sinus
Glossopharyngeal nerve (CN9)
What are the afferent nerve fibres of the peripheral chemoreceptors in the aortic arch
Vagus nerve (CN10)
Which nucleus does the afferent nerves from the peripheral chemoreceptors feed into
NTS
Describe what happens when the peripheral chemoreceptors are stimulated but respiration cannot increase
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 .
What happens when the peripheral chemoreceptors are stimulates and the respiration can increase
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
When does systemic hypoxia occur when respiration cannot increase
Paralysed muscle
After spinal injury
Long dive under water
Severe respiratory disease
When does systemic hypoxia occur when respiration can increase
Hypoxic atmosphere
High altitude
Less severe respiratory disease
What is the diving reflex
When respiration decreases heart rate decreases
Describe the diving reflex
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
