CV and Respiratory interactions

Question 1

How does the mechanical action of respiration cause a local effect on CVS?

Answer 1

On inspiration, VR increased due to the respiratory pump, increaseing EDV and therefore increases SV.

Question 2

How does respiration change the neural interaction with CVS?

Answer 2

On inspiration, HR increases due to a change in activity of CN X supplying SAN = sinus arrythmia

Question 3

Which two ways will influence cardiac vagal and NA activity?

Answer 3

1) Central inspiratory neurons INHIBIT vagal activity to heart to increase HR.
2) A reflex initiated by pulmonary stretch receptors in the respiratory airways, via vagal afferents

Question 4

What reflex is produced on inspiration?

Answer 4

As inspiration occurs, inspiratory motor neurons cause widening of the airways, activating the pulmonary stretch receptors. This stimulates NTS but inhibits NA, for inhibition of parasympathetic activity and therefore HR rises.

Question 5

How does inspiration influence the heart?

Answer 5

Mechanical increase in VR due to respiratory pump = increased SV
Central inspiratory neurons inhibit NA to inhibit parasympathetics for increased HR.
On inspiration, the airways widen, pulmonary receptors detect the stretch, exicite NTS to inhibit NA further.

Question 6

What happens during systemic hypoxia?

Answer 6

Peripheral chemoreceptors detect a fall in PaO2 below 60mmHg. The reflex stimulates NTS to inhibit NA for increased HR and PaO2 is regulated by increasing inspiration which impacts CNS.

Question 7

Where are the receptors that detect hypoxia?

Answer 7

Peripheral chemoreceptors are near the baroreceptors.
The carotid body lies at CCA bifurcation
The aortic body lies within the baroreceptors of the aortic arch

Question 8

What is the innervation to the peripheral chemoreceptors?

Answer 8

Carotid body afferents travel via sinus N to CN XI. Aortic body afferents travel via Aortic N to CN X.

Question 9

What is the hypoxic reflex superimposed on?

Answer 9

On local responses to hypoxia to increase inspiration and HR via both CV and respiratory systems.

Question 10

What factors stimulate peripheral chemoreceptors?

Answer 10

Fall in PaO2 or pH

Rise in PaCO2

Question 11

What happens if inspiration cannot increase despite chemoreceptor stimulation?

Answer 11

It causes a primary CV reflex to reduce HR and vasoconstrict for O2 conservation.
Hypoxia normally excites higher inspiratory neurons to inhibit NA to increase HR but there is no increase in respiration to activate the pulmonary stretch receptors for an enhanced response.
Instead the chemoreceptors excite NA with a stronger influence thatn the hypoxic inhibition to reduce HR and excite RVLM for vasoconstriction.
= O2 conserving reflex

Question 12

In what situations may will a pt have the inability to increase respiration?

Answer 12

Muscle relaxant
Spinal damage above phrenic N
Long dive
Fetus
Severe respiratory disease

Question 13

What effects result from the hypoxic reflex when inspiration can increase?

Answer 13

The effects of inspiration on HR dominate and the stimulation of pulmonary stretch receptors inhibits NA and CN X for increased HR.

Question 14

What is the o2 conserving reflex superimposed on ?

Answer 14

On local effects of hypoxia to enhance the reduced HR and contractility. The local effects include:
O2 available goes to the brain via vasodilation and pulmonary vasoconstriction. Muscle vasodilates due to its sensitivity to hypoxia.

Question 15

What can pulmonary vasoconstriction lead to? In what type of pts will this arise?

Answer 15

Pulmonary oedema and RV failure (back up of blood into RA as same SV entering but less leaving to lungs)
In pts with chronic hypoxia in respiratory disease = Blue Bloater

Question 16

Why are the effects of peripheral chemoreceptors overcome by the effects of increased inspiration?

Answer 16

The inspiration allows an enhanced response via pulmonary stretch receptors to increase respiration further to restore PaO2 and to increase HR to increase CO and flow to the brain by generalised vasoconstriction.

Question 17

How will a pt present if they are increasing their alveolar ventilation to overcome hypoxia?

Answer 17

Pink Puffer

Question 18

What stimulates trigeminal receptors?

Answer 18

Cold water on face / diving reflex, sinus washing, irritant vapours, intubation, bronchoscopy, laryngoscopy, food in larynx, quadraplegic mucous aspiration triggering receptors in sinuses, pharynx and larynx.

Question 19

What happens during the reflex evoked by stimulation of trigeminal receptors?

Answer 19

• Inhibition of central inspiratory neurons causes expiratory apnoea (sudden breathe out to reduce lung volume).
• Heart rate falls as vagal activity increase due to the removed inhibition that central neurons elicit. May cause bradycardia.
• Vasoconstriction due to increased sympathetic activity for the o2 conserving reflex.

Question 20

What can a strong trigeminal reflex result in?

Answer 20

Excitatory apnoea and cardiac arrest

Question 21

How can apnoea be terminated?

Answer 21

Ventilation of the thorax to reverse the effect by stimulating the pulmonary stretch receptors for increased inspiration. Restores rhythmic breathing and heart rhythm.

Question 22

How can the trigeminal reflex be used in tachycardia?

Answer 22

An ice bag applied to trigger the trigeminal receptors stimulates a reduction in HR.

Question 23

What do central inspiratory neurones do?

Answer 23

Stimulate inspiratory motor neurons for inspiration and therefore enhancing the effect through pulmonary stretch receptors.
Inhibit NA to inhibit parasympathetic activity for increased HR