Physiological Consequences of Respiratory Centre Depression

Question 1

What is the purpose of the respiratory system?

Answer 1

To keep blood oxygen at 100mmHg, carbon dioxide at 40mmHg and pH at 7.40

Question 2

How is the respiratory system controlled?

Answer 2

By controlling the respiratory muscles, chest wall and airways to alter ventilation

Question 3

Can gas exchange be controlled?

Answer 3

No - because it is a passive process but it is altered indirectly via ventilation

Question 4

Where is the central controller of the respiratory system?

Answer 4

The brain stem (pons and medulla) and the cortex

Question 5

What is the role of the neurons in the brain stem?

Answer 5

To generate a an automatic rhythm of inspiration

Question 6

What is the major output of the respiratory centre?

Answer 6

The phrenic nerves

Question 7

What is the role of the cortex in the respiratory centre?

Answer 7

To give voluntary control to alter the output of the brainstem

Question 8

What receptors feed in to the central controller?

Answer 8

Central chemoreceptors, peripheral chemoreceptors, stretch receptors in the lung, irritant receptors in the lung, stretch receptors in the muscle, joint position receptors in the muscle, receptors for touch, temperature and pain, emotional stimuli acting through the limbic system

Question 9

Where are the central chemoreceptors located?

Answer 9

on the ventral surface of the medulla where they are in contact with the CSF

Question 10

What do central chemoreceptors respond to?

Answer 10

CSF H+

Question 11

Where are the peripheral chemoreceptors located?

Answer 11

in the carotid bodies at the bifurcation of the common carotid and in the aortic bodies at the arch of the aorta

Question 12

What do peripheral chemoreceptors respond to?

Answer 12

H+, CO2 and O2

Question 13

What is the result of a small increase in CO2?

Answer 13

Rapid increase in ventilation

Question 14

What is the result of a small fall in O2?

Answer 14

No change in ventilation

Question 15

What O2 pressure is required to influence ventilation?

Answer 15

<60mmHg

Question 16

What is the relationship between work and minute ventilation?

Answer 16

Linear - match ventilation with oxygen consumption

Question 17

What is the relationship between PaO2, PaCO2 and pH with work?

Answer 17

Blood gases remain constant while work increases

Question 18

What happens at high levels of work?

Answer 18

There is anaerobic metabolism which generates extra acid, so to compensate there is a further increase in ventilation - this leads to a decrease in CO2 and an increase in O2 to allow pH to return to just below normal

Question 19

What happens to breathing in anxiety?

Answer 19

There is excessive ventilation for oxygen consumption and CO2 production so the result is respiratory alkalosis

Question 20

What is hypoventilation?

Answer 20

When ventilation is not meeting the metabolic requirements for oxygen consumption and carbon dioxide production

Question 21

What is the result of acute hypoventilation?

Answer 21

respiratory acidosis

Question 22

What is the result of chronic hypoventilation

Answer 22

metabolic alkalosis?

Question 23

What are the causes of hypoventilation?

Answer 23

Reduced respiratory centre activity, neuromuscular disease, chest wall deformity, gross obesity, sleep disordered breathing

Question 24

What are the 3 types of sleep disordered breathing?

Answer 24

obstructive sleep apnoea, central sleep apnoea, obesity hypoventilation syndrome

Question 25

What is obstructive sleep apnoea?

Answer 25

A transient obstruction to the throat during sleep which prevents breathing

Question 26

Why does the obstruction occur in OSA?

Answer 26

airway muscles relax in sleep, the throat is already narrowed e.g. by obesity and the tongue falls backward if supine

Question 27

What makes you wake up in OSA?

Answer 27

Reduced O2 and increased CO2

Question 28

What is the management for OSA?

Answer 28

weight loss, CPAP, lying on side, mandibular advancement splint, surgery

Question 29

What is the long term consequence of sleep disordered breathing?

Answer 29

The brainstem will start to accept higher levels of CO2 and lower levels of O2 so that sleep can continue without being disrupted - leads to chronic hypercapnea with normal pH and high bicarbonate (compensated respiratory acidosis)

Question 30

What will happen to respiratory drive in long term sleep disordered breathing?

Answer 30

Will become dependent on hypoxic drive - more dependent on PaO2

Question 31

What will happen if you give someone with hypoxic drive supplementary oxygen?

Answer 31

They will develop acute hypoventilation