Control of Ventilation

Question 1

What part of brains is involved in subconscious ventilation

Answer 1

Pons

Medulla

Question 2

What nerves

Answer 2

Phrenic = diaphragm
Intercostal = external intercostal

Question 3

What part of medulla set breathing pattern

Answer 3

DRG - control muscles of inspiration through phrenic and intercostal, receive sensory from vagus

VRG - control muscles of larynx / pharynx

PRG - receive sensory info from DRG, speak with higher brain to initiate and terminate inspiration

Question 4

How do you change respiratory drive

Answer 4

Emotion via limbic
Voluntary 
Mechano-sensory
Swalloing inhibits 
Drugs 
Chemical composition detected by chemoreceptors

Question 5

What is the primary stimulus for changes in ventilation

Answer 5

CO2
Detected by central chemoreceptors in medulla
More sensitive to small changes in PCo2

Question 6

How do central chemoreceptors work

Answer 6

Detect changes in H+ in CSF which are related to CO2

Question 7

What happens when there is an increase in CO2

Answer 7

Rate and depth of breathing increases to remove CO2

Question 8

Where are peripheral receptors located

Answer 8

Carotid and aortic bodies

Question 9

What do peripheral receptors detect

Answer 9

Change in arterial Po2 NOT CONTENT

Relatively insensitive and require a significant fall in Po2 or rise in H

Question 10

Can you override peripheral

Answer 10

No
Effects are instantaneous 
Increased RR and TV 
Blood flow directed to kidney and brain 
INceased CO

Question 11

When are peripheral chemoreceptor important

Answer 11

If chronic elevation of PCO2
Central response is blunted
Patients go into hypoxic drive and rely on peripheral receptors to detect O2 falling

Question 12

Why do you have to be careful in patients who rely on peripheral

Answer 12

Careful when giving O2 to patients with chronic lung disease e.g. COPD
They will have elevated PCO2
Rely only on O2 levels for their breathing

Question 13

What does hypoventilation cause

Answer 13

Increased CO2
Blood = acidic
COPD / neuro / chest wall

Question 14

What does hyperventilation cause

Answer 14

Decreased CO2 and alkaline blood
Decreases free Ca = paraesthesia / cramps
Anxiety / HF / PE

Question 15

What drugs affect ventilation

Answer 15

Opiods / barbiturates = depress
Anasthetic = increase RR but decrease TV
NO = blunts peripheral chemo so if chronic lung = no way to control ventilation

Question 16

What happens at altitude

Answer 16

Peripheral detect fall in O2 = hyperventilation
Resulting hypocapnia and alkalosis stop any increase in RR due to central chemoreceptors
After a few days kidney works to remove alkalosis so peripheral takes over again
Rise in DPG
Polycythaemia - physiological as erythropoietin produced from kidney but can cause hypervisocotyi

Question 17

If an anaemic patient has o2 content 1/2 normal what happens to RR + depth

Answer 17

No change
Receptors respond to partial pressure
Amount of O2 in plasma is normal but just decreased RBC to hold O2 so content reduced
Haem saturation will be the same

Question 18

What is more uncomfortable
1- a high PCo2 and low Po2
2- a low o2 and no CO2

Answer 18

1

PACO2 increased and impairs the gradient so will stay in blood