Resp 6 - Control of breathing

Question 1

Define hypoxia:

Answer 1

Deficiency in amount of oxygen reaching the tissues

O2 saturation < 94%

Question 2

Define hypercapnia:

Answer 2

Abnormally high concentration of CO2 in the blood

Question 3

Define Hypocapnia:

Answer 3

Abnormally low concentration of CO2 in the blood

Question 4

Define hyperventilation:

How does it affect plasma pH?

Answer 4

Abnormally fast or deep breathing

Increases plasma pH, as causes loss of CO2 from the blood

Question 5

Define hypoventilation:

How does it affect plasma pH?

Answer 5

Abnormally slow breathing

Decreases plasma pH, as less CO2 removed from the blood

Question 6

Where are the peripheral chemoreceptors located?

Answer 6

• Carotid bodies (carotid sinus)

- Aortic bodies (Aortic arch)

Question 7

What is detected by peripheral chemoreceptors?

How do they respond?

Answer 7

Large drops in PO2, or large rise in PCO2

• ^ respiratory rate
• Change heart rate
• Change blood flow distribution

Question 8

Where are the central chemoreceptors located?

Answer 8

Ventral surface of Medulla (exposed to CSF)

Question 9

What is detected by the central chemoreceptors?

Answer 9

Small changes (~ 0.3 kPa) in PCO2 (via H+ from the CSF)

Question 10

How does the body compensate for persisting hypoxia, to avoid brain damage (ie COPD)?

Answer 10

• Initially, detected by peripheral chemoreceptors = ^ ventilation rate (but PCO2 falls = alkalosis)
• Choroid plexus cells compensate for altered PCO2 by adding H+ to the CSF
  = central chemoreceptors accept new PCO2 as normal level
• Increased renal production of erythropoetin
  = Increased production of RBC = increased carrying capacity of blood for O2

Question 11

How does the body compensate for persisting hypercapnia, to avoid brain damage?

Answer 11

• Peripheral and central chemoreceptors detect drop in plasma pH = ^ ventilation rate
• Choroid plexus cells compensate for altered PCO2 by adding HCO3- to CSF to protect neurones
  = central chemoreceptors accept new PCO2 as normal level

Question 12

What is the choroid plexus, and what is its main functions?

Answer 12

• Vascular structure of pia mater located in ventricles of the brain
• Acts as barrier between capillaries and CSF (one of the blood-brain-barriers)
• Makes ~ 500 ml of CSF per day
• Can selectively pump H+ or HCO3- into CSF to maintain suitable pH for neurones (contains Carbonic Anhydrase)

Question 13

Name the cells/structures which produce CSF:

Answer 13

• Choroid plexus

- Eppendymal cells

Question 14

What is the normal volume of CSF?

Answer 14

~ 140 - 270 ml

Question 15

Give the main 4 constituents of CSF:

Answer 15

1) Water
2) Glucose
3) NaCl
4) Protein

Question 16

Which 2 cell types can be found in CSF normally?

Answer 16

• Monocytes/macrophages

- Lymphocytes

Question 17

List some molecules that can cross the blood-brain-barrier easily:

Answer 17

• O2
• CO2
• H2O
• Ethanol
• Nicotine
• Glucose

Question 18

Which of the following can easily cross the blood-brain-barrier?

O2
Glycine
Catecholamines
Ethanol
H2O
Nicotine
H+
HCO3-

Answer 18

O2
Ethanol
H2O
Nicotine

Question 19

What are the 4 types of hypoxia?

Answer 19

1) Hypoxaemic
2) Anaemic
3) Ischaemic
4) Histiotoxic

Question 20

What type of hypoxia is caused by high altitude?

Answer 20

Hypoxaemic

Question 21

What type of hypoxia is caused by iron deficiency?

Answer 21

Anaemic

Question 22

What type of hypoxia is caused by a myocardial infarction?

Answer 22

Ischaemic

Question 23

What type of hypoxia is caused by cyanide?

Answer 23

Histiotoxic

Question 24

How does cyanide cause hypoxia?

Answer 24

Cyanide inhibits cytochrome c oxidase (the last electron acceptor in the ETC - complex IV)
= no ATP = inhibits anaerobic respiration
= Histiotoxic hypoxia

Question 25

What is the normal range of O2 saturation?

Answer 25

94 - 98%

Question 26

Define Type I Respiratory Failure:

Answer 26

PO2 < 8 kPa
O2 saturation < 90%
Normal or low PCO2

Question 27

Define Type II Respiratory Failure:

Answer 27

PO2 < 8 kPa
O2 saturation < 90%
HIGH CO2 > 6.7 kPa

Question 28

What is the ideal ventilation:perfusion ratio?

Answer 28

Ideal V/Q = 1

~ 5 L/min

Question 29

What happens to alveolar PO2 and PCO2 if the V/Q ratio < 1?

Answer 29

PO2 decreases

PCO2 increases

Question 30

How does ventilation perfusion mismatch cause Type I Respiratory failure?

Answer 30

• Alveolar PO2 decreases, and PCO2 increases
• Chemoreceptors cause hyperventilation, normalising PCO2 levels
  = Type I Respiratory failure

Question 31

What may cause a ventilation perfusion mismatch?

Answer 31

Reduced ventilation of part of lung:

• Pneumonia (alveoli filled with exudate)
• Respiratory distress syndrome (collapsed alveoli)
• Acute Asthma/COPD (narrowed airways)

Reduced perfusion of part of lung:
- Pulmonary embolism

Question 32

In diseases causing diffusion impairment (ie Fibrosis/Emphysema), why is O2 diffusion affected, but not CO2 diffusion? Therefore what type of respiratory failure is caused?

Answer 32

CO2 is 20x more soluble than O2, so diffusion is unaffected

Type I Respiratory failure

Question 33

List some causes of hypoventilation:

Answer 33

Opiates/brain stem injury
Trauma to spinal cord
Guillan-Barre syndrome
Myasthenia Gravis
Myopathy/Motor neurone disease
Severe obesity
Kyphoscoliosis
Flail segment
Pneumothorax
Pleural effusion
Newborn respiratory distress syndrome
Lung fibrosis
Upper airway obstruction
Acute asthma
Late COPD

Question 34

Name the commonest cause of type II respiratory failure:

Answer 34

Late COPD

Question 35

What is the treatment for type I respiratory failure?

Answer 35

• Oxygen therapy

- Treat underlying cause

Question 36

What are the signs/symptoms of hypoxia?

Answer 36

• Exercise intolerance
• Tachypnoea
• Confusion
• Central cyanosis (+ peripheral cyanosis)

Question 37

Central cyanosis is a sign that SaO2 is below what value?

Answer 37

SaO2 < 85%

Question 38

What is polycythaemia, and why is it caused by chronic hypoxia?

Answer 38

Abnormally high haemoglobin in the blood

Increases O2 delivery to tissues

Question 39

What are the signs/symptoms of chronic hypercapnia?

Answer 39

• Warm hands
• Bounding pulse
• Flapping tremors