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Semester 3 - Respiratory > Session 5 - Control of breathing, Hypoxia and Respiratory Failure > Flashcards

Session 5 - Control of breathing, Hypoxia and Respiratory Failure Flashcards

1
Q

What is hypoxia?

A

• A fall in alveolar, thus arterial pO2

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2
Q

What is hypercapnia?

A

• A rise in alveolar, thus arterial CO2

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3
Q

What is hypocapnia?

A

• A fall in alveolar, thus arterial CO2

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4
Q

What is hyperventilation?

A
  • Ventilation increases with no change in metabolism

* (breathing more than you actually have to)

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5
Q

What is hypoventilation?

A
  • Ventilation decreases with no change in metabolism

* (breathing less than you have to)

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6
Q

How does hyperventilation affect plasma pH?

A
  • pCO2 down

* pH increases

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7
Q

How does hypoventilation affect CO2 and plasma pH?

A
  • pCO2 up

* pH down

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8
Q

What is the normal metabolic pH?

A

• 7.4

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9
Q

What is the body’s normal pH range?

A

• 7.38 - 7.42

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10
Q

What happens if plasma pH falls below 7.0?

A
  • Plasma k+ rises to dangerous levels and enzymes are lethally denatured
  • Function of heart affected
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11
Q

What happens if plasma pH rises above 7.6?

A
  • Free calcium concentration falls enough to produce fatal tetany
  • Calcium salts soluble in acid conditions - In alkalosis, calcium forms complexes. Nerves become excitable, causing tetany
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12
Q

Give two events which will occur when hypoventilation occurs?

A
  • Hypercapnia
  • Respiratory acidosis
  • pH falls below 7.0
  • Enzymes become lethally denatured
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13
Q

Give two events which will occur when hyperventilation occurs?

A

• Hypo capnia and respiratory alkalosis
• pH rises above 7.6
• Free calcium concentration falls enough to produce fatal tetany
○ Ca2+ is only soluble in acid, so pH rises Ca2+ cannot stay in blood. Nerves become hyperexcitable.

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14
Q

What is respiratory acidosis?

A
  • CO2 produced more rapidly than it is removed by the lungs (hypoventilation).
  • pCO2 rises, so (dissolved CO2) rises more than HCO3-, producing a fall in plasma pH
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15
Q

What is compensated respiratory acidosis?

A

• Respiratory acidosis persists, and the kidneys responsd to low pH by reducing excretion of HCO3-, thus restoring ratio of (dissolved CO2) to (HCO2-), producing a rise in pH

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16
Q

How long does compensation take?

A

• 2-3 days

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17
Q

What is respiratory alkalosis?

A
  • CO2 is removed from alveoli more rapidly than it is produced (hyperventilation)
  • Alveolar pCO2 decreases, changing the ratio of (dissolved CO2) to (HCO3-) producing an increase in plasma pH
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18
Q

What is compensated respiratory alkalosis?

A

• Respiratory Alkalosis persists, and the kidneys respond to the high pH by excreting HCO3-, thus restoring the ratio of [Dissolved CO2] to [HCO3-], and therefore the pH.

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19
Q

What is metabolic acidosis?

A
  • HCO3- displaced by metabolically produced acids

* Blood pH form

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20
Q

How can metabolic acidosis be compensated for?

A

• Ratio of (dissolved CO2) to (HCO3-) may be restored to near normal by increasing ventilation rate to decrease pCO2

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21
Q

What does acidosis mean?

A
  • Reduction in HCO3-

* NOT PH

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22
Q

What is metabolic alkalosis?

A
  • Plasma HCO3- rises, causing the pH of blood to rise (after vomiting?)
  • Stomach produces HCO3- when acid generated
  • If acid removed from stomach, gastrin released which produces more acid
  • HCO3- produced in excess as a result of this increased production
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23
Q

How can metabolic alkalosis be compensated for?

A
  • Ratio of dissolved CO2 to HCO3- may be restored to near normal by raising pCO2
  • Lungs decrease ventilation to correct pH
  • Dangerous
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24
Q

What is the control of our breathing moderated by?

A
  • pH

* Oxygen requirements are secondary

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25
Q

Give three variables which affect breathing?

A
  • pH
  • Decrease O2
  • Increased CO2
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26
Q

What occurs when there is falling inspired pO2?

A
  • Detected by peripheral chemoreceptors located in carotid and aortic bodies
  • Increase the tidal volume and rate of respiration
  • Changes in circulation direction more blood to the brain and kidney
  • Increased pumping of blood by the heart
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27
Q

What occurs when there is an increase in inspired pCO2

A
  • Central chemoreceptors in medulla more sensitive than peripheral
  • Small rise in pCO2 -> Increase ventilation
  • Small decrease in pCO2 -> Decrease ventilation
  • Basis of negative feedback control of breathing
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28
Q

What is low O2 detected by?

A

• Peripheral chemoreceptors

29
Q

Where are peripheral chemoreceptors found?

A
  • Carotid bodies

* Aortic bodies

30
Q

Why do peripheral chemoreceptors only respond to large changes in O2?

A
  • High blood flow in carotid and aorta

* Lots of O2, usually

31
Q

What are peripheral chemoreceptors stimulated by?

A
  • Low O2

* High CO2 (minor function)

32
Q

Give three ways in which chemoreceptors response to a decrease in O2

A
  • Increase tidal volume and rate of respiration
  • changes in circulation directing blood to the brain and kidney
  • Increased pumping of blood by the heart
33
Q

What is a central chemoreceptor and where is it found?

A
  • Found in medulla of the brain

* Much more sensitive, altering breathing on a second to second basis

34
Q

What do the central chemoreceptors do in response to arterial pCO2?

A
  • Small rise in pCO2 -> Increase ventilation

* Small fall in pCO2 -> Decrease ventilation

35
Q

hat do central chemoreceptors respond to?

A
  • Changes in the pH of cerebro-spinal fluid (CSF)

* CSF separated from blood by the blood-brain barrier

36
Q

What is CSH (HCO3-) controlled by?

A

• Choroid plexus cells

37
Q

What out of HCO3-, CO2 and H+ can cross the BBB

A

• CO2 only

38
Q

What is the pH of the CSF governed by?

A

• The ratio of HCO2- to pCO2

39
Q

How is regulation of brain pH different to that of the rest of the body?

A

• Occurs within hours

40
Q

Apart from pCO2 and pO2, what do the central chemoreceptors respond to?

A

• Changes in pH of CSF

41
Q

How is the CSF separated from the blood?

A

• By the blood brain barrier

42
Q

What is the CO2 of the CSF determined by?

A
  • Arterial pCO2

* HCO3- and H+ cannot cross

43
Q

What is CSF (HCO3-) controlled by?

A

• Choroid plexus cells

44
Q

What is the pH of CSF determined by?

A
  • The ratio of HCO3- to pCO2
  • In the short term HCO3- is fixed, so falls in pCO2 -> increase in pH
  • Rise in pCO2 -> lower pH
  • Persisting changes compensated for by choroid plexus cells altering CSF
45
Q

What is the oxygen transport chain?

A

• Air -> Airways -> Alveolar gas -> alveolar membrane -> Arterial blood -> Regional arteries -> Capillary blood -> Tissues

46
Q

Define hypoxia

A

• A fall in alveolar, thus arterial pO2

47
Q

Give conditions which cause diffusion impairments

A

• Fibrotic lung disease
○ Thickened alveolar membrane slows gas exchange
• Pulmonary oedema
○ Fluid in interstitial space increases diffusion distance
• Emphysema
○ Destruction of alveoli reduces surface area for gas exchange

48
Q

What is respiratory failure?

A
  • Not enough oxygen enters the blood

* Not enough CO2 leaves the blood

49
Q

What is type 1 respiratory failure?

A
  • Arterial hypoxia (pO2 below 8kPa), accompanied by normal or low pCO2
  • Breathlessness, Exercise intolerance, central cyanosis
50
Q

What alveoli can t1 respiratory failure effect?

A

• Some or all alveoli

51
Q

Give three symptoms of T1 Respiratory failure

A
  • Breathlessness
  • Exercise intolerance
  • Central cyanosis
52
Q

Can ventilation perfusion matching bring lungs to 100% capacity

A

no

53
Q

Give four possible causes of T1 respiratory failure can be caused by conditions affecting some alveoli

A
  • Pulmonary embolism
  • Pneumonia
  • Consolidation
  • Early stages of acute asthma
54
Q

Give two possible causes of T1 respiratory failure which can be caused by conditions affecting most alveoli

A 
• Pulmonary oedema
• Fibrosis
	○ Pneumoconiosis
	○ Asbestosis
	○ Extrinsic allergic alveolitis
55
Q

What is type 2 respiratory failure?

A
  • Arterial hypoxia, accompanied by an elevated pCO2

* (Arterial hypoxia = 8kPa)

56
Q

How is O2 saturation measured?

A
  • Pule oximeter

* Blood gas analysis

57
Q

Give three causes of T2 respiratory failure

A 
• Poor respiratory effort 
	○ Narcotics
	○ Muscle weakness (upper and lower motoneurone)
• Chest wall problems
	○ Scoliosis/Kyphosis
	○ Trauma
	○ Pneumothorax
• Hard to ventilate lungs
	○ High airway resistance
	○ COPD
	○ Asthma
58
Q

What is emphysema?

A
  • Destruction of lung tissue ( lack of a1-antitrypsin)
  • Changes in compliance
  • Ventilation perfusion mismatch
  • Affects O2 supply
  • Initally T1 failure, then T2
59
Q

What happens in the body to solve chronic hypoxia?

A
  • There is a renal correction of acid base balance

* Increase in ventilation

60
Q

Outline the acute effects of Type 2 respiratory failure

A 
• pCO2 rises
• Central chemoreceptors detects
• Breathlessness
	○ Some compensation 
	○ Poor ventialtion prevents full compensation
61
Q

What happens in chronic type 2 respiratory failure

A
  • CSF acidity corrected by choroid plexus
  • Central chemoreceptors rest to high CO2 level
  • Persisting hypoxia
  • Reduction of respiratory drive, which is now driven by hypoxia
62
Q

What happens if you give O2 to someone with COPD (T2 respiratory failure)

A

• They may stop breathing

63
Q

What effect does T2 respiratory failure have on pulmonary circulation?

A 
• Effects of hypoxia on pulmonary arterioles
	○ Pulmonary hypertension
	○ Right heart failure
	○ Cor pulmonale
• Increased O2 transport capacity
• Hb increased
• 2,3 BPG
64
Q

Give five factors necessary to maintain arterial pO2, problems with which will cause hypoxia

A
  • Low pO2 in inspired air
  • Hypoventilation
  • Diffusion impairment
  • Ventilation perfusion mismatch
  • abnormal right to left cardiac shunts
65
Q

What causes low pO2 in inspired air?

A

• Everything is normal, air has low pO2

66
Q

What is hypoventilation often associated with?

A

• Increased pCO2 (type 2 respiratory failure)

67
Q

What are neuromuscular causes of hypoventilation?

A
  • Respiratory depression due to opiate overdose • Head injury
  • Muscle weakness (NMJ/Nerve/Muscle diseases)
68
Q

What are some Chest wall problems (Mechanical) of hypoventilation

A
  • Scoliosis/kyphosis
  • Morbid obesity
  • Trauma
  • Pneumothorax
69
Q

Give three things which make it hard to ventilate lungs

A
  • Airway obstruction
  • COPD & Asthma when the airway narrowing is severe and widespread
  • Severe fibrosis

Semester 3 - Respiratory (18 decks)

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