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

1
Q

What is hypoxia?

A

• A fall in alveolar, thus arterial pO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is hypercapnia?

A

• A rise in alveolar, thus arterial CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is hypocapnia?

A

• A fall in alveolar, thus arterial CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is hyperventilation?

A
  • Ventilation increases with no change in metabolism

* (breathing more than you actually have to)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is hypoventilation?

A
  • Ventilation decreases with no change in metabolism

* (breathing less than you have to)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does hyperventilation affect plasma pH?

A
  • pCO2 down

* pH increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does hypoventilation affect CO2 and plasma pH?

A
  • pCO2 up

* pH down

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the normal metabolic pH?

A

• 7.4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the body’s normal pH range?

A

• 7.38 - 7.42

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Give two events which will occur when hypoventilation occurs?

A
  • Hypercapnia
  • Respiratory acidosis
  • pH falls below 7.0
  • Enzymes become lethally denatured
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How long does compensation take?

A

• 2-3 days

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is metabolic acidosis?

A
  • HCO3- displaced by metabolically produced acids

* Blood pH form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What does acidosis mean?

A
  • Reduction in HCO3-

* NOT PH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the control of our breathing moderated by?

A
  • pH

* Oxygen requirements are secondary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Give three variables which affect breathing?
* pH * Decrease O2 * Increased CO2
26
What occurs when there is falling inspired pO2?
* 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
27
What occurs when there is an increase in inspired pCO2
* 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
28
What is low O2 detected by?
• Peripheral chemoreceptors
29
Where are peripheral chemoreceptors found?
* Carotid bodies | * Aortic bodies
30
Why do peripheral chemoreceptors only respond to large changes in O2?
* High blood flow in carotid and aorta | * Lots of O2, usually
31
What are peripheral chemoreceptors stimulated by?
* Low O2 | * High CO2 (minor function)
32
Give three ways in which chemoreceptors response to a decrease in O2
* 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
What is a central chemoreceptor and where is it found?
* Found in medulla of the brain | * Much more sensitive, altering breathing on a second to second basis
34
What do the central chemoreceptors do in response to arterial pCO2?
* Small rise in pCO2 -> Increase ventilation | * Small fall in pCO2 -> Decrease ventilation
35
hat do central chemoreceptors respond to?
* Changes in the pH of cerebro-spinal fluid (CSF) | * CSF separated from blood by the blood-brain barrier
36
What is CSH (HCO3-) controlled by?
• Choroid plexus cells
37
What out of HCO3-, CO2 and H+ can cross the BBB
• CO2 only
38
What is the pH of the CSF governed by?
• The ratio of HCO2- to pCO2
39
How is regulation of brain pH different to that of the rest of the body?
• Occurs within hours
40
Apart from pCO2 and pO2, what do the central chemoreceptors respond to?
• Changes in pH of CSF
41
How is the CSF separated from the blood?
• By the blood brain barrier
42
What is the CO2 of the CSF determined by?
* Arterial pCO2 | * HCO3- and H+ cannot cross
43
What is CSF (HCO3-) controlled by?
• Choroid plexus cells
44
What is the pH of CSF determined by?
* 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
What is the oxygen transport chain?
• Air -> Airways -> Alveolar gas -> alveolar membrane -> Arterial blood -> Regional arteries -> Capillary blood -> Tissues
46
Define hypoxia
• A fall in alveolar, thus arterial pO2
47
Give conditions which cause diffusion impairments
• 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
What is respiratory failure?
* Not enough oxygen enters the blood | * Not enough CO2 leaves the blood
49
What is type 1 respiratory failure?
* Arterial hypoxia (pO2 below 8kPa), accompanied by normal or low pCO2 * Breathlessness, Exercise intolerance, central cyanosis
50
What alveoli can t1 respiratory failure effect?
• Some or all alveoli
51
Give three symptoms of T1 Respiratory failure
* Breathlessness * Exercise intolerance * Central cyanosis
52
Can ventilation perfusion matching bring lungs to 100% capacity
no
53
Give four possible causes of T1 respiratory failure can be caused by conditions affecting some alveoli
* Pulmonary embolism * Pneumonia * Consolidation * Early stages of acute asthma
54
Give two possible causes of T1 respiratory failure which can be caused by conditions affecting most alveoli
``` • Pulmonary oedema • Fibrosis ○ Pneumoconiosis ○ Asbestosis ○ Extrinsic allergic alveolitis ```
55
What is type 2 respiratory failure?
* Arterial hypoxia, accompanied by an elevated pCO2 | * (Arterial hypoxia = 8kPa)
56
How is O2 saturation measured?
* Pule oximeter | * Blood gas analysis
57
Give three causes of T2 respiratory failure
``` • 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
What is emphysema?
* Destruction of lung tissue ( lack of a1-antitrypsin) * Changes in compliance * Ventilation perfusion mismatch * Affects O2 supply * Initally T1 failure, then T2
59
What happens in the body to solve chronic hypoxia?
* There is a renal correction of acid base balance | * Increase in ventilation
60
Outline the acute effects of Type 2 respiratory failure
``` • pCO2 rises • Central chemoreceptors detects • Breathlessness ○ Some compensation ○ Poor ventialtion prevents full compensation ```
61
What happens in chronic type 2 respiratory failure
* 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
What happens if you give O2 to someone with COPD (T2 respiratory failure)
• They may stop breathing
63
What effect does T2 respiratory failure have on pulmonary circulation?
``` • Effects of hypoxia on pulmonary arterioles ○ Pulmonary hypertension ○ Right heart failure ○ Cor pulmonale • Increased O2 transport capacity • Hb increased • 2,3 BPG ```
64
Give five factors necessary to maintain arterial pO2, problems with which will cause hypoxia
* Low pO2 in inspired air * Hypoventilation * Diffusion impairment * Ventilation perfusion mismatch * abnormal right to left cardiac shunts
65
What causes low pO2 in inspired air?
• Everything is normal, air has low pO2
66
What is hypoventilation often associated with?
• Increased pCO2 (type 2 respiratory failure)
67
What are neuromuscular causes of hypoventilation?
* Respiratory depression due to opiate overdose • Head injury * Muscle weakness (NMJ/Nerve/Muscle diseases)
68
What are some Chest wall problems (Mechanical) of hypoventilation
* Scoliosis/kyphosis * Morbid obesity * Trauma * Pneumothorax
69
Give three things which make it hard to ventilate lungs
* Airway obstruction * COPD & Asthma when the airway narrowing is severe and widespread * Severe fibrosis