Respiratory Control Of Breathing

Question 0

Define hypercapnia

Answer 0

Abnormally high carbon dioxide concentration in the blood

Question 1

Define hypoxia

Answer 1

Deficiency of oxygen in tissues

Question 2

Define hypocapnia

Answer 2

Abnormally low concentration of carbon dioxide in the blood

Question 3

Define hyperventilation

Answer 3

Breathing at an abnormally rapid rate at rest

Ventilation changes with no change in metabolism

Question 4

Define Hypoventilation

Answer 4

Breathing at an abnormally shallow and slow rate

Question 5

What is the effect of hypo and hyperventilation on carbon dioxide concentration in the blood?

Answer 5

Hypoventilation - increases carbon dioxide concentration, decreases pH
Hyperventilation - decreases carbon dioxide concentration, increases pH

Question 6

What is respiratory failure?

Answer 6

When not enough oxygen enters the blood
When not enough carbon dioxide leaves the blood
Don’t necessarily have to occur together

Question 7

What is type I respiratory failure?

Answer 7

Not enough oxygen enters the blood but carbon dioxide removal is normal
Low oxygen, normal or low carbon dioxide

Question 8

What is type II respiratory failure?

Answer 8

When not enough oxygen enters the blood and not enough carbon dioxide leaves the blood
pO2 in arterial blood is low
pCO2 is high

Question 9

What happens to carbon dioxide and oxygen in hyperventilation?

Answer 9

pCO2 will fall

pO2 will rise

Question 10

What can severe hyperventilation lead to?

Answer 10

Rise in pH
Respiratory alkalosis
Lethal tetany because free calcium concentration falls

Question 11

Why does an increase in pH cause tetany?

Answer 11

Calcium is only soluble in acid
Leaves blood when pH rises
Nerves become hyperexcitable

Question 12

What happens in hypoventilation?

Answer 12

pCO2 rises and pO2 falls

If pH falls below 7.0, enzymes become lethally denatured

Question 13

Define respiratory acidosis

Answer 13

When lungs cannot remove enough carbon dioxide produced by the body, causing a fall in pH

Question 14

Define respiratory alkalosis

Answer 14

Wher hyperventilation raises blood pH

Associated with hypocapnia

Question 15

Define compensated respiratory acidosis

Answer 15

When respiratory acidosis persists, kidneys respond to low pH by reducing excretion of HCO3-, thus restoring ratio of CO2:HCO3

Question 16

Define compensated respiratory alkalosis

Answer 16

When respiratory alkalosis persists, kidneys respond to high pH by excreting HCO3 and restoring ratio of CO2:HCO3
Takes 2-3 days

Question 17

What are the values for it to be classed as metabolic acidosis?

Answer 17

pH < 7.35 and

Plasma [HCO3-] < 22mmol/L

Question 18

What normally occurs with metabolic acidosis?

Answer 18

Respiratory compensation - hyperventilation

Question 19

What is metabolic alkalosis?

Answer 19

When plasma pH rises and [HCO3-] rises

Question 20

What value does pO2 need to be kept above?

Answer 20

8kPa

Question 21

Which gas needs to be controlled precisely? Why?

Answer 21

Carbon dioxide

To avoid acid-base problems

Question 22

Where are peripheral chemoreceptors located and what do they respond to?

Answer 22

Carotid and aortic bodies
Changes in carbon dioxide by a rise of 1.3kPa
Fall in pO2
Change in H+ concentration of blood

Question 23

Pros and cons of peripheral chemoreceptors?

Answer 23

Not particularly sensitive

Respond quickly to large pCO2 changes

Question 24

If pCO2 rises, what is the chemoreceptors response?

Answer 24

Send impulses to medulla oblongata This sends nervous impulses to external intercostal muscles and diaphragm via intercostal nerve and phrenic nerves This increases tidal volume and rate of respiration Changes circulation, directing more blood to brain and kidneys Increases pumping of blood by heart

Question 25

Where are central chemoreceptors located?

Answer 25

Medulla of the brain

Question 26

What do central chemoreceptors do?

Answer 26

Detect changes in pH a of cerebrospinal fluid

Question 27

If there is an increase in carbon dioxide, what do central chemoreceptors do?

Answer 27

Stimulate breathing

Question 28

What controls the concentration of HCO3 in CSF and why?

Answer 28

Choroid plexus cells | HCO3- cannot diffuse across the blood brain barrier so cannot be controlled by the kidneys

Question 29

What controls the CSF pCO2?

Answer 29

Arterial CO2

Question 30

Why are central chemoreceptors more sensitive?

Answer 30

[HCO3-] of CSF is fixed in the short term because it cannot diffuse across the BBB Change in pCO2 will change the pH (increase in CO2, fall in pH)

Question 31

What is the feedback control for central chemoreceptors?

Answer 31

Elevated pCO2 drives CO2 into CSF across BBB CSF pH falls, detected by central chemoreceptors Drives increased ventilation, lowers pCO2, restores CSF pH

Question 32

Role of choroid plexus in setting pH?

Answer 32

CSF [HCO3-] determines which pCO2 is associated with a 'normal' CSF pH Therefore CSF [HCO3-] sets control system to a pCO2 Can reset by changing [HCO3-]

Question 33

Symptoms of type 1 respiratory failure?

Answer 33

Exercise intolerance Breathlessness Central cyanosis

Question 34

What can cause type I respiratory failure?

Answer 34

(Reduced transfer of oxygen to blood from alveoli) Poorly perfused alveoli due to a pulmonary embolism Poorly ventilated alveoli due to pneumonia, consolidation, early stages of acute asthma

Question 35

When, in type I respiratory failure, is ventilation and perfusion not matched?

Answer 35

Poor oxygen uptake in some alveoli cannot be compensated by increased uptake in others

Question 36

What problems can lengthen the diffusion pathway?

Answer 36

``` Pulmonary oedema Asbestosis Fibrosis alveolitis Extrinsic allergic alveolitis Pneumoconiosis ```

Question 37

What is type 2 respiratory failure due to? (Oxygen not getting in)

Answer 37

A ventilation failure

Question 38

What can cause type II respiratory failure? (Oxygen not getting in and Co2 not getting out)

Answer 38

Respiratory depression due to narcotics - opioid analgesics Muscle weakness (upper/lower motor neurones) Chest wall problems - scoliosis/kyphosis - trauma - pneumothorax Difficulty ventilating lungs due to - high airway resistance - COPD - asthma

Question 39

Acute effects of type II resp failure?

Answer 39

Increased pCO2 and decreased pO2 | Breathlessness

Question 40

Chronic effects of type II resp failure where there is CO2 retention?

Answer 40

Co2 retention - CSF acidity corrected by choroid plexus (produce more HCO3-) - central chemoreceptors reset to higher CO2 level - persisting hypoxia - reduction of respiratory drive, now driven by hypoxia via peripheral chemoreceptors

Question 41

What are the chronic effects of the pulmonary circulation with type II respiratory failure?

Answer 41

Effects of hypoxia on pulmonary arterioles - pulmonary hypertension - right heart failure - cor pulmonale

Question 42

What are other effects of hypoxia?

Answer 42

Increased oxygen transport capacity Increased haemoglobin (polycythaemia) 2,3-BPG

Question 43

What can cause a barrel shaped chest?

Answer 43

Narrowing of small airways. | Makes it difficult to force air through them during forced expiration