Session 5 - Control of breathing, and asthma

Question 1

Define hypoxia

Answer 1

Falls in po2

Question 2

Define hyper and hypocapnia

Answer 2

Hypercapnia – Rises in pCO2

Hypocapnia – Falls in pCO2

Question 3

Define Hyper and hypoventilation

Answer 3

Hyperventilation – Ventilation increase with no change in metabolism

Hypoventilation – Ventilation decrease with no change in metabolism

Question 4

Describe the effects of hyperventilation on plasma PH

Answer 4

Hyperventilation will result in an increase in pO2 and decrease in pCO2 of blood, therefore plasma pH will increase

Question 5

Define respiratory acidosis

Answer 5

Acidosis of the blood caused by hypercapnia which in turn is caused by hypoventilation.

Question 6

Define respiratory alkalosis

Answer 6

Alkalosis of the blood caused by hypocapnia which in turn is caused by hyperventilation.

Question 7

At what pH point are acidosis and alkalosis lethal? What happens in each scenario?

Answer 7

If plasma pH falls below 7.0 enzymes are lethally denatured.

If plasma pH rises above 7.6, free calcium concentration falls enough to produce fatal tetany.

Question 8

How does the body compensate for chronic increases or decreases in pco2?

Answer 8

Kidneys can produce or excrete hco3

Question 9

Define metabolic acidosis

Answer 9

If tissues produce acid, this reacts with HCO3 to lead to a fall in pH

Question 10

Define metabolic alkalosis

Answer 10

If plasma [HCO3] rises, e.g. after vomiting, then plasma pH rises

Question 11

How can the body compensate for acute cases of metabolic acidosis / alkalosis?

Answer 11

Breathing more or less to increase or decrease ppCO2

Question 12

How is hypoxia detected by the body?

Answer 12

Arterial pO2 monitored by peripheral chemoreceptors in the carotid and aortic bodies

Chemoreceptors designed to detect when they do not have enough oxygen to meet their metabolic needs.

Chemoreceptors have a very high blood flow and so will not be hypoxic until pO2 falls very low.

Question 13

How is hyper / hypocapnia detected by the body? How is any changes in co2 corrected?

Answer 13

Central chemoreceptors.

• Respond to changes in the pH of the CSF which separated from the blood by the BBB.
• CSF [HCO3] controlled by choroid plexus cells
• CSF pCO2 determined by arterial pCO2.
• Therefore, CO2 in the CSF rises alongside the arterial CO2, and since [HCO3] can’t cross the BBB, the pH in the CSF will decrease. o Will result in increased ventilation – Lowering pCO2 and restoring CSF pH
• Persistent changes in pH corrected by choroid plexus cells which change the [HCO3]

Question 14

Define type 1 respiratory failure

Answer 14

pO2 of arterial blood is low.

Question 15

Define type 2 respiratory failure

Answer 15

pO2 of arterial blood is low and pCO2 is high.

Question 16

Give 3 ways in which type 1 respiratory failure can occur and examples of each way

Answer 16

Thickening of the alveolar membrane – slows gas exchange, pCO2 crosses alveolar membrane more easily than oxygen, therefore oxygen affected first, e.g. Fibrotic lung disease.

Destruction of alveoli – Reduces surface area for gas exchange, e.g. Emphysema. Affects O2 first.

Fluid in Interstitial space – Increases diffusion distance, e.g. pulmonary oedema. Affects O2 first

Question 17

Give 3 ways in which type 2 respiratory failure can occur and examples of each.

Answer 17

Type 2 Resp failure is caused by ineffective respiratory effort, this can be due to:

• Poor respiratory effort – respiratory depression by narcotics, muscle weakness by upper or lower motor neurone disease.
• Chest wall problems – Trauma, scoliosis, or pneumothorax
• Difficulty ventilating the lungs – High airway resistance, COPD, asthma

Type 2 respiratory failure results from a decrease in oxygen and an increase in CO2, caused by ventilation failure.

Question 18

Define asthma

Answer 18

A chronic disorder characterised by airway wall inflammation and airway wall remodelling with reversible airflow obstruction.

Question 19

Describe the pathophysiology of asthma

Answer 19

Airway smooth muscle (ASM) contracts due to triggers – Muscarinic agonists, histamine, cold air, etc.

Over time the ASM may become thicker due to remodelling and restrict air flow In allergic asthma, the allergen triggers an inflammatory response in the lungs, resulting in alveolar destruction, much like emphysema

Question 20

What are the symptoms of asthma?

Answer 20

• Wheeze – caused narrowed airways
• Breathlessness – With exercise or during acute exacerbations, due to airways not relaxing
• Chest tightness
• Cough – Dry cough, often worse at night.
• Variable airflow obstruction

Question 21

What would you hear upon chest auscultation of an asthma sufferer?

Answer 21

polyphonic wheeze

Question 22

What would airway function tests reveal in an asthma patient?

Answer 22

Low PEFR and low FEV1/FVC ratio which is increased following salbutamol

Question 23

Describe the management of asthma

Answer 23

• Education – Correct recognition of symptoms, use of medication, personal asthma action plan
• Stop smoking
• Get fresh air
• Weight loss
• Exposure to allergens/triggers
• Use airway relaxants – B2 agonists, muscarinic antagonists
• Use anti-inflammatory agents – corticosteroids, leukotriene receptor antagonist