Session 5 - Control of breathing, and asthma Flashcards
Define hypoxia
Falls in po2
Define hyper and hypocapnia
Hypercapnia – Rises in pCO2
Hypocapnia – Falls in pCO2
Define Hyper and hypoventilation
Hyperventilation – Ventilation increase with no change in metabolism
Hypoventilation – Ventilation decrease with no change in metabolism
Describe the effects of hyperventilation on plasma PH
Hyperventilation will result in an increase in pO2 and decrease in pCO2 of blood, therefore plasma pH will increase
Define respiratory acidosis
Acidosis of the blood caused by hypercapnia which in turn is caused by hypoventilation.
Define respiratory alkalosis
Alkalosis of the blood caused by hypocapnia which in turn is caused by hyperventilation.
At what pH point are acidosis and alkalosis lethal? What happens in each scenario?
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.
How does the body compensate for chronic increases or decreases in pco2?
Kidneys can produce or excrete hco3
Define metabolic acidosis
If tissues produce acid, this reacts with HCO3 to lead to a fall in pH
Define metabolic alkalosis
If plasma [HCO3] rises, e.g. after vomiting, then plasma pH rises
How can the body compensate for acute cases of metabolic acidosis / alkalosis?
Breathing more or less to increase or decrease ppCO2
How is hypoxia detected by the body?
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.
How is hyper / hypocapnia detected by the body? How is any changes in co2 corrected?
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]
Define type 1 respiratory failure
pO2 of arterial blood is low.
Define type 2 respiratory failure
pO2 of arterial blood is low and pCO2 is high.
Give 3 ways in which type 1 respiratory failure can occur and examples of each way
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
Give 3 ways in which type 2 respiratory failure can occur and examples of each.
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.
Define asthma
A chronic disorder characterised by airway wall inflammation and airway wall remodelling with reversible airflow obstruction.
Describe the pathophysiology of asthma
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
What are the symptoms of asthma?
- 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
What would you hear upon chest auscultation of an asthma sufferer?
polyphonic wheeze
What would airway function tests reveal in an asthma patient?
Low PEFR and low FEV1/FVC ratio which is increased following salbutamol
Describe the management of asthma
- 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
