2020A Question 15
Discuss the effects of ageing on the respiratory system.
Examiner Report
The major domains assessed in this question were:
- Mechanics of ventilation; in particular the changes seen with ageing on the thoracic cage, lung parenchyma and respiratory muscle function
- Ventilation and perfusion; in particular impacts on different physiological volumes and capacities, V/Q matching and gas exchange in the elderly
- Control of ventilation
Credit was given for other correct relevant material when put in context with the physiological changes.
Given the integrated nature of the major domains, errors and contradictions cast doubts over a cohesive understanding of the topic. Simple lists of changes also failed to demonstrate any understanding.
Model Answer
Structure:
- Summary
- Upper airway
- Mechanics
- Volumes
- Gas exchange
- Control of breathing
Summary
| Factor | Detail |
|---|---|
| Changes | - Degeneration of tissues - Progressive functional impairment from ~35 years |
| Implications | - Reduced reserve - Poor tolerance of stress (e.g. Exercise, post-laparotomy) - Susceptible to types 1 and 2 failure |
Upper Airway
| Factor | Detail |
|---|---|
| Musculature | - ↓ Pharyngeal dilator muscle tone → ↑ Risk OSA |
| Reflexes | - ↓ Airway reflexes → ↓ Clearance of secretions → ↑ Risk aspiration |
Mechanics
| Factor | Detail |
|---|---|
| Airway resistance | - Senile emphysema → ↓ Radial traction → ↑ Dynamic compression in forced expiration → ↓ PEFR, ↓ FEV1 |
| Lung compliance | - Senile emphysema → ↓ Elastic recoil → ↑ Risk of breath stacking during mechanical ventilation |
| Chest wall compliance | - ↓ Compliance → ↓ Outward recoil → ↑ Work of breathing: Due to - Calcification of costal cartilage - Joint degeneration - Barrel shape → Flattened diaphragm → Mechanical disadvantage - Osteoporosis → Kyphosis, ↑ A-P diameter |
| Musculature | |
| Breathing pattern | - Small ↑ airflow resistance - Large ↓ resp system compliance |
Volumes
| Factor | Detail |
|---|---|
| Volumes | - Senile emphysema → - ↑↑ RV (~1%/year), ↑ FRC (~0.2%/year) - ↓ FVC (~0.5%/year), ↓ ERV - Complex effect on TLC; minimal change overall - ↑ Lung compliance → ↑ TLC - ↓ Chest wall compliance → ↓ TLC - Atrophy of intervertebral discs → ↓ Thoracic height → ↓ TLC - Altered geometry → Hyperinflation → ↑ TLC
|
| Closing capacity | - Senile emphysema → ↓ Airway splinting in expiration - ↑ Closing capacity → ↑ Shunt → ↓ PaO2 - Present when standing - Worse when standing
|
Gas Exchange
| Factor | Detail |
|---|---|
| Ventilation | - Senile emphysema → ↓ Radial traction → Small airway closure → ↓ PaO2 - Sarcopaenia → ↓ MVV |
| Perfusion | - ↓ Cardiac output → ↓ O2 transfer (perfusion-limited in health) |
| Matching | - Widening of V&Q scatter from apex to base → Impaired gas exchange - ↑ Alveolar dead space (but ↔PaCO2) - ↑ Shunt (with ↓ PaO2) |
| Diffusion | - ↑ Alveolar thickness (fibrosis) - ↓ Alveolar surface area (senile emphysema) → ↓ DLCO (0.2mL.mmHg-1.year-1) |
| Overall | - ↓ O2 transfer + ↓ Max cardiac output + Sarcopaenia→ ↓ VO2max (~1% per year) |
Control of Breathing
| Factor | Detail |
|---|---|
| Chemoreceptors | - Dysfunction of central and peripheral receptors |
| Respiratory centre | - ↑ Periodic breathing - ↓↓ Response to ↓ PaO2 and ↑ PaCO2 - ↑ Toxicity of opioids |