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

- Sarcopaenia (type II > type I) → ↓ PEFR, ↓ FEV1, ↓ MV

Breathing pattern

- Small ↑ airflow resistance

- Large ↓ resp system compliance

- Hence ↑ RR, ↓ RV but ↔MV

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)
→ ↓ PaO2 if diffusion-limited exchange

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


Last updated 2021-08-23

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