Describe the effects of ageing on the respiratory system.
5% of candidates passed this question.
Answers should have included the effects of ageing on the efficiency of gas exchange, how the expected PaO2 changes with age, and its causation. Anatomical changes should have been included as should changes in lung volumes, particularly the significance of an increased closing volume. Marks were not awarded for the effects of disease states.
Definition
- Ageing is the accumulation of irreversible molecular and cellular damage over time
- Respiratory System maximal function is reached at age 20 (F) and 25 (M)
- Throughout the remainder of life, ageing is associated with a progressive decline in respiratory performance
Compliance/Resistance
Ageing
Effect on Compliance/Resistance
Rib cage calcification and osteoporotic changes in the shape of the thorax
↓CW Compliance
Imbalance of crosslinking in elastic fibre network → static elastic recoil pressure declines
Loss of elastic recoil of lung parenchyma (increased distensibility)
Peripheral airway closure contributes minimally to total RAW and when adjusted for lung volume changes
RAW stable
Lung Volumes/PFTs
Ageing
Effect on Lung Volumes/PFTs
↓supporting tissue of small airways → premature airway closure
↑Closing Volume
↓bronchiole diameter
↓Expiratory Flow
↓elastic recoil → lungs more distensible |
↑Residual Volume
↑CW elastic recoil + ↓elastic recoil of lung parenchyma (ie breathing at higher lung volumes)
↑FRC
↓elastic recoil counterbalanced by increased elastic load of CW
TLC not much change
↓CW Compliance + Increased Lung distensibility (reduced elastic recoil parenchyma)
↓FEV1
↓FVC
↓Peak Flow
Reduction of maximal inspiratory flow will determine bronchodilator use; lung deposition will not be achieved if high insp flow rates required
WoB
Ageing
Effect on WoB
Osteoporosis & Vertebral fractures → Increased AP diameter & Kyphosis → modify curvature & compliance of Diaphragm
↓ability to generate force = Increased WoB
Increased FRC
Elderly breathe at higher lung volumes cf younger subjects → increasing elastic load on CW
↑WoB during normal tidal breathing
↓nutrition = ↓respiratory muscle strength
↑WoB
Kyphosis + Increase AP diameter = ↓ force generation by diaphragm
↑WoB
Respiratory muscle dysfn
Hypoventilation, SOB, reduced exercise tolerance, resp failure
Gas Exchange
Ageing
Effect on Gas Exchange
Increase in V/Q units with high ratio (dead space) + low V/Q ratio (shunt/venous admixture)
Large no’s of low V/Q units due to an increase Closing Volume (as CV approaches/= FRC) → premature airway closure
Especially prominent in the peripheral airways due to loss of supporting tissues
↓PaO2
↓A-a difference
Reduction in transfer of CO due to;
increased V/Q heterogeneity, reduced alveolar SA, rection in capillary blood volume
↓TLCO
Dilation of alveoli and enlargement of air spaces
↓SA for gas exchange
Control of Ventilation
Ageing
Effects on Ventilation
MV same at rest
with↑ RR and ↓Vt
Reduced ability to receive signals, integrate and generate appropriate output
↓response to hypoxia & hypercapnia