2020A15 Discuss the effects of ageing on the respiratory system.

 

List:

·         Summary

·         Upper airway

·         Mechanics

·         Volumes

·         Gas exchange

·         Control of breathing

 

Summary:

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:

Musculature

·   ↓Pharyngeal dilator muscle tone -> ↑risk OSA

Reflexes

·   ↓Airway reflexes -> ↓clearance of secretions -> ↑risk aspiration

 

Mechanics:

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

o  Calcification of costal cartilage

o  Joint degeneration

o  Barrel shape -> flattened diaphragm -> mechanical disadvantage

o  Osteoporosis -> kyphosis, ↑A-P diameter

Musculature

·   Sarcopaenia (type II > type I) -> ↓PEFR, ↓FEV1, ↓MVV

Breathing pattern

·   Small ↑airflow resistance

·   Large ↓resp system compliance

·   Hence ↑RR, ↓RV but ↔MV

 

Volumes:

Volumes

·   Senile emphysema ->

o   ↑↑RV (~1%/year), ↑FRC (~0.2%/year)

o   ↓FVC (~0.5%/year), ↓ERV

·   Complex effect on TLC; minimal change overall

o   ↑Lung compliance -> ↑TLC

o   ↓Chest wall compliance -> ↓TLC

o   Atrophy of intervertebral discs -> ↓thoracic height -> ↓TLC

o   Altered geometry -> hyperinflation -> ↑TLC

 

Closing capacity

·   Senile emphysema -> ↓airway splinting in expiration

o   ↑closing capacity -> ↑shunt -> ↓PaO2

§   Present when standing

§   Worse when standing

 

Gas exchange:

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

o   ↑Alveolar dead space (but ↔PaCO2)

o   ↑Shunt (with ↓PaO2)

Diffusion

·   ↑Alveolar thickness (fibrosis)

·   ↓Alveolar surface area (senile emphysema)

-> ↓DLCO (0.2mL/mmHg/year)
-> ↓PaO2 if diffusion-limited exchange

Overall

·   ↓O2 transfer + ↓max cardiac output + sarcopaenia-> ↓VO2max
(~1% per year)

 

Control of breathing:

Chemoreceptors

·   Dysfunction of central and peripheral receptors

Respiratory centre

·   ↑Periodic breathing

·   ↓↓Response to ↓PaO2 and ↑PaCO2

·   ↑Toxicity of opioids

 

 

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