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, ↓TV but ↔MV for a given lean mass

 

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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