Applied Respiratory Physiology — Ageing

Basic Changes

• Limited reserve
• ↓ Airway protective reflexes
• ↓ Respiratory Muscle Strength
  • ↓ Maximal inspiratory pressure, Transdiaphragmatic pressure
  • ↓ Maximum voluntary ventilation
• ↓ Elastic recoil of lung tissue (changes in the spatial arrangement and/or crosslinking of the elastic fibre network)
• Stiffening of chest wall and calcification of costal cartilages, ↓ in size of intervertebral spaces
• Loss of alveolar surface area and pulmonary capillary blood volume
• Compliance
  • Chest wall compliance decreased (due to stiffening and structural changes)
  • Lung compliance – normal or increased
  • Total respiratory compliance normal or decreased

Static Respiratory Compliance (= Slope)

W = Chest wall
L = Lung
RS = Respiratory system

A – 20yr old man
B – 60 year old man

In elderly:
Compliance ↓ , RV & FRC ↑ ­, Static recoil pressure ↓

Static pressure–volume curves of the lungs.

Static recoil pressure (~transpulmonary pressure) plotted against lung volume

Lung Function

PFT:

• ↓ FEV1 (non-linear, accelerating in decline after 70 yrs)
• ↓ FVC
• TLC unchanged
• ↓ VC
• ↑ FRC (due to structural chest wall changes – kyphosis, increasing AP diameter)
• ↑ RV (Increased air trapping)
• ↑ CV/CC → airways close during normal TV (due to reduction in supporting tissues)

Gas Exchange:

• Anatomical dead space increases
• Ventilation-perfusion matching is increasingly mismatched
  • Increase in units with low V/Q (dependent parts)
• pO2 falls ~ 0.3mmHg/yr
• Decreased Diffusion capacity

Others

Exercise capacity

• ↓ VO2 max
• ↑ Dead space ventilation

Immunology

• Bronchial fluid
  • ↑ Neutrophils %
  • ↑ Ratio of CD4+/CD8+ cells
• ↓ Epithelial lining fluid antioxidants

Regulation of Breathing

• Diminished Ventilatory response to hypoxia and hypercapnoea
• Increased oxygen cost of breathing for a given Minute ventilation
• Obstructive pattern develops even in lifetime non-smokers

Source: https://thoracickey.com/aging-of-the-respiratory-system/

JC 2019

Answer by JC