Altered Lung Mechanics in Disease

Fibrotic lung disease

• Compliance is reduced, and pressure volume curve is reduced and shifted to the right
• Flow is normal or even increased
• Also occurs in interstitial and alveolar oedema, sarcoidosis, ARDS
• Pulmonary tissue viscous resistance also increases in fibrotic disease - resistance of lobes etc rubbing over each other
• FEV and FVC both reduced therefore in restrictive conditions - the ratio remains normal or is even increased

Emphysema

• Steeper curve, shifted to the left
• Dynamic compression of airways can occur with mild exercise causing severe disability
• FEV reduced more than FVC - ratio <0.8 - due to loss of elastic tissue recoil surrounding the airways

Asthma/bronchitis

• Parallel curve shifted upwards - meaning compliance does not change, although lung volume needs to be increased
• increased airway resistance due to bronchospasm
• FEV reduced more than FVC