Expansion
Impaired clearance, carboxyhaemoglobin, protease imbalance and accelerated decline in FEV1
Expansion
Immediate
- Carboxyhaemoglobin of 5 to 10 per cent, reducing oxygen carriage and shifting the curve left
- Nicotine-induced tachycardia, hypertension and vasoconstriction
- Bronchoconstriction and increased airway resistance
Short term
- Cilia are slowed and destroyed, so mucociliary clearance fails
- Goblet cell hyperplasia with mucus hypersecretion
Long term
- Protease-antiprotease imbalance: smoke recruits neutrophils and macrophages releasing elastase, and oxidises alpha-1 antitrypsin so that it cannot inhibit it. The result is emphysema
- Accelerated FEV1 decline, from about 30 ml per year to 60 to 90 ml per year in susceptible smokers
- Small airway fibrosis, and loss of the alveolar capillary bed
Reversibility is an important point for counselling. Carbon monoxide clears within a day and cilia recover over months. The rate of FEV1 decline returns towards normal after stopping, so lung function already lost is not regained but further loss is slowed, and stopping is beneficial at any age.