Pathophysiology
II-13. Effects of prolonged smoking on airways and lung elastic fibers
長期喙煙の気道・肺弾性線維への影響
Obstructive Lung Disease
- Examples: COPD (emphysema), bronchial asthma (allergic inflammation + lower airway hyperresponsiveness).
- Initially hypoxemic (type 1) → long-term hypercapnic/global (type 3) failure; comorbidities (cardiac failure).
Effects of Cigarette Smoking on Lungs
- Epithelial cells: express pro-inflammatory mediators → chronic inflammation (TGF-β → fibroblasts, IL-8 → neutrophils, TNF-α → alveolar macrophages).
- Alveolar macrophages: chemotactic factors → activate fibroblasts, neutrophils, CD8⁺ T-cells.
- Neutrophils: neutrophil elastase digests interstitial elastic structures → ↓elasticity, ↑compliance → emphysema (hyperinflation); mucus hypersecretion.
- Fibroblasts: → lung fibrosis.
- Net: smoking + irritants → oxidant production → emphysema + mucus hypersecretion.
Smoking-Induced Systemic Inflammation
- One inflammatory mechanism amplifies another. Smoking →:
- ↑ROS (systemic) → cardiovascular disease, T2DM, cachexia, osteoporosis.
- ↑TNF-α (CRP-mediated) → COPD, CVD, T2DM, cachexia, osteoporosis.
- Heart failure link: smoking → atherosclerotic plaque formation/inflammation → coronary AS → ↓myocardial contractility → ↓CO → pulmonary congestion (diastolic HF) → interstitial edema → ↓O₂ diffusion.
- Pulmonary congestion → airway narrowing (obstructive disorder) + ↓lung compliance (restrictive disorder).
Cardiac & Musculoskeletal Effects
- ↓pO₂ → mean pulmonary arterial pressure ↑ linearly = pulmonary hypoxic vasoconstriction (physiological).
- Skeletal muscle wasting: disability relates to musculoskeletal dysfunction. Inactivity (dyspnea) + inflammation/oxidative stress → ↓protein synthesis + ↑degradation → muscle wasting (shared COPD + heart failure mechanism, smoking background).
一問一答
▶What are the two main obstructive lung diseases and their basis?
COPD (emphysema) and bronchial asthma (allergic inflammation + lower airway hyperresponsiveness).
▶How do epithelial cells contribute to smoking-induced lung inflammation?
They express pro-inflammatory mediators: TGF-β (→ fibroblasts), IL-8 (→ neutrophils), and TNF-α (→ alveolar macrophages), driving chronic inflammation.
▶How does neutrophil elastase cause emphysema?
Neutrophil elastase digests interstitial elastic structures → ↓elasticity, ↑compliance → emphysema (hyperinflation), with mucus hypersecretion.
▶What are the net pulmonary effects of smoking and irritants?
Oxidant production causing emphysema plus mucus hypersecretion (and fibroblast-driven fibrosis).
▶What is the role of alveolar macrophages in smoking-induced lung damage?
They release chemotactic factors that activate fibroblasts, neutrophils, and CD8⁺ T-cells.
▶How does smoking link to heart failure?
Smoking → atherosclerotic plaque/inflammation → coronary AS → ↓myocardial contractility → ↓CO → pulmonary congestion (diastolic HF) → interstitial edema → ↓O₂ diffusion.
▶How does smoking cause systemic inflammation via ROS and TNF-α?
↑ROS (systemic) → cardiovascular disease, T2DM, cachexia, osteoporosis; ↑TNF-α (CRP-mediated) → COPD, CVD, T2DM, cachexia, osteoporosis.
▶How can pulmonary congestion cause both obstructive and restrictive defects?
It narrows airways (obstructive disorder) and reduces lung compliance (restrictive disorder).
▶What is pulmonary hypoxic vasoconstriction?
A physiological response where decreasing pO₂ raises mean pulmonary arterial pressure linearly, redirecting blood from poorly ventilated regions.
▶How does skeletal muscle wasting develop in COPD/heart failure?
Inactivity (from dyspnea) plus inflammation/oxidative stress → ↓protein synthesis + ↑degradation → muscle wasting (a shared mechanism on a smoking background).
▶How does emphysema change lung mechanics?
Loss of elastic fibers decreases elasticity and increases compliance, leading to hyperinflation.
▶Which immune cell type is recruited in smoking-related airway inflammation alongside neutrophils?
CD8⁺ T-cells (activated by alveolar macrophage chemotactic factors).
▶How does obstructive lung disease typically progress in terms of respiratory failure?
It begins hypoxemic (type 1) and becomes hypercapnic/global failure long-term, often with cardiac failure comorbidity.
▶Which mediator from epithelial cells recruits neutrophils in smoking-induced inflammation?
IL-8.
▶Which epithelial mediator activates fibroblasts to drive lung fibrosis in smokers?
TGF-β.
▶What systemic diseases are promoted by smoking-driven chronic inflammation?
Cardiovascular disease, type 2 diabetes, cachexia, and osteoporosis (via ROS and TNF-α).
▶Why is COPD considered a systemic, not just pulmonary, disease?
Smoking-driven systemic inflammation (one mechanism amplifying another) links it to cardiovascular disease, T2DM, cachexia, osteoporosis, and muscle wasting.
▶How does smoking reduce O₂ diffusion through a cardiac mechanism?
It causes pulmonary congestion (diastolic heart failure) → interstitial edema, which thickens the diffusion barrier.
▶What is the basis of bronchial asthma as an obstructive disease?
Allergic inflammation combined with lower airway hyperresponsiveness.
▶What relates disability to musculoskeletal dysfunction in COPD?
Skeletal muscle wasting from inactivity plus inflammation/oxidative stress is a major contributor to disability.