4.2
慢性閉塞性肺疾患 II: 病態生理学
慢性閉塞性肺疾患 (COPD) の病態生理学は複雑で多面的であり、生理学的プロセスの複雑な相互作用が関係しています。これらのメカニズムを理解することは、COPD を効果的に管理および治療するために不可欠です。ここでは、COPD の病態生理学における重要な要素について詳しく説明します。
慢性炎症
- 刺激…
慢性閉塞性肺疾患(COPD)は、主にタバコの煙、ほこり、大気汚染などの刺激物への曝露による慢性的な気道の炎症によって引き起こされます。
リンパ球、マクロファージ、好中球などの炎症細胞が気道壁に侵入し、ロイコトリエンやサイトカインなどの有害なメディエーターを放出します。
これらの炎症細胞によって産生される吸入粒子と酸化剤は、炎症を悪化させます。
酸化剤は、肺組織の破壊から保護する抗プロテアーゼ化合物を阻害します。
同時に、それらは肺組織を分解するプロテアーゼ酵素の活性を高めます。
この不均衡は、プロテアーゼと抗プロテアーゼの間の自然なバランスを乱し、肺胞の劣化や肺の弾力性の喪失につながります。
その結果、気道が狭くなり、空気の流れが妨げられ、過剰な粘液の生成が促進され、肺に体液が蓄積します。
COPDでは、慢性炎症が酸化ストレスを引き起こし、フリーラジカルを放出して肺組織に損傷を与え、水疱の形成や肺胞壁の悪化を引き起こし、ガス交換を損ないます。
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Q1: What causes chronic airway inflammation in COPD?
COPD develops from chronic exposure to irritants like cigarette smoke, dust, and air pollution. These irritants trigger inflammatory cells—lymphocytes, macrophages, and neutrophils—to infiltrate airway walls and release harmful mediators such as leukotrienes and cytokines. This perpetuates ongoing inflammation and progressive lung damage characteristic of the disease.
Q2: How does the protease-antiprotease imbalance damage lung tissue in COPD?
Oxidants from cigarette smoke impair antiproteases like alpha-1 antitrypsin that normally protect lung tissue. Simultaneously, oxidants increase protease activity, particularly elastase, which degrades extracellular matrix components. This imbalance causes destruction of alveolar walls and lung parenchyma, leading to emphysema and loss of lung elasticity.
Q3: What role do free radicals play in COPD pathophysiology?
Chronic inflammation generates reactive oxygen species (ROS) like superoxide anions and hydroxyl radicals from cigarette smoke and inflammatory cells. These free radicals damage cellular structures, proteins, lipids, and DNA, further promoting inflammation and lung tissue deterioration. This oxidative stress perpetuates the cycle of tissue destruction in COPD.
Q4: How does airway narrowing occur in COPD?
Chronic inflammation causes structural changes and constriction in airways, reducing airflow. Mucus hypersecretion and mucosal edema exacerbate narrowing, while smooth muscle constriction further impedes airflow. Additionally, increased vascular permeability from inflammation leads to fluid accumulation in lungs, contributing to obstruction and airway blockage.
Q5: What structural changes occur in the lungs during COPD?
Ongoing tissue destruction causes alveolar enlargement and bullae formation—large air pockets within lung tissue. Destruction of alveolar walls reduces surface area for gas exchange, impairing oxygen uptake and carbon dioxide elimination. These structural changes decrease lung compliance and elasticity, leading to reduced oxygen uptake and shortness of breath.
Q6: How do inflammatory mediators perpetuate lung damage in COPD?
Inflammatory cells release cytokines, leukotrienes, and other mediators that perpetuate the inflammatory response. These mediators recruit additional inflammatory cells and sustain the release of proteases and oxidants. This creates a self-perpetuating cycle of inflammation and tissue destruction that characterizes COPD progression.
Q7: Why is gas exchange impaired in COPD?
Destruction of alveolar walls reduces the surface area available for oxygen and carbon dioxide exchange. Combined with fluid accumulation and airway obstruction, these structural changes impair gas exchange efficiency. Understanding these mechanisms is essential for developing effective chronic obstructive pulmonary disease management strategies.