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肺塞栓症 I: 序論
肺塞栓症（PE）は、血栓、脂肪または空気塞栓、羊水、または腫瘍組織が一つまたは複数の肺動脈を塞ぐことによって発生します。これらの塞栓は、静脈系または右心系から起こります。
病因
PEは主に深部静脈血栓症（DVT）と、先天性血栓性素因などの他の高凝固状態から発生します。その他の病因としては、肥満に見ら…
肺塞栓症は、血栓、羊水、腫瘍組織、脂肪、または空気塞栓が静脈を通って移動し、1つ以上の肺動脈を塞ぐときに発生します。
これは通常、深部静脈血栓症の脱落または断片化、遺伝性血栓症などの凝固亢進状態、および肥満の静脈うっ滞から発生します。
肺塞栓症は、脱落した血栓または塞栓が静脈系を通って移動し、右心房と心室を通過して肺動脈に入るときに始まります。
小さな塞栓が末端の肺細動脈を塞ぎ、複数の小さな肺梗塞や虚血性肺組織壊死を引き起こす可能性があります。
血栓が大きいと、肺動脈が閉塞し、血流が乱れ、換気と灌流の不一致を引き起こし、低酸素血症を引き起こす可能性があります。
この閉塞はまた、炎症反応を引き起こし、局所的な血管収縮を引き起こし、血管透過性を高めます。これらの変化は、肺動脈と右心室の圧力を上昇させ、右心室不全を引き起こす可能性があります。
小さな塞栓は、呼吸困難、胸痛、パチパチという音や喘鳴、肺の心音の強調を引き起こす可能性があります。
大規模な塞栓は心肺停止を引き起こす可能性があります。
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Q1: What causes a pulmonary embolism to develop?
A pulmonary embolism occurs when a thrombus, fat, air, amniotic fluid, or tumor tissue travels through the venous system and blocks pulmonary arteries. It commonly arises from dislodged deep vein thrombosis, hypercoagulable states like inherited thrombophilias, and venous stasis in obesity. Risk factors include prolonged immobility, recent surgery, cancer, oral contraceptives, and pregnancy.
Q2: How does a blood clot travel to the lungs during pulmonary embolism?
When a thrombus dislodges, it travels through the venous system, passing through the right atrium and ventricle before lodging in the pulmonary arteries. Small emboli may block terminal pulmonary arterioles, causing multiple small lung infarctions. Larger thrombi obstruct major pulmonary arteries, disrupting blood flow and causing ventilation-perfusion mismatch.
Q3: What happens to the lungs when a pulmonary embolism blocks blood flow?
Pulmonary artery obstruction increases vascular resistance and elevates pressures in the pulmonary arteries and right ventricle, potentially causing right ventricular failure. The blockage triggers an inflammatory response, causing local vasoconstriction and increased vascular permeability. This creates a ventilation-perfusion mismatch where lung areas receive ventilation but lack perfusion, impairing gas exchange and leading to hypoxemia.
Q4: What are the symptoms of a small pulmonary embolism?
Small emboli may cause vague and transient symptoms including dyspnea, mild to moderate hypoxemia, tachypnea, cough, chest pain, hemoptysis, wheezing or crackles, fever, tachycardia, accentuation of the pulmonic heart sound, and syncope. Symptoms begin gradually or appear suddenly depending on the degree of pulmonary arterial blockage.
Q5: What are the signs of a massive pulmonary embolism?
Massive pulmonary emboli may result in sudden changes in mental status, feelings of impending doom, hypotension, and cardiorespiratory arrest. These severe manifestations reflect the degree of pulmonary arterial blockage and the severity of hemodynamic and respiratory compromise. Prompt recognition and intervention are critical to manage massive PE and mitigate the risk of fatal outcomes.
Q6: What risk factors increase the likelihood of developing pulmonary embolism?
Risk factors for pulmonary embolism include prolonged immobility, recent pelvic or lower extremity surgery, history of venous thromboembolism, cancer, obesity, oral contraceptives or hormone therapy, smoking, prolonged air travel over four hours, heart failure, and pregnancy. Endothelial injury from surgery and trauma also increases PE risk.
Q7: How does obesity contribute to pulmonary embolism development?
Obesity promotes pulmonary embolism through venous stasis, a condition where blood flow slows in the veins, increasing the risk of thrombus formation. Venous stasis combined with hypercoagulable states and endothelial injury creates an environment favoring clot development and dislodgement. This mechanism makes obesity a significant etiological factor in PE pathogenesis.