Which pathophysiology best explains the patient’s dyspnea after a long flight and a negative stress test?

• A. Arterial thrombosis
• B. Venous thrombosis in calf vein that travelled to the lungs
• C. Bacterial pneumonia
• D. Air embolism

Answer: (B)

Prolonged immobility during a long flight can lead to venous thrombosis in the calf. If a clot breaks free, it can travel to the lungs and cause a pulmonary embolism. When a thrombus lodges in branches of the pulmonary arteries, it obstructs blood flow to parts of the lung, creating a ventilation–perfusion mismatch and increasing dead space. This mismatch triggers sudden or worsening dyspnea and often tachycardia, with hypoxemia contributing to the symptom. A negative stress test makes cardiac ischemia a less likely cause of the dyspnea, pointing toward a pulmonary origin. The other options don’t fit as well: arterial thrombosis would affect the systemic circulation and limbs rather than cause acute pulmonary symptoms; bacterial pneumonia would typically present with fever and productive cough; air embolism is less likely in this scenario without a provoking event.