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Which condition is most likely responsible for these findings?
Dr. Shoaib Ahmad Baig
December 15, 2024
🔍 Question
A 63-year-old man presents with a 1-week history of worsening shortness of breath and a persistent cough. He reports difficulty breathing when lying flat and uses three pillows to sleep comfortably. Two weeks ago, he underwent treatment for a heart attack, including the placement of two stents in the left anterior descending artery. His medical history includes hypertension and type 2 diabetes mellitus. On examination, his blood pressure is 120/80 mm Hg, heart rate 92/min, respiratory rate 22/min, and oxygen saturation 89% on room air. Auscultation reveals bilateral lung crackles and an S3 heart sound.
Which condition is most likely responsible for these findings?
A. Decreased alveolar surface tension
B. Decreased lung compliance
C. Increased dead space ventilation
D. Increased functional residual capacity
E. Left-to-right cardiac shunting
Correct Answer: B. Decreased Lung Compliance
⚙️
🔻 Step 1: Myocardial Infarction
Acute MI → Ischemic injury to LV ⚙
⬇
🧠 Reduced left ventricular (LV) contractility → Systolic dysfunction
⬇
↑ LV end-diastolic pressure (LVEDP) → Blood backs up to pulmonary veins
⬇
Pulmonary venous congestion 🧠
⬇
Fluid leaks into alveoli → Pulmonary edema (causes dyspnea, crackles, hypoxemia)
🔻 Step 2: Pulmonary Edema Effects
Fluid in alveoli ⚙
⬇
🧠 ↓ Lung compliance (stiff lungs → harder to breathe)
⬇
⚖ Orthopnea: Supine position redistributes fluid → Worsens dyspnea
⬇
S3 gallop → Marker of LV volume overload
🔻 Step 3: Exam Findings & Diagnostic Reasoning
• Crackles: Fluid in alveoli due to pulmonary congestion
• S3 Gallop: LV dysfunction (systolic overload)
• Hypoxemia: Impaired gas exchange in flooded alveoli
🪣 Pulmonary Edema as an Overflowing Bucket
• Think of the LV as a pump, and the pulmonary veins as a bucket.
• When the pump fails (LV dysfunction), the bucket fills with water (blood).
• If the bucket overflows, water (fluid) spills into the alveoli → Pulmonary edema.
🧠 Orthopnea as a Tipped Bucket
• Supine position tips the bucket → Redistributes fluid to the lungs → Worsens dyspnea.
⚖️ Explanation of Other Differentials
Differential | Reason |
|---|---|
Decreased alveolar surface tension | Alveolar tension is maintained by surfactant. Pulmonary edema increases tension (opposite effect). 🧠 |
Increased dead space ventilation | Dead space = ventilation without perfusion. Pulmonary edema impairs oxygenation but does not cause dead space. 🔍 |
Increased functional residual capacity (FRC) | FRC = lung volumes after normal exhalation. Pulmonary edema ↓ FRC (stiff lungs). ⚖ |
Left-to-right cardiac shunting | Requires congenital defect or structural abnormality (e.g., VSD). Not present here. 🧠 |
📝 Flashcards
Stay Hungry, Stay Curious!
Your Brother In This Struggle
Dr. Shoaib Ahmad
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