After careful auscultation, the treating paramedics conclude that James’ respiratory distress is secondary to pulmonary oedema. What is the primary mechanism of acute pulmonary oedema in a patient with this type of cardiomyopathy? (Multiple Choice)

Question

BlackTom AI · Accepted Answer

Left ventricular systolic dysfunction elevates left ventricular end-diastolic pressure (LVEDP), and that backward transmission of pressure into the pulmonary veins and capillaries is the key mechanism producing pulmonary oedema in cardiomyopathy.

1) Relevant knowledge points and concepts
- Heart failure due to cardiomyopathy commonly produces elevated LVEDP because the failing left ventricle cannot eject sufficient blood.
- Starling forces across pulmonary capillaries determine fluid movement: net filtration ∝ (Pc − Pi) − σ(πc − πi), where Pc = capillary hydrostatic pressure, Pi = interstitial hydrostatic pressure, πc = capillary oncotic pressure, and σ = reflection coefficient.
- An increase in Pc (pulmonary capillary hydrostatic pressure) drives fluid from capillaries into the interstitium and alveoli → pulmonary congestion and alveolar oedema.

2) Step-by-step reasoning
- Systolic dysfunction → reduced stroke volume and higher end-systolic volume.
- Increased end-systolic volume and stiffness/poor emptying raise LV end-diastolic pressure (LVEDP).
- Elevated LVEDP is transmitted retrograde to the left atrium and pulmonary veins, raising pulmonary capillary hydrostatic pressure (Pc).
- Raised Pc increases net filtration from capillaries into pulmonary interstitium/alveoli, overwhelming lymphatic clearance → pulmonary oedema and respiratory distress.

3) Calculational illustration (intermediate steps)
- Use simplified Starling difference: Net driving pressure ≈ (Pc − Pi) − (πc − πi). If baseline Pc = 10 mmHg and oncotic difference ≈ 20 mmHg, net driving force is negative (no oedema). If LV failure raises Pc to 20 mmHg, net driving force increases by ~10 mmHg toward filtration. With constant Kf, that increased driving pressure produces markedly more fluid extravasation into lungs.

4) Why the correct answer is correct
- "Increased left ventricular end-diastolic pressure leading to pulmonary congestion" directly describes the backwards hydrostatic transmission from a failing LV into the pulmonary circulation, which is the classic primary mechanism of cardiogenic (cardiac) pulmonary oedema.

5) Why the other options are incorrect
- Increased pulmonary vascular resistance: raises right-sided pressures and can cause pulmonary hypertension and right heart strain, but does not primarily cause the hydrostatic pulmonary oedema seen with left ventricular cardiomyopathy.
- Coronary artery occlusion causing ischemic pulmonary injury: acute MI can precipitate pulmonary oedema by causing sudden LV failure, but the option describes direct ischemic injury to the lung rather than the correct mechanism (elevated LVEDP). It’s a secondary pathway and not the primary mechanism described.
- Decreased renal function leading to fluid overload: renal failure can cause volume overload and contribute to pulmonary oedema, but in the context of left-sided cardiomyopathy the dominant primary mechanism is backward transmission of elevated LVEDP, not renal fluid retention.

6) Conclusion
The primary mechanism is increased left ventricular end-diastolic pressure leading to pulmonary congestion, which matches the provided correct answer: "2. Increased left ventricular end-diastolic pressure leading to pulmonary congestion."

After careful auscultation, the treating paramedics conclude that James’ respiratory distress is secondary to pulmonary oedema. What is the primary mechanism of acute pulmonary oedema in a patient with this type of cardiomyopathy? (Multiple Choice)单项选择题

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