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What causes dyspnea in heart failure

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"Heart Failure"[MeSH Terms] AND dyspnea

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heart failure dyspnea mechanism pulmonary venous congestion increased filling pressure

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Dyspnea in heart failure is mainly caused by elevated left-sided cardiac filling pressures, leading to pulmonary venous congestion.
  1. Backward pressure into the lungs
    When the left ventricle cannot fill or pump effectively, pressure rises in the left atrium and pulmonary veins. This increases pulmonary capillary hydrostatic pressure.
  2. Interstitial and alveolar pulmonary edema
    Fluid moves from pulmonary capillaries into the interstitium and, if severe, alveoli. This makes the lungs stiffer, reduces compliance, and increases the work needed to breathe. It also stimulates pulmonary vagal receptors, producing a sensation of breathlessness.
  3. Impaired gas exchange in more severe congestion
    Alveolar fluid causes ventilation-perfusion mismatch and can reduce oxygenation, which further intensifies dyspnea.
  4. Reduced cardiac output during exertion
    Exercise increases oxygen demand, but a failing heart cannot increase output adequately. Rising pulmonary pressures plus inadequate systemic oxygen delivery cause early exertional dyspnea.
  5. Why orthopnea and PND occur
    • Orthopnea: lying flat increases venous return from the legs and abdomen and raises the diaphragm, worsening pulmonary congestion.
    • Paroxysmal nocturnal dyspnea: during sleep, redistribution of fluid from peripheral tissues to the central circulation can progressively worsen pulmonary edema, waking the patient gasping for breath.
This is why dyspnea is especially characteristic of left-sided heart failure. The underlying pulmonary congestion and edema are described in Robbins & Kumar Basic Pathology, p. 346. The Merck Manual overview also notes that dyspnea can occur even before major gas-exchange abnormalities, likely from elevated pulmonary venous pressure and increased work of breathing.
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