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Difficulty: EasyCardiovascular System

A 7171-year-old man is evaluated in the emergency department for severe, progressive shortness of breath over the past two days. He has a complex medical history that includes ischemic cardiomyopathy and chronic obstructive pulmonary disease. On physical examination, he is tachypneic and sitting upright in bed. Auscultation of the lungs reveals diffuse bilateral expiratory wheezing with faint crackles at the bases. To help distinguish between a pulmonary and a cardiovascular etiology for his acute presentation, the physician orders a rapid serum laboratory test that measures a specific endogenous polypeptide. The test results show a markedly elevated concentration of this polypeptide, supporting acute decompensated heart failure as the primary cause of his symptoms.

What is the primary physiologic stimulus for the secretion of the polypeptide measured in this patient?

  1. Ventricular myocyte stretchingAnswer
  2. B
    Decreased alveolar partial pressure of oxygen
  3. C
    Reduced renal perfusion pressure
  4. D
    Bronchial mucosal inflammation
  5. E
    Decreased central venous return

Answer

Ventricular myocyte stretching
The clinical scenario describes a patient with dyspnea of unclear etiology where a serum polypeptide confirms acute decompensated heart failure. This diagnostic polypeptide is Brain Natriuretic Peptide (BNP). The primary physiologic stimulus for the synthesis and secretion of BNP is the stretching of ventricular myocytes due to volume expansion and pressure overload. BNP acts to promote diuresis, natriuresis, and vasodilation to counteract this fluid overload.

Step-by-Step Solution

1
Identify the clinical dilemma and the diagnostic test used.
The patient has symptoms common to both COPD and heart failure (wheezing, dyspnea). The specific polypeptide measured to differentiate these conditions is Brain Natriuretic Peptide (BNP).
Wheezing can occur in heart failure (cardiac asthma), making clinical differentiation difficult. BNP is the standard biomarker used to confirm a cardiac etiology.
2
Determine the pathophysiologic trigger for the release of this biomarker.
BNP is synthesized and secreted by the ventricular myocardium in response to stretch and increased wall tension.
Volume overload in heart failure causes ventricular stretch, triggering BNP release to promote diuresis and vasodilation to counteract the overload.

Key Concept

Brain Natriuretic Peptide (BNP) is a hormone secreted primarily by ventricular myocytes in response to increased ventricular wall tension and stretching caused by volume or pressure overload.
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Topics

Cardiovascular System

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