Why does the click in pulmonic valve stenosis decrease with inspiration?

Why the Click in Pulmonic Valve Stenosis Decreases with Inspiration

The click in pulmonic valve stenosis decreases with inspiration primarily because the increased venous return to the right heart during inspiration leads to increased right ventricular volume, which temporarily reduces the tension on the stenotic pulmonary valve, thus diminishing the audibility of the ejection click.

Physiological Mechanism

Respiratory Variation in Heart Sounds

• During inspiration, the negative intrathoracic pressure increases venous return to the right heart 1
• This increased preload causes:
  • Increased right ventricular (RV) filling
  • Temporary dilation of the RV chamber
  • Increased RV end-diastolic volume

Effect on Stenotic Pulmonary Valve

• In pulmonic stenosis, the ejection click is produced when the stenotic valve suddenly domes during ventricular systole
• During inspiration:
  • The increased RV volume reduces the initial tension on the pulmonary valve leaflets
  • The valve cusps are already partially opened due to the increased volume
  • This reduces the force and abruptness of valve opening
  • The result is a diminished or absent ejection click

Contrast with Left-Sided Murmurs

• This respiratory variation helps differentiate right-sided from left-sided cardiac pathology
• Right-sided murmurs (like pulmonic stenosis) typically increase with inspiration
• Left-sided murmurs typically become louder during expiration 1
• However, the ejection click in pulmonic stenosis follows the opposite pattern - decreasing with inspiration

Clinical Significance

Diagnostic Value

• The respiratory variation of the pulmonic ejection click is a key diagnostic finding
• This characteristic helps distinguish pulmonic valve stenosis from other valvular conditions
• The click is typically heard best at the left upper sternal border
• It occurs early in systole, before the murmur

Relationship to Severity

• The intensity of the click may correlate with the severity of stenosis
• In severe stenosis with significant RV hypertrophy, the click may be less prominent
• In mild to moderate stenosis, the click is usually more distinct

Other Auscultatory Findings in Pulmonic Stenosis

• Systolic ejection murmur at left upper sternal border
• The murmur itself typically increases with inspiration (unlike the click)
• Possible right ventricular heave
• Possible widely split S2 with delayed P2 component

Hemodynamic Principles

Intrathoracic Pressure Effects

• Inspiration decreases pleural pressure (more negative) 2
• This creates a pressure gradient favoring blood flow into the thorax
• The increased venous return primarily affects the right heart chambers

Right Heart Response

• The right ventricle is highly compliant and sensitive to changes in preload
• During inspiration, the increased filling temporarily alters RV mechanics
• This changes the dynamics of pulmonary valve opening

Clinical Examination Tips

• Listen carefully during slow, deep breathing to appreciate the respiratory variation
• Compare the intensity of the click during inspiration versus expiration
• The ejection click is best heard with the diaphragm of the stethoscope
• Position the patient slightly on the left side to enhance auscultation

Diagnostic Evaluation

• Transthoracic echocardiography is the gold standard for confirming pulmonic stenosis
• Echocardiography can determine:
  • Severity of stenosis
  • Valve morphology (doming, dysplastic)
  • Right ventricular size and function
  • Pulmonary artery pressure

Remember that understanding the physiological basis for this respiratory variation in the pulmonic ejection click helps in accurate diagnosis and assessment of pulmonic valve stenosis.