Lung Sounds Overview
While this course focuses on cardiac auscultation, understanding basic lung sounds is essential for two reasons: (1) respiratory variation affects cardiac sounds, particularly S2 splitting and right-sided murmurs, and (2) you need to distinguish cardiac from pulmonary findings.
Normal Breath Sounds
Vesicular Breath Sounds
Location: Peripheral lung fields
Character: Soft, low-pitched rustling sound heard throughout inspiration and early expiration. Think "wind through leaves."
Bronchial Breath Sounds
Location: Normally heard over the trachea/major bronchi
Character: Loud, high-pitched, hollow sound. Inspiration and expiration are equally loud with a gap between them.
Clinical Pearl: If heard over peripheral lung fields, suggests consolidation (pneumonia) – sound is transmitted through solid lung tissue.
Adventitious (Abnormal) Lung Sounds
Crackles (Rales)
Sound: Discontinuous, brief, popping sounds
Mechanism: Small airways popping open during inspiration
Clinical Significance:
- Fine crackles (high-pitched, late inspiration) → Pulmonary edema, pulmonary fibrosis
- Coarse crackles (low-pitched, early inspiration) → Pneumonia, bronchitis, COPD
💧 Heart Failure Connection
Bilateral fine crackles at the lung bases + S3 gallop = classic presentation of decompensated heart failure. The crackles represent pulmonary edema from elevated left atrial pressure.
Wheezes
Sound: Continuous, musical, high-pitched sounds
Mechanism: Airflow through narrowed airways (bronchospasm)
Timing: Usually expiratory (easier to hear when airways are smaller)
Clinical Pearl: Wheezing is NOT a cardiac sound, but cardiac asthma (pulmonary edema causing bronchospasm) can mimic true asthma.
Pleural Rub
Sound: Creaking, grating sound like "leather rubbing on leather"
Mechanism: Inflamed pleural surfaces rubbing against each other
Timing: Both inspiration and expiration
⚠️ Don't Confuse With Pericardial Rub!
Pleural rub: Changes/disappears when patient holds breath
Pericardial rub: Persists when patient holds breath (it's cardiac, not respiratory)
Respiratory Variation & Cardiac Auscultation
Why Respiration Matters
Inspiration:
- Negative intrathoracic pressure draws more blood into right heart
- Increases right ventricular filling → delays pulmonic valve closure → S2 splitting
- Right-sided murmurs (TR, PS) get louder
Expiration:
- Increased intrathoracic pressure pushes blood into left heart
- Left-sided murmurs (MR, AS) may be slightly louder
- S2 components fuse (normal)
💡 Practical Tip: Carvallo's Sign
Tricuspid regurgitation murmur increases with inspiration (more venous return → more regurgitant flow). This is one of the most useful respiratory variations in cardiac auscultation.
Distinguishing Cardiac vs Pulmonary Sounds
| Feature | Cardiac Sounds | Lung Sounds |
|---|---|---|
| Timing | Precisely tied to heartbeat (S1, S2) | Tied to breathing |
| Location | Best at specific valve areas | Throughout lung fields |
| With Breath-Holding | Persist when breathing stops | Disappear when breathing stops |
| Character | Discrete sounds (lub-dub) | Continuous or intermittent |
Clinical Applications
Patient with dyspnea: Always auscultate both heart AND lungs. The differential diagnosis includes:
- Cardiac: Heart failure (S3 + crackles), valvular disease (murmur ± crackles)
- Pulmonary: Pneumonia (crackles + bronchial sounds), COPD (wheezes), pneumothorax (absent breath sounds)
- Combined: Pulmonary edema from heart failure (cardiac and pulmonary findings coexist)
📊 Integration Point
As you progress through this course, you'll learn how to integrate cardiac and pulmonary findings into a cohesive clinical picture. For now, just remember: always listen to both.
Next: Now that you understand the basics of lung sounds and respiratory variation, you're ready to learn about the physics of sound generation.