A 52-year-old man with a long-standing history of hypertension presents with chest pain and is found to have a systolic ejection murmur at the right upper sternal border. On examination, the blood pressure is 160/100 mmHg, and the murmur is best heard with the patient leaning forward and in end-expiration. The murmur increases in intensity with Valsalva maneuver. Echocardiography shows left ventricular hypertrophy with a bicuspid aortic valve and severe stenosis. Which physiological principle explains why the murmur intensity increases during Valsalva maneuver?

Explanation

## Aortic Stenosis Murmur and Valsalva Maneuver ### Physiology of Aortic Stenosis Murmur **Key Point:** Aortic stenosis (AS) produces a systolic ejection murmur because a narrowed aortic valve orifice forces blood through a restricted opening, creating turbulent flow and a pressure gradient between the left ventricle and aorta. ### The Valsalva Maneuver: Hemodynamic Effects Valsalva (forced expiration against a closed glottis) has two phases: **Phase II (Strain phase):** 1. **Increased intrathoracic pressure** compresses the thorax 2. **Decreased venous return** to the right heart (blood pools in the venae cavae) 3. **Decreased left ventricular preload** (reduced LV filling) 4. **Decreased left ventricular volume** and chamber size 5. **Increased blood flow velocity** across the stenotic valve (same volume ejected from a smaller chamber) 6. **Louder murmur** due to higher flow velocity **High-Yield:** The murmur of AS **increases** with Valsalva because reduced preload increases flow velocity across the fixed stenotic orifice. This is a classic bedside maneuver to confirm AS. ### Comparison of Murmur Responses to Valsalva | Murmur Type | Response to Valsalva | Mechanism | |---|---|---| | **Aortic Stenosis** | **Increases** | ↓ Preload → ↓ LV volume → ↑ flow velocity across fixed orifice | | Mitral Regurgitation | Decreases | ↓ Preload → ↓ LV volume → ↓ regurgitant flow | | Hypertrophic Cardiomyopathy | Increases | ↓ Preload → ↓ LV cavity → ↑ outflow obstruction | | Aortic Regurgitation | Decreases | ↓ Preload → ↓ regurgitant flow | | Mitral Stenosis | No change | Stenotic lesion; flow determined by gradient | **Clinical Pearl:** Valsalva is superior to handgrip for distinguishing AS (murmur increases) from MR (murmur decreases) at the bedside. ### Why This Patient's Findings Fit Aortic Stenosis - **Systolic ejection murmur:** Begins after S1, peaks mid-systole, ends before S2 - **Right upper sternal border location:** Aortic area - **Increases with forward lean and end-expiration:** Brings aorta closer to chest wall and reduces lung interference - **Bicuspid aortic valve:** Predisposes to early stenosis and calcification - **Left ventricular hypertrophy:** Chronic pressure overload from stenosis - **Severe stenosis on echo:** Explains the prominent murmur and symptoms ```mermaid flowchart TD A[Valsalva Maneuver]:::action --> B[↑ Intrathoracic Pressure]:::outcome B --> C[↓ Venous Return]:::outcome C --> D[↓ LV Preload]:::outcome D --> E[↓ LV Volume]:::outcome E --> F[Same SV from Smaller Chamber]:::outcome F --> G[↑ Flow Velocity]:::outcome G --> H[Louder AS Murmur]:::action ``` [cite:Harrison 21e Ch 237]