U01.07.028 Normal cardiac pressures

Cardiac pressures are crucial to understanding heart function and pathology. In this section, we will focus on the Pulmonary Capillary Wedge Pressure (PCWP) and its relationship with left atrial pressure and left ventricular pressures.

1. Pulmonary Capillary Wedge Pressure (PCWP)

Definition: PCWP is a valuable clinical measurement that approximates the left atrial pressure. It is commonly measured using a pulmonary artery catheter (also known as a Swan-Ganz catheter).
Normal Range: The typical range for PCWP is 5-12 mm Hg.
- Measuring Technique: The Swan-Ganz catheter is inserted into the pulmonary artery, and a balloon is inflated to obtain a pressure reading from the pulmonary capillaries, reflecting the pressure in the left atrium.

2. PCWP in Mitral Stenosis

In mitral stenosis, the pressure in the left atrium is elevated due to the obstruction at the mitral valve. As a result, PCWP becomes greater than the left ventricular end-diastolic pressure (LVEDP).
Key Point:
- PCWP > LVEDP in cases of mitral stenosis.

3. Normal Cardiac Pressures Overview

Pressure Measurement	Normal Range (mm Hg)	Significance
Pulmonary Capillary Wedge Pressure (PCWP)	5 – 12 mm Hg	Approximation of left atrial pressure. Measured with Swan-Ganz catheter.
Left Ventricular End-Diastolic Pressure (LVEDP)	3 – 12 mm Hg	Reflects left ventricular filling pressure.
Mitral Stenosis	PCWP > LVEDP	In mitral stenosis, the left atrial pressure increases, making PCWP > LVEDP.

4. Example Pressures (Clinical Context)

Measurement	Value (mm Hg)	Clinical Relevance
PCWP in Mitral Stenosis	25/5	Elevated PCWP due to increased left atrial pressure.
PCWP in Severe Mitral Stenosis	25/10	Further increase in PCWP in severe cases.
Normal PCWP	< 5 mm Hg	Indicative of normal left atrial pressure.
PCWP in Severe Heart Failure	130/10	Very high pressure indicating severe heart failure.

Key Takeaways for USMLE Step 1

PCWP is an essential diagnostic measure of left atrial pressure, particularly useful in assessing conditions such as mitral stenosis and heart failure.
Understanding the relationship between PCWP, LVEDP, and mitral stenosis is vital for clinical decision-making.

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