Arterial elastance (Ea) is approximately end-systolic pressure divided by stroke volume; higher Ea means higher afterload.

Arterial elastance (Ea) is approximately end-systolic pressure divided by stroke volume; higher Ea means higher afterload.

• A. Ea ≈ mean arterial pressure / heart rate; a global afterload indicator.
• B. Ea ≈ end-diastolic pressure / stroke volume; a global afterload indicator.
• C. Ea ≈ stroke volume / cardiac output; a global afterload indicator.
• D. Ea ≈ end-systolic pressure / stroke volume; a global afterload indicator; higher Ea means higher afterload.

Answer: (D)

Arterial elastance (Ea) is a single-number proxy for the arterial system’s load the left ventricle must overcome. It encapsulates how stiff the arteries are and how much blood the ventricle ejects. By defining Ea as end-systolic pressure divided by stroke volume, you get a quantity that rises when the arterial system is less compliant or when the ventricle ejects less blood for a given pressure. That’s why Ea is a global afterload indicator, and higher Ea means higher afterload. The other ideas don’t fit: mean arterial pressure divided by heart rate mixes pressure with rate and isn’t a direct measure of afterload; end-diastolic pressure reflects preload, not afterload; and stroke volume divided by cardiac output isn’t a pressure-to-volume measure of afterload (since CO = heart rate × SV). The correct relationship uses end-systolic pressure and stroke volume, and increasing Ea indicates greater afterload.

Arterial elastance (Ea) is a single-number proxy for the arterial system’s load the left ventricle must overcome. It encapsulates how stiff the arteries are and how much blood the ventricle ejects. By defining Ea as end-systolic pressure divided by stroke volume, you get a quantity that rises when the arterial system is less compliant or when the ventricle ejects less blood for a given pressure. That’s why Ea is a global afterload indicator, and higher Ea means higher afterload.

The other ideas don’t fit: mean arterial pressure divided by heart rate mixes pressure with rate and isn’t a direct measure of afterload; end-diastolic pressure reflects preload, not afterload; and stroke volume divided by cardiac output isn’t a pressure-to-volume measure of afterload (since CO = heart rate × SV). The correct relationship uses end-systolic pressure and stroke volume, and increasing Ea indicates greater afterload.