Aortic Compliance Index (ACI): Explanation and Clinical Context The Aortic Compliance Index (ACI) represents the ability of the aorta to expand and contract with each cardiac cycle in response to changes in blood pressure. It reflects the elastic properties of the aortic wall and serves as a surrogate marker of arterial stiffness.
The formula used is: ACI = Stroke Volume / Pulse Pressure where Stroke Volume (SV) is the volume of blood ejected from the left ventricle per beat, and Pulse Pressure (PP) is the difference between systolic and diastolic blood pressure.
A high ACI value indicates a more compliant (elastic) aorta, whereas a low ACI suggests increased arterial stiffness. Decreased aortic compliance is associated with aging, hypertension, diabetes, and atherosclerosis. Clinically, it has been correlated with increased left ventricular afterload, myocardial oxygen demand, and adverse cardiovascular outcomes.
Normal values of ACI vary depending on population and measurement method, but typically range from 1.5 to 2.5 mL/mmHg in healthy adults.
In echocardiographic studies, a reduced ACI has been independently associated with increased left ventricular mass and impaired diastolic function, especially in hypertensive patients.
Reference:
- Chen CH, Ting CT, Lin SJ, et al. “Which arterial and cardiac parameters best predict left ventricular mass?” Circulation. 1998;98(5):422–428.
- Nichols WW, O'Rourke MF. McDonald's Blood Flow in Arteries: Theoretical, Experimental and Clinical Principles. 6th ed. CRC Press; 2011.
- Cavalcante JL, Lima JAC, Redheuil A, Al-Mallah MH. “Aortic stiffness: current understanding and future directions.” J Am Coll Cardiol. 2011;57(14):1511–1522.