The cardiovascular effects of aortic clamping and unclamping

The most common descriptor of afterload in the clinical setting is peripheral vascular resistance. Nonetheless, this is only one of the elements of afterload. A comprehensive descriptor of left ventricular extrinsic afterload is contained in the 3-element Windkessel (wind-chamber) model. Although this Windkessel circulatory model contains only characteristic impedance, aortic compliance and peripheral (systemic) vascular resistance, it can accurately re‹ ect all the forces that comprise afterload external to the ventricle.Using an electrical analogue of the Windkessel model, afterload can be described mathematically (Equation 1). Inspection of this equation reveals that impedance is a complex, frequency dependent parameter. The frequency dependent component is a result of wave re‹ ections that originate at arterial and arteriolar branches.