Arterial elastance. In the cartoon (left panel) a compliant and no resistive young hungry snake eats a big sheep easily. In the cardiovascular system the hydraulic load, namely effective arterial elastance, is described by the formula: End Systolic Pressure/Stroke Volume/Body Surface Area (right panel). Intuitively a well compliant and no resistive vascular system easily accomplish a big stroke volume without great increase of systemic pressure: steady End Systolic Pressure/Stroke Volume ratio; "low-good" arterial elastance. Intuitively a bad compliant and resistive vascular system difficultly accomplish the stroke volume with greater increase of systemic pressure: increased End Systolic Pressure/Stroke Volume ratio; "high-bad" arterial elastance. On the basis of the windkessel model, effective arterial elastance E
a is a steady-state arterial parameter that incorporates peripheral resistance, characteristic impedance, and total lumped arterial compliance and that also incorporates systolic and diastolic time intervals. Since the pioneer work of Kelly et al. , which confirmed the clinical applicability of this concept in humans, effective arterial elastance E
a has been used to quantify arterial load during aging, in hypertensive patients, and in various forms of cardiac disease. Ees = left ventricular end-systolic elastance, ESV = end-systolic volume, ESP = end-systolic pressure, EDV = end-diastolic volume.