Noninvasive estimation of systolic and diastolic arterial compliance

An analog circuit model has been developed to compute systolic and diastolic compliances of the arterial system in the human using a single noninvasive displacement transducer located at the superficial carotid artery. The LICO model (Local Impedance, Compliance and Output model) is driven by a step input of pressure equal in amplitude to the pulse pressure. The timing of the resulting flow is determined from the carotid pulse contour. A study of records from one hundred and two cardiac surgery patients shows that the LICO model compliance correlates well with a common measure of compliance; the ratio of the stroke volume to the pulse pressure, ΔV/ΔP (systolic compliance r=0.821, p<0.001, diastolic compliance r=0.843, p<0.001). Although the diastolic value is computed from a first order pressure decay, the systolic and diastolic compliance values correlate well with one another (r=0.972, p<0.001). The change in compliance over the cardiac cycle, calculated as the difference between the diastolic and systolic values, also compares well to ΔV/ΔP (r=0.903, p<0.001)