Evaluation of methods for estimation of total arterial compliance

Abstract

Seven classic and recently proposed methods used for the estimation of total arterial compliance have been evaluated for their accuracy and applicability in different physiological conditions. The pressure and flow data are taken from a computer model that provides realistic simulations of the nonlinear-distributed systemic arterial tree. Besides the great flexibility in simulating different physiological or pathological cases, the major advantage of the computer model is that it allows precise knowledge of the pressure-dependent total arterial compliance, which is the variable of interest. The results show that the methods based on the two-element windkessel (WK) model are more accurate than those based on the three-element WK model. The classic exponential decay and the diastolic area method yield essentially similar results, and their compliance estimates are accurate within 10% except at high heart rates. The later part of diastole, i.e., from the time that the systolic pressure wave has reached all peripheral beds, gives the best results. The newly proposed two-area and pulse pressure methods, both based on the two-element WK model, are accurate (errors in general < 10%) and can be applied to other locations in the arterial tree where the decay time and area method cannot. Methods based on the three-element WK model consistently overestimate total arterial compliance (> or = 25%). The errors in the methods based on the three-element WK model arise from the fact that the input impedance in that model deviates significantly from the true input impedance at low frequencies. The strong dependence of compliance on pressure (elastic nonlinearity) does not invalidate the compliance estimates.(ABSTRACT TRUNCATED AT 250 WORDS)

The arterial Windkessel

“…Using the three-element Windkessel the value of compliance is overestimated [50] but this is not the case using the four-element Windkessel [63], however, the inertance estimate is usually poor. Also the inverse procedure may be followed, pressure can be fed into the Windkessel model and optimization of flow is then performed [60].…”

The metabolic syndrome in elderly individuals is associated with greater muscular, but not elastic arterial stiffness, independent of low-grade inflammation, endothelial dysfunction or insulin resistance—The Hoorn Study

“…The estimates of artery stiffness were determined as described earlier with the use of arterial ultrasonography, echocardiography and radial applanation tonometry 28,32,33 according to the following: distensibility-an indicator of local arterial elastic properties: ((2DD Â D þ DD 2 )/(DP Â D 2 ) in 10 À3 kPa À1 ; compliance-an indicator of local arterial buffering capacity: p(2D Â DD þ DD 2 )/(4 Â DP) in mm 2 kPa À1 ; Young's elastic modulus-an indicator of local intrinsic elastic wall properties: (D/(IMT) Â distensibility) in kPa (where DP stands for local pulse pressure, 34,35 D for diameter, (DD) for distension and IMT for carotid intima-media thickness); total systemic arterial compliance-an indicator of total arterial buffering capacity-by the exponentialdecay method based on the Windkessel model 36 and the ratio of stroke volume to aortic pulse pressure; 37 aortic augmentation index-an indicator of total stiffness and wave reflection-by the use of a generalized transfer function; 38 and carotid-femoral transit time-an estimate of regional stiffness closely associated with the gold standard estimate of stiffness: pulse wave velocity-by the time delay from the electrocardiograph trigger to 10% of the ascending slope of the distension curve of both arteries subtracted from one another. 39 …”

A comparison of methods for assessing total arterial compliance

“…This equation is only valid when local flow is zero, so that it can only be applied to the ascending aortic wave form in diastole because for normally functioning heart valves, diastolic flow is zero. 10,11 The SVPP is an index, which is a ratio of the stroke volume of the heart, calculated from the 2D echo dimensions and pulsed-wave Doppler velocity of the aortic outflow, and the pulse pressure (systolic-diastolic blood pressure). It is not generally accepted as a calculation or estimation of C but rather an index of normal/abnormal compliance.…”