Development and validation of a novel method to derive central aortic systolic pressure from the MR aortic distension curve.

PURPOSE: Central aortic systolic pressure (CASP) is a more accurate measure of load and cardiovascular risk than brachial pressure. Unfortunately, CASP is difficult to measure using current methods. In this study we report three methods of determining CASP by combining MR-derived aortic area curves with different models of the pressure-area relationship.
MATERIALS AND METHODS: CASP was derived by calibrating aortic area curves to the brachial mean and diastolic pressure, using: linear, exponential, and arctangent models in 20 volunteers using a high temporal resolution spiral PC-MR flow sequence. The arctangent model also required calibration with pulse wave velocity. Carotid tonometry CASP was used as the reference standard.
RESULTS: Brachial systolic pressure correlated only moderately with carotid CASP r(2)  = 0.46 (P = 0.01). However, arctangent, exponential, and linear CASP correlated strongly with carotid CASP, r(2)  = 0.90, r(2)  = 0.86, r(2)  = 0.85, respectively (P < 0.0001). There was excellent agreement between carotid CASP and both arctangent (bias 1.5; SD 3.3) and exponential CASP (bias 0.6; SD 3.6). There was a slight underestimation using the linear model (bias -2.3; SD 3.8) and poor agreement and overestimation using brachial systolic pressure (bias 12.9; SD 8.0).
CONCLUSION: We have shown that CASP can be derived from MR data: arctangent and exponential methods being superior to the linear method. The superior correlation of MR derived CASP over brachial systolic BP suggests these measures will allow more comprehensive assessment of systemic arterial hypertension.