Development and Validation of a Novel Method to Derive Central Aortic Systolic Pressure From the Radial Pressure Waveform Using an N-Point Moving Average Method

Abstract

The purpose of this study was to develop and validate the novel application of a simple n-point moving average (NPMA)--a mathematical low pass filter--to noninvasively derive central aortic systolic pressure (CASP) from the radial artery pressure waveform (RAPWF) in humans. CASP may be an important independent determinant of clinical outcomes. Development of simple, well-validated methods to noninvasively derive CASP is necessary to facilitate the routine clinical measurement of CASP. Three studies in different population cohorts were used to develop and validate the NPMA method to derive CASP in humans: 1) a development study (n = 217), describing the optimal application of the NPMA to derive CASP; 2) a validation study comparing NPMA-CASP with CASP derived using a generalized transfer function (GTF-CASP [SphygmoCor system, AtCor, Sydney, Australia]) using 5,349 RAPWFs from the CAFE (Conduit Artery Function Evaluation) study; and 3) an invasive validation study (n = 20) comparing NPMA-CASP with direct aortic root pressure measurements during cardiac catheterization. In the development study, when using the NPMA, a denominator of n/4 (where n = tonometer sampling frequency) most accurately defined CASP relative to GTF-CASP. Validation of NPMA-CASP using RAPWFs from the CAFE study revealed excellent correlation and agreement (r(2) = 0.993, mean difference 0.3 ± 1.0 mm Hg). The agreement remained robust after stratification by sex, age, treatment, and diabetes status. There was also excellent correlation and agreement (r(2) = 0.98, p < 0.001) between directly measured aortic root systolic pressures (Millar's catheter) at cardiac catheterization versus NPMA-CASP, derived simultaneously from noninvasive RAPWFs. We show that an NPMA with a denominator of one-quarter of the tonometer sampling frequency accurately defines CASP when applied to noninvasively acquired RAPWFs in man. These novel findings have important implications for the simplification of noninvasive CASP measurement and its wider application in clinical trials and clinical practice.