N-point moving average: A special generalized transfer function method for estimation of central aortic blood pressure

Abstract

Objective: N-point moving average (NPMA) is a simplified method of central aortic systolic pressure (CASP) estimation in comparison with the generalized transfer function (GTF). The fundamental difference or similarity between the methods is not established. This study investigates theoretical properties of NPMA relative to GTF and explores the integer and fractional denominator for the averaging process in the NPMA. Methods: Convolution of a specified square wave and the radial (or brachial) blood pressure waveform constituted the NPMA. A single uniform tube model-based TF (MTF) was employed to investigate potential physiological meaning of NPMA. In experimental analysis, invasive, simultaneously recorded aortic and radial pressure waveforms were obtained in 62 subjects under control conditions and following nitroglycerin administration. CASP was estimated by NPMA (CASP N P M A ), GTF (CASP G T F ), and MTF (CASP M T F ) from radial waveforms by tenfold cross validation. Results: Theoretical analysis showed that NPMA was an inversed constant TF. Its spectrum matched that of MTF in low frequency (<4 Hz for radial and <5 Hz for brachial) by optimizing reflection coefficient and propagation time. Experiment results showed the NPMA optimized fractional denominator of K = 4.4 significantly decreased the mean difference between CASP N P M A and measured CASP to 0.0 ± 4.7 mmHg from -1.8 ± 4.6 mmHg for integer denominator of K = 4. CASP N P M A correlated with CASP M T F and CASP G T F (r 2 = 0.99 and 0.97, mean difference: -0.3 ± 1.8 and 0.5 ± 2.7 mmHg). Conclusion: This study demonstrated that NPMA is similar in nature to the GTF.