Intrinsic frequency for a systems approach to haemodynamic waveform analysis with clinical applications

Abstract

The reductionist approach has dominated the fields of biology and medicine for nearly a century. Here, we present a systems science approach to the analysis of physiological waveforms in the context of a specific case, cardiovascular physiology. Our goal in this study is to introduce a methodology that allows for novel insight into cardiovascular physiology and to show proof of concept for a new index for the evaluation of the cardiovascular system through pressure wave analysis. This methodology uses a modified version of sparse time-frequency representation (STFR) to extract two dominant frequencies we refer to as intrinsic frequencies (IFs; v 1 and v 2 ). The IFs are the dominant frequencies of the instantaneous frequency of the coupled heart þ aorta system before the closure of the aortic valve and the decoupled aorta after valve closure. In this study, we extract the IFs from a series of aortic pressure waves obtained from both clinical data and a computational model. Our results demonstrate that at the heart rate at which the left ventricular pulsatile workload is minimized the two IFs are equal (v 1 ¼ v 2 ). Extracted IFs from clinical data indicate that at young ages the total frequency variation (Dv ¼ v 1 2 v 2 ) is close to zero and that Dv increases with age or disease (e.g. heart failure and hypertension). While the focus of this paper is the cardiovascular system, this approach can easily be extended to other physiological systems or any biological signal.

Intrinsic Frequency and the Single Wave Biopsy

“…Figure 1B shows the decomposition of S and D into two intrinsic frequencies ω 1 and ω 2 respectively: Δω denotes the difference between the two. Previously, 15 we applied the algorithm to clinical data (pressure wave forms) obtained from subjects with established cardiovascular disease as well as from healthy controls. We showed that ω ) corresponded specifically to vascular disease.…”

“…Clinical monitoring of PWV, while noninvasive and well correlated with insulin resistance, is decidedly impractical. In a recently published study, 15 we applied a novel signalprocessing algorithm, intrinsic frequency method (IFM), to clinical data (pressure wave forms) obtained from subjects with established cardiovascular disease along with healthy controls. The algorithm successfully screened and analyzed an array of cardiovascular pathologies.…”

“…Figures 1 and 2 were generated from a computational model 15 we have previously published. Parameters were varied to demonstrate the changes in ω Figures 3, 4, and 5 make use of healthy patient data described and seen in the tables.…”

Proof-of-concept for a non-invasive, portable, and wireless device for cardiovascular monitoring in pediatric patients

“…IF can be computed using this formula in a fraction of second. Details regarding mathematical formulation of IF method [12], its computational procedure [12], and its convergence/accuracy [19] can be found in previous publications [12,17,19].…”

“…Pahlevan et. al [12] recently introduced a new mathematical method, called the intrinsic frequency (IF) method, that is suitable for the dynamic analysis of coupled physiological systems such as the LV and the arterial network. IF uses an integrative systems approach that considers the LV and arterial network as a coupled dynamical system (LV + arterial tree) that is decoupled upon closure of the aortic valve [13][14][15][16].…”