Signal processing of heart signals for the quantification of non-deterministic events

Abstract

BackgroundHeart signals represent an important way to evaluate cardiovascular function and often what is desired is to quantify the level of some signal of interest against the louder backdrop of the beating of the heart itself. An example of this type of application is the quantification of cavitation in mechanical heart valve patients.MethodsAn algorithm is presented for the quantification of high-frequency, non-deterministic events such as cavitation from recorded signals. A closed-form mathematical analysis of the algorithm investigates its capabilities. The algorithm is implemented on real heart signals to investigate usability and implementation issues. Improvements are suggested to the base algorithm including aligning heart sounds, and the implementation of the Short-Time Fourier Transform to study the time evolution of the energy in the signal.ResultsThe improvements result in better heart beat alignment and better detection and measurement of the random events in the heart signals, so that they may provide a method to quantify nondeterministic events in heart signals. The use of the Short-Time Fourier Transform allows the examination of the random events in both time and frequency allowing for further investigation and interpretation of the signal.ConclusionsThe presented algorithm does allow for the quantification of nondeterministic events but proper care in signal acquisition and processing must be taken to obtain meaningful results.

Enhancement of signal processing technique for quantification of non-deterministic events of pathological heart signals using wavelet transform

“…Wang et al [2] suggests that PCG signal S(n) can be modeled as shown in equation (3) S(n) = F(n)+O(n) = F(n)+C(n)+N(n) (3) where F(n) represents the fundamental components of the heart sounds S 1 and S 2 (SOI), and O(n) represents other sounds which can be decomposed into C(n), other heart sound components (such as murmurs, etc) and N(n), the noise component.…”

“…The non-deterministic energy of the signal with S1 peaks aligned [3] follows the Johansen algorithm [4] with the modification made in the segmentation algorithm [3]. By Johansen algorithm, the level of nondeterministic energy is defined as the difference between the deterministic energy and the total energy as in the following equation (8): (8) where the E non-det represents the non-deterministic energy of the signal which is the energy of interest.…”

“…The energy is determined for each segmented and truncated heart beat [3] and averaged which becomes the total energy given by the following equation (11):…”

“…E-mail: priyadharshinieee.v@gmail.com 2 Faculty, Department of Biomedical Instrumentation Engineering, Faculty of Engineering, Avinashilingam University, Coimbatore. E-mail: judithvjn@yahoo.com murmur) from the comparatively loud backdrop of the beating of the heart itself [3].…”

“…But since blood is not a transparent fluid, the cavitation near a mechanical heart valve has to be detected acoustically for in vivo studies [4]. The acoustic evidence of cavitation is defined by the highfrequeny pressure fluctuations (HPPFs) associated with transient bubble collapse [4,3].…”