Hybrid duplex: a novel method to study the contractile function of heterogeneous myocardium

Abstract

In an earlier study, we experimentally mimicked the effects of mechanical interaction between different regions of the ventricular wall by allowing pairs of independently maintained cardiac muscle fibers to interact mechanically in series or in parallel. This simple physiological model of heterogeneous myocardium, which has been termed "duplex," has provided new insight into basic effects of cardiac electromechanical heterogeneity. Here, we present a novel "hybrid duplex," where one of the elements is an isolated cardiac muscle and the other a "virtual cardiac muscle." The virtual muscle is represented by a computational model of cardiomyocyte electromechanical activity. We present in detail the computer-based digital control system that governs the mechanical interaction between virtual and biological muscle, the software used for data analysis, and working implementations of the model. Advantages of the hybrid duplex method are discussed, and experimental recordings are presented for illustration and as proof of the principle.

Alternative Approach for Studying Contractility of the Isolated Muscle Preparations in Real-Time Mode

“…Method of studying the mechanical (length-force) interaction between two isolated myocardial preparations in real-time mode during a "contraction-relaxation" cycle was chosen to check the adequacy of the hardware and software experimental complex [13]- [16]. Rather small processing and control time discrete (100 μs) practically doesn't distort electromechanical processes of force generation occurring in the muscles and brings them interaction closer to physical interaction.…”

“…The presence of the two channels of the experimental complex allows exploring myocardial contractility for two preparations at the same time in isolation or in their interaction under different load conditions [13] [16]. During the experiment it is possible to register mechanical properties of muscles, electrical characteristics, as well as dye fluorescence (this functionality will be implemented in near future) in real-time mode.…”

“…In the "parallel duplex" mode the interaction of two muscles, fixed to a mutual base and pulling the mutual load, is simulated (see more details in [13] [16]). The forces of preparations in this approach are added (their sum is equal to the force of the duplex), i.e.…”

“…In this case, the apparent homogeneous mechanical activity at the level of whole organ (heart) is determined by the spatio-temporal coordination of inhomogeneous cardiomyocytes in different layers of heart wall [2]. Independently of assigned task, the mechanical measurements on striated muscle require monitoring and control of the varying parameters such as muscle length, strain (as a function of the length), hardware-software complex built on the basis of HyperKernel subsystem for Windows [13]. The control algorithms for length changes of two myocardial preparations contracted in isolation and during their mechanical interaction (by parallel and series connection as the experimental model of whole heart wall segments interaction) were developed on the basis of this complex [13].…”

“…Independently of assigned task, the mechanical measurements on striated muscle require monitoring and control of the varying parameters such as muscle length, strain (as a function of the length), hardware-software complex built on the basis of HyperKernel subsystem for Windows [13]. The control algorithms for length changes of two myocardial preparations contracted in isolation and during their mechanical interaction (by parallel and series connection as the experimental model of whole heart wall segments interaction) were developed on the basis of this complex [13]. However, HyperKernel subsystem has a number of limitations: Windows version should be no newer than XP Professional Service Pack 2; the system kernel is limited by Standard PC or Standard PC with ACPI; there is no support Hyper-threading technology.…”