Elsevier

International Journal of Cardiology

Volume 221, 15 October 2016, Pages 155-160
International Journal of Cardiology

Noise enhanced the electrical stimulation-contractile response coupling in isolated mouse heart

https://doi.org/10.1016/j.ijcard.2016.06.130Get rights and content

Abstract

Background

Stochastic resonance is a phenomenon that allows a system to improve its capability to detect stimulus when a limited amount of noise is added to the stimuli. It has experimentally been shown that noise enhances the homeostatic function of the blood pressure regulatory system. This study aimed to investigate whether the noise can enhance the contractile response in the whole heart.

Methods

Experiments were conducted in isolated mouse hearts (0.040 kg, n = 8), a Langendorff heart preparation is used to obtain two variables of the contractile response contraction force and heart rate. The contractile response due to an electrical stimulation perturbed with Gaussian noise was recorded.

Results

The results show that the intensity of noise induced in the electrical stimuli has an effect on the electrical stimulation-contractile response coupling. With 10% noise induced, the bandwidth where the synchronization effect is presented was increased from (7–11 Hz) to (6–12 Hz), and the irregular dynamic threshold was changed to 13 Hz.

Conclusions

We find that the noise increases the synchronization bandwidth in the electrical stimulation-contractile response coupling. We have experimentally demonstrated the stochastic resonance in isolated mouse heart.

Introduction

The heart is an organ with continuous activity whose heart rate and strength contractions are modulated by several mechanisms including the autonomic nervous system, the renin–angiotensin system, vasopressin, among others [1], [2].

In particular, the nervous system transmits electrical signals to the heart across neurons. Neurons are essentially noisy [3], [4]. During the past years, numerous researchers have suggested that the nervous system and the cardiovascular system appear to leverage the noise to improve information transfer. Stochastic resonance (SR) is a phenomenon that allows the system to improve its capability to detect signals when a limited amount of noise is added on signal [5].

SR has been demonstrated experimentally in neurophysiological systems [6], [7], [8], [9], [10]. Furthermore, it has been studied in auditory and visual perceptions [11], [12]. In the cardiovascular system, some researchers have suggested that SR could enhance the homeostatic function of the human blood pressure regulatory system. Hidaka et al. [13] demonstrate that noise enhances the homeostatic function of the human blood pressure regulatory system, and also SR is present within the baroreflex human center [14]. However, few researchers have addressed in the fact that the noise can enhance contractile response in the whole heart.

This paper focuses on the electrical stimulation-contractile response coupling and demonstrates experimentally that the noise can enhance the contractile response in the whole heart. A Langendorff preparation was used to obtain two variables from the whole heart. First, heart rate (HR) driven by the pacemaker in the sinoatrial node. Second, contraction force (CF), since the force is measured through a suture and a force-transducer placed at the apex of the heart and the heart is composed of several layers of muscle fibers oriented in different directions, and then an approximate measurement of the force of muscular contraction was obtained [15]. To obtain these two variables, an electrical stimulation was applied to the right atrium, in order to induce a depolarization followed by the action potential and a contraction [16].

To the best of our knowledge, this is the first experimental test in whole heart focused on analyzing the contractile response due to electrical stimulation perturbed with Gaussian white noise. We found that, contrasting the findings in the control experiment where the heart was electrically stimulated without noise, the heart maintain the electrical stimulation-contractile response coupling in a wider range of frequencies of electrical stimulation.

Section snippets

Methods

For the purpose of this work, a Langendorff heart preparation is used to obtain two variables: contraction force and heart rate in mouse isolated heart. The heart was paced in the right atrium from the spontaneous heart rate to 20 Hz. All animal procedures were conducted in accordance with Federal Regulations for Animal Experimentation and Care and were approved by the Animal Care Committee of CINVESTAV (CINVESTAV Zacatenco, D.F., Mexico).

Results

The Langendorff perfused heart model has proved to be an excellent tool to study, among other properties, the contractile response of the whole heart. In this model, the heart is removed from the body and in the absence of preload and afterload of blood, the heart does not lose its contractile property. In this study, the contractile response of the heart was analyzed as follows: the heart rate (HR), the frequency of the contraction–relaxation event, and the intensity of the contractile force

Discussion

Stochastic resonance (SR) is a phenomenon observed when increases in levels of noise cause an increase in any metric of the quality of signal transmission or detection performance, rather than a decrease [5], [7], [26]. During the past several years, a plethora of excellent manuscripts have been published regarding SR in biology. Douglass et al. 1993 published the first manuscript showing experimental SR in a living system [10]. The neurons of crayfish, mechanoreceptor/photoreceptor system,

Study limitations

However there are some limitations in our study. Firstly, the force is measured through a suture and a force-transducer placed at the apex of the heart. Although this method is enough to obtain an approximate measurement of the contractile force, a ventricular fibrillation threshold in response to noise stimuli could be determined if the intra-ventricular pressure and the action potential were recorded. Then, a better understanding about these pathologies of the heart, arrhythmia and

Conclusions

In this study, the effect of noise on the electrical stimulation-contractile response coupling in isolated mouse heart was analyzed. This work describes the excitation–contraction coupling response under noisy electrical stimulus and, to the best of our acknowledgment this is the first report showing stochastic resonance in isolated heart. The best way to enhance the synchronizability was with an optimal noise intensity, in which the 1:1 synchronization was preserved at higher frequencies, and

Conflict of interest

The authors report no relationships that could be construed as a conflict of interest.

Acknowledgments

This research was partially supported by Consejo Nacional de Ciencia y Tecnología (CONACYT, Mexico) under grant no. 105649.

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    All authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.

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