Effects of mental tasks on the cardiorespiratory synchronization

Abstract

The cardiovascular and respiratory systems are functionally related to each other, but it is unclear if the cerebral cortex can affect their interaction. The effect of a mental task on the synchronization between cardiovascular and respiratory systems was investigated in the article. Electroencephalogram (EEG), electrocardiogram (ECG) and respiratory signal (RES) were collected from 29 healthy male subjects during the mental arithmetic (MA) task and the synchrogram was used to estimate the strength of cardiorespiratory synchronization. Our results showed that MA task significantly increased the breath rate, the heart rate and the EEG power spectral energy in theta band at FC3, FC4 and C4 electrodes (p < 0.01), decreased the duration of cardiorespiratory synchronization epochs (p < 0.05). Moreover the duration of cardiorespiratory synchronization epochs during MA task was negatively correlated with the EEG power spectral energy in theta band at FC3, FC4 and C4 electrodes and the sympathetic activity (p < 0.05). The results demonstrated that ANS and cerebral cortex are implicated in the changes of cardiorespiratory synchronization during MA task.

Introduction

The cardiovascular and respiratory systems are functionally related to each other and it has been found that heart rate can be modulated by respiration as the respiratory sinus arrhythmia (RSA), i.e., the heart rate will increase during inspiration and decrease during expiration. It is widely accepted that the interaction is concerned in the mechanical interaction and the control with central nervous system (CNS). In mechanical sense the intrathoracic pressure cyclically changes with the respiratory motion, which could affect the sinus node and modulate the heart rate (Mase et al., 2009). In neurological sense the respiration and heartbeat oscillators are controlled by CNS and work together to guarantee a continuous supply of oxygen and the clearance of metabolic waste products (Hoyer et al., 1998). It has been demonstrated that there is no synchronization found in subjects suffered from coma or heavily sedated and ventilated via a respirator, in whom the cardiac and the respiratory systems were disconnected from their mutual influences (Stefanovska et al., 2001). It seems that mechanical factors are not so important for the cardiorespiratory synchronization. CNS can regulate the cardiac and respiratory rhythm in responding to the stress and the change of physiological condition. Many of the scientists paid much attention to the effect of nervous system on the interaction between the cardiovascular and respiratory systems and suggested that CNS plays a dominant role in cardiorespiratory coupling (Schafer et al., 1998, Schafer et al., 1999, Toledo et al., 1999, Toledo et al., 2002, Bartsch et al., 2007).

The phase synchronization was used to analyze the interaction between the cardiovascular and respiratory systems (Schafer et al., 1998, Schafer et al., 1999, Kenwright et al., 2008). The cardiorespiratory synchronization was stronger in young athletes (Schafer et al., 1999), or during Zen meditation (Cysarz and Bussing, 2005) and recitation of hexameter verse (Cysarz et al., 2004a, Cysarz et al., 2004b). Cardiorespiratory synchronization was diminished under conditions of strain (Stefanovska et al., 2001). Moreover, phase synchronization between heartbeat and breathing was significantly enhanced during non-rapid-eye-movement (non-REM) sleep and reduced during REM sleep (Bartsch et al., 2007). Generators of cardiac and respiratory rhythm are located in the brainstem and it was believed that cardiac and respiratory oscillators are affected by the activity of higher brain regions. Musizza and Stefanovska found that the direction and strength of synchronizaton between cardiorespiratory and cerebral slow delta-oscillators were associated with the state of anaesthesia (Musizza et al., 2007). These results indicated that cardiorespiratory synchronization would be affected by the activity of cerebral cortex. The mental stress tasks can arise the activity of cerebral cortex and its effect on cardiorespiratory synchronization was investigated in the article.