| Heart-brain interactions (HBI) play a vital role in regulating the normalphysiological functions of the cardiovascular system (CVS), which, however, couldbe broken due to various factors (e.g., brain injury, mental stress, and so on),resulting in malfunction of the cardiovascular nervous system (CNS) and thusincreasing risk of kinds of cardiovascular diseases (CVDs). According to WorldHealth Statistics 2009, CVDs are still the leading killer of mankind at present.Every year, almost 3.01 of population in the world and 2.79 of population inChina die from CVS. On the other hand, currently there are no e?cacious meth-ods for evaluating the changes of the strength of HBI following hypoxic-ischemicbrain injury (e.g., brain injury following cardiac arrest (CA)), and it has not beenwell known how the brain activities under mental stress (e.g., time pressure) arein relation to the modulability of the CNS either. With these considerations, inthis dissertation, we mainly investigated the e?ects of both brain injury after CAand time pressure during the computer work on the regulation of the CNS andHBI by means of electrophysiological signal processing.Two experimental paradigms, including: a) brain injury following cardiacarrest (CA) in the rat and neuroprotective e?ects of NAALADase inhibitor (i.e.2-PMPA), b) time pressure during the computer work, were implemented toachieve the objectives of this work. In each paradigm, the following two researchapproaches were successively taken:(1) The changes in CNS were investigated by means of heart rate variability(HRV), according to the priori knowledge that changes in the brain wouldalter the activities of CNS.(2) Not only the brain activities were investigated by means of EEG, but therelationship between the brain and the CNS was further studied by analyzingthe interaction between HRV and qEEG.The objectives of the 1st paradigm were to investigate changes of the vulner-ability of the CNS and HBI before and after CA, and the neuroprotection of CNS and HBI by 2-PMPA. The rats were randomly assigned to three groups, includingcontrols treated with saline instead of 2-PMPA, low-dose group treated with lowdose 2-PMPA (100 mg/kg of initial dosage before injury and 10 mg/kg/h afterthe injury) and high-dose group treated with high dose 2-PMPA (200 mg/kgof initial dosage before injury and 20 mg/kg/h after the injury). Then, takingthe 1st research approach, we calculated the scaling properties of HRV in dif-ferent sessions before and after CA by centered-moving-average-based detrendedfluctuation analysis (DFA). Our results showed that:(1) The scaling exponents of HRV in each group decreased continuously in thefirst 4 hours after CA, which were close to Brownian motion in baselinesession and shifted to a 1/f noise-like rhythm 4 hours after CA. However,the scaling exponents of HRV showed no significant differences between anytwo groups in every session.(2) By modeling the scaling factor following CA with an exponent decayingequation, we found that the high-dose 2-PMPA would change the processof the alteration of the CNS after CA. But in the aspect of scaling factorafter 4 hours following CA, 2-PMPA didn't show protection on the CNSfrom hypoxic-ischemic brain injury.According to the results above, the low dose 2-PMPA showed no significantinfluences on the CNS. Thus, when taking the 2nd research approach, we measurethe phase synchronization in different EEG subbands and HRV just in the controlgroup and the high-dose group. The main findings were as follows:(1) There was significant phase synchronization between the power of each EEGsubband and HRV in rats. The synchronization decreased significantly afterCA, and didn't show any obvious recovery in the first 4 hours following CA.(2) The high-dose 2-PMPA could only protect the phase synchronization betweenthe power of EEG subbands and HRV from hypoxic-ischemic brain injury inthe early recovery of after CA.Moreover, compared with the spectral parameters of EEG and HRV, the phasesynchronization between the power of different EEG subbands and HRV wasconsidered to be effective in evaluating the strength of the relations betweenactivities of brain and CNS following CA. In the experiment of time pressure, the subjects were also assigned to twodi?erent experiments. In the first experiment, we took the 1st research approach,and investigated the in?uences of time pressure on long-range correlations in HRVand the effects of relaxation on the cardiovascular regulation system. Moreover,in the second experiment, we took the 2nd research approach to study the re-lationship between changes of the brain activities and those of the CNS duringcompter-mouse work under time pressure.Volunteer subjects in the first experiment participated in a computer-mousetask consisting of five sessions, i.e., baseline session (BSS) which was free of timepressure, followed by sessions with 80% (SS80), 100% (SS100), 90% (SS90) and150% (SS150) of the baseline time. Electrocardiogram (ECG) and task perfor-mance were recorded throughout the experiments. Two rest sessions before andafter the computer-mouse work, i.e., RS1 and RS2, were also recorded as com-parison. More performance errors as well as higher heart rate in more stressfulsessions indicated that our experimental paradigm successfully created a stressfulwork situation. Then, HRV series were subsequently analyzed by both conven-tional power spectral analysis and DFA.(1) The long-term scaling exponentα2 by DFA was significantly lower in SS80than that in other sessions, but no significant differences were found betweenany two sessions by conventional power spectral analysis. DFA outperformedthe spectral analysis in discriminating the states of cardiovascular autonomicmodulation under time pressure.(2) The short-term release of time pressure had positive influences on the car-diovascular system, i.e., theα2 in RS2 was significantly higher than that inSS80, SS100 and SS90.According to results of the previous experiment, the second experiment wasreduced to three sessions, i.e., rest session (RSS) before computer-mouse work,baseline session (BSS) which was free of time pressure, and time pressure (TP)session during which the displaying time of a six-digit number was 85% of baselinetime, to minimize the influences of some interference factors (e.g., fatigue) on theexperimental results. We first analyzed the EEG and HRV series by power spectrain each session, then we investigated how the di?erences of spectral parametersof HRV between two successive sessions are correlated with those of EEG. Themain findings were as follows: (1) Compared with RSS, the digit input task in BSS elevated the subjects'cog-nitive complexity and attention level, which resulted in significantly higherrelativeθband power in the left hemisphere. The relative inactivation in theleft hemisphere was strongly correlated with the decrease of low frequency(LF) component in HRV.(2) Compared with BSS, the time pressure in TP significantly enhanced thesubjects'relativeβband power in the right posterolateral region. Moreover,the increases of relativeβband power in F3 and F4 were both stronglycorrelated with the high frequency (HF) component in HRV.(3) The significant increment of heart rate and LF/HF in TP implied that therelative hyper-activation in the right posterolateral brain cortex caused bytime pressure had more in?uences on CNS regulation than the relative hypo-inactivation in the left brain region caused by digit input task.In conclusion, by quantitative analysis of the EEG and HRV series, we notonly proposed the e?cacious methods for evaluating the changes of CNS regu-lation function and the strength of the HBI following CA, to provide possiblemeans for assessing the risks of recurrences of CVDs following cardio-pulmonaryresuscitation, but also investigated the changes of CNS and the relationship be-tween changes of brain activities and those of CNS regulation function under timepressure, to afford the company or the institution some grounds for getting thebalance between greater work e?ciency and protecting the health of the sta?s.
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