Acuet Stress Induced Cardiac Electrophysiological Alteraitons Among Military Personnel And Its Potential Mechanisms

BACKGROUND: Stress is a comprehensive response status that's created when wemeet with exterior and interior environment upheaval. Intensity or long-time of stresscould arouse severe influence on the mankind's physical and mental health. The lightlevel of stress can lead to physiological function disorder. When the stress become tooseriously, it can cause stress diseases. Military personnel is a special community,usually be placed in special environment and particular affairs. Military stress hasbecome one of the main causes of non-combat attrition. Therefore, many countriesgreatly pay attention to prevent of damage related to military stress. China's militarystress research is still on beginning stage. The reports about the mechanism thatmilitary stress can hurt cardiovascular function, particularly cause arrhythmia wererare.This research focuses on the influence on cardiac electrophysiology related toacute military stress by using some data collected from the scene of militaryoperations, and also focuses on the mechanisms how the stress lead to arrhythmias byusing laboratory data that mimic stress situation.PURPOSE:This eassy first part inquire into military stress influence on cardiac electrophysiologyof Chinese soldiers from the scene of military operations. We compare the Holter datato study the incidence and the type of stress-induced arrhythmia. We analyze HRV,HRT and TWA to investigate function of autonomic nervous system leading toarrhythmia related to stress.The second part is to imitate military stressor diversityand polytropy characteristics, build up acute guinea pig stress model. We measure theconcentrations of CRH, ACTH, CORT, Hcy, hs-CRP and TNI, combine the changesof electrocardiogram to explore the mechanism that stress factor and inflammatoryfactor which cause arrhythmias in acute stress situation.The third part we record thechanges of AP, DADs, ICa,Land Itiin ventricular myocytes of guinea pigs in ISO and normal situation by using patch clamp. From cellular level to reveal the mechanism ofacute military stress causing arrhythmias. Medicate with MET to make clearmolecular mechanism of β-blocker preventing arrhythmias.Part1The influence on cardiac electrophysiology of military personnel becauseof acute military stressTIME:2006Mar.-2009Dec.METHODS: Collected the Holter data of103soldiers in one Beijing military as atest group. At the same time, collected the Holter data of other150soldiers act as thecontrol group. By comparing the data of two groups, we studied the incidence andtype of arrhythmia, analyzed the changes of HRV, HRT and TWA.RESULT:1. All the soldiers' Holter recording times were22h-24h. The recording times of thesetwo groups had no significant difference.2. The sum of heart rate, the average heart rate, the maximum heart rate and theminimum heart rate in the test group were all faster than those of the control group.They all had statistically different.3. The incidence of atrial premature in the test group was a litter lower than that of thecontrol group. But the average number of atrial premature was higher in the test group(P <0.01). The incidence of paroxysmal atrial tachycardia in the test group was higherthan that of the control group (P <0.01).4. There was no difference of the incidence of ventricular premature in two groups.But the average number of ventricular premature was higher in the test group (P<0.01).In the test group,3soliders had attacked ventricular tachycardia. Fortunately,no people in the control group had this terrible thing.5. In the time domain indices of HRV, in the test group the SDNN, SDANN, PNN50,and HRVTI were all lower than those in the control group (all P <0.05).6. We analyzed HRT of both groups. TO was higher in the test group, while otherindices such as TS and TD were lower than those in the control group (all P <0.05).7. We compared TWA of30pair consecutive sinus rhythm at maximum heart rate andin the morning8:00in two groups. The results showed: the TWA of maximum heartrate and8:00Am in test group were significantly higher than those in the controlgroup (all P <0.01).8. There were3soliders had attacked ventricular tachycardia in the test group.Combined these3men's data, we found2soliders of these men had significantly higher in the sum heart rate, the average heart rate, the maximum heart rate and theminimum heart rate than the average level of the test group. The other man had a littlehigher. One solider's HRV was obviously decreased. The other two men's HRV wereslight decreased. Two of these men had positive all indices of HRT, one had positiveTS and TD. All these men's TWA were higher than the average level of the test group.CONCLUSION:1. In stressful situations, military personnel have more atrial arrhythmia, ventriculararrhythmia than usual, and the severity of arrhythmia increased. Stress is one reasonfor arrhythmia happened or increased in our military personnel.2. Stress provoke misbalance of military personnel's autonomic nervous system,especially vagus nerve malfunction.3. The disorder of military personnel's autonomic nervous system may increaseunstable of cardiac myocytes' electric activity and raise the risk of arrhythmia.4. Combined with several markers reflecting the function of autonomic nervoussystem may increase ability to identify high risk of SCD people.Part2Function of acute multiple stressors to the guinea pigMETHODS: Combined with noise, light, foot sole electric shock and constraint asthe stressors to stimulate guinea pigs for16hours to build up acute stress animalmodels. Recorded ECG, and measured the concentrations of guinea pigs' serum CRH,ACTH, CORT, Hcy, hs-CRP and TNI.RESULT:1. Signs of Stress: guinea pigs which were experienced stress showed some of thefollowing signs, yelping, all over the body muscle contraction, hurried and confusedescaped, defecation increased, hair became upright and lost fur. One guinea pig wasdead.2. The average heart rate of stressed guinea pigs was faster than the control group (P<0.01).3. During the observation period, in the control group there was no arrhythmia. Butfour guinea pigs in the test group had different types of arrhythmia. Every type ofarrhythmia did not last long time. One guinea pig was attacked ventricular fibrillationto dead.4. The concentrations of CRH, ACTH and CORT in serum of stressed guinea pigswere higher than those in the control group (P<0.01or P<0.05). 5. The levels of Hcy and hs-CRP were significantly higher in the stress group thanthose in the control group (all P <0.01).6. In the stress group, TNI was1.43±0.29ug/L higher than that in the control group0.27±0.04ug/L (P<0.01).CONCLUSION:1. Multiple stressors successfully build up acute stress animal models. Animals showmain symptoms resemble to mankind in stressful situation.2. In stress state, animals manifest abnormality of electrocardio activity and damageof myocardium.3. The changes of stress factor and inflammatory factor are related to arrhythmias inacute stress situation.Part3Cellular mechanisms for stress-induced arrhythmiaMETHODS: Isolated guinea pigs ventricular myocytes by using enzymatic method.Selected guinea pigs' single ventricular myocyte which was in good condition andcalcium-resistant to establish whole-cell patch clamp mode. Applicated ISO30.0nmol/L as a tool for medicine, to establish a cell model of hypercatecholamine state.Recorded AP, DADs, ICa,L, and Itiof guinea pig single ventricular myocyte by patch toanalyzed cellular mechanisms for stress-induced arrhythmia. Medicate with MET tomake clear molecular mechanisms of β-blocker preventing arrhythmias.RESULT:1. Guinea pig single ventricular cell was successfully isolated and established ofwhole-cell patch clamp mode.2. Recorded AP in stressed guinea pigs single ventricular myocytes and interferedwith MET.Using30.0nmol/L ISO to perfuse in the cell pool, the APD of single ventricularmyocyte shortened significantly. APD₅₀of guinea pig ventricular myocytes in thecontrol group were shorted from177.6±6.2ms to130.3±9.9ms(P<0.01, n=10), andAPD₉₀of them were shorted from311.8±13.5ms to262.1±11.6ms (P <0.01, n=10).No changes in APA and RMP. Used30.0nmol/L ISO+1.0μmol/L MET, APD₅₀recovered to145.7±8.8ms, and APD₉₀recovered to297.5±15.5ms. But APA andRMP had no significant changes.3. Effects on DADs of guinea pigs single ventricular myocytes by ISO. Using30.0nmol/L ISO to perfuse in the cell pool, given1.0Hz frequencystimulus may occasionly induce DADs. Both amplitude and incidence of DADs werelittle.3.0Hz frequency stimulus could induce a series of DADs. The amplitude ofDADs was high at the beginning, and then got short. The incidence of DADs wasincreased and nearly lasted for the whole resting potential.5.0Hz frequency stimulusinduced TAs. TAs took on apparent spontaneous depolarization of the4th phase. Butits amplitude of action potential was lower than stimulus-induced potential.Using30.0nmol/L ISO, given1.0-3.0-5.0Hz frequency train stimulus couldinduce DADs and TAs. After1.0Hz frequency stimulus, only one DADs emerged.Several DADs emerged after3.0Hz frequency stimulus and more DADs emergedafter5.0Hz frequency stimulus and then led to TAs.4. Effects on ICa,Lof guinea pigs single ventricular myocytes by ISO and interferedwith MET.ICa,Lincreased significantly after using30.0nmol/L ISO. ICa,Lcurrent density wasgreatly increased, especially at about0mV. No changes were detected in activationpotential, peak potential and the shape of I-V curve after given ISO. While perfusedwith30.0nmol/L ISO+1.0μmol/L MET, ICa,Lcurrent density at all voltages wasdecreased to nearly the control level.30.0nmol/L ISO made the steady-state activation curve of ICa,Lshift right. Thechannel half-inactivation voltage (V_1/2) shifted to depolarization, from-38.84±1.9mVmoved to-28.89±3.18mV (n=20, P <0.01), but did not change the curve slope (k).Used30.0nmol/L ISO+1.0μmol/L MET, V_1/2was partly recovered to-34.45±1.75mV,but k didn't change.30.0nmol/L ISO made the steady-state inactivation curve of ICa,Lalso shift right.V_1/2shifted to depolarization, from-40.77±3.58mV moved to-24.79±2.26mV (n=20,P <0.01). Interfered with MET, V_1/2was recovered to-36.58±3.00mV. Neither ISOnor ISO+MET, k changed notablely.Because the steady-state inactivation curve of ICa,Lshifted right more greatlythan the steady-state activation curve, window current was increased ultimately.Interfered with MET, window current was decreased to nearly control level.Both ISO and ISO+MET did not affect the recovery from inactivation curve ofICa,L.5. Effects on Itiof guinea pigs single ventricular myocytes by ISO and interfered withMET. Itiincreased significantly after using30.0nmol/L ISO. The current density at-50mV increased from-0.69±0.18pA/pF to-3.24±0.24pA/pF(P<0.01, n=18).Perfused30.0nmol/L ISO+1.0μmol/L MET, the current density changed little to-1.21±0.19pA/pF.From the I-V curve of the current, we could see the current was activated at-70mV, reached peak potential at-50mV, and then inward current decreased. Using30.0nmol/L ISO, Iticurrent density was increased at every voltage, especially at aboutpeak potential, and the channel activation voltage moved early to-100mV. The shapeof curve changed from converse clock to triangle, but no change the location of peakcurrent. Interfered with MET, Iticurrent density was decreased slightly.30.0nmol/L ISO made the steady-state activation curve of Itishift left. V_1/2shifted from-61.02±3.09mV to-89.76±7.58mV. Used30.0nmol/L ISO+1.0μmol/LMET, V_1/2was partly recovered to-72.96±7.69mV.CONCLUSION:1. ISO shorts APD50and APD90in guinea pig single ventricular myocyte. Shortenof APD could induce reentry arrhythmias.2. MET may ameliorate the shorten of APD from ISO, extend effective refractoryperiod, inhibit formation of reentry loop to reduce arrhythmias.3. ISO could induce DADs and TAs in guinea pig single ventricular myocyte. Thisfunction shows frequency-depend.4. ISO inhibits both activation and inactivation of L-type calcium channel, and theinactivation is influenced greatly. So the final effect is window current is increased.Window current is the important reason for DADs. Interfered with MET, windowcurrent could recovery to nearly control level. Which decreases the concentration ofintracellular Ca2+, ameliorates Ca2+overload and lessens triggering mechanism.5. Itiis main component of DADs. ISO increases Itiof single guinea pig ventricularmyocyte by altering the activation characters of Iti. MET could inhibit Itiat differentmembrane potentials, which could reduce the incidence of DADs and TAs.