Effects Of Vagosympathetic Trunks Stimulation On Heart Rate And Heart Rate Variability In The Toads

IntroductionHeart rate variability(HRV) is an accepted term to describe the oscillation in the R-R interval between consecutive heart beats.The autonomic nervous system(ANS) makes heart rate quick or slow via ANS's modulation to sinus heart rate,and so makes the happening of HRV.The modulation of the sympathetic nervous system(SNS) and the parasympathetic nervous system(PNS) can be expressed by the change of HRV.So HRV could reflect the action of ANS and quantitative estimate the tone and balance of SNS and PNS.This makes HRV could judge pathogenetic condition and prognosis of cardiovascular disease patients.HRV is affected by many factors in vivo,eg.nerves,respiration,position, baroreceptor,thermoregulation,so it is complex to analyze.It is still less known about the effect of ANS to HRV in vitro.Present studies suggest that the power spectrum of HRV do not directly reflect the action of nerve,but more precisely reflect the modulation of ANS in the level of heart.But the nervous regulation mechanism of HRV is not clear at the moment.This study was designed to observe the effect of PNS on HR and HRV when the vagosympathetic trunks were stimulated without the influence of humor and temperature,and analyzed the potential mechanism.Generally, the regulation modulation of PNS to circulation and respiration are homogenous in toads and human,so this study could provide some foundation for basic investigation in HRV. Materials and methods1.Animals and disposalZhonghua toads(35-50g) were raised by the manpower and held at(24±2)℃,RH (55±5)%.The animals were divided into groups randomly.All experimental trials were carried out after 9:30 am.2.Experiment groups and protocolThe animals were divided into two groups randomly,control group and medicine group,the details were as follows:(1) Control group(C_PP group,n=10):the isolated hearts were perfused with Ringer's solution all along..(2) Medicine group(Phe+Pro group,n=10):the isolated hearts were purfused with Ringer's solution for 40min,then purfused with Phe(1.5μmol/L) and Pro(1.5μmol/L) all along.3.Electrocardiogram recordingThe animals were prepared to be specimen of isolated heart with vagosympathetic trunks.The isolated hearts were connected to water incubator by catheters and purfused in the same pressure.The nerves were put on stimulating electrode.The recording electrode of electro-cardio-signal collecting system was connected to water incubator and computer.Collect the electrocardiograms of the isolated hearts until the experiments were over.4.Vagosympathetic trunks stimulationStimulated the nerves after the hearts being isolated 80min in group Control and 40min in group P+P.Each frequency was intermittent 10min,and the frequency was selected randomly.5.Heart rate variability analysisSelect 5min continuous ECG or electro-cardio-signal records,analyzed all data with HRV software. 6.Statistical analysisExperimental data were indicated as mean±SD,the differences between groups were assessed by student's test with SPSS softwareResults1.The heart in group Control was clearly decreased after stimulated by different frequency.But there was no difference between the different frequency levels.SDNN was clearly increased in 0.4Hz,significantly increased in 0.6Hz and 0.8Hz.RMSSD was significantly increased in every frequency.There was no difference between frequencies.LF was clearly decreased in 0.4Hz,significantly decreased in others.No difference was fotind in frequencies.HF was clearly increased in 0.6Hz,significantly increased in others.No difference was found in frequencies.LF/HF was clearly decreased in all frequencies.It was obviously different between 0.2Hz and 0.8Hz. There was no difference between pre-stimulus and post-stimulus.2.With the increasing of stimulus frequency,HR was significantly decreased in group P+P.It was obviously different between 0.2Hz and 0.6Hz,0.4Hz and 0.8Hz,0.2Hz and 0.8Hz.SDNN and RMSSD were significantly increased in every frequency,and no difference was found between every frequency.LF and HF changed significantly in 0.2Hz,changed obviously in 0.4Hz,changed little in 0.6Hz and 0.8Hz.There was significantly different between 0.2Hz and 0.8Hz.LF/HF was clearly decreased in 0.2Hz, while it was near to that of post-medicine in 0.8Hz.There was significantly different between 0.2Hz and 0.8Hz.After stimulus,each index was increased compared to pre-stimulus,but there was no statistical meaning.DiscussionThe balance of SNS and PNS was disturbed when the nerve was stimulated,and the HR and HRV were both changed in group Control and group P+P.In group Control, HR was decreased in every frequency,and no difference in every level of frequency. While in group P+P,as Phe and Pro had blocked the HR increasing effect of SNS,HR was decreased significantly,and it was clearly different between 0.2Hz and 0.6Hz, 0.4Hz and 0.8Hz,0.2Hz and 0.8Hz.The decreasing velocity of HR in group P+P was bigger than that in group Control.These results indicate that the effect of vagus stimulus frequency was in according with the decreasing of HR:the frequency was high,the HR was slow.SDNN and RMSSD significantly increased after stimulus both in group Control and P+P.But there was no difference in every level of frequency.It was proposed that simple measurement of HRV in the time domain could not be likely to provide a quantitative measure of vagal or sympathetic tonic activity in the absence of physiological modulation of cardiac autonomic activity.In group Control,HF increased clearly when vagosympathetic trunks were stimulating.Because of the regulation of sympathetic,HF didn't have any difference between different frequencies.In group P+P,HF increased obviously in 0.2Hz and 0.4Hz,but not in 0.6Hz and 0.8Hz.Accordingly,LF/HF changed similarly.These results indicate that sympathetic nerve also plays an important role in the regulation of HRV.In a lower stimulus frequency,HF presented higher,while LF/HF lower.It was indicated that the regulations of vagal on HR and HRV may be different in the absence of regulation of sympathetic.ConclusionVagal regulates HR directly;the regulations of vagal on HR and HRV may be different in the absence of regulation of sympathetic.