| IntroductionHeart rate variability is time variance between beat to beat in specified times of sinus rhythm.It is different from average heart rate whose unit is per minute,heart rate variability reflects heart rate continuous monment fluctuation.However,the fluctuation of heart rate is affected or modulated by many factors such as nervous system or humoral system.Therefore,heart rate variability is affected by many factors,too.Among these factors,temperature is one of the most important factors.At present,many researches think VLF of heart rate variability is associated with temperature modulation,but the concrete nervous modulation mechanism originated by the temperature change haven't been reported.Moreover,the effect of temperature on heart rate whether or not through directly affects heart sinoaurial node pacing cell,this problem haven't discuses clearly.This experiment analyzed the effect of temperature on heart rate variability and the nervous modulation mechanism by collecting electrocardiogram of isolated heart in the toads in three different temperatures.Materials and methods1.Animals and disposal2.Adult healthy zhonghua toads weighting 45-70 gram were held under a 12h light:12h dark regime,keeping room temperature on 22±2℃,humidity on (50±10)%.The animals were raised by the manpower and divided into groups randomly.All experiment trials were carried out in 2-6pm. 3.Experiment groups and protocolThe toads were divided into three groups randomly,which was prepared for isolated heart specimens,i.e.34℃group,22℃group,10℃group.Every group was divided into subgroup as follow:(1)sympathetic blocking agent(Atr)group(n=10)(2)vagal blocking agent(Phe+Pro)group(n=10)(3)sympathetic blocking agent and vagal blocking agent(Atr+Phe+Pro)group (n=10)4.Electrocardiogram recordingPrepared the isolated heart perfusion specimen,then connected the specimen to water incubator by catheters,and collected the ECG of isolated heart.5.Heart rate variability analysisSelect 30min 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 software.Results1.During low temperature,the heart rate reduce;during high temperature,the heart rate increases.2.When temperature changes more than 12℃,VLF increases when cooling; oppositing,VLF reduces when warming.The changes of HF are same with VLF.3.In three temperatures conditions(10℃,22℃,34℃),after medication with Atr, VLF decreases while LF/HF increases;after medication with Phe+Pro,results reverse; during room temperature,after medication with Atr+Phe+Pro,LF/HF decreases.DiscussionAfter heart was isolated,during low temperature fluid perfuses,the heart rate reduces;during high temperature fluid perfuses,the heart rate increases.This indicates that the effect of temperature on heart rate can directly act on sinoatrial node cell of heart.But during low temperature fluid perfuses,not only the effect of temperature on heart rate can directly act on sinoatrial node cell of heart but also the effect of parasympathetic nerve system.However,when the difference of temperature is more than 12℃,VLF is inverse radio to temperature.This suggest that VLF is modulated by temperature.Meanwhile, the changes of HF is same with VLF.From this,we can suppose that VLF reflect vagus nerves action partly.In three temperatures conditions(10℃,22℃,34℃),after medication with Atr, VLF decreased while LF/HF increased;after medication with Phe+Pro,results reversed.From this,we can suppose again that VLF is modulated by parasympathetic nerve system.During room temperature,after medication with Atr+Phe+Pro,LF/HF decreases.This suggest that the modulation of intracardiac sympathetic nerve is predominant after the heart is isolated.ConclusionThe effect of temperature on heart rate can directly act on sinoatrial node cell of heart.VLF is modulated by temperature.Moreover,VLF is mainly modulated by parasympathetic nerve system.
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