| IntroductionHeart rate variability ( HRV ) is the time variance of sinus beat-to-beat in a period of time . The analysis methods include mainly : Time domain (indices : SDNN and rMSSD and so on ) and Frequency domain ( indices : TP , VLF , LF , HF , and ratio of LF/HF ). The physiological mechanism of frequency domain indices of HRV is complex . Most of researchers think that TP reflects both activities of a sympathetic and parasympathetic nerve system ; and LF rereflects the activities of sympathetic nerve system ; and HF mainly reflects parasympathetic activities ; and the ratio of LF/HF reflects sympathovagal balance.And HRV has the important roles in predicting the prognosis of many clinical diseasea.It is a well-established risk factor for arrhythmic events and mortality among post-myocardial-infarction patients ; Reduced HRV identifies diabetic patients with autonomic neuropathy and so on . Patients with hypertension and congestive heart failure associated with a lower HRV than normal and plasma angiotensin (?) ( Ang (?)) concentration increased . Therefore , in patients with hypertension and congestive heart failure Ang(?) may be a major factor leading to lower HRV . So far , the reports about the effects of Ang (?) on HRV are less . Whether the roles of Ang (?) on HRV happen in the central autonomic nervous system or peripheral autonomic nervous system has not been elaborated . Therefore , this study was given intravenously Ang (?) in rabbits , and give ganglion block blocker hexamethonium bromide (HEXB) to block the central autonomic nervous system activity , to investigate the direct effects of Ang (?) on HRV , and learn the mechanism of the effects of Ang (?) on HRV . Materials and MethodsAdult healthy rabbits 40(2．3-2．7 kg , 6-7 months old) , sex not limited , obtained form the Experimental Animal Center of China Medical University , were used in this study . Animals were caged individually and free access to food and water . The ambient temperature of animal room was ( 23(?)2 )(?) , and the humidity ( 55(?)5 )% ; light and darkness were alternated with light 8:00 to 20:00 . Three days before the experiment , each rabbit was placed in a rabbit-box without restraint for 1-2h to adapt the experiment. All electrocardiogram(ECG) were measured in 1-4pm .The rabbits were divided randomly into four groups: control group, Ang(?) group, HEXB group , HEXB+Ang (?) group . 10 rabbits randomly selected were given intravenously Ang (?) 50ng/kg/min , as Ang(?) group. 10 rabbits randomly selected were given intravenously HEXB 0．8mg/kg/min , as HEXB group . 10 rabbits randomly selected were given intravenously HEXB 0．8mg/kg/min , 20 minutes later , Meanwhile given Ang(?) 50ng/kg/min , as HEXB+Ang (?) group . 10 rabbits randomly selected were given intravenously saline , as control group . Then ECG and blood pressure were measured in each group . Then data of ECG was analysized by special software to obtain the indices of HRV , then the data was statistic by SPSS software .ResultsThe blood pressure in the rabbits given Ang (?) increased significantly (P<0．01 ) , no significant differences in heart rate ( P >0．05 ) , the SDNN and rMSSD of time domain decreased significantly (P <0．01 ) , TP(?) HFn of frequency domain decreased significantly, LF/HF increased significantly ( P<0．01 ) , LF increased ( P <0．05) , compared with the control group ; The blood pressure in the rabbits given HEXB decreased significantly (P <0．01) , Heart rate was significantly increased ( P <0．01 ) ; the SDNN and rMSSD of time domain decreased significantly (P <0．01) ; TP(?) HFn(?)LFn of frequency domain decreased significantly (P <0．01) , compared with the control group ; The blood pressure in the rabbits given HEXB+Ang (?) increased significantly ( P<0．01 ) , no significant difference in Heart rate and all time domain and frequency domain indices (P>0．05 ) , compared with the HEXB group .ConclusionThe indices of time domain SDNN and rMSSD decrease , and the indices of frequency domain TP(?) HF decreased , LF increased in Ang(?) group , that means Ang (?) increased sysmpathetic nerve tone and decreased vagal tone, then decreased the HRV.HEXB can block the effects of Ang (?) on HRV by blocking the central automic nerve . Therefore , Ang (?) is suggested impact the central autonomic nerve to decrease HRV. |
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