Relationship between hypothermia and heart rate variability,blood pressure variability

AIM: To study the function of autonomic nervous system by the method of heart rate variability (HRV) and arterial blood pressure variability (BPV).METHODS: The rectal temperature of rats decreased gradually with their body surfaces contacted with ice,the range of the rectal temperature varied from 19 ℃ to 37 ℃.Both the dynamic electrocardiogram (ECG) signals and dynamic blood pressure signals were recorded,respectively.RESULTS: Using the method of HRV,there was an increase in RR interval (RRI),which implied a corresponding decrease in heart rate with the rectal temperature varying from 19 ℃ to 29 ℃ (P<0.01).There was a decrease in the value of normalized low frequency power (LFn) (P<0.05) and an increase in the value of normalized high frequency power (HFn) (P<0.01) with the rectal temperatures varying from 19 ℃ to 21 ℃.Therefore,the balance control of cardiac autonomic nervous was transferred to increase of vagal nerve drive (P<0.05).Using the method of BPV,there was an increase (P<0.01) in the value of HFn related to respiratory with the body temperatures falling to 31 ℃.While the body temperature varied from 19 ℃ to 29 ℃ (except 27 ℃),there was an increase in the value of HFn related to respiratory rates (P<0.05 or P<0.01) and the balance control of autonomic nervous was transferred to increase of vagal nerve drive (P<0.05).CONCLUSION: As the body temperature reduces,the vagal nerve activity in cardiovascular system increases,and the effect of hypothermia on HRV is sensitive to BPV.