| Summary: | 碩士 === 中原大學 === 醫學工程學系 === 87 === Analysis of heart rate variability (HRV) has been widely used as a measurement of the sympathetic and parasympathetic activities of the autonomic nervous system (ANS). The effect of these two neural activities on the heart can be identified by analyzing the frequency components of the HRV power spectra at the low frequency (LF, 0.08 ~ 0.15Hz) and high frequency (HF, 0.15 ~ 0.4Hz). Additionally, the ratio of the LF power and HF power (LF/HF) has been used as an index of sympathetic-vagal balance.
During anesthesia, the agents can help patients going thorough the operation by letting them conscienceless. However, it is known that the HRV characteristic changes differently under different anesthesia agents or methods. Nevertheless, it is unclear how HRV is influenced.
Since that these is no clear guideline for proper time interval for intubation. Improper anesthesia procedure can not only cause pain but also induce high blood pressure or danger reaction of the cardiovascular system. Thus, in this study, the time frequency analysis method was used to exam the HRV characteristic during anesthesia. The effect of intubation after different time intervals was examined in order to unsolve the best time interval for intubation.
We have examined the spectral components of HRV during induction of anesthesia with inhalation of Halothane-nitro oxide and tracheal intubation of 28 children. The effect of 10, 15 and 20 minutes induction on the spectra power were examined at the following periods (1) baseline (2) pre-intubation (3) post-intubation and (4) maintenance phases. Marked reductions in the power of HRV spectra, at all frequencies, were found at pre-intubation, indicating the Halothane decreased total ANS activity. LF, HF and total powers increased after intubation. The LF/HF ratio decreased to about 60% of baseline in both pre-intubation and maintenance phase, indicating ANS stays at a dynamic balance situation after anesthesia. In addition, the Halothane depressed LF further than HR. For 20 minutes induction, the pre-intubation reduction and post-intubation increase in LF are significantly different then 10 and 15 minutes induction. Thus, it is concluded that when the LF power decreased to 20% of the baseline value may indicate adequacy amount of anesthesia for tracheal intubation and surgery.
Despite the anesthesiologists’ enthusiasm, there has been little success in arriving at an objective index for monitoring the procedure of anesthesia using physiologic signals. The results of this study indicate that the time-frequency analysis of HRV can be a useful tool for monitoring the depth of anesthesia and for accessing the ANS activity during anesthesia.
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