- 學位論文
利用即時心率變異度評估麻醉深度
A Real Time Heart Rate Variability System for Evaluating the Depth of Anesthesia
摘要
心率變異度的頻譜分析已經被證實可用來代表自主神經系統的活性，其中在心率變異度的功率頻譜圖中，低頻能量代表交感與副交感神經系統共同作用，高頻能量則代表副交感神經系統作用的情形。由之前研究中發現麻醉劑會對自主神經系統產生抑制作用，導致心率變異度功率頻譜下降。一般認為氣管插管對於病人的交感神經系統刺激最大，因此可以藉由觀察氣管插管所引起的反應評估麻醉狀態。而在功率頻譜的頻帶範圍中，低頻帶能量可以反應交感神經系統的活性，本研究並且配合BIS（bispectral index）指數來與本研究做比較。本研究利用之前提出的方法為基礎，將之運用在以數位訊號處理器為架構的即時運算系統上，並在計算心率變異度後，能將其低、高頻能量每隔兩秒儲存在系統的外部記憶體中並且即時顯示在液晶顯示器上。由實驗結果得知，在以吸入性麻醉劑sevoflurane麻醉誘導過程中，當低頻能量參數下降到基準時段的40%時，再進行氣管插管不會引起劇烈的自主神經系統反應，而且可以在麻醉維持階段時，提供足夠的麻醉深度以利醫師進行插管及手術。但在相同的條件下，利用BIS指數作為插管的參考，在麻醉維持階段時病人的低頻能量仍居高不下。由此可知，以心率變異度確能作為麻醉深度的參考指標。而此實驗結果亦證實了以本系統作為即時心率變異度分析的可行性。
並列摘要
The power spectrum analysis of the heart rate variability (HRV) has been confirmed that it can provide information about the activation of the autonomic nervous system (ANS). Additionally, we knew the relationship between the frequency bands and sympathovagal effects from the previous studies. The low frequency band ( LF, 0.04~0.15Hz ) is mainly mediated by the sympathetic and parasympathetic nervous system and the high frequency band ( HF, 0.15~0.4Hz ) is effected by the parasympathetic nervous system.The anesthetic suppress the ANS. It results in the decrease in HRV power. However, the LF power could still show changes under the stimulation of intubation. The LF power is influenced by the sympathetic nervous system. Therefore, it can be used for evaluating the depth of anesthesia. The previous result indicates that when the LF power decreased to the 30% of the baseline value indicating adequate depth of anesthesia. On the other hand, the BIS index ( bispectral index ) is also used for judging the patients’ state of anesthesia in this study.In this study a fixed- point DSP ( TMS320C50 , Texas Instruments, Inc.) is used to process the signal and executes all the necessary calculation which includes heart rate, interpolation and power spectrum. After processing, the results are displayed on a 128*64 dots matrix LCD. The proposed system is capable of storing the above information in the internal SRAM.We have examined the spectral components of the HRV during the pre-induction of anesthesia with inhalation of sevoflurane and intubation of 21 patients. The patients are divided into 2 groups and the spectra power are examined at the following periods (1) pre-induction (2) pre-intubation (3) post-intubation (4) maintenance phases. In one group, the intubation time is determined by the HRV index when the LF power in the pre-intubation period decreased to 40% of the pre-induction. The other group is determined by the BIS index when its value is below 40). In the HRV group, marked reduction in the LF power at the maintenance phase. On the other hand, in the BIS index group, the LF power varies significantly. The results of this study indicate that the HRV index can be a useful tool for monitoring the depth of anesthesia. And also, we can conclude the HRV index can be implemented in the real-time monitoring system. If we could combine the BIS index system with this proposed system to monitoring the depth of anesthesia, it would be a safe and reliable anesthesia monitoring system.