The Changes of Differences of Pulse Transit Time between Toe and Finger in General and Epidural Anesthesia / 대한마취과학회지

BACKGROUND: Pulse wave velocity (PWV) and pulse transit time (PTT) are influenced by the arterial wall stiffness and compliance. Also, the PTT is dependent on blood pressure changes that can be accompanied by the anesthesia. The simply measured PTT has difficult to discriminate the arterial compliance changes from blood pressure changes. Therefore, we investigated that the differences of PTT between toe and finger as an independent parameter on blood pressure. METHODS: Eighteen patients scheduled for elective lower abdominal gynecologic surgery were studied. General anesthesia was achieved with sevoflurane and epidural block was done with 0.2% ropivacaine and fentanyl 100microgram via epidural catheter inserted into L1 - L2 epidural space. PTT was measured in a finger (PTTf) and a toe (PTTt) by the time difference between the ECG R wave and the pulse wave of PPG. Blood pressure and PTT was measured at three instances such as preinduction (Pre), 5 minutes after intubation (Int5) and 30 minutes after injection of epidural dose (Epi). The time delay of PTT between toe and finger (PTTt-f) was measured. RESULTS: PTTf and PTTt was prolonged at Int5 and Epi. But the PTTt-f was not different between the Int5 and Epi because of prolonged PTTf caused by the blood pressure decrement after the epidural block. CONCLUSIONS: PTTf, PTTt and PTTt-f can be a one of the convenient measurement of the arterial compliance but it was suggested that there need to be a parameter less dependent on the blood pressure changes.

Effects of Enflurane on Pulse Transit Time / 대한마취과학회지

BACKGROUND: In Anesthetic state, many hemodynamic parameters including blood pressure, heart rate and arterial compliance are changed. Moreover pulse transit time (PTT) is influenced by heart rate, blood pressure changes, and the compliance of the arteries. METHODS: In this study, we investigated PTT changes in patients under enflurane anesthesia. PTT of the finger was measured by photoplethysmography (PPG) and electrocardiography (ECG). PTT values were calculated as the time interval between the peak of the ECG R wave and the peak of the second derivatived of the PPG in the finger tip. RESULTS: ECG amplitude and heart rate increased reflecting hemodynamic chnages after enflurane anesthesia, and the PTT increased after enflurane anesthesia treatment by 16.68 ms (n = 24). Moreover, PTT was found to be inversely proportion to aging. CONCLUSIONS: The increase of PTT in the finger due to relaxation of the arterial wall muscle after enflurane anesthesia was used as an indicator of sympathetic block on muscle tone. This result suggests that PTT is strongly related with anesthetic state. And PTT may be one of useful surrogative methods for anesthetic monitoring, but PTT is unfortunately only qualitative.

Monitoring System during Enflurane Anesthesia Using Heart Rate Variability / 대한마취과학회지

BACKGROUND:We performed spectral analysis and determined the 1/f noise of heart rate variability during enflurane anaesthesia in order to assess the effect of the activity of the autonomic nervous system. METHODS: Data were acquired from 15 patients (ASA I-II) who received gynecological surgery under general anesthesia using enflurane, nitrous oxide and oxygen. We analyzed the spectral components of heart rate variability (HRV) according to the following five periods: 1) before premedication, 2) after induction, 3) during skin incision, 4) during recovery, and 5) after surgery. For each power spectrum the density and frequency components were identified as follows: (1) low frequency (LF) component (0.04-0.15 Hz) was associated with parasympathetic and sympathetic tone, and was affected by body temperature, the renin-angiotensin system, baroreceptor and vasomotor sympathetic modulation, (2) high frequency (HF) component (0.15-0.5 Hz) was mediated parasympathetic tone and reflected the mechanical influence of the ventilation. In addition the LF/HF ratio, which reflected cardiac sympathovagal balance was monitored. RESULTS: The LF/HF ratio, which reflects the balance of the autonomic nervous system increased remarkably during skin incision and recovery. Also, the beta index, which is related to body activity decreased during skin incision and recovery. CONCLUSIONS: Increased LF/HF was found to be caused by mechanical stimulation, which reflects autonomic nervous system balance, and the beta index was useful for the assessment of body activity.

Simulation of the Cardiovascular System Using PID Control Model / 대한의료정보학회지

OBJECTIVE: The electric analog circuit model can be used to analyse the various function of the cardio vascular system and the dynamic characteristics on each part of human body. According to the previous studies, viscous resistance, flow inertia, and vascular compliance in the cardiovascular system are analogous to resistance, inductance, and capacitance in electric circuit, so the cardiovascular system models have been represented by the electric circuit models. These approaches were to propose suitable models for the interested part of body and to simulate the various characteristics on the cardiovascular system. METHODS: This paper tried to put the characteristics of morphologic structure into the suggested electric circuit model. After setting parameter values of the model the dynamic characteristics of the cardio vascular system is simulated using VisSim, which is one of the simulation tools. RESULTS: The derived simulation results have represented major cardiovascular functions of normal adults. Also simulation results reflect the variation due to the pathophysiological state. CONCLUSION: The controller by baroreceptor, which is one of controllers to control the cardiovascular system, is appended in the model. The dynamic response characteristics and the procedure to restore blood pressure to normal state was observed by simulation lasted a certain period of bleeding.