Hui-Hsun Huang

Time-frequency analysis of heart rate variability during transient segments

AbstractThe spectral characteristics of heart rate variability (HRV) are related to the modulation of the autonomic nervous system. As the physiological condition is changed by such external stimuli such as drugs, postural changes, and anesthesia, or by internal deregulation such as in syncope, adjective autonomic responses could alter HRV characteristics. Time-frequency analysis is commonly used to investigate the time-related HRV characteristics. An alteration of the autonomic regulation resulting in a change in mean heart rate induces a transient component in heart rate, which, with any analysis method based on signals from multiple beats, results in the apparent spread of the spectrum of frequencies. This obscures the spectral components related to the autonomic function. In this paper we investigated the influence of the transient component in several time-frequency methods including the short-time Fourier transform, the Choi-Williams distribution, the smoothed pseudo Wigner–Ville distribution (SPWVD), the filtering SPWVD compensation, and the discrete wavelet transform. One simulated signal and two heart rate signals during general anesthesia and postural change were used for this assessment. The result demonstrates that the filtering SPWVD compensation and the discrete wavelet transform have small spectrum interference from the transient component.

Analgesic Effect of Lidocaine Patch 5% in the Treatment of Acute Herpes Zoster: A Double-Blind and Vehicle-Controlled Study

Background and Objectives: Although lidocaine patch 5% has been widely used for postherpetic neuralgia, its analgesic effect on the intense pain associated with acute herpes zoster has not been investigated because of its potential hazard to damaged skin. Methods: Forty‐six patients suffering from moderate to severe pain caused by acute herpes zoster infection (within 4 weeks of onset) were enrolled in a randomized, double‐blind, vehicle‐controlled, parallel study. Lidocaine patch 5% or vehicle patch were applied to the intact portion of the painful skin area without blisters at 12‐hour intervals twice a day for 2 consecutive days. Analgesic efficacy and side effect profiles were assessed before and 48 hours after patch application. Results: We found that both groups of patients experienced significant pain relief during rest and movement. Differences of mean reduction of pain intensity between the two groups were 14.7 (4.7‐24.8, P = 0.005) during rest and 10.4 (1.6‐19.3, P = 0.007) during movement, favoring the lidocaine patch. The lidocaine patch produced a greater percentage change in a patients global impression than the vehicle patch. The incidence and severity of adverse events were low with both treatments. Conclusions: This study demonstrates that lidocaine patch 5%, applied twice a day, could serve as a well tolerated and effective modality to relieve moderate to severe pain associated with acute herpes zoster presumably through its pharmacological action and physical barrier effect on sensitized skin.

Preamplifier with a second-order high-pass filtering characteristic

A new preamplifier for suppressing low-frequency interference is presented. The proposed preamplifier, with its front end being implemented by an instrumentation amplifier, enjoys the following advantages: differential high-pass filtering, high input impedance, high common--mode rejection ratio and low passive sensitivity. This circuit can be realized with commercial operational amplifiers with enough phase margin, or fabricated in a chip for practical measurement of physiological signals.

Upper Airway Obstruction After Cervical Spine Fusion Surgery: Role of Cervical Fixation Angle

Upper airway obstruction is one of the life-threatening events in cervical spine surgery. The risk is particularly great during the period immediately after operation. We present the case of a 56-year-old female with breast cancer and metastasis to the cervical spine. The surgical procedure involved C2-C3 laminectomy, posterior fixation (C0-C5), and C2 neurectomy. Tracheal extubation was carried out in the intensive care unit, and upper airway obstruction immediately followed. Emergency cricothyrotomy was performed under well-managed ventilation with a laryngeal mask after several failed intubation attempts. Over-flexion of the cervical spine fixation and severe prevertebral soft tissue swelling were the most probable causes of upper airway obstruction. With a well-adjusted angle for fixation of the cervical spine under fluoroscopic guidance before the procedure, such a surgical mishap could be avoided. Reintubation with a fiberscope might be considered first, and sustaining intubation for 2-3 days postoperatively could be safer in such high risk patients.

Effect of ropivacaine on endothelium-dependent phenylephrine-induced contraction in guinea pig aorta

Background:  Previous studies have shown that ropivacaine has biphasic vascular effects, causing vasoconstriction at low concentrations and vasorelaxation at high concentrations. This study was designed to examine the role of the endothelium during accidental intravascular absorption of ropivacaine, and to elucidate the mechanisms responsible.

Sample entropy analysis of EEG signals via artificial neural networks to model patients' consciousness level based on anesthesiologists experience.

Electroencephalogram (EEG) signals, as it can express the human brains activities and reflect awareness, have been widely used in many research and medical equipment to build a noninvasive monitoring index to the depth of anesthesia (DOA). Bispectral (BIS) index monitor is one of the famous and important indicators for anesthesiologists primarily using EEG signals when assessing the DOA. In this study, an attempt is made to build a new indicator using EEG signals to provide a more valuable reference to the DOA for clinical researchers. The EEG signals are collected from patients under anesthetic surgery which are filtered using multivariate empirical mode decomposition (MEMD) method and analyzed using sample entropy (SampEn) analysis. The calculated signals from SampEn are utilized to train an artificial neural network (ANN) model through using expert assessment of consciousness level (EACL) which is assessed by experienced anesthesiologists as the target to train, validate, and test the ANN. The results that are achieved using the proposed system are compared to BIS index. The proposed system results show that it is not only having similar characteristic to BIS index but also more close to experienced anesthesiologists which illustrates the consciousness level and reflects the DOA successfully.

Lack of intravenous lidocaine effects on HRV changes of tracheal intubation during induction of general anesthesia.

BACKGROUND Intravenous lidocaine has been widely used for suppressing the autonomic activation from tracheal intubation during induction of general anesthesia. Conventionally, researches of its effectiveness through assessment of heart rate and blood pressure changes obtained by common clinical methods result in the conclusions deduced of much controversy. Heart rate variability is a noninvasive measurement of autonomic regulation and is suitable for the study of this subject. METHODS 36 ASA class I-II patients undergoing general anesthesia were divided into 3 groups. Besides induction agents, intravenous lidocaine was given 5 min before tracheal intubation in group A, 3 min before intubation in group B and nothing in group C. HRV spectral powers were measured at awake state, anesthetized state before tracheal intubation and anesthetized state after tracheal intubation by time frequency spectral analysis method and comparison was made between the three groups. RESULTS The HRV spectral power in high frequency (HF) and mid-frequency (MF) power bands and their ratios (MF/HF) were not significantly different among the 3 groups during the 3 observation periods. CONCLUSIONS There was no evidence to indicate the effectiveness of intravenous lidocaine on the autonomic regulation during tracheal intubation under the influence of induction agents used in general anesthesia.

Elimination of interference component in Wigner-Ville distribution for the signal with 1/f spectral characteristic

A new technique for interference-term suppression in Wigner-Ville distribution (WVD) is proposed for the signal with 1/f spectrum shape. The spectral characteristic of the signal is altered by f alpha filtering before time-frequency analysis and compensated after analysis. With the utilization of the proposed technique in smoothed pseudo Wigner-Ville distribution, an excellent suppression of interference component can be achieved.

Differences in Temperature Changes Between Pediatric and Adult Patients After Cardiopulmonary Bypass

Nasopharyngeal (NPT) and rectal (RT) temperatures were continuously monitored in 51 adult or pediatric patients undergoing cardiac surgical procedures until 1 hour after the termination of cardiopulmonary bypass (CPB). The measurement also included the lowest NPT achieved and the dwelling time at that temperature on CPB, the rewarming time, the time on CPB, and the time that the chest remained opened after CPB. After the termination of CPB, the decrease of NPT (afterdrop) was significantly greater in the adult group than in the pediatric group. The mean decrease in adult patients was 1.34 +/- 0.65 degrees C versus 0.63 +/- 0.8 degrees C in pediatric patients. The combination of the NPT at the end of bypass (EndNPT), body weight times the EndNPT, and the dwelling of the lowest temperature times the EndNPT could predict 45% of the afterdrop. It is concluded that afterdrop occurs to a lesser degree in pediatric patients than in adults. This may be due to more efficient supplying of external heat to pediatric patients in whom there is a larger body surface area to weight ratio.

Differential change in cardiac baroreflex sensitivity estimated by sequence and spectral analysis during etomidate anesthesia.

Spontaneous baroreflex sensitivity, high-frequency gain, (0.15–0.35 Hz), and mid-frequency gain (0.07–0.14 Hz) are noninvasive measures of cardiac baroreflex function derived by spontaneous sequence and cross-spectral analysis. To demonstrate the difference between these baroreflex estimates, 14 patients received etomidate (0.3 mg/kg bolus and 0.9 mg/kg/h infusion), lidocaine (60 mg), and vecuronium (0.1 mg/kg) by intravenous injection. The authors found that spontaneous baroreflex sensitivity and high-frequency gain were decreased (p<0.05) after etomidate anesthesia, whereas mid-frequency gain was maintained. Spontaneous baroreflex sensitivity, high-frequency gain, and mid-frequency gain, although compared simultaneously, did not change in a parallel manner. In another 5 patients, who received normal saline only, measures were unchanged. The authors conclude that spontaneous baroreflex sensitivity, high-frequency gain, and mid-frequency gain are not interchangeable. Experimental results on baroreflex control depend on the parameter selected.