Wyun Kon Park

Propofol and Thiopental Depression of Myocardial Contractility A Comparative Study of Mechanical and Electrophysiologic Effects in Isolated Guinea Pig Ventricular Muscle

The purpose of the study was to compare the actions of propofol and thiopental on myocardial contractility and cellular electrophysiologic behavior. Isometric tension of isolated guinea pig right ventricular papillary muscle was studied in normal and 26 mM potassium Tyrodes solutions at various stimulation rates (after rest up to 3 Hz). Normal and slow action potentials were also recorded by conventional microelectrodes. Propofol (30,100, and 300 μM) applied in the commercial 10% Intralipid emulsion caused dose-dependent depression of contractions at all stimulation rates, whereas Intralipid alone had no effect. Thiopental (10, 30, and 100 μM) caused depression similar to the threefold greater concentrations of propofol. Although neither drug altered the normal action potential (AP) amplitude or dV/dt max, thiopental (30 μM) increased AP duration. In the partially depolarized (26 mM potassium) β-adrenergically stimulated myocardium, propofol and thiopental caused dose-dependent contractile depression similar to that in normal Tyrodes solution. Whereas propofol did not alter slow AP characteristics, 30–100 μM thiopental increased slow AP duration (consistent with decreased potassium conductance), and 100 μM thiopental depressed dV/dt max (consistent with decreased calcium channel ionic influx). Comparing the clinical plasma concentration ranges required for an equivalent anesthetic effect, propofol depresses myocardial contractility less than thiopental.

Myocardial depressant effects of desflurane: mechanical and electrophysiologic actions in vitro.

Background:The authors determined whether desflurane altered myocardial excitation-contraction coupling and electrophysiologic behavior in the same manner as isoflurane and sevoflurane. Methods:The effects of desflurane on isometric force in guinea pig ventricular papillary muscles were studied in modified standard and in 26 mm K+ Tyrode solution with 0.1 &mgr;m isoproterenol. Desflurane effects on sarcoplasmic reticulum Ca2+ release were also determined by examining its actions on rat papillary muscles, guinea pig papillary muscles in low-Na+ Tyrode solution, and rapid cooling contractures. Normal and slow action potentials were recorded using a conventional microelectrode technique. Ca2+ and K+ currents of guinea pig ventricular myocytes were examined. Results:Desflurane (5.3% and 11.6%) decreased peak force to approximately 70% and 40% of the baseline, respectively, similar to the effects of equianesthetic isoflurane concentrations. With isoproterenol in 26 mm K+ Tyrode solution, desflurane markedly depressed late peaking force and modestly depressed early peak force. The rested state contractions of rat myocardium or guinea pig myocardium in low-Na+ Tyrode solution were modestly depressed, whereas rapid cooling contractures were virtually abolished after desflurane administration. Desflurane significantly prolonged the action potential duration. Desflurane reduced L-type Ca2+ current and the delayed outward K+ current but did not alter the inward rectifier K+ current. Conclusions:Myocardial depression by desflurane is due to decreased Ca2+ influx, whereas depolarization-activated sarcoplasmic reticulum Ca2+ release is modestly depressed, similar to the actions of isoflurane and sevoflurane. Desflurane depressed the delayed outward K+ current associated with significant lengthening of cardiac action potentials.

Effect of propofol on calcium homeostasis in hypoxia-reoxygenated neonatal rat cardiomyocytes

Intracellular Ca2+ overload induced by hypoxia-reoxygenation alters Ca2+ homeostasis, which plays an important role in myocardial cell injury. Even though propofol is known as a radical scavenger with Ca2+ channel blocking properties, little is known about cardioprotective effect associated with Ca2+ homeostasis in cardiomyocytes. In the present study, we showed that propofol protects cardiomyocytes against hypoxia-reoxygenation injury. In propofol-treated cardiomyocytes, we observed a decrease in the expression of pro-apoptotic protein Bax, cytochrome c, caspase-3 activation and intracellular Ca2+ content. We also found that propofol treatment enhanced expression of anti-apoptotic protein Bcl-2 and activation of ERK concerned with survival. Propofol attenuated alterations of genes involving Ca2+-regulatory mechanism and significantly modulated abnormal changes of SERCA2a genes in hypoxia-reoxygenated neonatal cardiomyocytes. These results suggest that propofol modulates the expression of genes involved in Ca2+ homeostasis, thereby producing cardioprotective effects through a reduction in apoptotic cell death.

A biometric study of C‐shaped root canal systems in mandibular second molars using cone‐beam computed tomography

AIM To investigate the configuration of C-shaped canals in mandibular second molars, canal wall thickness and the orientation of the thinnest area at 1-mm intervals from the canal orifice to the apex by using cone-beam computed tomographic (CBCT) images. METHODOLOGY Three-dimensional CBCT images of 92 Korean mandibular second molars having C-shaped root canals were analysed to determine their configuration using a modification of Meltons classification, as well as the thinnest walls and their location. Associations between configuration type and distance from the canal orifice to the apex, as well as associations between the directional orientation of the thinnest root wall and distance from the canal orifice to the apex, were assessed by Fishers exact test. Because serial measurements of minimum wall thicknesses were correlated with individual teeth, a mixed-effects analysis was applied. RESULTS The most common configuration types were Meltons type I in the coronal region and Meltons type III in the apical region. Mean thicknesses of the thinnest root canal walls were 1.39 ± 0.38, 0.85 ± 0.25 and 0.77 ± 0.20 mm in the coronal, middle and apical regions, respectively. The thicker the root canal walls at the orifice region, the greater the decrease in thickness towards the apical region (P < 0.05), with the linguo-central root area being the thinnest. The pattern of decreasing thickness from the orifice to the apex formed a nonlinear cubic curve. CONCLUSIONS The most prevalent configuration types were Meltons type I (coronal region) and type III (apical region). The linguo-central root area was the thinnest in C-shaped root canals of Korean mandibular second molars. These anatomical variations should be considered during surgical or nonsurgical endodontic procedures.

Electrophysiologic mechanism underlying action potential prolongation by sevoflurane in rat ventricular myocytes.

Background:Despite prolongation of the QTc interval in humans during sevoflurane anesthesia, little is known about the mechanisms that underlie these actions. In rat ventricular myocytes, the effect of sevoflurane on action potential duration and underlying electrophysiologic mechanisms were investigated. Methods:The action potential was measured by using a current clamp technique. The transient outward K+ current was recorded during depolarizing steps from −80 mV, followed by brief depolarization to −40 mV and then depolarization up to +60 mV. The voltage dependence of steady state inactivation was determined by using a standard double-pulse protocol. The sustained outward current was obtained by addition of 5 mm 4-aminopyridine. The inward rectifier K+ current was recorded from a holding potential of −40 mV before their membrane potential was changed from −130 to 0 mV. Sevoflurane actions on L-type Ca2+ current were also obtained. Results:Sevoflurane prolonged action potential duration, whereas the amplitude and resting membrane potential remained unchanged. The peak transient outward K+ current at +60 mV was reduced by 18 ± 2% (P < 0.05) and 24 ± 2% (P < 0.05) by 0.35 and 0.7 mm sevoflurane, respectively. Sevoflurane had no effect on the sustained outward current. Whereas 0.7 mm sevoflurane did not shift the steady state inactivation curve, it accelerated the current inactivation (P < 0.05). The inward rectifier K+ current at −130 mV was little altered by 0.7 mm sevoflurane. L-type Ca2+ current was reduced by 28 ± 3% (P < 0.05) and 33 ± 1% (P < 0.05) by 0.35 and 0.7 mm sevoflurane, respectively. Conclusions:Action potential prolongation by clinically relevant concentrations of sevoflurane is due to the suppression of transient outward K+ current in rat ventricular myocytes.

Sex Differences in Remifentanil Requirements for Preventing Cough during Anesthetic Emergence

Purpose Target-controlled infusion (TCI) of remifentanil can suppress coughing during emergence from general anesthesia; nevertheless, previous studies under different clinical conditions recommend significantly different effective effect-site concentrations (effective Ce) of remifentanil for 50% of patients (EC50). The differences among these studies include type of surgery and patient sex. In recent years, study of sex differences in regards to anesthetic pharmacology has drawn greater interest. Accordingly, we attempted to determine the effective Ce of remifentanil for preventing cough for each sex under the same clinical conditions. Materials and Methods Twenty female and 25 male ASA physical status I-II grade patients between the ages of 20 and 46 years who were undergoing thyroidectomy were enrolled in this study. The effective Ce of remifentanil for preventing cough was determined for each sex using the isotonic regression method with a bootstrapping approach, following Dixons up-and-down method. Results Isotonic regression with a bootstrapping approach revealed that the estimated EC50 of remifentanil for preventing coughing during emergence was significantly lower in females {1.30 ng/mL [83% confidence interval (CI), 1.20-1.47 ng/mL]} than in males [2.57 ng/mL (83% CI, 2.45-2.70 ng/mL)]. Mean EC50 in females was also significantly lower than in males (1.23±0.21 ng/mL vs. 2.43±0.21 ng/mL, p<0.001). Mean arterial pressure, heart rate, and respiratory rate over time were not significantly different between the sexes. Conclusion When using remifentanil TCI for cough prevention during anesthetic emergence, patient sex should be a considered for appropriate dosing.

Phosphodiesterase inhibition by naloxone augments the inotropic actions of β-adrenergic stimulation

Background: In a shock state, naloxone generates the cardiovascular pressor effect by displacing the endogenous opiate‐like peptide β‐endorphin, resulting in restoration of the normal response to catecholamines. In addition to this opioid antagonistic effect, the non‐opiate receptor‐mediated effect has also been proposed. The aim of this study was to define the mechanism of non‐opiate receptor‐mediated action of naloxone.

Usefulness of a Cook® airway exchange catheter in laryngeal mask airway-guided fiberoptic intubation in a neonate with Pierre Robin syndrome -A case report-

The case of a 33-day-old boy with Pierre Robin syndrome using a Cook® airway exchange catheter in laryngeal mask airway-guided fiberoptic intubation is presented. After induction with sevoflurane, classical reusable laryngeal mask airway (LMA) #1 was inserted and ultrathin fiberoptic bronchoscope (FOB) was passed through. A Cook® airway exchange catheter (1.6 mm ID, 2.7 mm OD) was passed through the LMA under the guidance of the FOB but failed to enter the trachea despite many trials. Then, an endotracheal tube (3.0 mm ID) was mounted on the FOB and railroaded over the FOB. After successful intubation, the Cook® airway exchange catheter was placed in the midtrachea through the lumen of the endotracheal tube. Even though the tracheal tube was accidentally displaced out of the trachea during LMA removal, the endotracheal tube could be easily railroaded over the airway exchange catheter.

Ionic Mechanisms of Desflurane on Prolongation of Action Potential Duration in Rat Ventricular Myocytes

Purpose Despite the fact that desflurane prolongs the QTC interval in humans, little is known about the mechanisms that underlie these actions. We investigated the effects of desflurane on action potential (AP) duration and underlying electrophysiological mechanisms in rat ventricular myocytes. Materials and Methods Rat ventricular myocytes were enzymatically isolated and studied at room temperature. AP was measured using a current clamp technique. The effects of 6% (0.78 mM) and 12% (1.23 mM) desflurane on transient outward K+ current (Ito), sustained outward current (Isus), inward rectifier K+ current (IKI), and L-type Ca2+ current were determined using a whole cell voltage clamp. Results Desflurane prolonged AP duration, while the amplitude and resting membrane potential remained unchanged. Desflurane at 0.78 mM and 1.23 mM significantly reduced the peak Ito by 20±8% and 32±7%, respectively, at +60 mV. Desflurane (1.23 mM) shifted the steady-state inactivation curve in a hyperpolarizing direction and accelerated inactivation of the current. While desflurane (1.23 mM) had no effects on Isus and IKI, it reduced the L-type Ca2+ current by 40±6% (p<0.05). Conclusion Clinically relevant concentrations of desflurane appear to prolong AP duration by suppressing Ito in rat ventricular myocytes.

Autotransplantation of an ectopic impacted premolar with sinus lift and allogenic bone graft

AIM This article presents a case report of autogenous tooth transplantation to a site which had insufficient bone volume using a sinus lift and allogenic bone graft. SUMMARY An ectopic, fully impacted premolar tooth was autotransplanted from its ectopic impaction site into its original site, where there was insufficient recipient vertical bone volume because of sinus expansion. The deciduous tooth was extracted from the recipient site, and the sinus membrane detached and elevated via the alveolar socket. Allogenic bone grafting was performed, and the impacted premolar was transplanted into the prepared site. To improve adaptation, the recipient site was prepared using a rapid prototype tooth model, a replica tooth which allowed complete socket preparation in advanced of the actual removal of the donor tooth. The donor tooth was fixed with sutures and maintained for 17 days to allow physiologic movement. Root canal treatment was initiated 24 days after autotransplantation, and an intra-canal medicament was used for 4 months. Canal filling was completed 5 months after autotransplantation. There was no root resorption of the transplanted tooth, and the grafted bone was well preserved and had no signs of infection. KEY LEARNING POINTS When the recipient bone volume is insufficient, autotransplantation can be preceded by bony augmentation. The preparation of the recipient tooth socket using a tooth replica from CBCT reduces the extra-oral time of the actual tooth and promotes better periodontal ligament healing. Careful evaluation of the pulp status of the donor tooth is important in advance of timely endodontic treatment.