Laparoscopic cholecystectomy under epidural anesthesia in patients with chronic respiratory disease

BACKGROUND: Laparoscopic cholecystectomy (LC) has become firmly established as a procedure of choice for gallstone disease. The procedure usually necessitates general anaesthesia and endotracheal intubation to prevent aspiration and respiratory embarrassment secondary to the induction of pneumoperitoneum. There is a paucity of data in the literature on the procedure being performed under regional (epidural) anaesthesia, especially in patients with coexisting pulmonary disease and pregnancy, who are deemed high risk for general anaesthesia. We report our preliminary experience with LC using epidural anaesthesia in patients with chronic obstructive pulmonary disease (COPD). METHODS: We performed LC in six patients (one man and five women), with a median age of 56 years (range, 38-74), under epidural anaesthesia over an 8-month period. All patients were ASA grade III/IV and the mean FEB1/FVC was 0.52 (range, 0.4-0.68), due to chronic asthma (two cases) and COPD (four cases). They were admitted a day prior to surgery for pulmonary function tests, nebulisers, and chest physiotherapy. An epidural catheter was introduced at T10/11 intervertebral space, and a bolus of 0.5% Bupivacaine was administered. Depending on the patient's pain threshold and the segmental level of analgesia achieved, incremental doses of 2 ml of 0.5% Bupivacaine along with boluses of intravenous 100 mcg Alfentanil was given to each patient. The patients were breathing spontaneously. No nasogastric tube was inserted, and a low-pressure (10 mmHg) pneumoperitoneum was created. LC was performed according to the standard technique. RESULTS: All the patients tolerated the procedure well and made an uneventful postoperative recovery. Median operating time was 50 min; average length of hospital stay was 2.5 days (range, 2-4). The epidural catheter was removed the morning after the operation. Only one patient required postoperative opioid analgesia. Two patients complained of persistent shoulder tip pain during surgery and required intraoperative analgesia (Alfentanil). There was no change in the patient's cardiorespiratory status, including PO2 and pCO2, and no complications occurred either intra- or postoperatively. CONCLUSIONS: LC can be performed safely under epidural anaesthesia in patients with severe COPD. Intraoperative shoulder tip or abdominal pain does not seem to be a major deterrent and can be effectively controlled with small doses of opioid analgesia.     

Dielectric relaxation behaviour of poly(cyclobutyl methacrylate)s

Dielectric behaviour of two poly(methacrylate)s with cyclobutyl groups in the side‐chains has been studied. This investigation was performed by determining the dielectric permittivity and loss in terms of frequency and temperature for poly(cyclobutyl methacrylate) (PCBuM) and poly(cyclobutylmethyl methacrylate) (PCBuMM). Dynamic dielectric measurements show sub‐glass relaxations, probably due to motions in the lateral chain, including the cyclobutyl ring. The effect of the insertion of a flexible spacer group into the side‐chain is also analyzed. The α relaxations were analyzed in terms of the Havriliak–Negami equation and the free volume theory tested according to the Vogel–Fulcher–Tamman–Hesse equation. The conductive and interfacial phenomena were studied by hopping and MacDonald–Coelho models. © 2002 Society of Chemical Industry     

Dynamic mechanical and dielectric relaxation behaviour of poly(methacrylate)s containing saturated rings with seven and eight members in the side‐chains

Dynamic mechanical and dielectric behaviour of poly(cycloheptyl methacrylate), poly(cycloheptylmethyl methacrylate) and poly(cyclooctyl methacrylate) have been investigated. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity ?*. Results are discussed in terms of the effect of the size and structure of the side ring. The saturated ring group shows mechanical and dielectric activity at low temperature that is analyzed in terms of the Fuoss–Kirkwood equation. The free volume for the three polymers was determined. The conductive and interfacial phenomena were studied by MacDonald and Coelho models, where the dipolar contribution was introduced. © 2002 Society of Chemical Industry     

Effect of an obstacle during processing on the weld line of injection‐molded glassy polystyrene: Microhardness study

The microhardness (H) technique is used to characterize the quality of the weld line in injection‐molded glassy polystyrene by means of a cylindrical obstacle. In particular, the effect of the indentation location (closer or further from the obstacle edge parallel to the injection direction and across the weld line), both on the surface and in the bulk, was examined. Only for surface measurements close to the obstacle (up to 10 mm) a well‐pronounced decrease in H (～30%), followed by a sharp increase in a narrow distance (0.20–0.25 mm), was observed. For the bulk measurements on the same location a slight decrease in H was detected. Additional H measurements made up to 60 mm from the obstacle for both cases showed that the weld line remains undetectable. The results obtained reveal that the presence of a cylindrical obstacle causes the formation of a weld line on and near the surface only at distances not exceeding the obstacle diameter. At larger distances, because of the effective mutual interdiffusion of polymer chains, the two parallel fronts coming from the two sides of the obstacle developed a homogeneous material without any weld line according to the microhardness test. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3362–3367, 2004     

Polarity determination by electron energy-loss spectroscopy: application to ultra-small III-nitride semiconductor nanocolumns

Channeling-enhanced electron energy-loss spectroscopy is applied to determine the polarity of ultra-small nitride semiconductor nanocolumns in transmission electron microscopy. The technique demonstrates some practical advantages in the nanostructure analysis, especially for feature sizes of less than 50 nm. We have studied GaN and (Al, Ga)N nanocolumns grown in a self-assembled way by molecular beam epitaxy directly on bare Si(111) substrates and on AlN buffer layers, respectively. The GaN nanocolumns on Si show an N polarity, while the (Al, Ga)N nanocolumns on an AlN buffer exhibit a Ga polarity. The different polarities of nanocolumns grown in a similar procedure are interpreted in terms of the specific interface bonding configurations. Our investigation contributes to the understanding of polarity control in III-nitride nanocolumn growth.     

Polymorphism of isotactic polybutene-1 as revealed by microindentation hardness. Part II: correlations to microstructure

The influence of polymorphism on the micromechanical properties of isotactic polybutene-1 (iPBu-1) has been investigated by means of the microhardness technique. Hardness data, H, of form I (hexagonal) are shown to be notably larger than those of form II (tetragonal). The H values of both polymorphic forms are shown to depend on the molecular weight, M_w, and the crystallization temperature, T_c. The hardness behaviour with M_w and T_c has been correlated to the changes of degree of crystallinity and nanostructure as derived from small angle X-ray scattering. The hardness values for iPBu-1 infinitely thick crystals (H_c^∞), of forms I and II, have been calculated for the first time. H_c^∞ of form I is shown to be notably larger than that of form II. This result is a consequence of the denser packing of the hexagonal crystal modification, and accounts for the large difference in H values found for forms I and II. Finally, the variation of the mechanical b-parameter, proportional to the surface-free energy of the crystals, with molecular weight is discussed.     

Ultra-microindentation at the surface of silk membranes

Ultra-microindentation was used to measure the microhardness and modulus of silk (Bombyx mori) membranes, cast from 20 to 80 °C. The microhardness and modulus were determined from the loading/unloading curves. The membranes exhibit microhardness of about 400 MPa which is larger than the values for most common synthetic polymers (50-300 MPa) implying a greater scratch resistance. The moduli are of the order of those measured by the other means for B. mori silk membranes (5 GPa), and fibers (7-11 GPa). There is some correlation between microhardness and the dimensions of the grains/nanofibrils, but none with surface roughness. The results extend the range of an empirical correlation between microhardness and modulus. The present data together with previous data from other polymers fit the equation, H=0.55E0.74, with a correlation coefficient of 0.94. Finally, it is shown that elastic recovery of the silk membranes is an increasing function of the maximum load applied.     

Properties of elongational flow injection-molded polyethylene. Part 1: Influence of mold geometry

Injection molding of polyethylene was carried out using molds that introduce axial elongational flow during the filling process, As compared with conventional injection-molding methods, the present technique yields polyethylene materials having higher mechanical strengths (σ ≈ 150 MPa). The σ-value of the moldings can be systematically monitored by adequately varying the elongational flow through modification of the mold geometry. Geometrical features of the volume containing the melt before injection as well as geometry of the die, the extruder, and the inlet influence the overall elongational flow, and thus, the mechanical strength of the moldings.     

Transient negative photocurrent and out-of-well dipole kinetics in novel piezoelectric InGaAs/GaAs MQW pin diodes

In 111B InGaAs/GaAs pin structures with a multiple quantum well (MQW) embedded region, the average internal field in the active MQW region can be tailored to obtain device configurations with a negative average field (NAF), opposite to the built-in field. In 111 NAF diodes, carriers photogenerated at the wells become trapped early at the potential minima located at the ends of the active region thus creating an electric dipole. In this work, in 111 NAF devices with a 0.17 In mole fraction layers, by using time-resolved photocurrent and a novel optical-pump electrical-probe techniques, we report the presence of a negative transient photocurrent, a direct quantitative evidence of such dipole formation, and we present measurements of its extinction kinetics at room temperature.     

Effect of p-doped overlayer thickness on RF-dispersion in GaNjunction FETs

Successive reactive ion etchings (RIE) were performed on the access regions of p⁺-n GaN JFETs. A decrease in the n-layer sheet resistance, with a consequent increase in I_DSS was detected after complete removal of the p-layer, due to a reduction in the n-layer depletion region. An increase in RF-dispersion was experienced, as a result of the progressive reduction of screening from surface-states originally provided by the overlying p-cap layer. No dispersion was detected before cap removal. A continuous increase in f _t and f_max was detected even before complete removal of the p-layer, due to virtual gate length reduction. It is expected that an optimized p-doped overlayer will provide current slump suppression without degradation in cutoff frequency or breakdown