Measurement of contact impedance of electrodes used for deep brain stimulation

High frequency electrical stimulation by means of electrodes implanted into the brain has become an accepted technique for treatment of Parkinson's disease. The electrical field distribution normally inserted into the sub thalamic nucleus minimise abnormal brain activity. Square wave pulses of 1–3.6 V with duration of 60–90 μs at a frequency range of 130–185 pps are generally used. Every electrode unit consists of four cylindrical electrodes positioned in a row and can be switched on independently. This paper determines the contact impedance of the electrodes for different frequencies and proposes improvement to reduce the contact impedance between the electrodes and the brain. Measurements were performed by placing the electrodes in a tank filled with saline. Different frequencies were applied on two electrodes via a resistor. The current was measured through the resistor and the voltage was registered between one of the electrodes and a third non current carrying electrode. The obtained values were used to calculate the contact impedance. The result shows large contact impedance for the used frequency compared to the impedance of the treated tissue, which means that variation in contact impedance can result in variation in the electrical field applied to the tissue.     

Identification and antibiotic prophylaxis of high-risk patients in elective colorectal surgery

High-risk patients undergoing elective colorectal surgery were identified by culturing irrigation fluid samples taken peroperatively, and the effect of supplementary antibiotics in this group was evaluated. All patients (n =267) got 600 mg doxycycline intravenously as a preoperative prophylaxis. The day after operation the high-risk patients could be identified by a count of bacteria cultured from the irrigation fluid. They were randomly allocated either to group A (n=40), no further antibiotics, or to group B (n=45), combination of cefuroxime and metronidazole. The rate of postoperative septic complications was 20% in group A and 4.4% in group B (p<0.05). It is concluded that high-risk patients undergoing elective colorectal surgery can be identified by culturing the irrigation fluid taken peroperatively. With supplementary antibiotic prophylaxis, the postoperative complication rate can be lowered significantly.

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Resumen Los pacientes en alto riesgo de desarrollar complicaciones sépticas postoperatorias en cirugía colorrectal electiva fueron identificados mediante el cultivo de muestras de líquido de irrigación tornados peroperatoriamente, y el efecto de la administración suplementaria de antibióticos en este grupo de pacientes fue evaluado. Todos los pacientes (n=267) recibieron doxiciclina i.v. como profilaxis preoperatoria. Al día siguiente a la operación se procedió a identificar los pacientes de alto riesgo por el conteo de bacterias cultivadas en el líquido de irrigación. En seguida fueron adjudicados al azar al grupo A (n=40), el cual no recibió antibióticos adicionales, o al grupo B (n=45) que recibió una combinación de cefuroxime y metronidazol. La tasa de complicaciones sépticas postoperatorias fue de 20% en el grupo A y de 4.4% en el grupo B (p<0.05). Nuestra conclusión es que los pacientes de alto riesgo sometidos a cirugía colorrectal electiva pueden ser identificados mediante el cultivo del líquido de irrigación tornado peroperatoriamente. La profilaxis antibiótica suplementaria reduce en forma significativa la tasa de complicaciones postoperatorias.

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Résumé Les patients à risque soumis à une intervention chirurgicale élective colo-rectale ont été reconnus en soumettant à la culture des spécimens de liquide prélevés au cours de l'intervention. L'action d'un supplément d'antibiotiques a été étudiée chez eux. Tous les malades (n=267) ont reçu 600 mg d'oxycycline par voie intra-veineuse avant l'intervention à titre prophylactique. Le jour suivant l'intervention le patient dit à risque fut identifié par le nombre élevé de bactéries cultivées. Deux groupes d'opérés à risque furent ainsi étudiés: le groupe A réunissant 40 sujets qui ne reçurent pas d'antibiotiques; le groupe B rassemblant 45 opérés qui reçurent une combinaison de cefuroxine et de metronidazole. Le taux respectif des complications fut de 20% pour le groupe A et de 4.4% pour le groupe B (p<0.05). On peut conclure de cette étude que des malades soumis à une intervention chirurgicale colo-rectale élective peuvent être définis comme malades à haut risque par l'identification des germes contenus dans le liquide prélevé au moment de l'intervention. Grâce à l'emploi supplémentaire d'antibiotiques efficaces le taux des complications dans ces cas diminue de manière significative.

     

Combined portal vein embolization and preoperative chemotherapy prior to liver resection for colorectal cancer metastases

Abstract Objective. Compare perioperative course and long-term mortality after liver resection for colorectal cancer (CRC) metastases between patients who had preoperative treatment with portal vein embolization (PVE) and chemotherapy or chemotherapy alone. Methods. Among patients undergoing liver resection for CRC metastases following preoperative chemotherapy treatment, 17 patients who had received preoperative PVE (group A) were compared with 17 matched controls who had no PVE (group B). Perioperative course and long-term mortality were compared between groups A and B and between group A and the entire group of 75 cases with preoperative chemotherapy (group C). Results. Baseline characteristics for the matched groups A and B were similar. Group C included less major resections. Median intraoperative bleeding was 1600 ml in group A, 1200 ml in group B, and 1000 ml in group C (p < 0.05 vs. group A). Median postoperative stay was comparable in all groups (8-9 days). Operation time was 542 min in group A and 464 min in group B (p < 0.01). Mortality after 30 days and 1, 2, and 5 years was similar in all groups. Conclusion. Perioperative outcome and long-term survival did not differ when comparing liver resection for CRC liver metastases preceded by PVE and chemotherapy or chemotherapy alone, except for the operation time. The study supports the safety of this "aggressive" combination approach in patients in need of tumor "downstaging" by chemotherapy and PVE to increase the remnant liver volume.     

Applicability of a modified Edman procedure for measurement of protein adducts: mechanisms of formation and degradation of phenylthiohydantoins

Adducts to N-terminal valine residues in hemoglobin (Hb) are used for monitoring in vivo doses of electrophiles and are quantitated by means of a modified Edman procedure, the "N-alkyl Edman procedure". In the reaction with pentafluorophenyl isothiocyanate, N-alkylated valines cyclize and detach from the protein as pentafluorophenylthiohydantoins (PFPTHs) much more efficiently than do unsubstituted N-terminal valine residues. The mechanisms of this reaction, and of possible degradation reactions, have been studied with model compounds using phenyl- and pentafluorophenyl isothiocyanate. The rapid cyclization to N-alkylvaline-PTHs occurs as a consequence of the influence of substituents on ring formation. This facilitated cyclization favors a direct attack by the thiocarbamoyl nitrogen atom on valine-C-1, and is also observed to occur slowly at unsubstituted N-terminal valines. Such cyclization is favored in protic solvents. Under alkaline conditions and in the presence of air, hydrolytic and oxidative processes give rise to degradation products. The PTH derivatives of N-alkylvaline are less apt to undergo such reactions than are the corresponding derivatives of unsubstituted valine. We conclude that the presence of an N-substituent exerts a greater influence on the cyclization process than the structure of the amino acid or of the Edman reagent. For adducts of different structures, the method has broad applicability, for which the limits, however, are not yet explored. The knowledge from the studies is valid not only for the N-alkyl Edman procedure, but also, to some extent, for the classical Edman degradation reaction. The oxidative side reaction gave rise to the invention of a novel synthesis route for insertion of nucleophiles at carbon-5 in thiohydantoins. The present investigation provides a basis for the N-alkyl Edman procedure, facilitating new toxicological applications.     

Evidence for phosphate adducts in DNA from mice treated with 4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK)

The weakly alkylating capacity of phosphotriesters (PTE) has been used for the determination of adducts to phosphate groups in DNA by specific transfer to the strongly nucleophilic compound cob(I)alamin [Cbl(I)]. When enzymatically degraded liver DNA from mice treated with 1-(N-methyl-N-nitrosamino)-4-(3-[3H]pyridyl)-4-oxobutane ([3H]NNK) was added to Cbl(I), a 4-(3-[3H]pyridyl)-4-hydroxy-1-butyl-cobalamin ([3H]PHB-Cbl) complex was formed and determined by HPLC and liquid scintillation counting. The PHB-Cbl formed was compared with a synthetic standard verified by LC/MS and 1H NMR and corresponds to phosphate adducts formed from the pyridyloxobutylating species from NNK and from the pyridylhydroxybutylating species from NNAL, NNK being to a large extent converted to NNAL in vivo. It was concluded that about 22% of the total level of pyridyl (oxo or hydroxy) butyl adducts to DNA was bound to phosphate groups.     

The effect of diverting colostomy on anastomotic healing after resection of left colon obstruction

A standardized stenosis of the left colon was created in the rat model. After four days the stenosis was resected and a primary anastomosis made. Half of the animals (n=21) were randomized to a proximal diverting colostomy and the other half to a non-colostomy control group. On postoperative days two and seven anastomotic complications were recorded and anastomotic strength was determined. Collagen content in the anastomotic area was measured. In the colostomy group no anastomotic complications occurred, while 6/21 (29%) animals in the non-colostomy group had complications. On day two there was no difference between the groups as regards anastomotic strength and collagen content. After a week, however, the control group showed a significant increase in both anastomotic strength and collagen content which was not observed in the colostomy group. The absence of increase in anastomotic strength in the colostomy group had no adverse effect on anastomotic healing, as judged by complications. Thus, a diverting colostomy may be of value in reducing anastomotic complications after resection of a left colon obstruction.     

Effects of tobacco-smoke on radiation-induced pneumonitis in rats.

To investigate the effect of exposure to tobacco smoke (TS) on the development of irradiation-induced pneumonitis in rats, five groups of animals were investigated including controls (C), tobacco smoke exposed (S), irradiated (RNS) and irradiated and tobacco smoke exposed (RS). An additional group (RS/NS) was exposed to tobacco before irradiation but not afterwards. Rats were exposed to diluted mainstream cigarette smoke at a concentration of about 0.4 mg/l in a nose-only exposure system for 1/day, 5 days/week for 10 weeks. Exposure to TS started 3 weeks before irradiation in which the basal one-third of both lungs was exposed to a single dose of 28 Gy. In previous studies this dose had been shown to cause significant pneumonitis. All the animals were killed at 7 weeks after irradiation. Examination of the morphology of lung sections showed less pulmonary inflammation in the RS group than in the RNS group. This was also reflected in the results of bronchoalveolar lavage (BAL) which showed a decline in cell recovery and a marked decrease in the numbers of mast cells and neutrophils in the RS rats compared with the RNS animals. The concentration of hyaluronan in lavage fluid was increased in the RNS and RS/NS group while no increase was found in the RS group. A marked increase in BAL protein was also seen in the RNS and RS/NS groups as compared with the RS group but all were significantly higher than in unirradiated controls. This indicates that smoking suppresses the radiation-induced inflammation but to a lesser degree affects the radiation-induced increase in membrane permeability as reflected by increased protein levels in BAL. Moreover, the marked effects on the numbers of mast cells and neutrophils in the RS group may indicate that these cells play an important role in the mechanism by which tobacco smoke modulates the effects of irradiation. When exposure to tobacco smoke was terminated immediately after irradiation (RS/NS), the inflammatory response was unaffected.     

Shoulder function in patients with unoperated anterior shoulder instability

A functional analysis, including Rowe score and measurements of isokinetic peak torque and range of motion of the shoulder, and a subjective assessment were performed in 26 consecutive patients (23 males and 3 females) with unoperated anterior shoulder instability. Patients experienced the initial dislocation at an average age of 23 +/- 8 years and 58% occurred during sports activity. No patient had gone through any controlled rehabilitation program. In this study, an average of 7 years (range, 1 to 28) had passed since the initial dislocation. Fifty-nine percent of the patients complained of markedly reduced ability to perform in sports because of instability, impaired strength, decreased range of motion, and pain induced by activity. The majority (65%) of the patients reported instability only during physical activity. The average Rowe score was 68 +/- 14 on a scale of 100. In comparison with the healthy side, the injured shoulder had a significantly lower isokinetic peak torque during abduction and internal rotation, as well as a reduced range of motion in extension, abduction, and external rotation, but not in flexion. The severity of impairment (Rowe score, deficit in range of motion, and peak torque) was not related to the number of dislocations sustained or to the duration of instability.