Separation of long linear polymers in gel electrophoresis with alternating electric fields: a theoretical study using the necklace model.

The necklace model, which mimics the reptation of a chain of N beads in a square lattice, is used to study the drift velocity of charged linear polymers in gels under an applied electric field that periodically changes its direction. The characteristics of the model allow us to determine the effects of the alternating electric field on the chains' dynamics. We explain why chains of different N can be made to move in opposite directions with a nonuniform electric field with certain values of intensity and frequency. The key point is that, when alternating electric fields are applied, longer chains spend more time out of the steady-state regime than lower chains. Numerical results are obtained by means of Monte Carlo simulations and they are qualitatively in agreement with experiments of DNA migration in gel electrophoresis.

Cytoreductive surgery (cs) and hyperthermic intraperitoneal chemotherapy (hipec) in treatment of peritoneal surface malignances: report of a phase II clinical study.

Peritoneal surface malignancy is the expression of a spectrum of disease involving the peritoneum primary or secondary to gastrointestinal and gynecological neoplasms. Even if intraperitoneal therapy has now been demonstrated in multiple randomized trials to improve the outcome of chemotherapy for patients with optimally debulked or small volume ovarian carcinoma, it is believed that peritoneal carcinomatosis is considered an advanced stage of disease; for this reason, it is treated with systemic chemotherapy and surgery plays only a palliative role (1). In the last twenty years, some centres have developed surgical treatment of peritoneal carcinomatosis that involves aggressive cytoreductive surgery associated with hyperthermic intraperitoneal chemotherapy. This treatment has improved and prolonged survival, despite the associated high morbidities and mortalities (3-14).

Diffusion in the two-dimensional necklace model for reptation.

An extension of a recently introduced one-dimensional model, the necklace model, is used to study the reptation of a chain of N particles in a two-dimensional square lattice. The mobilities of end and middle particles of a chain are governed by three free parameters. This new model mimics the behavior of a long linear and flexible polymer in a gel. Noninteracting and self-avoiding chains are considered. For both cases, analytical approximations for the diffusion coefficient of the center of mass of the chain, for all values of N , are proposed. The validity of these approximations for different values of the free parameters is verified by means of Monte Carlo simulations. Extensions to higher dimensions are also discussed.

Drift velocity for a chain of beads in one dimension.

The one-dimensional motion of a chain of N beads is studied to determine its drift velocity when an external field is applied. The dependences of the drift velocity with the chain length and field strength are addressed. Two cases are considered, chains with all their beads charged and chains having an end bead charged. In the last case, an analytical expression for the drift velocity is proposed for all N . Results are tested with the help of Monte Carlo simulations.

Window effect in a discretized model for diffusion of a chain in one dimension.

We introduce a model to study the diffusion of chains in microporous solids. The difficulties a chain has to escape from a pore where it is confined is found to strongly depend on the ratio between the chain length and the cage size. This dynamic effect implies a nonstandard behavior of the diffusion coefficient. We found a window effect that can be explained without using any energy argument.

Exact diffusion coefficient for a chain of beads in one dimension using the Einstein relation.

The one-dimensional motion of a chain of N beads is studied to determine its diffusion coefficient. We found an exact analytical expression for all through two methods by resorting to the Einstein relation. Results are tested with the help of Monte Carlo simulations.

Hemangiopericytoma and temporal bone.

Hemangiopericytoma is a vascular tumor arising from the pericyts. The tumor involves usually the muskuloskeletal system and the skin. A hemangiopericytoma of the temporal bone is an extremely rare lesion. This paper describes a case of hemangiopericytoma located in temporal bone, its radiologic diagnosis and its therapeutic options as well.

An analysis of Ca2+ release by DGEA: mobilization of two functionally distinct internal stores in Saos-2 cells.

Osteoblasts can be activated by their collagen matrix and in particular the DGEA peptide motif. We have reported that DGEA is able to activate Ca2+ signaling pathways in the human osteoblast-like cell line, Saos-2, by a tyrosine kinase-dependent pathway (T. J. McCann, W. T. Mason, M. C. Meikle, and F. McDonald. Matrix Biol. 16: 271-280, 1997). In the present study, we show that this activity is due to coupling of the signal to intracellular Ca2+ stores, since the DGEA action is not blocked by La3+ but is lost when Ca2+ stores are depleted with 2 microM and blocked by 10 microM ryanodine. The activated stores also differ functionally from those activated by thrombin, as blockade with U-73122 obstructs only thrombin-activated Ca2+ release. We have shown that the DGEA activity was not due to its high-charge density, since the two acidic residues can be substituted with their uncharged homologues (asparagine and glutamine) without significant loss of activity. This was in turn measured by an adhesion assay that also demonstrated this level of specificity. Furthermore, by constructing DGEA bound to FITC, we have shown that DGEA binding was dependent on divalent cations. We have also demonstrated that an intact actin cytoskeleton is not required for Ca2+ activation by inhibiting actin polymerization with the addition of cytochalasin B. These data strengthen the argument that collagen has a significant role in regulating osteoblast function via this peptide motif.

Petrous bone cholesteatoma and facial paralysis.

This paper describes a series of patients with a petrous temporal bone cholesteatoma paying particular attention to the complications and their management. Sixteen patients who underwent surgery in our department were reviewed. Topographically, the petrous bone cholesteatomas were grouped into five categories according to the classification proposed by Sanna et al. There were five massive labyrinthine; five infralabyrinthine; one apical; four supralabyrinthine; and one infralabyrinthine-apical. Clinically, the presenting symptom of these lesions were facial nerve paralysis (10 patients) and unilateral deafness (13 patients). Total removal of the cholesteatomas was achieved in all patients using different surgical approaches according to their site and extent. Recurrences were observed in two patients after 8 months and 24 months, respectively. The facial nerve was infiltrated and compressed by the cholesteatoma in eight patients. Seven were managed with cable grafts using sural nerve. One of these patients was treated using a facial-hypoglossal anastomosis because of the failure of the graft. In the remaining patient, a baby-sitter procedure was employed. In the other two patients, the preoperative facial paralysis was due to compression by the cholesteatoma, and its removal allowed partial recovery of facial function. The rationale of the surgical management of petrous bone cholesteatoma is its radical and total removal. Our present policy is to prefer approaches which result in a closed cavity obliterating the eustachian tube and closing the auditory canal as a blind sac. Facial nerve function is the main complication of these lesions, Facial nerve involvement requires rapid management because the duration of the paralysis is directly related to poor recovery of facial function.

Encephalocele with spontaneous CSF otorrhea.

Spontaneous encephalocele of the temporal bone is an uncommon condition (37 cases to date) associated with cerebrospinal fluid otorrhea. It results from a congenital dehiscence of the tegmen tympani and tegmen mastoideum. The AA. report 3 additional cases and review methods for diagnosing and surgical treatment.

Labyrinthine fistula as a complication of cholesteatoma.

HYPOTHESIS: The objective of this study was to present the authors' experience in the management of labyrinthine fistula caused by cholesteatoma. METHODS: The clinical charts of 92 patients who underwent surgical procedures for cholesteatoma complicated by labyrinthine fistula between 1979 and 1975 were reviewed retrospectively. In this period, 1,205 patients were operated on for cholesteatoma. In each patient, the site and size of the fistula were evaluated during surgery and the hearing thresholds were compared before and after surgery. RESULTS: The fistula involved the lateral semicircular canal in 71 patients. Multiple fistulas were observed in nine patients. Postoperative hearing levels were unchanged or improved in 83.7% of patients. Comparison between hearing outcomes and size of the fistula showed better findings when smaller size fistulas were found. No significant differences between open and closed techniques were detected. Favorable outcomes were obtained in patients treated with surgical obliteration of the interrupted labyrinth. CONCLUSIONS: The current study confirmed that careful manipulation of the labyrinthine fistula is mandatory to preserve hearing functions for these patients. According to the authors' experience, the future trend for fistula treatment could be directed toward less conservative techniques compared with the previous indications favoring methods of interruption and subsequent obliteration of the semicircular canals.

Functional hearing results in revision stapes surgery.

OBJECTIVE: The object of our study was to review the results of 63 revision stapes surgeries performed from 1978 to 1994. RESULTS: The most common cause of failure was the displacement of the prosthesis, followed by ossicular chain problems and oval window fibrosis. Postoperative hearing improvement within a 20-dB air-bone gap was achieved in 58.7% of the patients. Hearing gain was closely linked to the operative findings. Better results occurred when prosthesis problems were found. Evaluation of the hearing results by using Glasgow benefit plot gave evidence of symmetric normal hearing in only 40% of the cases. CONCLUSIONS: Prevention of the cause of failure during the primary stapes surgeries, lessening the surgical trauma, seems to provide the most favorable hearing results.

Glomus tumor in pediatric age.

Glomus tumor of the middle ear and mastoid is exceedingly rare in children. This report details our management of a 13-year-old boy affected by tympanic glomus complicated by chronic middle ear infection that obscured the tumor. A review of the English literature revealed only 12 other patients suffering from glomus tumor in pediatric age. Diagnosis, therapy and the differential characteristics of pediatric glomus are discussed.

Spectral analysis of short term R-Tapex interval variability during sinus rhythm and fixed atrial rate.

Analysis of heart rate variability has been proven useful in stratifying post myocardial patients at risk and in evaluating autonomic dysfunction. Recently augmented inter-lead variability of the QT interval has been associated with increased mortality as a result of arrhythmia and proposed as a marker of dispersion of ventricular repolarization. As the duration of the QT interval is largely dependent upon the length of the preceding cardiac cycle it is tempting to analyse whether neural mechanisms might also directly exert additional modulation. Using autoregressive algorithms we therefore analysed RR and R-Tapex interval variabilities in 15 normal subjects during sinus rhythm and in six patients with a fixed atrial rate. In controls mean R-Tapex interval and variance measured on the vector magnitude were, respectively, 245 +/- 6 ms and 5.1 +/- 0.7 ms2. Spectral analysis of R-Tapex indicated the presence of two spectral components which corresponded to the low and high frequency components of heart rate variability. In R-Tapex variability, high frequency (44 +/- 4 nu) was predominant over low frequency (29 +/- 4 nu). During controlled respiration, a manoeuvre associated with enhanced vagal modulation of sinus node, there was a further increase in high frequency (58 +/- 4 nu) whereas during tilt the low frequency component of R-Tapex variability became predominant (57 +/- 6 nu). In patients with a fixed atrial rate, variance was extremely low (3 +/- 0.9 ms2) and only a respiration-related high frequency component was recognizable in spectral analysis of RR and R-Tapex variabilities. This component was likely to depend upon mechanically induced changes in cardiac vector orientation. These data indicate that during sinus rhythm short-term R-Tapex interval variability is characterized by the same rhythmical components present in RR variability. However, the presence of a very low variance and of only a high frequency component in patients in whom the physiological variability of sinus node is abolished by atrial pacing. suggests that neural modulatory mechanisms do not exert a direct effect on the length of the R-Tapex interval.

Connecticut emergency department physicians survey. Implications for graduate medical education.

A survey conducted in mid-1989 of 36 Connecticut hospital emergency departments sought to determine the nature of physician staffing and the volume and the acuteness of patient problems. Overall, only 31% of emergency department staffing is provided by board certified emergency physicians in the state of Connecticut. In addition to emphasizing the lack of board certified emergency physicians available in the state, this survey also indicated a relative deficiency in emergency department physician staffing in general with approximately 20% of all positions currently unfilled statewide. The implications of these findings for graduate medical education in Connecticut are discussed.

A computer protocol to predict myocardial infarction in emergency department patients with chest pain.

To achieve more appropriate triage to the coronary care unit of patients presenting with acute chest pain, we used clinical data on 1379 patients at two hospitals to construct a simple computer protocol to predict the presence of myocardial infarction. When we tested this protocol prospectively in 4770 patients at two university hospitals and four community hospitals, the computer-derived protocol had a significantly higher specificity (74 vs. 71 percent) in predicting the absence of infarction than physicians deciding whether to admit patients to the coronary care unit, and it had a similar sensitivity in detecting the presence of infarction (88.0 vs. 87.8 percent). Decisions based solely on the computer protocol would have reduced the admission of patients without infarction to the coronary care unit by 11.5 percent without adversely affecting the admission of patients in whom emergent complications developed that required intensive care. Although this protocol should not be used to override careful clinical judgment in individual cases, the computer protocol for the most part yields accurate estimates of the probability of myocardial infarction. Decisions about admission to the coronary care unit based on the protocol would have been as effective as those actually made by the unaided physicians who cared for the patients, and less costly. Whether physicians who are aided by the protocol perform better than unaided physicians cannot be determined without further study.

Clinical characteristics and natural history of patients with acute myocardial infarction sent home from the emergency room.

In a prospective multicenter investigation of emergency room patients with acute chest pain, physicians admitted 96% of patients with acute myocardial infarction (AMI) and discharged 4%. Of 35 patients who were sent home with AMI, only 11 (31%) returned to the same hospital because of persistent symptoms. Compared with a control group of 105 randomly selected patients with AMI who were admitted from the emergency room, patients in whom AMI was missed were significantly younger, had less typical symptoms and were less likely to to have had prior AMI or angina or to have electrocardiographic evidence of ischemia or infarction not known to be old. Despite the less typical presentations of patients in whom AMI was missed, after controlling for age and sex, the short-term mortality rate was significantly higher among patients in whom AMI was missed but in whom it was detected through our follow-up procedures than in admitted AMI patients. As determined by independent reviewers, 49% of the missed AMIs could have been diagnosed through improved electrocardiographic reading skills or by admission of patients with recognized ischemic pain at rest or ischemic electrocardiographic changes not known to be old.