Search PubMed⌕ Search

Biomedical subjects

R H Davis

Publications and source records attributed to R H Davis.

304 records · Page 17Linked to original sources
PubMedDate not supplied

A study of the interviewing skills of trainee assistants in general pactice.

The effect of specific teaching of interviewing techniques, measured by a rating scale, was compared in experimental and control groups of trainee general practitioners. The subjects were given the opportunity to observe their own consultations on audio-visual recordings. No significant overall effect was demonstrated, but more detailed analysis revealed trends that suggested that the effect of the teaching only occurred in the latter half of the training year and was accompanied by an increase in the time of the consultation. It is our conclusion that the study should be repeated with larger numbers. It is possible that the absence of any effect of teaching interviewing techniques in the early part of the training period could be due to the traumatic experience of moving from hospital practice to primary care.

Communication↗
PubMedDate not supplied

Long-term response to subtotal colectomy in colonic inertia.

The purpose of this study was to determine the long-term outcome of patients who had previously undergone subtotal colectomy for severe idiopathic constipation at the University of Florida between 1983 and 1987. In addition, we aimed to determine whether preoperative motility abnormalities of the upper gastrointestinal tract are more common among those patients who have significant postoperative complications after subtotal colectomy. We evaluated 13 patients who underwent subtotal colectomy for refractory constipation between 1983 and 1987 at the University of Florida. Preoperatively, all patients exhibited a pattern consistent with colonic inertia as demonstrated by means of radiopaque markers. Each patient was asked to quantitate the pain intensity and frequency of their bowel movements before and after surgery. In seven patients an ileosigmoid anastomosis was performed, whereas in six patients an ileorectal anastomosis was used. Abdominal pain decreased after subtotal colectomy. Patients with abnormal upper gastrointestinal motility preoperatively experienced greater postoperative pain than those with normal motility regardless of the type of anastomosis. In addition, the number of postoperative surgeries was similar in those patients with abnormal upper motility compared to those with normal motility. Overall, the total number of bowel movements per week increased from 0.5 +/- 0.03 preoperatively to 15 +/- 4.5 (P < 0.007) postoperatively. The results of our study suggest that patients with isolated colonic inertia have a better long-term outcome from subtotal colectomy than patients with additional upper gastrointestinal motility abnormalities associated with their colonic inertia.

Adolescent↗
PubMedDate not supplied

Continuous recombinant bacterial fermentations utilizing selective flocculation and recycle.

Selective recycle has successfully been used to maintain an unstable plasmid-bearing bacterial strain as dominant in a continuous reactor, whereas the culture reverts to 100% segregant cells when selective recycle is not used. The plasmid-bearing strain is slower growing and flocculent; however, when the cells lose their plasmid, the resulting segregant cells are nonflocculent and grow at a faster rate due to their decreased metabolic burden. Both types of cells exit a chemostat and enter an inclined settler where the flocculent plasmid-bearing cells are separated from the nonflocculent segregant cells by differential sedimentation. The underflow from the cell separator, which is enriched with plasmid-bearing cells, is recycled back to the chemostat, while the segregant cells are withdrawn off the top of the settler and discarded. The experimental results agree well with selective recycle reactor theory. On the basis of the theory, a criterion is presented that has been shown to successfully predict whether or not a selective recycle reactor can maintain a plasmid-bearing strain.

Biotechnology↗
PubMedDate not supplied

Optimal chemostat cascades for periplasmic protein production.

This theoretical work predicts the optimal system design for the steady-state production of secreted protein in a chemostat cascade, using bakers' yeast (Saccharomyces cerevisiae) as the host organism. The protein of interest, mutant invertase, is secreted to the periplasmic space instead of the culture medium on account of its large size. This work uses the secretion model developed and tested by Park and Ramirez (1988). It is shown that the highest productivity is achieved when the chemostat cascade contains two stages, although the improvement over the single-stage productivity is small. When no recycle is used, the advantage of two stages results from the tradeoff between maximizing the cell concentration and maximizing the rate of protein production per cell. When recycle is used, the cell concentration and protein productivity are increased, and the advantage of two stages results from the tradeoff between maximizing the specific protein production rate and maximizing the specific protein secretion rate. Cascades with three stages were also investigated, but these were found to have no improvement over the corresponding two-stage cascades.

Cloning, Molecular↗
PubMedDate not supplied

Inclined sedimentation for selective retention of viable hybridomas in a continuous suspension bioreactor.

The continuous separation of nonviable hybridoma cells from viable hybridoma cells by using a narrow rectangular channel that is inclined from the vertical has been investigated experimentally. The effectiveness of the settler in selectively retaining viable hybridomas in the bioreactor while permitting the removal of nonviable hybridomas has been shown to depend on the flow rate through the settler. Intermediate flow rates through the settler have been found to provide the highest removal of nonviable hybridomas relative to viable hybridoma retention. At high dilution rates through the chemostat, over 95% of the viable cells could be partitioned to the bottom of the settler while over 50% of the nonviable cells are removed through the top of the settler. This successful separation is due to the significantly larger size of the viable hybridomas than the nonviable ones. A continuous perfusion experiment was performed in which an external inclined settler was used to retain virtually all of the viable hybridomas in the culture, while selectively removing from the culture approximately 20% of the nonviable cells that entered the settler. A stable viable cell concentration of 1.0 x 10(7) cells/mL was achieved, as was an antibody productivity of over 50 micrograms/(mL.day). These represent 3- and 6-fold increases, respectively, over the values obtained from a chemostat culture without cell retention.

Animals↗
PubMedDate not supplied

Electrokinetic isolation of vesicles and ribosomes derived from Serratia marcescens.

Ribosomes and vesicles derived from the bacterium Serratia marcescens were separated from each other and from solubles using density gradient electrophoresis. Transport relationships were used to determine the electrophoretic mobilities of the particles. The effects of convection, sedimentation and diffusion were found to be negligible. The electrophoretic mobility obtained for the ribosome peak is -7 x 10(-5) cm2/(V.s). Under appropriate conditions, two vesicles peaks were obtained, the first with a mobility of -4 x 10(-5) cm2/(V.s) and the second with -9 x 10(-6) cm2/(V.s). This information can be used to predict the resolution of the separands in large-scale electrophoretic separations.

Electrophoresis↗
PubMedDate not supplied

Crossflow microfiltration of yeast suspensions in tubular filters.

Crossflow microfiltration experiments were performed on yeast suspensions through 0.2-microns pore size ceramic and polypropylene tubes at various operating conditions. The initial transient flux decline follows dead-end filtration theory, with the membrane resistance determined from the initial flux and the specific cake resistance determined from the rate of flux decline due to cake buildup. For long times, the observed fluxes reach steady or nearly steady values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increase with increasing shear rate and decreasing feed concentration, and they are nearly independent of transmembrane pressure. The steady-state fluxes for unwashed yeast in deionized water or fermentation media are typically 2-4 times lower than those predicted by a model based on the properties of nonadhesive, rigid spheres undergoing shear-induced back-diffusion. In contrast, the steady-state fluxes observed for washed yeast cells in deionized water are only 10-30% below the predicted values. The washed yeast cells also exhibited specific cake resistances that are an order of magnitude lower than those for the unwashed yeast. The differences are due to the presence of extracellular proteins and other macromolecules in the unwashed yeast suspensions. These biopolymers cause higher cell adhesion and resistance in the cake layer, so that the cells at the top edge are not free to diffuse away. This is manifested as a concentration jump from the edge of the cake layer to the sheared suspension adjacent to it.(ABSTRACT TRUNCATED AT 250 WORDS)

Biotechnology↗
PubMedDate not supplied

RNA transcription from immobilized DNA templates.

We describe an RNA transcription protocol based on the multiple reuse of solid-phase synthetic DNA templates. The templates are assembled onto streptavidin-coated agarose beads via a single 5'-terminal biotin located on the noncoding template strand. Transcription occurs in an aqueous buffered suspension containing solid-phase DNA, dissolved enzyme (T7 RNA polymerase), and nucleoside triphosphate substrates (NTPs). A direct comparison of solution and solid-phase templates under standard transcription conditions reveals similar initial reaction rates and overall yields. Immobilized templates store stably for periods of several months and are easily recovered by mild centrifugation. We demonstrate the successive reuse of these templates throughout 15 rounds of transcription. The templates remained active, although an incremental decay in transcription was observed beyond five rounds. Template activity was partially restored by supplementing the support-bound oligonucleotide with fresh coding-strand DNA. These findings indicate that multiple reuse of template is a viable strategy for reducing the amount of DNA template required in RNA transcription.

Autoradiography↗
PubMedDate not supplied

Application of solution equilibrium analysis to in vitro RNA transcription.

Solution equilibrium analysis of in vitro RNA transcription has been applied to examine changes in pH, free magnesium concentration, and concentrations of all chemical ionization species as a transcription reaction proceeds. With this method, the progress of a transcription reaction can be accurately determined as a function of measured pH. In addition, it is demonstrated that this method has significant value as a tool for achieving improved understanding of the effects of varying solution conditions on the dynamics of RNA transcription. Magnesium concentration was found to be a critical factor for efficient transcription. Below 5 mM free Mg2+ concentration, the transcription rate and the efficiency at which nucleoside triphosphates (NTPs) are incorporated are greatly reduced. While inorganic pyrophosphate (PPi), a byproduct of the reaction, was found to directly inhibit the rate of transcription, its detrimental effects on transcription were determined to be primarily due to sequestering of magnesium. The PPi forms a precipitate with magnesium which was determined to have a molar composition of 2:1 of Mg:PPi. Transcription rate and efficiency of NTP incorporation are also reduced with increasing ionic strength. It is shown that these reductions can be partially alleviated by replacing chloride with acetate anions.

Base Sequence↗
PubMedDate not supplied

Application of a fed-batch system to produce RNA by in vitro transcription.

A novel fed-batch method is presented for the production of RNA by in vitro transcription performed in a stirred-cell reactor with pH-controlled addition of reaction components. Solution equilibrium analysis is applied to determine the ratios of feed components (including nucleoside triphosphates (NTPs), magnesium salt, and base) which allow the desired NTP concentrations, free magnesium concentration, and pH to be maintained during the reaction. Results are presented for fed-batch and batch reactions performed with two DNA templates encoding a 12mer RNA and a 38mer RNA. For the dodecamer RNA, the fed-batch mode is only modestly better than batch reactions, with no significant increase in the efficiency of NTP incorporation but with 40% improvement in the amount of RNA produced per unit of polymerase or DNA. For the 38mer, fed-batch transcription provides a substantial increase in the efficiency of NTP incorporation and 100% improvement in the production of RNA per unit of polymerase or DNA. Cost analyses are presented which show how optimal NTP concentrations in batch and fed-batch reactions will be dependent on the relative costs of NTPs, T7 RNA polymerase, and DNA templates for the particular application. The use of a fed-batch mode appears to have the potential for substantial improvement in the economics of RNA production for at least some RNA sequences.

Acid Anhydride Hydrolases↗
PubMedDate not supplied

Time required for elimination of Neisseria gonorrhoeae from the urogenital tract in men with symptomatic urethritis: comparison of oral and intramuscular single-dose therapy.

BACKGROUND AND OBJECTIVES: The spread of sexually transmitted diseases (STDs), including gonorrhea, is affected by the duration of infection. Oral antibiotic therapy for gonococcal infection has been shown to be as effective as conventional intramuscular injection with ceftriaxone. Rapid cure would be expected to limit further spread of gonorrhea. However, the speed with which Neisseria gonorrhoeae is eliminated from the urogenital tract has not been evaluated. GOAL OF THIS STUDY: To determine the time required for elimination of Neisseria gonorrhoeae for the urine, mucosa, and semen in male subjects after treatment with ceftriaxone (250 mg intramuscularly), ciprofloxacin (500 mg by mouth, single dose) or cefixime (400 mg by mouth, single dose.) RESULTS: In 14 subjects, gonococci were eliminated from the urine within 4 hours of therapy and the mucosa within 24 hours after therapy. In 9 additional subjects, gonococci were eliminated from the semen by 24 hours after therapy. CONCLUSIONS: These results support the efficacy of single-dose oral therapy for gonorrhea and suggest that earlier follow-up for proof of cure in clinical trials of new antibiotics for gonorrhea may be acceptable. Rapid elimination of gonorrhea reduces the risk for continued transmission of the organism.

Administration, Oral↗
PubMedDate not supplied

The influence of disulfide bonds in proteins on the determination of sulfide.

Acid-labile sulfide content of proteins can be determined spectrophotometrically by procedures leading to the formation of methylene blue. A method has been proposed (involving addition of sulfide) to take into account absorption of dye by samples, but it has been found that recovery of sulfide is influenced by disulfide bonds, resulting in non-linear responses. A simplified procedure has been used to determine acid-labile sulfide in mitochondria from chicken liver and kidney, and linear responses to the amount of protein have been obtained.

Animals↗
PubMedDate not supplied

A retrospective study of the Swanson great toe hemi-prosthesis.

This work is the summation and analysis of data received from a questionnaire forwarded to all Board Certified podiatric surgeons regarding their experience with the Swanson great toe hemi-prosthesis. The responses pertaining to a variety of concerns, including erosive changes, years in vivo, signs and symptoms indicating retrieval, percentage of surgeons polled performing retrieval and perceived reasons for observed erosive changes, were recorded and analyzed. The resultant data reveal significant erosive changes occur early after implantation with a plateau effect within 3 years. Persistent pain following implantation was the most common reason for removal followed by limited range of motion and nonspecific swelling. These three concerns comprised 70% of the reasons for retrieval followed by 18 other cited problems. The results of this poll originate from subjective and objective impressions of surgeons. It is clear that further work is required to scientifically identify and document the specific reasons for these findings, including the circumstances that result in successful implantation of this prosthesis.

Humans↗