Biomedical subjects

G B Chapman

Publications and source records attributed to G B Chapman.

48 records · Page 3Linked to original sources

PubMed1966

Structure of a marine bacteriophage as revealed by the negative-staining technique.

Valentine, Artrice F. (Georgetown University, Washington, D.C.), Peter K. Chen, Rita R. Colwell, and George B. Chapman. Structure of a marine bacteriophage as revealed by the negative-staining technique. J. Bacteriol. 91:819-822. 1966.-The morphology of a marine bacteriophage has been determined by negative-staining techniques and electron microscopy. The virus possesses a head, 600 A in diameter, and a tail which may be from 860 to 1,000 A in lenght. No tail sheath is seen. The appearance of the terminal tail structure is discussed.

Bacteriophages↗

PubMed1966

Fine structure and host-virus relationship of a marine bacterium and its bacteriophage.

Valentine, Artrice F. (Georgetown University, Washington, D.C.), and George B. Chapman. Fine structure and host-virus relationship of a marine bacterium and its bacteriophage. J. Bacteriol. 92:1535-1554. 1966.-The fine structure of a gram-negative marine bacterium, Cytophaga marinoflava sp. n., has been revealed by ultrathin sectioning and electron microscopy. Stages in the morphogenesis of the bacterial virus NCMB 385, which has been shown to be highly specific for this organism, were also demonstrated in bacterial cells fixed according to the Kellenberger technique. The bacterium possessed a cell wall, cytoplasmic membrane, and nuclear and cytoplasmic regions typical of bacterial cells. Both the cell wall and the cytoplasmic membrane showed a tripartite structure, i.e., each was composed of two dense layers separated by a low-density zone. Intracytoplasmic membrane systems were also observed, especially in dividing cells and in cells in which new viruses were being formed. As many as 18 hexagonally shaped, empty phage heads (membranes only) were observed in untreated, infected bacterial cells. Phage heads, intermediate in density to empty heads and fully condensed ones, possibly representing stages in the morphological development of the virus, were also seen.

Bacteriophages↗

PubMed1962

Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate.

Chapman, George B. (Cornell University Medical College, New York, N.Y.). Cytological aspects of antimicrobial antibiosis. I. Cytological changes associated with the exposure of Escherichia coli to colistin sulfate. J. Bacteriol. 84:169-179. 1962-Broth cultures of Escherichia coli were exposed to different concentrations of the antibiotic colistin sulfate for various lengths of time. Control (untreated) and treated cells were fixed, dehydrated, and embedded in methacrylate or Epon. Ultrathin sections were examined in an RCA EMU2-D electron microscope. Two conspicuous cytological changes were noted. First, the nuclear material disappeared from its normal sites and was no longer demonstrable. Second, the cytoplasm lost its granularity and became homogeneous. Cells which showed these changes were nonviable.

Anti-Bacterial Agents↗

PubMedDate not supplied

Model studies of leukocyte-endothelium-blood interactions. II. Hemodynamic impact of leukocytes adherent to the wall of post-capillary vessels.

Computational fluid dynamics (CFD) and large scale model experiments were used to analyze the hemodynamic impact of leukocytes adherent to the wall of post-capillary venules. Using a large scale model and, with the aid of a finite element package, solving the Navier Stokes equations for low Reynolds number flow in a cylinder past an adherent sphere, we have developed a dimensionless correlation which permits the estimation of the pressure drop across an adherent leukocyte in an in vivo vessel. This relationship is: f.Re = exp[2.877+4.630 (d/D)4] where f is the Fanning friction factor, Re is the Reynolds number and d/D is the leukocyte to vessel diameter ratio. The friction factor is proportional to the pressure drop across the leukocyte, and does not significantly increase until d/D is greater than 0.5, and then increases rapidly with increasing d/D. Computations indicate that the length of the disturbed flow region generated by an adherent leukocyte increases with decreasing vessel size. The average wall stress in the disturbed flow region remains constant, and equal to the wall stress in the undisturbed region for d/D less than approximately 0.5. For d/D greater than 0.5, the average wall stress in the disturbed flow region increases rapidly with increasing d/D. There is an even larger increase, up to five times greater than the average disturbed stress, in the peak wall stress in the disturbed flow region. This indicates that significant wall stress gradients can be generated by an adherent leukocyte in post-capillary size vessels.

Cell Adhesion↗

PubMedDate not supplied

Shear stress gradient over endothelial cells in a curved microchannel system.

Our purpose was to test a scale model of the microcirculation by measuring the shear forces to which endothelial cells were exposed, and comparing this to computer simulations. In vitro experiments were performed to measure the 2-dimensional projected velocity profile along endothelial cell lined microchannels (D-shaped, 10-30 microns radius, n = 15), or in microchannels without endothelial cells (n = 18). Microchannels were perfused with fluorescently labeled microspheres (0.5 micron dia., < 1%) suspended in cell culture media. The velocity of individual microspheres was obtained off-line (videorecording), using an interactive software program; velocity was determined as the distance traveled in one video field (1/60 s). Mass balance was verified in the microchannels by comparing the microsphere velocities to the perfusion pump rate. In confluent endothelial cell lined microchannels, a velocity profile was obtained as microspheres passed an endothelial cell nucleus (identified by fluorescent dye), and again, for a paired region 100 microns away without nuclei (cytoplasm region). The velocity profile was significantly shifted and sharpened by the endothelial cell nucleus, as anticipated. Over the nucleus, data are consistent with a normal sized nucleus extending into the lumen, further confirming that this scale model can be used to determine the wall shear stress to which endothelial cells are exposed. Using the experimental bulk phase fluid parameters as boundary conditions, we used computational fluid dynamics (CFD) to predict the expected wall shear stress gradient along an endothelial cell lined D-shaped tube. The wall shear stress gradient over the nucleus was 2-fold greater in the radial versus axial directions, and was sensitive to lateral versus midline positioned nuclei.

Blood Flow Velocity↗

PubMedDate not supplied

Effects of patient education on decisions about breast cancer treatments: a preliminary report.

The authors examined the effects of materials for educating patients about treatment options for breast cancer on knowledge about the disease, preferences for alternative treatments, and how changes in knowledge and preferences were related. Eighty-two undergraduate students acted as advisors to a hypothetical patient. They completed a knowledge test and rated their preferences for three options--breast-sparing surgery with radiation, mastectomy followed by reconstructive surgery, and mastectomy followed by use of a breast prosthesis--before and after viewing a videotape or a booklet version of the educational materials. Both formats increased knowledge scores. Treatment preferences were not affected by reading the booklet, but viewing the videotape resulted in a preference shift toward breast-sparing surgery. This media difference may be due to features of the video that were not reproduced in the booklet, such as interviews with other patients. Knowledge gains were uncorrelated with preference changes.

Adolescent↗

PubMedDate not supplied

Valuing the future: temporal discounting of health and money.

Normative discounted utility theory specifies that the values of all future outcomes (for example, those related to health and money) should be discounted at a constant rate. Two experiments demonstrated that, contrary to this prescription, decision makers use different discount rates for health-related decisions and money-related decisions. Temporal discountings for health and money were similar in that both demonstrated two biases previously found in monetary decisions: discount rates were inversely related to magnitude of outcome and length of delay. The relatively large discount rates used by the subjects suggest why it is often difficult to implement preventive health measures that improve future health.

Decision Making↗

PubMedDate not supplied

Prostate cancer patients' utilities for health states: how it looks depends on where you stand.

Two versions of the time-tradeoff (TTO) method were compared. In the personal TTO version, 31 prostate cancer patients decided whether they personally would give up some longevity to have perfect health rather than a longer life in a state of poor health associated with prostate cancer. In the impersonal version, 28 patients compared two hypothetical friends, one of whom has perfect health but will live less time than the other who is in poor health, and decided which person they would rather be. All patients evaluated three hypothetical health states. The two TTO methods were assessed by examining 1) how well they distinguished three health states of varying degrees of dysfunction and 2) patients' willingness to trade time for quality of life. Patients using the impersonal TTO version were more likely than those using the personal version to order the three health states appropriately (68% vs 16%, p < 0.0001) and were more willing to trade off length of life for quality of life (p < 0.05).

Activities of Daily Living↗

PubMedDate not supplied

Clinical diagnosis and the order of information.

BACKGROUND: Information order can influence judgment. However, it remains unclear whether the order of clinical data affects physicians' interpretations of these data when they are engaged in familiar diagnostic tasks. METHODS: Of 400 randomly selected family physicians who were given a questionnaire involving a brief written scenario about a young woman with acute dysuria, 315 (79%) returned usable responses. The physicians had been randomized into two groups, and both groups had received the same clinical information but in different orders. After learning the patient's chief complaint, physicians received either the patient's history and physical examination results followed by the laboratory data (the H&P-first group) or the laboratory data followed by the history and physical examination results (the H&P-last group). The results of the history and physical examination were supportive of the diagnosis of UTI, while the laboratory data were not. All physicians judged the probability of a urinary tract infection (UTI) after each piece of information. RESULTS: The two groups had similar mean estimates of the probability of a UTI after learning the chief complaint (67.4% vs 67.8%, p = 0.85). At the end of the scenario, the H&P-first group judged UTI to be less likely than did the H&P-last group (50.9% vs 59.1%, p = 0.03) despite having identical information. Comparison of the mean likelihood ratios attributed to the clinical information showed that the H&P-first group gave less weight to the history and physical than did the H&P-last group (p = 0.04). CONCLUSIONS: The order in which clinical information was presented influenced physicians' estimates of the probability of disease. The clinical history and physical examination were given more weight by physicians who received this information last.

Analysis of Variance↗

PubMedDate not supplied

Time preferences and preventive health behavior: acceptance of the influenza vaccine.

BACKGROUND: Many preventive health behaviors involve immediate costs and delayed benefits. Time preference is the extent to which decision makers value future outcomes relative to immediate ones. Consequently, people with future-oriented time preferences should be more likely to adopt preventive measures. The relationship between time preferences and acceptance of a free influenza vaccination was examined. SAMPLE: The participants were 412 corporate employees who were offered free influenza vaccinations at their workplace. MEASURES: Participants' time preferences were measured in each of two domains: money and health. They also reported on whether they had accepted the influenza vaccination and their beliefs and attitudes about the vaccine. RESULTS: There was a small (OR = 2.38) relationship of vaccination acceptance to monetary time preferences but not to the health time-preference measures. Other variables, such as perceived effectiveness of the vaccine, were more predictive. CONCLUSION: This study provides some evidence of a small relationship between time preferences and preventive health behavior.

Adult↗

PubMedDate not supplied

Are more options always better? The attraction effect in physicians' decisions about medications.

Consumer choice research has shown that, contrary to normative theory, the introduction of an inferior alternative to an existing choice set can increase the likelihood that one of the original alternatives will be chosen. This phenomenon, the attraction effect, is relevant to physician decision making, particularly when the physician is in the role of a consumer who must make decisions about prescribing medications when a number of alternatives are available. To investigate the attraction effect in physician decision making, 40 internal medicine residents reviewed three patient cases (concerning depression, sinusitis, and vaginitis) and then chose the most appropriate medication for each patient. In some versions of the cases, two medication options were available. Other versions included a third medication (the decoy) that was inferior in every way to one of the original options (the target) but not to the other (the competitor). The results showed that addition of the "decoy" medication increased the likelihood of choosing the target medication. That is, the attraction effect does occur in physicians' decisions about medications. Physicians should be aware of this bias when evaluating or suggesting several similarly attractive medications or treatment options for the same medical condition.

Adult↗

PubMedDate not supplied

Framing effects in choices between multioutcome life-expectancy lotteries.

AIM: To explore framing or editing effects and a method to debias framing in a clinical context. METHOD: Clinical scenarios using multioutcome life-expectancy lotteries of equal value required choices between two supplementary drugs that either prolonged or shortened life from the 20-year beneficial effect of a baseline drug. The effects of these supplementary drugs were presented in two conditions, using a between-subjects design. In segregated editing (n = 116) the effects were presented separately from the effects of the baseline drug. In integrated editing (n = 100), effects of supplementary and baseline drugs were combined in the lottery presentation. Each subject responded to 30 problems. To explore one method of debiasing, another 100 subjects made choices after viewing both segregated and integrated editings of 20 problems (dual framing). RESULTS: Statistically significant preference reversals between segregated and integrated editing of pure lotteries occurred only when one framing placed outcomes in the gain domain, and the other framing placed them in the loss domain. When both editings resulted in gain-domain outcomes only, there was no framing effect. There was a related relationship of framing-effect shifts from losses to gains in mixed-lottery-choice problems. Responses to the dual framing condition did not consistently coincide with responses to either single framing. In some situations, dual framing eliminated or lessened framing effects. CONCLUSION: The results support two components of prospect theory, coding outcomes as gains or losses from a reference point, and an s-shaped utility function (concave in gain, convex in loss domains). Presenting both alternative editings of a complex situation prior to choice more fully informs the decision maker and may help to reduce framing effects. Given the extent to which preferences shift in response to alternative presentations, it is unclear which choice represents the subject's "true preferences."

Adolescent↗