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Biomedical subjects

A Lewis

Publications and source records attributed to A Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1998

Stroke: anatomy of a catastrophic event.

Subarachnoid hemorrhage (SAH) resulting from the rupture of a cerebral aneurysm represents one major cause of stroke. SAH may be followed by a spontaneous severe contraction of major cerebral arteries, a condition referred to as cerebral vasospasm. Vasospasm may result in brain ischemia or actual tissue death. This constrictive vascular state is devastating, remains largely untreatable, and is a major cause of morbidity and mortality in SAH patients. Approximately 30,000 Americans are affected by this condition each year. The overall death rates are 25%, and significant neurological complications occur in 50% of individuals who survive the initial bleed. This report highlights some of the important aspects of this vascular disease.

Aneurysm, Ruptured↗
PubMed1998

A multistakeholder-driven model for developing an outcome management system.

Increasing demands for accountability in the delivery of public mental health services are engendering organized systems of treatment outcome monitoring. As such systems are designed and implemented, it is critical that key stakeholders be involved to the greatest extent possible in developing assessment instruments and methodologies so as to ensure relevance and acceptability of the outcome management system. A multistakeholder-based initiative for developing standardized outcome assessment for public mental health services in Virginia is described. Key components of the initiative include the process by which stakeholders were enlisted, the identification of recommended assessment instruments, and a pilot project that began the evaluation of the feasibility, utility, and cost-benefit of using the instruments. To illustrate features of this initiative, the child/adolescent mental health pilot project is described in detail. Implications for behavioral health administrators and next steps for Virginia's outcome management system are discussed, highlighting the role of key stakeholders.

Adolescent↗
PubMed1998

Effective light-induced hydroxylamine reactions occur with C13 = C14 nonisomerizable bacteriorhodopsin pigments.

The light-driven proton pump bacteriorhodopsin (bR) undergoes a bleaching reaction with hydroxylamine in the dark, which is markedly catalyzed by light. The reaction involves cleavage of the (protonated) Schiff base bond, which links the retinyl chromophore to the protein. The catalytic light effect is currently attributed to the conformational changes associated with the photocycle of all-trans bR, which is responsible for its proton pump mechanism and is initiated by the all-trans --> 13-cis isomerization. This hypothesis is now being tested in a series of experiments, at various temperatures, using three artificial bR molecules in which the essential C13==C14 bond is locked by a rigid ring structure into an all-trans or 13-cis configuration. In all three cases we observe an enhancement of the reaction by light despite the fact that, because of locking of the C13==C14 bond, these molecules do not exhibit a photocycle, or any proton-pump activity. An analysis of the rate parameters excludes the possibility that the light-catalyzed reaction takes place during the approximately 20-ps excited state lifetimes of the locked pigments. It is concluded that the reaction is associated with a relatively long-lived (micros-ms) light-induced conformational change that is not reflected by changes in the optical spectrum of the retinyl chromophore. It is plausible that analogous changes (coupled to those of the photocycle) are also operative in the cases of native bR and visual pigments. These conclusions are discussed in view of the light-induced conformational changes recently detected in native and artificial bR with an atomic force sensor.

Bacteriorhodopsins↗
PubMed1998

Near-field optical imaging of unstained bacteria: comparison with normal atomic force and far-field optical microscopy in air and aqueous media.

Simultaneous near-field scanning optical and atomic force imaging of bacteria is presented. The bacteria imaged in these studies were unstained. The near-field optical images had excellent signal-to-noise and showed excellent contrast even in these unstained specimens. The images obtained were interpreted in terms of the images that have been obtained by transmission electron microscopy and X-ray imaging. The results show that bacterial near-field optical imaging is going to be a very important tool in the arsenal of the bacteriologist both in terms of understanding the fundamental processes in the life cycle of bacteria with and without cytochemical staining and in terms of clinical diagnostic applications.

Bacillus megaterium↗
PubMed1998

Fibrous dysplasia of the jaw bone: a review of 15 new cases and two cases of recurrence in Jamaica together with a case report.

The authors reviewed 15 new cases of fibrous dysplasia of the jaw bone and two cases of recurrence seen in Jamaica between 1980 and 1995. Only cases which had a histological confirmation of fibrous dysplasia were included. The clinical behaviour and radiological findings of these cases were studied from the case files, either at the Cornwall Regional Hospital or the Kingston Public Hospital in Jamaica.

Adolescent↗
PubMed1997

Microsecond atomic force sensing of protein conformational dynamics: implications for the primary light-induced events in bacteriorhodopsin.

In this paper a new atomic force sensing technique is presented for dynamically probing conformational changes in proteins. The method is applied to the light-induced changes in the membrane-bound proton pump bacteriorhodopsin (bR). The microsecond time-resolution of the method, as presently implemented, covers many of the intermediates of the bR photocycle which is well characterized by spectroscopical methods. In addition to the native pigment, we have studied bR proteins substituted with chemically modified retinal chromophores. These synthetic chromophores were designed to restrict their ability to isomerize, while maintaining the basic characteristic of a large light-induced charge redistribution in the vertically excited Franck-Condon state. An analysis of the atomic force sensing signals lead us to conclude that protein conformational changes in bR can be initiated as a result of a light-triggered redistribution of electronic charge in the retinal chromophore, even when isomerization cannot take place. Although the coupling mechanism of such changes to the light-induced proton pump is still not established, our data question the current working hypothesis which attributes all primary events in retinal proteins to an initial trans<==>cis isomerization.

Bacteriorhodopsins↗
PubMed1997

An optical submicrometer calcium sensor with conductance sensing capability.

The identification of chemical species and the measurement of their concentrations with high (submicrometer) spatial resolution are of considerable importance in cell biology. In this article we report the first successful development of a > or = 0.1-micron Ca2+ sensor based on a pulled micropipet, filled with a conducting porous sol-gel glass which was doped with the fluorescent calcium green 1 Ca2+ indicator. Such sensors are potentially capable of measuring Ca2+ concentrations as low as 10(-8) M, in confined volumes, with a three-dimensional resolution which exceeds approximately 0.1 micron. A major advantage of the sensor is its capability to be integrated into a multifunctional probe which will measure chemical analyte concentrations and ion conductance.

Animals↗
PubMed1997

Dynamics of ArF excimer laser-induced cavitation bubbles in gel surrounded by a liquid medium.

BACKGROUND AND OBJECTIVE: Cavitation bubbles have been shown to be the driving force of tissue cutting in 193 nm ArF excimer laser-based vitreoretinal microsurgery. In the present work we investigate the dynamics of cavitation bubbles inside a gelatin gel in a saline environment using fast flash microphotography. STUDY DESIGN/MATERIALS AND METHODS: The screening influence of the saline medium was found to restrict the maximal distance between the tip and the tissue at which cavitation bubbles are created to < 100 microns at an energy fluence up to 0.3 J/cm2/pulse (the maximal energy fluence applied in vitreoretinal surgery). RESULTS AND CONCLUSION: Single laser pulses did not cause disruption of gelatin at an energy fluence of up to 0.4 J/cm2/pulse. During the application of repetitive pulses small insoluble gas-containing bubbles were produced and often trapped between the tip and the tissue. They completely changed the shape of the subsequent cavitation bubbles and caused deep crater formation in the gel.

Biomechanical Phenomena↗
PubMed1997

Atomic Force Sensing of Light-Induced Protein Dynamics with Microsecond Time Resolution in Bacteriorhodopsin and Photosynthetic Reaction Centers

This paper reports on experiments that have monitored protein microsecond dynamics with a cantilevered near-field optical glass fiber. In these experiments two photoactive proteins, bacteriorhodopsin (bR) and the photosynthetic reaction center (PS I), are used to demonstrate that such probes can measure light-induced microsecond protein dynamics even though the resonance frequencies of the glass cantilevers used are on the order of a few hundred kilohertz. In the case of the light-driven proton pump, bR, the light-induced atomic force sensing (AFS) signal is negative (indicating contraction) in the microsecond time domain of the L photointermediate and becomes positive (corresponding to expansion) in the subsequent M intermediate that lives for milliseconds. Double pulse experiments from M to bR show that the latter process reverses the AFS signal. Thus, the AFS structural changes are coupled with the (optical) photocycle intermediates. Light-induced contraction and expansion phenomena are also observed in the case of PS I. In both systems the time regime of the dynamic phenomena that have been measured with AFS is five orders of magnitude faster than the fastest previously recorded atomic force detection of dynamic phenomena. This advance portends a new era in dynamic imaging of protein conformational changes.

Journal Article↗
PubMed1997

Evidence for a controlling role of water in producing the native bacteriorhodopsin structure.

The experiments reported in this paper, based on reconstitution of bacteriorhodopsin (bR) from apomembrane at varying environmental conditions, demonstrate that the presence of water is a controlling factor in generating a native wild-type bR conformation. If water is lacking during this reconstitution process, then a non-native bR structure is formed that exhibits altered M formation and decay kinetics, as well as different behavior following extensive dehydration. It is shown that mutants affecting the ability of bR to form appropriate structures of water in specific protein cavities also affect the ability to generate a native bR conformation. The results suggest that aspartic acid 96 plays a major role in anchoring the appropriate water structure conformation associated with bR. It is also demonstrated that the glutamic acid 204 residue is pivotal in controlling the protein/water affinity. This water affinity can be further controlled by modifying the charge environment of the protein with altered pH. These data, based on kinetic absorption spectroscopy and Fourier transform infrared spectroscopy, highlight the central role of water in this protein.

Aspartic Acid↗
PubMed1997

Evaluating neoadjuvant therapy effectiveness on systemic disease: use of a prostatic-specific membrane reverse transcription polymerase chain reaction.

OBJECTIVE: An on-going study at the Memorial Sloan-Kettering Cancer Center assessed the effectiveness of androgen deprivation therapy (ADT) prior to surgical removal of the prostate. In this report, we evaluate the effectiveness of ADT on systemic disease by monitoring the presence or absence of circulating prostatic epithelial cells using a reverse transcription polymerase chain reaction (RT-PCR) assay for prostatic-specific membrane antigen (PSM). METHODS: PSM RT-PCR was performed on a total of 38 prostate cancer patients. There were 12 pT2 patients in the ADT group and 10 patients in the control pT2 group and 5 pT3 patients in the ADT group and 11 pT3 patients in the control group. RESULTS: For pT2 patients, 2 of the 12 patients (17%) were positive for circulating prostatic cells during androgen deprivation therapy but before radical retroprostatectomy (RRP). Within a 6-month period after RRP, 3 of 12 patients (25%) were positive. For the period between the 7th and 12th month after RRP, 6 of 12 patients (50%) were positive. For the period 12-36 months after RRP, 2 of the 12 patients (17%) remained positive for circulating prostatic cells. In contrast, the pT2 control group had higher positive rates in comparable periods: 4 of 10 patients (40%) were positive prior to surgery; 6 of 10 patients (60%) were positive during the 6 months following surgery. For the period between the 7th and 12th month following surgery, 4 of 7 patients (57%) were positive for PSM. Finally, 3 of 6 patients (50%) were positive for the period longer than 12 months. Regarding patients who have extraprostatic disease (stage pT3), the ADT group had a lower rate of circulating PSM positive cells. Before RRP and during androgen deprivation therapy, 1 out of 5 patients (20%) in the ADT group were positive as compared to 4 out of 11 patients for the control group. Within a 6-month period after RRP, the ADT group had 4 out of 9 (44%) patients positive for PSM as compared to 9 of 11 (82%) for the control group. For the period between the 7th and 12th months postsurgery, 1 of 5 patients (20%) of the ADT group were positive as compared to 4 of 7 (57%) of the control patients. CONCLUSIONS: These results indicate that patients with pT2 and pT3 lesions who receive neoadjuvant ADT are less likely to have circulating tumor cells detected compared to a control group both prior to and after surgery. In addition, irrespective of ADT or control group, there were increases in the detection of circulating tumor cells in the period after RRP, and this rise gradually decreased, suggesting that surgical manipulation may cause hematogenous dissemination of tumor cells and that ADT reduces such dissemination of tumor cells. Overall, these results indicate that the use of neoadjuvant ADT decreases the number of circulating prostatic cells. These data represent the initial results of an on-going study. As additional patients are added to the studies, attempts to correlate PSM positivity and serum PSA values postoperatively, recurrence, and margin positivity will be made.

Androgen Antagonists↗
PubMed1997

Case studies in disease management for congestive heart failure.

Today, case management is neither science nor art. Successful programs have little in common except corporate commitment, the right people for the right job, and an understanding of the playing field. The author provides three case studies of HMOs who tried to jump into the field, with varying levels of success.

Case Management↗