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PubMed1988

Characterization of complex gramicidin monolayers by light reflection and Fourier transform infrared spectroscopy.

The reflectivities of monomolecular films of water-insoluble fatty alcohols and fatty acid methyl esters are measured at the air/water interface. A correlation between chain length and reflectivity of the monofilm is established which agrees with calculated values derived from a theoretical model. The correlation is used to estimate thickness of a monolecular film of gramicidin A. Fourier transform infrared (FTIR) spectroscopy is applied to transferred mixed layers of ion-channel-forming gramicidin A and dioctadecyldimethylammonium bromide in order to evaluate the structure of gramicidin. Transfer conditions for these monofilms are elaborated. Results of the reflection method and FTIR spectroscopy demonstrate that gramicidin exists as double-stranded beta-helix inside the monolayer at a lateral pressure similar to that found in biomembranes.

Fourier Analysis↗

PubMed1996

Reflective practice: reviewing the issues and refocusing the debate.

Reflective practice has emerged in the U.K. and beyond as an important issue not just in nursing but in many other professions. However, it remains problematic; it is difficult to conceptualize and many aspects of it are open to debate. Reflective practice is also contentious because, at a fundamental level, it raises a number of important issues for professional practitioners and the way they view their practice. The intention of this paper is to: explore some of the issues that have emerged as the profession of nursing and other professions have gained a better understanding of reflective practice; broaden the scope of the debate and refocus it; raise issues which are in need of further research.

Holistic Nursing↗

PubMed1991

Quantitation of solid-phase immunoassays using a fibre-optic reflectance spectrophotometer.

A reflectance measuring instrument (fibre-optic spectrometer linked to a personal computer) which will quantitate the results of immunoassays that result in the deposition of a coloured chromophore on a membrane or other similar solid phase (SP) is described and the reflectance spectra of some chromophores which are commonly produced or used in SP immunoassays are presented. The instrument has been used in conjunction with silver-enhanced SP-immunogold capture assays to determine the concentrations in serum of IgG and of IgM rheumatoid factor (RF) and the results have been compared with those obtained by rate nephelometry and latex agglutination assays, respectively. It is concluded that fibre-optic reflectance photometry is an accurate and useful means of quantitating SP immunoassays in which coloured chromophores are produced and that the results obtained from such immunoassays are comparable to those given by established procedures.

Agglutination Tests↗

PubMed1988

Fetal whole-body permeability--surface area product and reflection coefficient for plasma proteins.

The transcapillary distribution of protein between the vascular and interstitial spaces largely depends on the protein permeability characteristics of the capillary membranes, i.e., the reflection coefficient and permeability - surface area product for plasma proteins. Our purpose was to estimate whole-body values for these parameters in chronically catheterized, near-term fetal sheep. Average experimental changes in plasma protein concentration, blood volume and vascular pressures following fetal hemorrhage or intravascular saline infusion were analyzed using mathematical modeling and parameter optimization techniques. The mathematical model consisted of three interacting compartments: (1) fetal blood, (2) fetal interstitium, and (3) maternal blood. We found that the mean fetal whole-body protein reflection coefficient averaged 0.61 following hemorrhage and 0.80 after intravascular saline infusions. The protein permeability - surface area product averaged 0.36 ml/min/kg for the hemorrhages and 0.70 ml/min/kg following saline infusions. The major findings are that the fetus has (1) a permeability - surface area product averaging 15 times that of the adult, (2) a protein reflection coefficient approximately 70 to 90% of adult values, and (3) the ability to decrease its capillary surface area following hemorrhage.

Animals↗

PubMed1989

Objective and subjective comparisons of the observation of dental xeroradiographs with reflected and transmitted light.

One of the advantages of dental xeroradiography is that the radiographs may be viewed by either reflected or transmitted light. Both objective and subjective evaluations were carried out to evaluate which viewing method was more efficient. The components of contrast, resolution, and noise were compared by objective physical evaluation. The subjective evaluation measured the visibility of radiographic details. All results of the objective evaluation indicated an advantage for observation with reflected light. On the other hand, the subjective evaluation with transmitted light demonstrated better detectability. The discrepancy of these results could be explained by the difference in the amount of incident light on the radiographs, when a comparison was made of the same subjective evaluation under intense reflected light with the use of slide projectors.

Densitometry↗

PubMed1992

Reflective practice and nursing.

Reflective practice is a frequently used but in-frequently defined concept in nursing at the present time. Part of the reason for the lack of definition lies in the fact that there is no theory of practice. This paper lays the foundations for a theory of practice and paves the way for one useful way in which the relationship between theory and practice can be understood. It is suggested that thoughtful practice is often mistaken for reflective practice, but that the latter can only exist where practice is not taken for granted and so the outcome of practice is more learning from experience. The paper also maintains that for reflective practice to be practised within the profession it is necessary both to have the structures within which it can be encouraged and the theoretical foundation whereby efficient practice need not only be judged in terms of 'value for money'.

Education, Nursing↗

PubMed1994

Beyond reflection: practical wisdom and the practical syllogism.

The relationship between the way nurses think and the actions they perform is one of the key debates within the nursing profession. It has been assumed that the thinking that precedes and follows nursing actions has been described within the reflective practitioner doctrine. It is suggested that this is not so, as the reflective doctrine has not only failed to explicate the link between theory and practice but some reflective theorists have perpetuated the theory-practice gap by separating thought and action. Instead it is argued that Aristotle's conceptions of Practical Wisdom and the Practical Syllogism provide a framework in which the link between thinking and doing are described. Practical wisdom is a form of knowledge that can be claimed by those who purport to deal with human good. Unlike theoretical knowledge, practical wisdom ends not in an intellectual conclusion but in the actual performing of some action designed to produce good for fellow humans. These actions are taken only after the practically wise person decides, consciously or unconsciously, the most effective and morally right option. The practical syllogism is that particular feature of critical thinking that links theory and practice in practice professions. The practical syllogism describes the means-end considerations that underpin all actions undertaken by nurses. It is not suggested that all the deliberations of those with practical wisdom is syllogistic in nature but that this is a central feature of the way in which nurses approach the care they deliver.

Humans↗

PubMed1991

Time-resolved synchrotron X-ray diffraction studies of a single frog skeletal muscle fiber. Time courses of intensity changes of the equatorial reflections and intracellular Ca2+ transients.

Time-resolved X-ray equatorial diffraction studies on a single frog skeletal muscle fiber were performed with a 10 ms time resolution using synchrotron radiation in order to compare the time courses of the molecular changes of contractile proteins and the intracellular Ca2+ transient during an isometric twitch contraction at 2.7 degrees C. Measurements of the Ca2+ transient using aequorin as an intracellular Ca2+ indicator were conducted separately just before and after the X-ray experiments under very similar experimental conditions. The results, which showed a similar time course of tension to that observed in the X-ray experiment, were compared with the aequorin light signal, tension and the intensity changes of the 1,0 and 1,1 equatorial reflections. No appreciable change in both reflection spacings indicated that the effect of internal shortening of the muscle was minimized during contraction. The intensity change of the equatorial reflections generally occurred after the aequorin light signal. In the rising phase, the time course of increase in the 1,1 intensity paralleled that of the rise of the light signal and the intensity peak occurred 20-30 ms after the peak of the light signal. The decrease in the 1,0 intensity showed a time course similar to that of tension and the intensity minimum roughly coincided with the tension peak, coming at 80-90 ms and about 60 ms after the peaks of the light signal and the 1,1 intensity change, respectively. In the relaxation phase, the 1,1 intensity seemed to fall rapidly just before the tension peak and then returned to the original level in parallel with the decay of tension. The 1,0 intensity returned more slowly than the tension relaxation. Thus, the change of the 1,1 intensity was faster than that of the 1,0 intensity in both the rising and relaxation phases. When the measured aequorin light signal was corrected for the kinetic delay of the aequorin reaction with a first-order rate constant of either 50 or 17 s-1, the peak of the corrected light signal preceded that of the measured one by approx. 30 ms. Thus, the peak of the Ca2+ transient appeared earlier than the peaks of the 1,1 and 1,0 intensity changes by 50-60 and 110-120 ms, respectively. The time lag between the extent of structural change and the Ca2+ transient is discussed in relation to the double-headed attachment of a cross-bridge to actin.

Aequorin↗

PubMed1996

Effects of Photofrin on in vivo skin reflectivity.

Skin reflection spectra were measured before and 24 h after administration of Photofrin to nevoid basal-cell carcinoma syndrome patients. The presence of the drug reduced the reflectivity of uninvolved skin and increased the reflectivity of erythematous basal cell cancers. Data analysis with diffusion approximation and Monte Carlo simulation were employed to estimate the optical constant changes and localized drug concentration.

Animals↗

PubMed1995

Do ultrasound measurements on the os calcis reflect more the bone microarchitecture than the bone mass?: a two-dimensional histomorphometric study.

Few studies have analyzed the relationship between ultrasound measurements (US) and corresponding histomorphometric parameters of the calcaneus. To address this question we have compared US and histomorphometric parameters in 17 whole human os calcis from amputation or necropsy. Speed of sound (SOS), broadband ultrasound attenuation (BUA), and bone mineral density (BMD) were measured on the whole foot at the calcaneal site using an Achilles device and a DPX-L densitometer (Lunar). The os calcis was dissected and a 1-cm-wide transcortical parallelepiped extracted with a biopsy needle, focused on the center of the measured area. Histomorphometry was performed on undecalcified biopsies. Structural and connectivity parameters were measured on 7-microns-thick sections with both automatic (Biocom) and semiautomatic analyzers (Ibas 1, Kontron). We found that all ultrasonic and densitometric parameters reflected the true amount of bone and were correlated with only some of the parameters reflecting bone microarchitecture. From stepwise regression analysis, we found that 68%, 67%, 72%, and 74% of the variance of SOS, BUA stiffness, and BMD, respectively, were explained significantly by trabeculae thickness only. Ultrasonic measurements appear to reflect bone quantity rather than bone microarchitecture. The current conclusion is fairly negative with respect to the ability of ultrasound to assess structural parameters, but our limited sample size did not give enough power to our study to reach statistically significant correlations. In addition, the calcaneus is anisotropic and the ultrasound interaction in bone is a three-dimensional phenomenon. So, a three-dimensional study rather than a two-dimensional one should be performed.

Absorptiometry, Photon↗

PubMed2006

Fluorescence photobleaching recovery using total internal reflection interference fringes.

Lateral diffusion measurements on cell membrane molecules, most commonly accomplished through fluorescence photobleaching recovery (FPR or FRAP), provide information on such molecules' size, environment, and participation in intermolecular interactions. However, difficulties arise in FPR measurements of lateral dynamics of materials, such as visible fluorescent protein (VFP) fusion proteins, where fluorescent intracellular species contribute to the fluorescence recovery signal and thus distort measurements intended to reflect surface molecules only. A new method helps eliminate these difficulties. In total internal reflection interference fringe FPR, interfering laser beams enter a 1.65-numercial aperture (NA) Olympus objective at the periphery of the back focal plane where the NA exceeds 1.38. This creates an extended interference pattern totally internally reflected at the coverslip-medium interface which excites fluorescence only from fluorescent molecules located where the cell contacts the coverslip. The large illuminated area interrogates many more membrane receptors than spot methods and hence obtains more diffusion information per measurement while rejecting virtually all interfering intracellular fluorescence. We report successful measurements of membrane dynamics of both VFP-containing and conventionally labeled molecules by this technique and compare them with results of other FPR methods.

Animals↗

PubMed2005

A yellow ring-shaped macular reflection.

PURPOSE: To describe a yellow ring-shaped reflection in the macula of healthy subjects observed with a common indirect ophthalmoscope. DESIGN: Observational case series. METHODS: Fundus photographs of the macula were acquired with a slit lamp and 90-diopter lens in 5 healthy subjects (age range, 23-50 years) at a perpendicular angle and at an oblique angle to the retina. RESULTS: The perpendicular fundus photographs showed a yellow ring-shaped reflection with a diameter of approximately 5 degrees. The oblique photographs had a dark red spot in the center. CONCLUSIONS: To our knowledge, this phenomenon has hitherto escaped attention in the literature. We conclude that the shape, size, and location of the yellow reflection are consistent with a cone origin. This observation may be used for diagnostic purposes.

Adolescent↗

PubMed2005

Acute effects of caffeine on arterial stiffness, wave reflections, and central aortic pressures.

Caffeine is considered to be the most widely consumed pharmacologic substance in the world. Several recent sources of evidence suggest that caffeine, besides its well-established pressor effects, provokes further alterations in arterial stiffness, wave reflections, and especially aortic blood pressures, which are often overlooked. The increasing evidence regarding the prognostic value of the latter cardiovascular factors prompted us to seek additional information concerning the relationship of aortic blood pressures to caffeine consumption. The main purpose of the present review was to evaluate the acute influence of caffeine on arterial stiffness, wave reflections, and central systolic pressures, which are involved in the pathogenesis and prognosis of cardiovascular diseases. Current evidence supports the hypothesis that caffeine influences the cardiovascular system at least acutely, not only through a peripheral blood pressure elevation but also through an increase in arterial stiffness and an enhancement of arterial wave reflections. Moreover, it seems that peripheral pressure measurements might have underestimated caffeine pressor effects, as a significantly greater response is observed in aortic pressures. The mechanisms explaining these effects of caffeine are not always clear, and neither is the role of caffeine in cardiovascular risk. However, it is concluded that strategies aiming at the control of dietary caffeine consumption merit serious consideration.

Aorta↗

PubMed2005

Reflection spectrometry analysis of irradiated GAFCHROMIC XR type R radiochromic films.

The absorption spectra of the GAFCHROMIC XR type R radiochromic film measured with reflectance spectroscopy have been investigated in order to analyze the dosimetry characteristics of the film. Like the XR type T film, this film features two peaks in its absorption spectrum, approximately at 676 and 618 nm, whose intensities increase with increasing absorbed dose. When the main absorption peak at 676 nm is used, the XR GAFCHROMIC type R film is approximately 1.4 times more sensitive to radiation doses in the 0-5 Gy range than the XR type T film. The major difference of the films of this type from the original GAFCHROMIC film products is the opaque backing material, which permits only reflected, but not transmitted, light measurements as a means of analysis. A yellow dye is used as the opaque backing to enhance the visible color change for qualitative assessment of the delivered dose. The XR type R radiochromic film in combination with reflection spectroscopy can provide accurate assessment of doses.

Journal Article↗

PubMed2006

Measures of arterial stiffness and wave reflection are associated with walking distance in patients with peripheral arterial disease.

We hypothesized that measures of arterial stiffness and wave reflection influence functional capacity of patients with peripheral arterial disease (PAD). Consecutive patients (n=106, 69+/-10 years, 66% men) referred for lower extremity arterial evaluation were studied. Radial artery pulse waveforms were obtained by applanation tonometry and an ascending aortic pressure waveform derived by a transfer function. Aortic augmentation index (AIx) is the difference between the first and second systolic peak of the ascending aortic pressure waveform indexed to the pulse pressure (PP) and T(r) is the reflected wave arrival time. Ankle-brachial index (ABI) and walking distance were measured as per laboratory protocol after excluding patients with non-compressible vessels (ABI>1.5) and severe PAD (ABI<0.5). To account for right-censoring of walking distances in patients completing the 5 min walk (n=56), we used survival analysis to identify variables associated with walking distance. Mean (+/-S.D.) values were: AIx, 31.2+/-10.9%; T(r), 134+/-18 ms; PP, 66.5+/-17.1 mmHg; ABI, 0.87+/-0.22; walking distance, 177+/-75 m. In both multivariable accelerated failure time (AFT) and Cox proportional-hazards models, older age, female sex, greater body mass index, lower ABI, and a measure of arterial stiffness (higher AIx and PP, lower T(r)) were associated with a lower walking distance. Higher AIx and lower T(r) were associated with a lower walking distance even after adjustment for PP as well as in the subset of patients with PAD (ABI<0.9 at rest or post-exercise, n=82). In conclusion, measures of arterial stiffness and wave reflection are associated with walking distance in patients with PAD and may be a target of therapy in such patients.

Aged↗

PubMed2006

Gender influence on metabolic syndrome's effects on arterial stiffness and pressure wave reflections in treated hypertensive subjects.

BACKGROUND: In hypertensive subjects, aortic stiffness, an independent predictor of cardiovascular (CV) risk, measured from pulse wave velocity (PWV), contributes to enhance augmentation index (AI), a marker of the timing and amplitude of wave reflections. Whether PWV and AI are correlated and reflect CV risk in hypertensive men and women with metabolic syndrome (MS) remains unknown. METHODS: In a cohort of 613 (364 males) treated hypertensive subjects with and without MS (41% MS) pulse wave analysis was used to determine aortic PWV and carotid AI. CV risk was estimated from standard Framingham equations. RESULTS: In females, but not in males, aortic PWV was higher in subjects with MS, when compared with those without MS (12.7+/-0.3m/s versus 11.1+/-0.4m/s, p<0.001). This result was independent of age and blood pressure. Only in females AI was independently related to the presence of MS; AI did not differ between subjects with or without MS, both males and females. AI did not correlate with PWV, except in males without MS. The overall CV risk was strongly associated to PWV independently of MS and gender, but AI was associated to CV risk only in males. CONCLUSION: In treated hypertensive subjects, the effect of MS on PWV and AI is modulated by gender. The dissociation between PWV and AI observed in women with MS was due to "blunted" wave reflections. This finding is associated with the fact that PWV, but not AI, was a constant marker of CV risk in subjects with MS, whether men and women.

Antihypertensive Agents↗

PubMed2005

A dip in the chlorophyll fluorescence induction at 0.2-2 s in Trebouxia-possessing lichens reflects a fast reoxidation of photosystem I. A comparison with higher plants.

An unusual dip (compared to higher plant behaviour under comparable light conditions) in chlorophyll fluorescence induction (FI) at about 0.2-2 s was observed for thalli of several lichen species having Trebouxia species (the most common symbiotic green algae) as their native photobionts and for Trebouxia species cultured separately in nutrient solution. This dip appears after the usual O(J)IP transient at a wide range of excitation light intensities (100-1800 micromol photons m(-2) s(-1)). Simultaneous measurements of FI and 820-nm transmission kinetics (I(820)) with lichen thalli showed that the decreasing part of the fluorescence dip (0.2-0.4 s) is accompanied by a decrease of I(820), i.e., by a reoxidation of electron carriers at photosystem I (PSI), while the subsequent increasing part (0.4-2 s) of the dip is not paralleled by the change in I(820). These results were compared with that measured with pea leaves-representatives of higher plants. In pea, PSI started to reoxidize after 2-s excitation. The simultaneous measurements performed with thalli treated with methylviologen (MV), an efficient electron acceptor from PSI, revealed that the narrow P peak in FI of Trebouxia-possessing lichens (i.e., the I-P-dip phase) gradually disappeared with prolonged MV treatment. Thus, the P peak behaves in a similar way as in higher plants where it reflects a traffic jam of electrons induced by a transient block at the acceptor side of PSI. The increasing part of the dip in FI remained unaffected by the addition of MV. We have found that the fluorescence dip is insensitive to antimycin A, rotenone (inhibitors of cyclic electron flow around PSI), and propyl gallate (an inhibitor of plastid terminal oxidase). The 2-h treatment with 5 microM nigericin, an ionophore effectively dissipating the pH-gradient across the thylakoid membrane, did not lead to significant changes either in FI nor I(820) kinetics. On the basis of the presented results, we suggest that the decreasing part of the fluorescence dip in FI of Trebouxia-lichens reflects the activation of ferredoxin-NADP(+)-oxidoreductase or Mehler-peroxidase reaction leading to the fast reoxidation of electron carriers in thylakoid membranes. The increasing part of the dip probably reflects a transient reduction of plastoquinone (PQ) pool that is not associated with cyclic electron flow around PSI. Possible causes of this MV-insensitive PQ reduction are discussed.

Antimycin A↗

PubMed2006

Confocal reflection imaging of 3D fibrin polymers.

The reconstruction of extracellular matrix (ECM) by confocal reflection microscopy is a physical approach for monitoring the ECM structure, cell-matrix interactions and changes of ECM structure over time. We here show that confocal reflection imaging is useful in reconstructing the fibrillar architecture of 3D fibrin lattices and fibroblasts embedded therein at high resolution up to 250 nm. Together with confocal fluorescence microscopy of collagen deposited by fibroblasts, this technique allows the monitoring of fibrin remodeling by stromal cells. In conclusion, confocal reflection microscopy is a valuable technique for real-time monitoring of the remodeling of fibrin matrices, such as during thrombus formation, wound healing, and tumor formation.

Cell Line↗