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PubMed2003

Normal modes of a poroelastic plate and their relation to the reflection and transmission coefficients.

A poroelastic plate that obeys the Biot theory is considered. Compact new forms of its reflection and transmission coefficients, similar to those of the resonance scattering theory for an elastic plate, are derived. A numerical comparison of the reflection coefficient modulus with the plate normal modes, at low frequency, shows that a study of the reflection or transmission coefficient does not provide the same kind of information on the poroelastic plate than an investigation of guided leaky waves propagation.

Journal Article↗

PubMed1999

EEG alpha and theta oscillations reflect cognitive and memory performance: a review and analysis.

Evidence is presented that EEG oscillations in the alpha and theta band reflect cognitive and memory performance in particular. Good performance is related to two types of EEG phenomena (i) a tonic increase in alpha but a decrease in theta power, and (ii) a large phasic (event-related) decrease in alpha but increase in theta, depending on the type of memory demands. Because alpha frequency shows large interindividual differences which are related to age and memory performance, this double dissociation between alpha vs. theta and tonic vs. phasic changes can be observed only if fixed frequency bands are abandoned. It is suggested to adjust the frequency windows of alpha and theta for each subject by using individual alpha frequency as an anchor point. Based on this procedure, a consistent interpretation of a variety of findings is made possible. As an example, in a similar way as brain volume does, upper alpha power increases (but theta power decreases) from early childhood to adulthood, whereas the opposite holds true for the late part of the lifespan. Alpha power is lowered and theta power enhanced in subjects with a variety of different neurological disorders. Furthermore, after sustained wakefulness and during the transition from waking to sleeping when the ability to respond to external stimuli ceases, upper alpha power decreases, whereas theta increases. Event-related changes indicate that the extent of upper alpha desynchronization is positively correlated with (semantic) long-term memory performance, whereas theta synchronization is positively correlated with the ability to encode new information. The reviewed findings are interpreted on the basis of brain oscillations. It is suggested that the encoding of new information is reflected by theta oscillations in hippocampo-cortical feedback loops, whereas search and retrieval processes in (semantic) long-term memory are reflected by upper alpha oscillations in thalamo-cortical feedback loops.

Alpha Rhythm↗

PubMed2001

Early visual changes in reflected light on non-stained brain sections after focal ischemia mirror the area of ischemic damage.

There is no reliable, simple method for delineation of ischemic regions at early time points after ischemia. We propose that at early times after stroke, ischemic regions can be visualized as a subtle change in reflected light directly in thaw-mounted, dried 20 microm brain sections. In 15 male Sprague-Dawley rats, anesthetized with isoflurane, middle cerebral artery transection and permanent bilateral common carotid artery occlusion was performed and brains were processed in five different ways. Areas of reflective change (RC) on non-stained sections were compared with areas on the adjacent sections delineated by microtubule associated protein 2 (MAP2) antibody, a reliable marker for early post-stroke, in five rats each at 1, 3, and 6 h after focal cerebral ischemia. A statistically significant correlation between ischemic areas (IA) measured on non-stained brain sections (IA(RC)) and adjacent sections immunostained (IM) with MAP2 Ab (IA(IM)) (IA(RC)=0.05+0.88.IA(IM); R2=0.8; n=15; P<0.01) and a small mean difference +/-2 S.D. (-0.9+/-6.0%) indicated that the area measured on non-stained sections reflects the IA measured on MAP2 -IM sections. At 1 and 3 h after ischemia, the ratio between ischemic regions measured on the non-stained sections and on the adjacent sections immunostained with MAP2 Ab were not different from 100% (97.6+/-1.7%, 100.9+/-6.0%). At 6 h post-stroke, the IA measured on the non-stained sections was larger than on the IM sections (109.8+/-2.7%, P<0.01, compared to 100% ratio). Our study demonstrated that this quick and simple method for detection of damaged brain permitted the use of brain tissue for other assays and could be very useful for neuroprotective evaluation and for directed micro-sampling of brain tissue at early times after ischemia.

Animals↗

PubMed2002

Measurement of absolute values of hemoglobin oxygenation in the brain of small rodents by near infrared reflection spectrophotometry.

Reflection near infrared spectroscopy (reNIRS) has been proposed as a novel technique for the measurement of absolute values of total hemoglobin (tHb), oxygenated hemoglobin (oxHb), hemoglobin saturation (SO2), and cytochrome aa3 oxidation status (oxCyt aa3) in living tissue. In this study, we evaluated reNIRS during physiological cerebral blood flow conditions in rats (n=6) and during the induction of global cerebral ischemia in gerbils (n=6). ReNIRS parameters were assessed over the exposed cerebral cortex and compared to regional cerebral blood flow (rCBF) data obtained by laser Doppler flowmetry. Under physiological conditions, reNIRS measurements reflected the large intra- and interindividual variability of oxHb and tHb in the brain. The absolute values obtained by reNIRS for tHb (6.3 +/- 1.7 mg/ml), oxHb (3.7 +/- 1.1 mg/ml), and SO2 (61 +/- 5%) matched expected values. In contrast, measurements of oxCyt aa3 were unstable and results unreliable. reNIRS reliably detected cerebral ischemia, verified by a reduction of rCBF to 11% of baseline. tHb dropped to 74 +/- 7% of baseline (P<0.001), reflecting ischemic microvascular vasoconstriction. oxHb and SO2 dropped to expected near-zero values (2 +/- 4 and 3 +/- 5% of baseline, respectively; P<0.001). We conclude that reNIRS provides reliable and reproducible absolute values for brain tissue tHb, oxHb, and SO2 in small rodents. Determination of physiological values requires measurements at multiple locations, while cerebral ischemia is reliably detected by continuous recordings at a single location.

Animals↗

PubMed1999

Predictive value of acoustic reflectometry (angle and reflectivity) and tympanometry.

OBJECTIVE: Tympanometry and acoustic reflectometry are suggested tools for confirmation of otoscopic diagnosis of secretory otitis media. The issues on sensitivity and specificity of both devices are contradictory. In this study, our purpose was to compare sensitivity and specificity of both devices and to look for whether it is possible to reach higher values by combining them. METHODS: This study included 150 normal ears and 150 ears with chronic effusion. In tympanometry, only B tracings were accepted as predictor of effusion. In acoustic reflectometry, reflectivity (cut point: 5) and curve angle with two cut-points (75 degrees and 90 degrees) were used. RESULTS: Acoustic reflectometry presented higher specificity by both reflectivity (cut point: 5) and by curve angle (cut point: 75 degrees) (99.33% by both) than tympanometry (92%) (chi2 analysis, P < 0.001). But, their sensitivities (65.33 and 78%) were lower than tympanometry (96%) (chi2 analysis, P < 0.001). With curve angle of 90 degrees, specificity of acoustic reflectometry decreased to 85.33%, sensitivity increasing to 97.33%, which was not different from tympanometry (chi2 analysis, P > 0.1). When data of curve angle and tympanometry were combined, specificity and sensitivity of the combined test were found to be 91.33 and 100%, respectively. CONCLUSIONS: (i) Acoustic reflectometry should not be proposed as a better device than tympanometry, because its test efficiency was not higher than tympanometry. (ii) The only advantage of AR (reflectivity > or = 5 and curve angle < or = 75 degrees) was its high specificity to effusion. In addition, higher curve angles than 90 degrees were found to be highly predictive for normal ears as much as tympanometry. But, predictivity of curve angle between 76 degrees and 90 degrees was low. (iii) When tympanograms and curve angle were combined, it was found that prediction of this combination for curve angles between 76 degrees and 90 degrees was perfect. (iv) We consider that both test devices provide complementary data to each other, which would be particularly important for screening studies and that they are good tools for confirmation of clinical impression, particularly for less experienced clinicians.

Acoustic Impedance Tests↗

PubMed2003

Computer simulation of the skin reflectance spectra.

The reflectance spectra of the human skin in visible and near-infrared (NIR) spectral region have been calculated using the Monte Carlo technique, and the specular and internal reflection on the medium surface is taken into account. Skin is represented as a complex inhomogeneous multi-layered highly scattering and absorbing medium. The model takes into account variations in spatial distribution of blood, index of blood oxygen saturation, volume fraction of water and chromophores content. The simulation of the skin tissues optical properties and skin reflectance spectra are discussed. Comparison of the results of simulation and in vivo experimental results are given.

Biophysical Phenomena↗

PubMed1987

Safety parameters for avoiding acute ocular damage from the reflected CO2 (10.6 microns) laser beam.

Reflections from instruments in the surgical field involving the CO2 laser beam present a serious ocular hazard. In addition to the use of plastic or glass protective eyewear, this hazard can be minimized by utilizing anodized instruments and recognizing the specific distances at which various reflections are no longer hazardous depending upon certain variables, including laser output wattage, emergent beam lengths, and surface characteristics of the reflecting instruments.

Acute Disease↗

PubMed1998

Facilitating reflection: from a sage on stage to a guide on the side.

Reflection as a teaching and learning method has been well-established in nursing education. In this study, the aim is to discover the educational concepts which could be used by teachers of nursing in order to facilitate reflection. Participant observation and interviews were used to collect data. The study concludes that (1) purposefulness, (2) activity, (3) collaboration, (4) critical thinking and (5) confrontation and support are all key concepts which should be used by teachers in the operationalization of reflection. These concepts can also be easily remembered as a mnemonic--'PACTS'. Facilitation is about forming a PACTS with students enabling them to assume responsibilities for their learning, taking centre stage and the teacher moving aside to function as a guide. The role of the teacher in facilitation is thus moving a sage on stage to a guide on the side.

Attitude of Health Personnel↗

PubMed2004

Exploring field vegetation reflectance as an indicator of soil contamination in river floodplains.

This study investigated the relation between vegetation reflectance and elevated concentrations of the metals Ni, Cd, Cu, Zn and Pb in river floodplain soils. High-resolution vegetation reflectance spectra in the visible to near-infrared (400-1350 nm) were obtained using a field radiometer. The relations were evaluated using simple linear regression in combination with two spectral vegetation indices: the Difference Vegetation Index (DVI) and the Red-Edge Position (REP). In addition, a multivariate regression approach using partial least squares (PLS) regression was adopted. The three methods achieved comparable results. The best R(2) values for the relation between metals concentrations and vegetation reflectance were obtained for grass vegetation and ranged from 0.50 to 0.73. Herbaceous species displayed a larger deviation from the established relationships, resulting in lower R(2) values and larger cross-validation errors. The results corroborate the potential of hyperspectral remote sensing to contribute to the survey of elevated metal concentrations in floodplain soils under grassland using the spectral response of the vegetation as an indicator. Additional constraints will, however, have to be taken into account, as results are resolution- and location-dependent.

Environmental Monitoring↗

PubMed2000

Jugular vein temperature reflects brain temperature during hypothermia.

PURPOSE: The neuroprotective properties of mild to moderate hypothermia are well recognized but may not be employed correctly because brain temperature cannot usually be measured directly. This study investigated the jugular vein as a more accessible site that accurately reflects the actual brain temperature during mild, induced hypothermia. METHODS: We selected ten mongrel dogs (mean weight 12 +/- 2 kg) and measured temperatures of the brain, jugular vein, cisterna magna, pulmonary artery and rectum during hypothermia, including cooling and rewarming. The brain temperature needle probe was inserted 2.0 cm into the parenchyma. A temperature probe was placed in the cisterna magna with an epidural needle. Swan-Ganz thermistor probes measured the jugular venous and pulmonary artery blood temperatures. RESULT: The brain temperature decreased from 37.5 +/- 0.3 to 33.0 +/- 0.3 degrees C over an average 150 +/- 45 min cooling period. Stable cool was maintained for 245 +/- 32 min, followed by 165 +/- 50 min for rewarming from 33.5 +/- 0.3 to 37.5 +/- 0.3 degrees C. Jugular, cisterna magna and pulmonary arterial blood (PAB), but not rectal temperature, were close to brain temperature during stable cool. The mean jugular and cisterna magna temperatures were near the brain temperature at 0.1 degrees C higher and 0.1 degrees C lower, respectively. No significant effects of hypothermia were noted on hemodynamics in any phase. CONCLUSION: Jugular vein temperature, along with cisterna magna and pulmonary artery blood and rectal temperature, reflected brain temperature during hypothermia. The jugular vein and cisterna magna sites more sensitively reflected brain temperature than other sites.

Animals↗

PubMed2001

The periodic structure of vowel sounds is reflected in human electromagnetic brain responses.

Periodicity, which is caused by the vibration of the vocal folds, is an inherent feature of vowel sounds. Whether this periodic structure is reflected in cerebral processing of vowels was addressed via the use of non-invasive brain research methods combined with advanced stimulus production methodology. We removed the contribution of the source of the periodic structure, the glottal excitation produced by the vocal folds, from vowel stimuli and found that electromagnetic responses generated in the auditory cortex reflect this removal. The N1(m) amplitude decreased even though the rest of the acoustical features of the stimuli were identical. Thus, we conclude that speech production mechanisms have significant effects on human brain dynamics as reflected by magnetoencephalography and electroencephalograph.

Acoustic Stimulation↗

PubMed2001

Compositional analysis based on electron holography and a chemically sensitive reflection.

A method for compositional analysis of low-dimensional heterostructures is presented. The suggested procedure is based on electron holography and the exploitation of the chemically sensitive (0 0 2) reflection. We apply an off-axis imaging condition with the (0 0 2) beam strongly excited and centered on the optic axis. The first side band of the hologram is centered using an "empty" reference hologram obtained for a hole of the specimen. From the centered side band we use the phase of the central (0 0 0) and the amplitude of the (0 0 2) reflections to evaluate the local composition and the local specimen thickness in an iterative and self-consistent way. Delocalization effects that lead to a shift of the spatial information of (0 0 0) and (0 0 2) reflections are taken into account. The application of the procedure is demonstrated with an AlAs/GaAs(0 0 1) superlattice with a period of 5 nm. The concentration profiles obtained are discussed in relation to segregation. The measured segregation efficiency is R = 0.51 +/- 0.02.

Journal Article↗

PubMed2003

Analysis of ecstasy tablets: comparison of reflectance and transmittance near infrared spectroscopy.

Calibration models for the quantitation of commonly used ecstasy substances have been developed using near infrared spectroscopy (NIR) in diffuse reflectance and in transmission mode by applying seized ecstasy tablets for model building and validation. The samples contained amphetamine, N-methyl-3,4-methylenedioxy-amphetamine (MDMA) and N-ethyl-3,4-methylenedioxy-amphetamine (MDE) in different concentrations. All tablets were analyzed using high performance liquid chromatography (HPLC) with diode array detection as reference method. We evaluated the performance of each NIR measurement method with regard to its ability to predict the content of each tablet with a low root mean square error of prediction (RMSEP). Best calibration models could be generated by using NIR measurement in transmittance mode with wavelength selection and 1/x-transformation of the raw data. The models build in reflectance mode showed higher RMSEPs using as data pretreatment, wavelength selection, 1/x-transformation and a second order Savitzky-Golay derivative with five point smoothing was applied to obtain the best models. To estimate the influence of inhomogeneities in the illegal tablets, a calibration of the destroyed, i.e. triturated samples was build and compared to the corresponding data of the whole tablets. The calibrations using these homogenized tablets showed lower RMSEPs. We can conclude that NIR analysis of ecstasy tablets in transmission mode is more suitable than measurement in diffuse reflectance to obtain quantification models for their active ingredients with regard to low errors of prediction. Inhomogeneities in the samples are equalized when measuring the tablets as powdered samples.

Amphetamines↗

PubMed1998

Assay of effervescent tablets by near-infrared spectroscopy in transmittance and reflectance mode: acetylsalicylic acid in mono and combination formulations.

Near-infrared spectroscopy (NIRS) was used to determine acetylsalicylic acid (ASA) in three different effervescent tablet formulations. The nominal ASA concentrations were 14.9% in the single substance formulation (ASA Mono), 17.4% in the combination with ascorbic acid (ASA + C) and 8.7% in the combination with paracetamol and ascorbic acid (ASA Combi). In each case the tablet matrix was composed of seven excipients typical of effervescent tablets. All three formulations were measured as intact tablets in diffuse transmittance and reflectance and as powdered tablets in diffuse reflectance. Calibration was carried out by partial least square (PLS) regression of second derivative spectra. High-performance liquid chromatography (HPLC) was used as the reference method. The relative standard errors of calibration (RSEC) achieved for the three NIR methods were between 1.20 and 2.01% for ASA Mono, between 1.91 and 2.21% for ASA + C and between 2.41 and 4.50% for ASA Combi. The results obtained in transmittance mode were comparable with those obtained in reflectance mode, which is normally used in NIRS. In the test sets of ASA Mono and ASA + C relative root mean square (RRMS) values between 2.21 and 3.13% were obtained. The three NIR methods applied are thus suitable for the quantitative determination of ASA in effervescent tablets and have the advantage over HPLC of being rapid and simply carried out with little sample preparation; they are nondestructive and do not require any environmentally harmful reagents.

Acetaminophen↗

PubMed1999

Discrimination of herbal medicines according to geographical origin with near infrared reflectance spectroscopy and pattern recognition techniques.

Herbal medicines have an important role in clinical therapy in Asian countries such as Korea, Japan, and China. The objective of this study is to develop a nondestructive and accurate analytical method to discriminate herbal medicines according to geographical origin. Even though they are the same species, their qualities are different by growing conditions such as climate and soil. Near infrared (NIR) reflectance spectroscopy and a pattern recognition technique were applied for discrimination of herbal medicines according to geographical origin (Korea and China). Astragali Radix (AR), Ganoderma, and Smilacis Rhizoma (SR) were examined. It is shown that the representative NIR reflectance spectra in each group are different according to geographical origin after second derivatization to enhance spectral features. Also, the NIR reflectance spectra of Chinese and Korean samples were differentiated using principal component (PC) score plots. To establish the discrimination rule, Mahalanobis distance and discriminant analysis with PLS2 were utilized.

Astragalus propinquus↗

PubMed1999

In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement.

OBJECTIVES: The purpose of this study was to target acoustically reflective liposomes to atherosclerotic plaques in vivo for ultrasound image enhancement. BACKGROUND: We have previously demonstrated the development of acoustically reflective liposomes that can be conjugated for site-specific acoustic enhancement. This study evaluates the ability of liposomes coupled to antibodies specific for different components of atherosclerotic plaques and thrombi to target and enhance ultrasonic images in vivo. METHODS: Liposomes were prepared with phospholipids and cholesterol using a dehydration/ rehydration method. Antibodies were thiolated for liposome conjugation with N-succinimidyl 3-(2-pyridyldithio) propionate resulting in a thioether linkage between the protein and the phospholipid. Liposomes were conjugated to antifibrinogen or anti-intercellular adhesion molecule-1 (anti-ICAM-1). In a Yucatan miniswine model, atherosclerosis was developed by crush injury of one carotid and one femoral artery and ingestion of a hypercholesterolemic diet. After full plaque development the arteries were imaged (20-MHz intravascular ultrasound catheter and 7.5-MHz transvascular linear probe) after injection of saline, unconjugated liposomes and antibody conjugated liposomes. RESULTS: Conjugated liposomes retained their acoustically reflective properties and provided ultrasonic image enhancement of their targeted structures. Liposomes conjugated to antifibrinogen attached to thrombi and fibrous portions of the atheroma, whereas liposomes conjugated to anti-ICAM-1 attached to early atheroma. CONCLUSIONS: Our data demonstrate that this novel acoustic agent can provide varying targeting with different antibodies with retention of intravascular and transvascular acoustic properties.

Animals↗

PubMed1999

Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus.

OBJECTIVES: We sought to determine whether a simple index of pressure wave reflection may be derived from the digital volume pulse (DVP) and used to examine endothelium-dependent vasodilation in patients with type II diabetes mellitus. BACKGROUND: The DVP exhibits a characteristic notch or inflection point that can be expressed as percent maximal DVP amplitude (IP(DVP)). Nitrates lower IP(DVP), possibly by reducing pressure wave reflection. Response of IP(DVP) to endothelium-dependent vasodilators may provide a measure of endothelial function. METHODS: The DVP was recorded by photoplethysmography. Albuterol (salbutamol) and glyceryl trinitrate (GTN) were administered locally by brachial artery infusion or systemically. Aortic pulse wave transit time from the root of the subclavian artery to aortic bifurcation (T(Ao)) was measured by simultaneous Doppler velocimetry. RESULTS: Brachial artery infusion of drugs producing a greater than threefold increase in forearm blood flow within the infused limb was without effect on IP(DVP), whereas systemic administration of albuterol and GTN produced dose-dependent reductions in IP(DVP). The time between the first and second peak of the DVP correlated with T(Ao) (r = 0.75, n = 20, p < 0.0001). The effects of albuterol but not GTN on IP(DVP) were attenuated by N(G)-monomethyl-L-arginine. The IP(DVP) response to albuterol (400 microg by inhalation) was blunted in patients with type II diabetes mellitus as compared with control subjects (fall 5.9 +/- 1.8% vs. 11.8 +/- 1.8%, n = 20, p < 0.02), but that to GTN (500 microg sublingually) was preserved (fall 18.3 +/- 1.2% vs. 18.6 +/- 1.9%, p = 0.88). CONCLUSIONS: The IP(DVP) is influenced by pressure wave reflection. The effects of albuterol on IP(DVP) are mediated in part through the nitric oxide pathway and are impaired in patients with type II diabetes.

Adrenergic beta-2 Receptor Agonists↗

PubMed1996

Antihypertensive therapy and wave reflections.

Studies of pulsatile arterial hemodynamics have emphasized that the pulsatile component of pulse pressure has two important characteristics: (i) it increases from central to peripheral arteries for a similar value of mean arterial pressure, and (ii) it is dominantly influenced by the amplitude and timing of the backward pressure wave. Although these important aspects of wave reflections have been poorly investigated in the field of hypertension, they may be easily studied noninvasively in humans on the basis of the analysis of the pulse wave contour of carotid and aortic blood pressure. Increased wave reflections returning toward the thoracic aorta during systole may have deleterious consequences on the structure and function of the heart. Some (but not all) antihypertensive drugs may contribute to decrease and/or to delay wave reflections in association with blood pressure reduction.

Angiotensin-Converting Enzyme Inhibitors↗