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PubMed1991

Arterial compliance and wave reflection.

Left ventricular "afterload" is the wall stress developed during systole by the ejecting ventricle. For any given ventricular conformation, this is given by the time course of pressure change in the left ventricle during ejection, and is approximated by the pressure measured in the ascending aorta. For a given flow ejection from the left ventricle, pressure generated in the ascending aorta is determined by the ascending aortic impedance. Impedance in turn is dependent on three properties of the systemic circulation--resistance, compliance and wave reflection. In conventional studies of left ventricular load and hypertension, attention is usually focussed entirely on peripheral resistance. Recent studies have shown a poor relationship between left ventricular mass and peripheral resistance, but a better relationship with compliance and indices of wave reflection. Hence compliance (or its inverse, aortic stiffness) and wave reflection must be considered in evaluating hypertension (especially "systolic hypertension") and the effects of drugs on ventricular load. Under ideal circumstances, as seen in youth, aortic compliance is high and wave reflection late, with the consequence that aortic systolic pressure is low and pressure is boosted throughout early diastole. With progressive aortic degeneration as seen with aging and in hypertension, systolic pressure in increased both directly by decreased compliance, and indirectly by early return of wave reflection. The effect of early wave reflection is not apparent from recordings of brachial systolic or diastolic pressure, but can be inferred from indirectly recorded carotid pressure, or from contour of the peripheral pressure wave.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteries↗

PubMed1990

Reflection confocal laser scanning microscopy of eyespots in flagellated green algae.

The reflection properties of different types of eyespots in three unicellular, flagellated green algae (Tetraselmis chui, Chlamydomonas eugametos, Hafniomonas reticulata) were investigated using confocal laser scanning microscopy in the epireflection mode. The eyespots differed with respect to the number of eyespot lipid globule layers and surface appearance (concave/convex). A strong reflection signal was observed in all eyespots, and a detailed quantitative analysis by optical xy (horizontal) and xz (vertical) sectioning was performed. By applying both sectioning capabilities, multi- and single/double-layered eyespots as well as concave and convex eyespot surfaces could be distinguished using living, immobilized cells. Focusing of the reflected light was only observed in eyespots with concave surfaces. In xz series of multi-layered eyespots at reduced laser intensities (0.01%), the intensity profiles of the reflection revealed a series of alternating maxima and minima with increasing reflection intensities toward the cell surface. At very low laser intensities (0.001%), multi-layered eyespots exhibited about twice the reflection intensity at the presumptive photoreceptor site compared to single/double-layered eyespots. Our results provide the first experimental evidence to support the proposal that multi-layered eyespots act as interference reflectors in photoaxis of green algae.

Chlorophyta↗

PubMed1990

Spectral reflectance of human skin in vivo.

A newly developed skin reflectance spectrophotometer was evaluated for measurements of both melanin pigmentation and erythema. Physiological changes in blood flow and blood content in normal humans were induced by compression with an arm cuff during recording of skin reflectance spectra. Reflectance spectra of UV-induced erythema were also recorded and compared with laser-Doppler flow measurements. Spectral reflectance measurements were found to be highly sensitive in determining minimal erythema, which was not clinically detectable. The measurements of erythema using reflectance spectroscopy and UV irradiation were very highly correlated (r = 0.996). It was possible to calculate the in vivo absorbance of oxygenized haemoglobin. The melanin pigmentation following UV irradiation was quantified by reflectance spectroscopy and correlates highly with the dose of UV irradiation (r = 0.995). Furthermore, regional variations in skin melanin and haemoglobin were analysed for fair Caucasian skin.

Adult↗

PubMedDate not supplied

Effect of intracellular unstirred layer on apparent reflection coefficient for urea in inner medullary collecting duct: a computer simulation.

In the vasopressin-stimulated inner medullary collecting duct (IMCD), urea is transported through a pathway which is distinct from a water channel. Therefore, no frictional interaction between urea and water should occur at the membrane level, and the reflection coefficient for urea must be close to unity. However, the presence of unstirred layers in the vicinity of membranes causes solute concentration polarization, leading to an underestimation of the reflection coefficient (apparent reflection coefficient). When the value is determined across the perfused renal tubular wall, the intracellular space also constitutes an unstirred layer. The profile of solute and water transport across the system consisting of two membranes and the interposed intracellular space was simulated by a computer to examine the effect of unstirred layer on the value of apparent reflection coefficient. The model demonstrated that the imposed osmotic gradient across the tubular epithelial is decreased at each membrane interface. Under conditions of minimal unstirred layers in the bathing fluid, the existence of the intracellular constraints to diffusion cause considerable underestimation of the reflection coefficient. The higher the membrane permeability of urea and the smaller the diffusion coefficient of urea in the intracellular space, the greater becomes the magnitude of the underestimation. Thus, the measured apparent reflection coefficient for urea may become significantly less than the estimated value, leading to a reduction of the effective transmural osmotic driving force.

Animals↗

PubMed1994

[Comparison of a reflectance sensor and a transmittance sensor for pulse oximetry].

We have investigated a new optical reflectance sensor for pulse oximetry in 70 patients under general anesthesia. The reflectance sensor was applied to the forehead, the dorsal manus, the inguinal region, and the anterior crus of the patients. We could obtain a reliable SpO2 value when the reflectance sensor was applied on both forehead and anterior crus. It was difficult to obtain a reliable SpO2 value with the reflectance sensor without using an additional attachment especially for children. We compared the SpO2 value using the reflectance sensor attached to the forehead, with the SpO2 value obtained by the transmittance sensor attached to a finger or an ear lobe, in 7 volunteers who held the breath as long as possible. When we attached the probes on both ear lobe and forehead, the response time was faster, but and the maximum changing value was much larger, compared with those on the finger. We could obtain a reliable and stable SpO2 value using the reflectance sensor, when it was placed on the appropriate site as the forehead or the anterior crus.

Adolescent↗

PubMed1994

[Computer-assisted measurement of ocular misalignment in infants and young children using the digital Purkinje reflection pattern procedure].

A digital image recording and processing system is presented that allows a quick diagnosis of microstrabismus in non-cooperative children. It is thus particularly suited for screening purposes. METHOD: The Purkinje Reflection Pattern Evaluation (RPE) method is used: three small flashes are used to produce the desired Purkinje images. Two horizontal rows of the three 1st Purkinje images (anterior corneal reflections) and of the three 4th Purkinje images (posterior crystalline lens reflections) stemming from the three light sources form the characteristic Purkinje image reflection pattern. Each eye's position is calculated from the shift between the upper and lower rows of reflections by means of two simple formulae. From the angles obtained in binocular fixation and monocular fixation the manifest angle of strabismus corresponding to the angle measured in the simultaneous prism-and-cover test is computed. The measurement is performed at a fixation distance of 50 cm under natural viewing conditions. To obtain a picture one only has to get the child's attention for a short moment. The primary position is triggered with the fixation light, which is operated by a switch. APPARATUS: The digital image recording is done with a hand-held device comprising two miniaturized video cameras, three photo flashes and a fixation light that is operated manually. An IBM-compatible PC equipped with a hard disk and two frame grabbers was adapted for the storage and processing of the pictures. The pictures are evaluated interactively in a few minutes on the workstation's monitor immediately after the measurement. To this end specially designed menu-driven software was implemented. RESULTS: Examples of the measuring procedure and clinical results in infants with microtropic highlight the potential of the system as a screening apparatus and for the exact measurement of small and large squint angles. Usually even 1-year-old children can cooperate well enough to get good-quality pictures in binocular fixation. The new digital system allows easy and rapid application of the Purkinje Reflection Pattern Evaluation method since the time-consuming photographic film processing and evaluation are no longer necessary. For the first time small angles of strabismus under 5 degrees (10 PD) can be measured with a precision of less than 1 degree (2 PD) under clinical conditions in non-cooperative children.

Adult↗

PubMed1994

Hippocampal reflected optical patterns during sleep and waking states in the freely behaving cat.

We examined reflected light as a measure of neural activity from a 2 mm2 area of dorsal hippocampus and surrounding neocortex in nine freely behaving cats during sleep and waking states. Light reflectance at 660 or 700 nm was measured by a coherent fiber optic probe attached to a charge-coupled device video camera that allowed acquisition of images from subcortical structures. In the dorsal hippocampus, rapid eye movement sleep (REMS) and active waking (AW) resulted in a significant decline (-0.9% +/- 0.3 and -2.0% +/- 0.5, respectively) in overall reflected light from the dorsal hippocampus relative to quiet sleep (QS), while quiet waking (QW) resulted in an overall increase (+2.0% +/- 0.4). In the neocortical probe placement group, reflectance also decreased during AW (-1.6% +/- 0.5) and increased during QW (+1.7 +/- 0.6) as compared to QS. In contrast to the hippocampus, however, overall reflectance increased, rather than decreased, in the neocortex during REMS (+2.7% +/- 1.3). We interpret a decline in reflectance as representing increased activation of underlying neural tissue. Thus, the cat dorsal hippocampus increased overall activity during REMS as compared to QS, while neocortical structures decreased overall activity during the same state. These results concur with expected activity changes based on electrophysiologic and autoradiographic studies. The imaging procedure provided a continuous assessment of spatially organized neural activity changes in the freely behaving animal.

Animals↗

PubMed1998

Microtubule contribution to the reflectance of the retinal nerve fiber layer.

PURPOSE: The reflectance of the retinal nerve fiber layer (RNFL) arises from cylindrical light scattering elements distributed throughout its thickness. To determine whether these elements include axonal microtubules, eyecup preparations of the toad Bufo marinus were treated with the microtubule depolymerizing agent colchicine. METHODS: Some eyecups were incubated for various times in different colchicine concentrations and then fixed and prepared for electron microscopy (EM). In other eyecups the reflectance of the RNFL at 440 nm was measured by means of imaging microreflectometry. After a period of baseline measurements, the bathing solution was changed either to one of identical composition (control experiments) or to one containing 10 mM colchicine. Measurements then continued for 2 to 3 hours. RESULTS: Quantitative EM showed that colchicine caused the density of axonal microtubules to decrease by approximately one third in 2 hours. Reflectometry showed, in control experiments, that the RNFL reflectance remained near baseline for the duration of an experiment. In contrast, after changing to colchicine solution, the RNFL reflectance declined to a level 37% to 55% below baseline. CONCLUSIONS: Microtubules made a major contribution to the 440-nm reflectance of the unmyelinated axons of the toad RNFL and could make a similar contribution to the reflectance of human RNFL.

Animals↗

PubMed1997

Permanent and transient changes in the reflectance of CO2 laser-irradiated dental hard tissues at lambda = 9.3, 9.6, 10.3, and 10.6 microns and at fluences of 1-20 J/cm2.

BACKGROUND AND OBJECTIVE: Effective use of lasers for preventive dental treatments requires accurate knowledge of the amount and distribution of laser energy deposited during irradiation. At CO2 wavelengths, the reflection losses are considerable and reduce the laser energy absorbed by the tissue surface. STUDY DESIGN/MATERIALS AND METHODS: The specular and diffuse reflectance of enamel and dentin were measured at the 10.6-, 10.3-, 9.6-, and 9.3-microns wavelengths of the CO2 laser. Changes in reflectance during and after laser irradiation were investigated. RESULTS: The low-fluence reflectance (< 1 J/cm2) of calcified dental tissues at CO2 wavelengths varies between 9% and 50%. Permanent and transient changes in the reflectance are induced at higher irradiation intensities. CONCLUSION: These changes resulted in increased energy coupling during irradiation.

Animals↗

PubMed2001

Reflectance spectroscopy for in vivo characterization of ovarian tissue.

BACKGROUND AND OBJECTIVE: To explore whether reflectance spectroscopy can differentiate normal ovary, benign neoplasms, and ovarian cancer. STUDY DESIGN/MATERIALS AND METHODS: Reflectance spectra (390-600 nm) were measured at three source-detector separations (SDS) in vivo at 64 sites in 16 patients undergoing oophorectomy. Parameters with largest statistical differences were identified. Based on these parameters algorithms were developed and evaluated. RESULTS: Promising parameters were the reflectance intensity from 540 to 580 nm (SDS, 1.1 mm), the slope of the reflectance spectrum from 490 to 520 nm (SDS, 1.1 mm), the slope from 510 to 530 nm (SDS, 2.1 mm), and the slope from 510 to 530 (SDS, 3 mm). Average sensitivity and specificity were 86 +/- 6% and 79 +/- 5% to separate normal ovary from benign neoplasms and cancers. Average sensitivity and specificity were 86 +/- 4% and 80 +/- 8% to separate ovarian cancers from benign neoplasms and normal ovary. CONCLUSION: Reflectance spectroscopy should be further investigated for ovarian cancer screening.

Algorithms↗

PubMed1981

Heritability and components of phenotypic expression in skin reflectance of Mestizos from the Peruvian lowlands.

Skin reflectance was measured on the inner arm and forehead of a sample of 209 Mestizos ranging in age from 2 to 64 years living in the town of Lamas in the Eastern peruvian Lowlands. The sample consisted of 43 father-son, 42 father-daughter, 62 mother-son, and 70 mother-daughter pairs. The sample also consisted of 57 brother-brother, 60 sister-sister and 139 brother-sister pairs. The reflectance measurements were made with a Photovolt Reflection Meter, model 670. Stepwise polynomial regression techniques were used to derive standardized residual values. Then using these residual values parent-offspring, sibling intraclass correlations and components of the phenotype expression of skin reflectance were calculated. The study indicates that 1) the parent-offspring and sibling correlation coefficients conformed with the theoretical correlations expected assuming polygenic inheritance; 2) the husband-wife correlations indicate a high degree of assortative mating for skin color, but despite this effect the parent-offspring and sibling correlation coefficients are lower that the values expected under the influence of autosomal genes; 3) estimates of heritability and components of phenotypic expression indicate that about 55% of the total variability in skin reflectance could be attributed to the influence of additive genetic factors; and 4) there is no evidence of X-linkage in the inheritance of skin color.

Adolescent↗

PubMed2006

Fine structural dependence of ultraviolet reflections in the King Penguin beak horn.

The visual perception of many birds extends into the near-ultraviolet (UV) spectrum and ultraviolet is used by some to communicate. The beak horn of the King Penguin (Aptenodytes patagonicus) intensely reflects in the ultraviolet and this appears to be implicated in partner choice. In a preliminary study, we recently demonstrated that this ultraviolet reflectance has a structural basis, resulting from crystal-like photonic structures, capable of reflecting in the near-UV. The present study attempted to define the origin of the photonic elements that produce the UV reflectance and to better understand how the UV signal is optimized by their fine structure. Using light and electron microscopic analysis combined with new spectrophotometric data, we describe here in detail the fine structure of the entire King Penguin beak horn in addition to that of its photonic crystals. The data obtained reveal a one-dimensional structural periodicity within this tissue and demonstrate a direct relationship between its fine structure and its function. In addition, they suggest how the photonic structures are produced and how they are stabilized. The measured lattice dimensions of the photonic crystals, together with morphological data on its composition, permit predictions of the wavelength of reflected light. These correlate well with experimentally observed values. The way the UV signal is optimized by the fine structure of the beak tissue is discussed with regard to its putative biological role.

Animal Communication↗

PubMed1988

Reflection high resolution analytical electron microscopy: a technique for studying crystal surfaces.

Reflection electron microscopy (REM), reflection high energy electron diffraction (RHEED), reflection electron energy-loss spectroscopy (REELS), and energy dispersion x-ray spectroscopy (EDX) have been comprehensively used as a technique, termed reflection high resolution analytical electron microscopy (RHRAEM), for studying the structures of the bulk crystal GaAs (110) surfaces by transmission electron microscopy (TEM). The simultaneous observations of surface topography imaging, the surface diffraction mechanism with RHEED, surface atomic inner-shell excitations with REELS, and surface chemical compositions with EDX provide a systematic description of the atomic structure and chemical structure of the surface. The surface channelling effect has been observed in GaAs (110) with REELS, which may provide a basis for localizing surface foreign atoms with ALCHEMI. The theoretically predicted surface-resonance wave has been observed directly in the RHEED pattern; the surface-captured Bragg reflection wave have been identified. It is shown that surface chemical compositions can be determined by analyzing the EDX spectra obtained in the REM case. Finally, the surface monolayer resonance characteristic of the RHRAEM has been confirmed by calculations with dynamical RHEED theory.

Arsenic↗

PubMed1989

Reflectance during pulsed holmium laser irradiation of tissue.

Although generally ignored in considerations of laser ablation of tissue, reflectance of laser light from tissue during laser-induced ablation is a potentially important factor in determining ablation efficiency because it determines the amount of laser light coupled into the target. To determine the significance of reflectance changes induced by laser irradiation, we examined the reflectance of liver samples during pulsed holmium laser ablation by placing the target at one focus of an ellipsoidal reflector and a detector at the other focus. The temporal behavior, total reflectance, and effect of multiple pulses were examined. Tissue reflectance as large as 50% was observed during holmium laser irradiation but depended upon laser radiant exposure and number of laser pulses. These measurements suggest that changes in the optical properties of the target during ablation are important and should be considered in detailed modeling of the ablation process.

Animals↗

PubMed2006

A novel approach to age determination of traumatic injuries by reflectance spectroscopy.

BACKGROUND AND OBJECTIVES: Aging of injuries on a victim's body is an important aspect of forensic medicine. Currently, visual assessment and colorimetry based on empirical criteria are the most common techniques for this task, although the results are uncertain. A trauma causing localized vessel damage will rapidly result in a pool of blood in subcutaneous tissues. The color of the bruise is, however, primarily due to hemoglobin transport into dermis and secondarily to its breakdown products. This transport is analyzed in terms of hemoglobin diffusion followed by clearance by macrophage activity, lymphatic flow, and conversion to breakdown products such as bilirubin. The color of a bruise is caused by hemoglobin and hemoglobin breakdown products. The color will change with time, and such color changes can be recorded using reflectance spectroscopy. The aim of this study was to develop a mathematical model to describe blood diffusion within bruised skin, and to use this method to retrieve the age of a bruise from measured skin reflectance. STUDY DESIGN/MATERIALS AND METHODS: An analytic model was established to describe the development and fading of bruise color. The model, which is based on Darcy's law of convection flow and Fick's law of diffusion, describes the distribution of blood and hemoglobin breakdown products within a hematoma as a function of time after injury. The initial phase after injury is described by a convective extravascular blood flow in subcutaneous tissues, and further development of the bruise is described by diffusion and breakdown of whole erythrocytes and hemoglobin in dermis. Experimental data were used to verify the model. Reflection spectra in the 400-850 nm wavelength range were collected from normal and bruised skin using an integrating sphere setup. The subjects were adult patients admitted to the Department of cardiothoracic surgery, St. Olav's Hospital, Trondheim, Norway. The skin hematomas were caused by external trauma, cardiothoracic examinations, or surgery. RESULTS: Preliminary results show that measured and simulated skin reflectance agrees well. The model predicts the age of a hematoma with an accuracy of approximately 1 day. The accuracy of the method depends on precise information of skin thickness in the injured area. The quality of the estimates from the model will thus be enhanced if a reliable measure of skin thickness is collected concurrently with the reflection measurement. CONCLUSIONS: The time development of a skin hematoma is described with good accuracy by the implemented model. The analytic method provides a theoretical basis for developing an apparatus to determine the age of injuries in forensic medicine.

Adult↗

PubMedDate not supplied

Differential interference contrast and confocal reflectance imaging of collagen organization in three-dimensional matrices.

The remodeling of extracellular matrices by cells plays a defining role in developmental morphogenesis and wound healing as well as in tissue engineering. Three-dimensional (3-D) type I collagen matrices have been used extensively as an in vitro model for studying cell-induced matrix reorganization at the macroscopic level. However, few studies have directly assessed the process of 3-D extracellular matrix (ECM) remodeling at the cellular and subcellular level. In this study, we directly compare two imaging modalities for both quantitative and qualitative imaging of 3-D collagen organization in vitro: differential interference contrast (DIC) and confocal reflectance imaging. The results demonstrate that two-dimensional (2-D) DIC images allow visualization of the same population of collagen fibrils as observed in 2-D confocal reflectance images. Thus, DIC can be used for qualitative assessment of fibril organization, as well as tracking of fibril movement in sequential time-lapse 2-D images. However, we also found that quantitative techniques that can be applied to confocal reflectance images, such as Fourier transform analysis, give different results when applied to DIC images. Furthermore, common techniques used for 3-D visualization and reconstruction of confocal reflectance datasets are not generally applicable to DIC. Overall, obtaining a complete understanding of cell-matrix mechanical interactions will likely require a combination of both wide-field DIC imaging to study rapid changes in ECM deformation which can occur within minutes, and confocal reflectance imaging to assess more gradual changes in cell-induced compaction and alignment of ECM which occur over a longer time course.

Cell Line↗

PubMed1987

Estimation of tissue parameters derived from reflected ultrasound.

We propose a method of estimating two tissue parameters, that is, the reflection coefficient and attenuation coefficient from the reflected ultrasound for the purpose of improving the resolution of ultrasonic images and obtaining information on tissue characterization. The reflection coefficient is estimated by deconvolution technique using Kalman filter taking into account the distortion of the propagating pulse due to the frequency-dependent attenuation. The attenuation is estimated by adaptive processings based upon the criterion function calculated using estimates of the reflection coefficient. Simulated signals are used to investigate the ability of this method. Additionally, actual reflected signals from soft tissues are processed by the method. The results show that the method can be applied in clinical cases.

Animals↗

PubMed1988

Reflection contrast microscopy. Visualization of (peroxidase-generated) diaminobenzidine polymer products and its underlying optical phenomena.

Reflection contrast microscopy (RCM) has proven to be a useful tool for the study of living cells (Ploem 1975). Due to the effective suppression of aspecific reflected light by polarization optics combined with a quarter lambda plate at the front lens of the objective, low intensity reflection signals originating from minor amounts of precipitated diaminobenzidine (DABox) in immunocytochemically stained specimens, can be made visible. RCM has been successfully applied in demonstrating single copy nucleic acid sequences using in situ hybridization procedures (Landegent et al. 1984). We have systematically studied the aspects of image formation of DABox by RCM by using a model system consisting of glass slides coated with peroxidase containing protein layers to determine the conditions for optimal sensitivity of this detection method. Moreover, investigations were performed to study the relationship between the amount of reflected light and DABox depending on the thickness of the object. Both theoretical and practical evidence is obtained to show that DABox detection by RCM is based on interference phenomena occurring in the layer of DABox, and less on selective reflection. This restricts the type of specimen which can be used for sensitive detection of DABox by RCM. Consequently, in ultrathin (40 nm) sections osmificated DABox was visualized in peroxidatic positive cell organelles with high contrast and resolution. Similar results were obtained with immunoperoxidase stained material embedded in Lowicryl under conditions that did not allow visualization of the staining product by bright field microscopy.

3,3'-Diaminobenzidine↗