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Results for “reflection”

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At least 613 records · Page 34Linked to original sources

PubMed1996

Reflectance pulse oximetry in fetal lambs: subcutaneous vessels and vasoconstriction affect its reliability.

OBJECTIVE: Reflectance pulse oximetry (RPOX) has been introduced for intrapartum fetal surveillance. The purpose of this study was to describe two possible effects on the reliability of RPOX, namely the effect of the presence of a subcutaneous vein and the effect of vasoconstriction by adrenaline, both at fetal SaO2 levels. METHODS: In four anesthetized fetal lambs, a prototype 660/890 nm reflectance sensor (Nellcor Inc.) was placed on the fetal head, with the photodiode of the sensor precisely over a superficial subcutaneous vein. Measurements were made before and after coagulation of the vein. In five anesthetized fetal lambs, one or two reflectance sensors were placed on the fetal head and/or neck and adrenaline was administered in doses of 0.02 to 0.04 mg via a brachial artery. Pulse oximeter saturation readings (SpO2) were compared with continuous arterial oxygen saturation (SaO2) values obtained using a fiberoptic catheter (Opticath, Abbott) in the carotid artery. RESULTS: When the sensor was placed over the vein, the pulse oximeter read 18% to 24% too low at a SaO2 level of 20% to 50%. After coagulation of the vein, SpO2 readings were in agreement with fiberoptic SaO2 values. Administration of adrenaline resulted in a large overestimation of the SaO2 in 6 of the 7 measurements. CONCLUSIONS: Subcutaneous veins and vasoconstriction can affect the reliability of reflectance pulse oximetry. As comparable situations may occur during labor, SpO2 readings should be interpreted with caution when this kind or comparable types of RPOX sensors are used at low SaO2 levels.

Animals↗

PubMed1977

Reflection-impulsivity in normal and behavior-disordered children.

The primary index of reflection-impulsivity is Kagan's Matching Familiar Figures Test (MFF), which yields both a latency and an error score. To evaluate further the construct validity of these measures, both the latency and error scores of 9- and 15-year-old normal and "acting-out" behavior-disordered children were compared. Young behavior-disordered children were found to be more impulsive than the other groups on the MFF error measure. No differences occurred on the MFF latency measure. This result is consistent with previous findings with normal children in supporting the construct validity of the MFF error score and raising questions about the construct validity of the MFF latency score. Findings were inconsistent with Kagan's assertion that normal children become more reflective with age. The older behavior-disordered children were more reflective on the error measure than the younger behavior-disordered children and had equivalent error scores to both age groups of normals. This finding suggested a lag in the development of reflection in behavior-disordered children.

Adolescent↗

PubMed2003

Laser reflectance imaging of human forearms and their tissue-equivalent phantoms.

Laser back-scattered radiation from a human forearm is affected by the compositional variation in tissues and was imaged by a reflectance imaging system. The measurement probe consisted of one input fibre and one output fibre, separated by a distance of 0.3 cm. The diffuse reflectance data were collected by placing the probe on the forearm. By interpolation and median filtering of these data, the colour-coded reflectance images of the forearms of ten subjects were reconstructed. For comparative analysis of the mean reflectance, the forearm area was divided into ten regions. The mean normalised back-scattered intensity (NBI) near the ulnar region of the wrist was 4.76 +/- 0.24% and was significantly higher (p < 0.0005) compared with that at other regions, which varied from 3.49 +/- 0.17% to 4.43 +/- 0.14%. Tissue-equivalent phantoms of these, required for the clinical assessment of optical techniques, were constructed using various combinations of paraffin wax and dyes. The matching of the NBI images of these stable and inexpensive phantoms with those of the forearms of the respective subjects showed the similarity of their optical parameters.

Adult↗

PubMed2004

Autofluorescence and diffuse reflectance properties of malignant and benign breast tissues.

BACKGROUND: Fluorescence spectroscopy is an evolving technology that can rapidly differentiate between benign and malignant tissues. These differences are thought to be due to endogenous fluorophores, including nicotinamide adenine dinucleotide, flavin adenine dinucleotide, and tryptophan, and absorbers such as beta-carotene and hemoglobin. We hypothesized that a statistically significant difference would be demonstrated between benign and malignant breast tissues on the basis of their unique fluorescence and reflectance properties. METHODS: Optical measurements were performed on 56 samples of tumor or benign breast tissue. Autofluorescence spectra were measured at excitation wavelengths ranging from 300 to 460 nm, and diffuse reflectance was measured between 300 and 600 nm. Principal component analysis to dimensionally reduce the spectral data and a Wilcoxon ranked sum test were used to determine which wavelengths showed statistically significant differences. A support vector machine algorithm compared classification results with the histological diagnosis (gold standard). RESULTS: Several excitation wavelengths and diffuse reflectance spectra showed significant differences between tumor and benign tissues. By using the support vector machine algorithm to incorporate relevant spectral differences, a sensitivity of 70.0% and specificity of 91.7% were achieved. CONCLUSIONS: A statistically significant difference was demonstrated in the diffuse reflectance and fluorescence emission spectra of benign and malignant breast tissue. These differences could be exploited in the development of adjuncts to diagnostic and surgical procedures.

Algorithms↗

PubMed2003

Assessment of complex movements reflects dysfunction in Huntington's disease.

Results of various complex instrumental tools, rating scales, caudate atrophy and CAG repeat length may reflect the severity of Huntington's disease (HD). A simple assessment task for dysfunction due to disease is the standardized, computer based performance of peg insertion. The objectives of our study were to compare scored HD symptoms, computed bicaudate diameter ratio (BDR), age related genetic disease load (CAG index = [CAG-35.5 x age]) and peg insertion scores between asymptomatic 34 HD gene carriers, 89 previously untreated HD patients with psychiatric or motor symptoms, or both, and 51 treated HD patients. We measured the period of the total time taken to insert 25 pegs from a rack into a series of appropriate holes, calculated the CAG index, estimated the bicaudate diameter ratio (BDR) of a current brain CT and scored the HD patients under blind conditions. Times for the peg insertion task significantly differed between HD patients and controls, but not between HD gene carriers and controls. BDR and CAG index reflected the increase of symptoms in HD. Peg insertion results and scored severity of HD, BDR and CAG index significantly correlated with each other. Peg insertion scores are not specific diagnostic markers for HD, but they reflect clinical symptoms of neurodegeneration. The performance of peg insertion involves visuospatial cognition, self-elaboration of internal strategies, sorting and planning of movement. Therefore peg insertion particularly reflects executive dysfunction in early HD and additionally motor impairment in advanced HD.

Adult↗

PubMed2004

Correlation study of scanning acoustic microscope reflection coefficients and image brightness intensities of micrographed osteons.

Scanning acoustic microscopy (SAM) of Haversian bone at high frequency clearly shows differences in the brightness (gray) levels of individual osteons, which were observed to correspond to the differences in reflection coefficients measured with the SAM technique: the darker the bony regions on the SAM micrographs, the lower the SAM reflection coefficient values, and vice versa. We studied the correlation between differences in brightness and the related reflection coefficients of osteons on undecalcified transverse sections of goat tibial diaphysis using a 400-MHz burst mode lens on the Olympus UH3 SAM. Results showed that there was a strong linear correlation between brightness intensities and the corresponding reflection coefficients, with a correlation coefficient r = 0.99 ( P << 0.001) using gray level 210 as cutoff. This result suggested that the image brightness intensity of osteonic bone could be measured retrospectively to provide information on the stiffness of the corresponding bone matrix.

Acoustics↗

PubMed2006

Understanding the influence of emotions and reflection upon multi-source feedback acceptance and use.

INTRODUCTION: Receiving negative performance feedback can elicit negative emotional reactions which can interfere with feedback acceptance and use. This study investigated emotional responses of family physicians' participating in a multi-source feedback (MSF) program, sources of these emotions, and their influence upon feedback acceptance and use. METHODS: The authors interviewed 28 volunteer family physician participants in a pilot study of MSF, purposefully recruited to represent the range of scores. The study was conducted in 2003-2004 at Dalhousie University. RESULTS: Participants' emotional reactions to feedback appeared to be elicited in response to an internal comparison of their feedback with self-perceptions of performance. Those agreeing with their feedback; i.e., perceiving it as generally consistent with or higher than self-perceptions responded positively, while those disagreeing with their feedback; i.e., seeing it as generally inconsistent with or lower than self-perceptions, generally responded with distress. For the latter group, these feelings were often strong and long-lasting. Some eventually accepted their feedback and used it for change following a long period of reflection. Others did not and described an equally long reflective period but one which focused on and questioned MSF procedures rather than addressed feedback use. Participants suggested providing facilitated reflection on feedback to enhance assimilation of troubling emotions and interpretation and use of feedback. CONCLUSIONS: Negative feedback can evoke negative feelings and interfere with its acceptance. To overcome this, helpful interventions may include raising awareness of the influence of emotions, assisting recipients to focus their feedback on performance tasks, and providing facilitated reflection on feedback.

Education, Medical, Continuing↗

PubMed2004

The pulse in reflectance pulse oximetry: modeling and experimental studies.

OBJECTIVE: Reflectance pulse oximetry permits the use of alternative monitoring sites such as the face or torso, and is the approach commonly employed in fetal pulse oximetry systems. The purpose of this study is to investigate the impact of assumptions about the nature of arterial pulsatility on the calibration of such systems. METHODS: Monte Carlo simulations of reflectance pulse oximetry were run on a six-layer tissue model, varying depth and magnitude of the arterial pulse. SpO2 readings on and off the femoral artery obtained during desaturation studies in newborn piglets were compared to predictions. Results. Monte Carlo simulation results clarified the difference between deep and shallow pulsatility found with photon diffusion models, agreeing with earlier in vivo observations. Significant overestimation of SpO2 <75% and slight underestimation >75% is expected if a sensor is placed on a highly pulsatile site. The on- and off-artery SpO2 readings recorded during desaturation in the newborn piglet follow the model predictions. CONCLUSIONS: The sensitivity of reflectance pulse oximetry calibration to the depth and magnitude of arterial pulsatility reinforces the observation that monitoring site selection is of importance in optimizing reflectance pulse oximetry performance, particularly fetal pulse oximetry. Sites with palpable pulsatility should be avoided.

Animals↗

PubMed1991

Effect of pregnancy on the accuracy of light-reflection rheography.

Light-reflection rheography is a noninvasive method to detect venous obstruction by indirectly measuring venous emptying time. In nonpregnant women it has greater than 90% sensitivity when compared with venography but has not been tested during gestation. To determine if the nonthrombotic occlusion of venous outflow by the pregnant uterus might alter the performance of light-reflection rheography, we examined 17 normal patients with a vascular Accuscan (Hemodynamics, Inc., Boca Raton, Fla.) in the third trimester of pregnancy and 11 patients during the early second trimester. These results were compared with the defined normal (nonpregnant) rate of venous emptying (slope 0.54 +/- 0.06). The mean (+/- SD) for the entire sample was 0.58 +/- 0.23 mm/sec in the right leg and 0.52 +/- 0.19 mm/sec in the left leg measured in the standard sitting position (p = 0.21). The results did not vary with gestational age. A subset of patients in late pregnancy were used to compare the effect of various positions (supine, lateral decubitus, and sitting) on test performance. Positions other than sitting provided results that were inconsistent. It appears that the large pregnant uterus does not significantly obstruct venous outflow from the lower extremities in the standard sitting position; thus the results of light-reflection rheography are not affected. Comparison of light-reflection rheography versus venography in pregnant patients with suspected venous thrombosis is being investigated.

Female↗

PubMed1975

Sodium chloride reflection coefficient in rabbit gall bladder.

By means of the Kedem-Katchalsky thermodynamic description of active transport, a relationship has been derived between the apparent reflection coefficient and the Staverman reflection coefficient for passive transport of a solute which is both actively and passively transported. The relationship between volumetric flow and its driving forces, containing the Staverman reflection coefficient, was tested for sodium chloride in rabbit gall bladder and the reflection coefficient was evaluated.

Animals↗

PubMed1987

Determination of reflection coefficients of liposomes for some non-electrolytes by osmotic pressure measurement.

The reflection coefficients of bilayer lipid vesicles (liposomes) of various compositions have been determined for a number of non-electrolytes. The solutes were the same and the method of measurement was essentially the same as those which have been used to estimate an equivalent pore radius for erythrocytes. The method involves matching the osmotic pressure of solutions of a permeant test solute with that of a known inpermeant solute. Reflection coefficients for cholesterol-containing liposomes and those of erythrocytes are, when account is taken of those solutes known to permeate the erythrocyte by specialized pathways, not greatly different. Lipid bilayers can thus account for most of the permeability characteristics of the cell originally interpreted as due to aqueous pores. Reflection coefficients are significantly higher for egg phosphatidylcholine membranes that contain cholesterol than those which do not. There is a strong correlation between relative permeabilities derived from reflection coefficients and oil-water partition coefficients. There is also good agreement between these permeabilities and permeabilities measured by others, which exhibit an inverse dependence on molecular size. It is suggested that this tendency of membranes to pass small molecules more readily than large molecules, other properties being equal, is a consequence of the surface pressure of the constituent monolayers of the membrane.

Diffusion↗

PubMed1996

An examination of the use of reflection in the assessment of practice for undergraduate nursing students.

Reflection-on-practice by second year undergraduate nursing students was examined both during clinical placements and soon after. Students identified incidents which had occurred during their practice and discussed them with the researcher individually, in pairs and in a larger group. Data relating to both students' and the researcher's perceptions of these sessions were collected by questionnaire and from diary entries. It was concluded that the purpose of reflection as part of the assessment of practice needs to be clearly defined. Helping students to develop reflective skills is different to assessing their skills and the level of reflection demonstrated.

Clinical Competence↗

PubMed1994

A comparison of reflection and transmission ultrasonic techniques for measurement of cancellous bone elasticity.

A reflection ultrasonic technique, which offers several advantages over transmission ultrasonic techniques, has been described for elastic property measurement of bone. Ultrasonic velocities from specimens of cancellous bone were compared using a reflection ultrasound technique and the more traditional transmission ultrasonic technique. The two techniques were found to yield velocities which were reasonably well correlated (r2 = 0.74). However, a statistical difference was found between the line of identity and the regression between transmission and reflection velocities (due to an offset in the intercept). In spite of differences in intercept between velocities measured by the two techniques, significant correlation was found between the two methods, suggesting that the reflection technique can measure wave velocities meaningful to bone elasticity.

Animals↗

PubMed1986

Spectral reflectance of the human eye.

Spectral reflectance of the eye was assessed in four young Caucasian subjects with the Utrecht densitometer. Three retinal locations were studied, the fovea, the optic disk and a spot 12 deg temporal on the horizontal meridian. Reflectance was measured with the visual pigments bleached away. The measuring field subtended 2.5 deg. The reflectance factor, relative to an artificial eye with a focal distance of 21.3 mm, was found to be lowest in the blue (0.1% for 419 nm) and highest in the red (10% for 711 nm). A model with six parameters, four densities of (non-photolabile) ocular pigments and two reflectance factors, was proposed to explain the experimental findings. A good fit to the data was obtained and the calculated densities of the ocular pigments came close to data found in the literature.

Adult↗

PubMed1996

Vibrational spectrometry for the assessment of active substance in metoprolol tablets: a comparison between transmission and diffuse reflectance near-infrared spectrometry.

Near-infrared spectrometry (NIR) was used to quantify metroprolol succinate in controlled release tablets. Metoprolol tablets were made according to an experimental design using different strengths around a central strength of 47.5 mg per tablet. A comparison was made between NIR in the diffuse reflectance mode and the transmission mode. This showed that, although a narrower wavelength range was available in the transmission mode, predictions were much better for models based on transmission spectra than for models based on diffuse reflectance spectra. The main reason for this is that in the reflectance mode NIR spectrometry is very sensitive to the inhomogeneity of the material, while in the transmission mode this problem is less severe. This is due to the larger volume of the material scanned in the transmission mode compared to that in diffuse reflectance. Spectra were taken before and after the tablets were stored under humid conditions. This allowed the final calibration models to be made more robust towards variations in the amount of water in the tablet. Different batches of metoprolol pellets and microcrystalline cellulose were used during the production of the tablets. this resulted in models that were more robust towards possible batch-to-batch differences in the main constituents.

Drug Storage↗

PubMed2005

Red wine acutely induces favorable effects on wave reflections and central pressures in coronary artery disease patients.

BACKGROUND: To investigate red wine's acute effects on aortic pressures and arterial stiffness in patients with coronary artery disease (CAD). METHODS: Fifteen patients with CAD were recruited in a double-blind, cross-over study, which was comprised of 2 study days. Each volunteer consumed either 250 mL of regular or 250 mL of dealcoholized red wine. Wave reflections, expressed as augmentation index (AIx), as well as central and peripheral blood pressures (BP) were assessed at fast and 30, 60, and 90 min postprandially. RESULTS: Both regular and dealcoholized red wine caused a significant decrease in AIx by 10.5% +/- 1.4% (P = .001) and 6.1% +/- 1.4% (P = .011), respectively, whereas no significant change was induced in mean BP and timing of wave reflections expressing pulse wave velocity. Peripheral systolic BPs remained unaltered in both beverages, whereas a significant decrease in peripheral and central diastolic BPs was observed after the dealcoholized red wine consumption (P = .03 and P = .035, respectively). Central systolic BP was decreased after the consumption of regular (-7.4 +/- 2.4 mm Hg, P = .05) and dealcoholized red wine (-5.4 +/- 2.7 mm Hg, P = .019). CONCLUSIONS: Both types of red wine provoked favorable acute effects on wave reflections and central systolic pressures, whereas no such effect was evident at the brachial artery. Therefore, these findings could be attributed mainly to red wine antioxidant substances, rendering it a possible means of at least acute attenuation of increased wave reflections, arterial stiffness, and central pressures in patients with coronary artery disease.

Adult↗

PubMed2006

Circadian variation of arterial pressure wave reflections.

BACKGROUND: Various factors are implicated in the circadian pattern of cardiovascular vulnerability. The exact mechanisms involved in the peak incidence of cardiovascular events occurring during the early morning hours after awaking are not completely known. The purpose of our study was to investigate the circadian variation of timing and intensity of wave reflections in healthy individuals and to test the hypothesis that significant changes occur during the day. METHODS: Thirteen healthy non-smokers (seven women and six men, mean age 40.7 +/- 16.5 years) were examined. Aortic pulse wave analysis was performed to estimate surrogates of wave reflections intensity (augmentation index [AIx]) and timing. Twelve measurements separated by 1-h intervals were performed from 8 am to 7 pm each study day. RESULTS: Analysis of variance for repeated measures indicated significant changes during the 12-h period for heart rate corrected AIx (P = .033) and heart rate (P = .035). The AIx was maximal at 8 am within 1-h after awaking (17% +/- 3.6%); it was gradually diminished until 3 pm (9% +/- 4.1%) and again increased to a second (albeit lower) peak value during the late afternoon (7 pm). CONCLUSIONS: It is possible that the increased intensity of reflected waves occurring during the early morning in combination with the rising trend of blood pressure and heart rate at the same time results in an aggravated left ventricular afterload and an increase in myocardial oxygen demand. The morning-related enhancement of wave reflections may have potential implications for the increased risk for cardiovascular events during the early morning, which remains to be clarified.

Adult↗

PubMed2004

Lipoprotein lipase (LPL) mass in preheparin serum reflects insulin sensitivity.

Lipoprotein lipase (LPL) is one of the enzymes regulated by insulin and its plasma activity reflects insulin sensitivity. Although intravenous heparin injection is required to measure LPL activity, we can detect LPL mass in preheparin serum (Pr-LPL mass) by immunoassay. In this study, we examined whether Pr-LPL mass reflects insulin sensitivity. We measured Pr-LPL mass, insulin sensitivity (Si), and acute insulin release in response to a glucose bolus (AIRg) in subjects with normal glucose tolerance (NGT; n = 23), impaired glucose tolerance (IGT; n = 10), and Type II diabetes mellitus (DM; n = 48). Si and AIRg were determined by minimal model analysis. We also compared Pr-LPL mass with the homeostasis model assessment of insulin resistance (HOMA-R) and the urinary excretion of C-peptide (urine CPR). We found that Pr-LPL mass correlated significantly with Si ( r = 0.354, P < 0.01) in all the subjects. This correlation was still significant in the NGT group (P < 0.472, P < 0.05), DM group (r = 0.311, P < 0.01), and DM group with a fasting plasma glucose >150 mg/dl ( n = 20, r = 0.459. P < 0.05). Moreover, Pr-LPL mass correlated negatively with HOMA-R (r = -0.272. P < 0.05) and fasting IRI (r = -0.256, P < 0.05). By contrast, Pr-LPL mass was not correlated with either urine CPR or logAIRg that reflect the ability to secrete insulin. In conclusion, Pr-LPL mass reflects insulin sensitivity. We speculate that Pr-LPL mass might be used to assess insulin sensitivity not only in the general population but also in advanced diabetic patients.

Adult↗