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PubMed1994

Use of arterial blood with bedside glucose reflectance meters in an intensive care unit: are they accurate?

OBJECTIVE: To compare blood glucose values obtained from two different sampling sites (arterial catheter and capillary from finger puncture), which were analyzed by a bedside reflectance meter. A sample was also analyzed by standard methods (oxygen electrode oxidation in the laboratory). DESIGN: Prospective, cross-sectional clinical study. SETTING: Cardiovascular intensive care unit (ICU) designed for postoperative open-heart surgery patients in a 1,100-bed medical center. PATIENTS: Sequential sample of 50 patients immediately after open-heart surgery. MEASUREMENTS AND MAIN RESULTS: The blood glucose concentration of each patient was analyzed on the patient's arrival to the ICU (immediately postoperatively) by three methods: one blood specimen was obtained from an arterial catheter, divided and analyzed either at the bedside by a reflectance meter (glucose method 1) or in the hospital laboratory (glucose method 2); another sample was obtained by lancing the fingertip and the glucose concentration was analyzed at the bedside in the same reflectance meter (glucose method 3). Using paired analyses to compare the mean glucose values of the bedside arterial whole blood sample (method 1) with the arterial serum sample (method 2) demonstrated that the glucose concentration in the arterial whole blood sample (method 1) was significantly (p < .001) higher. For 46 of 50 comparisons, the glucose value in the arterial whole blood sample (method 1) was higher, with a mean difference of 30 mg/dL (1.7 mmol/L). Although the mean difference was reduced to 10 mg/dL (0.6 mmol/L) when the arterial whole blood sample (method 1) was corrected for the hematocrit (i.e., < 35% [< 0.35]), the mean glucose concentration in the arterial whole blood samples (method 1) remained statistically higher (p < .05). The glucose concentration in the arterial serum sample (method 2) was significantly higher than the value determined from the bedside capillary sample (method 3) before (p < .05) and after (p < .001) correction for hematocrit. The difference in mean glucose concentrations between the arterial serum sample (method 2) and bedside capillary sample (method 3) was 9 mg/dL (0.5 mmol/L) when the capillary specimen (method 3) was not corrected for hematocrit. This difference increased to 21 mg/dL (1.2 mmol/L) when low hematocrit values were considered and appropriate adjustments of the glucose values were made. At the bedside, one can accurately correct arterial whole blood glucose values to correspond to laboratory values by the following formula: (0.94 x arterial whole blood glucose) + (4.6 x hematocrit) + (-16.5 x [37 degrees C--patient's temperature])--132 = laboratory glucose value. CONCLUSIONS: Since arterial whole blood samples give higher glucose results than arterial serum, the use of arterial whole blood in combination with reflectance meters must be recommended with caution. This caution is especially advised if the glucose values obtained with arterial whole blood are used in conjunction with a sliding scale of insulin, which depends on threshold concentrations of glucose. In our hospital, use of arterial whole blood in combination with reflectance meters could have resulted in an incorrect dose of insulin in 31 of 50 patients.

Adult↗

PubMed2001

Estimating the acoustic reflex threshold from wideband measures of reflectance, admittance, and power.

OBJECTIVE: A method was developed to estimate the contralateral acoustic reflex threshold using shifts in wideband energy reflectance, admittance magnitude and power. DESIGN: In the first experiment contralateral reflex thresholds for a noise activator were estimated on three adult participants using reflectance, admittance and power measurements at frequencies from 250 to 8000 Hz. The reflex threshold was defined using a magnitude and a correlation technique, both having the property of examining the pattern of the reflex-induced shift across a fairly broad frequency range (250 to 2000 Hz). In the second experiment, the magnitude method was modified to include an F test for the comparison of the magnitude of reflex-induced shifts in reflectance, admittance and power relative to response differences in a no-activator baseline condition. Data from four additional participants then were analyzed across a broader frequency range using a method that combined magnitude and correlation methods of estimating reflex thresholds. RESULTS: Acoustic reflex thresholds were obtained using reflectance, admittance and power-level measures in all subjects in both experiments. Individual reflex threshold estimates were as much as 24 dB lower than with the clinical system, with an average of approximately 14 dB lower for the three participants in the first experiment, and approximately 18 dB lower for the four participants in the second experiment. CONCLUSIONS: Wideband measures of reflectance, admittance and power were successfully used to estimate acoustic reflex thresholds in seven participants. A reflex threshold test was devised based on the magnitude of the response shift in the presence of a contralateral activator, and the similarity of the response shift spectra across frequency between successive activator levels. Across all participants in the study, the new test yielded a more sensitive measure of the acoustic reflex threshold than the clinical method. This finding has both clinical and theoretical implications for the study of the acoustic reflex.

Acoustic Impedance Tests↗

PubMed2001

Gender differences in the timing of arterial wave reflection beyond differences in body height.

OBJECTIVES: The timing of arterial wave reflection affects the shape of the arterial waveform and thus is a major determinant of pulse pressure. This study assessed differences in wave reflection between genders beyond the effect of body height. METHODS: From 1123 elderly (aged 71 +/- 5 years) currently untreated hypertensives, we selected 104 pairs of men and women with identical body height (average 164 +/- 4 cm). All subjects underwent echocardiography, including measurement of aortic arch expansion, automated blood pressure measurements, measurement of ascending aortic blood flow and simultaneous carotid artery tonometry. RESULTS: Women had higher pulse (80 +/- 17 versus 74 +/- 17 mmHg, P < 0.05) and lower diastolic pressure (79 +/- 11 versus 82 +/- 10 mmHg, P < 0.05). Whilst heart rate was similar, women had a longer time to the systolic peak (210 +/- 28 versus 199 +/- 34 ms, P < 0.01) and a longer ejection time (304 +/- 21 versus 299 +/- 25 ms, P < 0.001). Wave reflection occurred earlier in women (time between maxima 116 +/- 55 versus 132 +/- 47 ms, P < 0.05) and augmentation index was higher (36 +/- 11 versus 28 +/- 12%, P < 0.001). Aortic diameter was smaller in women and the aortic arch was stiffer (median Ep 386 versus 302 kN/m2, P < 0.05). Hence, systemic arterial compliance was less in women (0.8 +/- 0.2 versus 1.0 +/- 0.3 ml/mmHg). CONCLUSIONS: We conclude that elderly hypertensive men and women have a different timing of both left ventricular ejection and arterial wave reflection when both genders are matched for body height. Women have smaller and stiffer blood vessels resulting in an earlier return of the reflected wave, which is likely due to an increased pulse wave velocity in women.

Aged↗

PubMed2003

Effect of caffeine on aortic elastic properties and wave reflection.

OBJECTIVE: Caffeine is the most widely used pharmacologically active substance. Aortic elastic properties and arterial wave reflection are important factors for the efficient performance of the cardiovascular system, as well as prognosticators of cardiovascular risk. We investigated the effect of caffeine on aortic elastic properties and wave reflection. DESIGN: We studied the effect of caffeine (250 mg) in 20 healthy subjects according to a randomized, placebo-controlled, double-blind, cross-over design. METHODS: Aortic stiffness was evaluated with carotid-femoral pulse wave velocity and wave reflection with augmentation index of the aortic pressure waveform. RESULTS: Pulse wave velocity increased (by 0.51 m/s, 0.001) denoting an increase in aortic stiffness. Augmentation index and augmented pressure increased (by 6.8%, and by 4.4 mmHg, respectively, P <0.001 for both) denoting increased wave reflections. Concurrently, both radial and aortic systolic, diastolic and pulse pressure increased significantly. However, this increase was 20 and 9% larger for aortic systolic pressure (at 30 and 60 min, P <0.001 and P <0.05, respectively) and 56% larger for aortic pulse pressure (at 30 min, P <0.001) compared with the corresponding upper limb values. This indicates that peripheral pressure measurements are not an accurate guide for the pressor effect of caffeine in central arteries. CONCLUSIONS: Caffeine affects unfavorably aortic stiffness and enhances wave reflections. This finding has implications for the impact of caffeine consumption on cardiovascular risk.

Adult↗

PubMed2004

Abnormal oral mucosal light reflectance in infantile hypertrophic pyloric stenosis.

OBJECTIVES: Infantile hypertrophic pyloric stenosis (IHPS) is the most common condition requiring surgical intervention during the first weeks of life. The etiology of IHPS is unknown, although both neuronal nitric oxide synthase upregulation and an extracellular matrix abnormality are suspected. Familial predisposition is an important feature. Phenotypical markers of IHPS, such as hypoplasia or agenesis of the inferior labial frenulum, have been described. The authors tested the hypothesis that IHPS is associated with abnormal reflectance of the oral mucosa. METHODS: Twenty-five children with surgically confirmed IHPS and 25 gender- and age-matched control subjects participated in the study. Reflectance of the lower gingival and vestibular oral mucosa in the optical spectrum was measured using an imaging spectrophotometer. RESULTS: Patients with IHPS had significantly higher light reflectance values in the violet, blue, blue-green, green, yellow, and orange sections of the spectrum (all P values < 0.0001), with a maximum distance between group means at the 450-nm wavelength (t-value: 27.66, df = 48). A reflectance cutoff >5.26% at the 450-nm wavelength identified patients with IHPS with 100% sensitivity and 100% specificity. CONCLUSIONS: This study reports a previously unrecognized mucosal reflectance abnormality of the oral mucosa in IHPS, thus offering a new, accurate, and noninvasive phenotypic marker for the condition.

Adult↗

PubMed2005

Recent findings in the use of reflectance oximetry: a critical review.

PURPOSE OF REVIEW: Pulse oximetry is ubiquitous but detailed understanding of the technology is poor. This is illustrated by publications addressing knowledge of pulse oximetry and those warning against the use of transmission pulse oximeter sensors in a reflectance manner, unintended by the manufacturers, owing to the potential for iatrogenic problems. Reflectance oximetry sensors are distinct and their application rather specific. Users must adhere to the manufacturer's guidelines to be assured of approximating the claimed accuracy and other specifications. Moreover, a thorough understanding of the device's shortcomings will optimize performance and avoid misuse. Cautious skepticism is appropriate with use of any technology but particularly with indirect measures of vital signs. RECENT FINDINGS: The studies of reflectance sensors described here illustrate a diversity of successful applications and opportunities for further research. The genesis of applications for some sensors, for example fetal sensors, has proven helpful in other clinical settings where low mean arterial pressure and need for accurate monitoring of a SpO2 of less than 80% is poorly provided by transmittance sensors. Reflectance sensors are more prone to placement over contaminating sources (for example arteries and pigmentation), but their more sophisticated design can provide greater versatility than transillumination methods. SUMMARY: This invited review highlights recent developments and applications of reflectance oximetry with an emphasis on the potential clinical and research advantages.

Journal Article↗

PubMedDate not supplied

Acute mental stress has a prolonged unfavorable effect on arterial stiffness and wave reflections.

OBJECTIVE: Large-artery stiffness and arterial wave reflections have been identified as independent markers and prognosticators of cardiovascular risk. Mental stress is a novel risk factor for coronary artery disease and has been associated with left ventricular dysfunction, myocardial ischemia and infarction, and sudden cardiac death. The purpose of this study was to assess the effect of acute mental stress on aortic stiffness and wave reflections. METHODS: The effect of a mental arithmetic test was assessed in 19 healthy individuals using a randomized, sham-procedure-controlled, crossover design. Carotid-femoral pulse wave velocity and augmentation index were measured as indices of aortic stiffness and wave reflections, respectively. RESULTS: Mental stress induced a sustained increase in central systolic and pulse pressure throughout the whole study (systolic: by 7.5 mm Hg, p < .05; pulse: by 5.7 mm Hg, p < .01). The increase in peripheral systolic and pulse pressure was not significant throughout the study, but only when their peak values were compared with baseline (systolic: by 6.2 mm Hg, peak at 0 minutes; pulse: by 6.6 mm Hg, peak at 5 minutes, p < .05 for both). There was a sustained increase in pulse wave velocity (by 0.57 m/s, p < .005) throughout the study denoting a sustained increase in aortic stiffness. Similarly, augmentation index showed a sustained increase with mental stress (by 6.16%, p < .05) denoting increased wave reflections from the periphery. CONCLUSION: Acute mental stress results in a prolonged increase in aortic stiffness and wave reflections. Given the important pathophysiologic and prognostic role of these parameters, our results provide important mechanistic links between acute mental stress and increased cardiovascular risk.

Adult↗

PubMed2006

Ultraviolet reflectance by the cere of raptors.

Ultraviolet (UV) signals have been shown to play key roles in social and sexual signalling in birds. Using a spectrophotometer, we analysed the colour of the cere (skin above the beak) of a diurnal raptor, the Montagu's harrier (Circus pygargus), and show that it reflects in the UV part of the spectrum. The cere is a well-known sexual signal in raptors, with carotenoid based pigmentation being indicative of quality. We thus hypothesized that UV reflectance also signals quality. Accordingly, we found that in our sample of wild males, the location of the UV peak was related to the orangeness of cere and correlated with male body mass and condition (mass corrected for size). Also, males with brighter UV were mated to females that laid earlier, as expected if UV reflectance relates to a male's quality and attractiveness. Future studies should investigate the relationships between UV reflectance and carotenoid pigmentation of cere, and test how UV reflectance influences mate choice.

Animals↗

PubMed2006

Why do red and dark-coloured cars lure aquatic insects? The attraction of water insects to car paintwork explained by reflection-polarization signals.

We reveal here the visual ecological reasons for the phenomenon that aquatic insects often land on red, black and dark-coloured cars. Monitoring the numbers of aquatic beetles and bugs attracted to shiny black, white, red and yellow horizontal plastic sheets, we found that red and black reflectors are equally highly attractive to water insects, while yellow and white reflectors are unattractive. The reflection-polarization patterns of black, white, red and yellow cars were measured in the red, green and blue parts of the spectrum. In the blue and green, the degree of linear polarization p of light reflected from red and black cars is high and the direction of polarization of light reflected from red and black car roofs, bonnets and boots is nearly horizontal. Thus, the horizontal surfaces of red and black cars are highly attractive to red-blind polarotactic water insects. The p of light reflected from the horizontal surfaces of yellow and white cars is low and its direction of polarization is usually not horizontal. Consequently, yellow and white cars are unattractive to polarotactic water insects. The visual deception of aquatic insects by cars can be explained solely by the reflection-polarizational characteristics of the car paintwork.

Animals↗

PubMed2006

Dark nests and egg colour in birds: a possible functional role of ultraviolet reflectance in egg detectability.

Owing to the conspicuousness of ultraviolet (UV) colour in dark environments, natural selection might have selected UV egg coloration because it would enhance egg detectability by parents in murky nests. Here, we tested this hypothesis by using comparative and experimental approaches. First, we studied variation in egg coloration of 98 species of European passerines measured using UV-visible reflectance spectrometry (300-700nm) in relation to nesting habits. Analyses based on raw data and controlling for phylogenetic distances both at the species and the family levels revealed that hole-nester species produced eggs with higher UV reflectance than those nesting in open habitats. The experimental approach consisted of the manipulation of UV reflectance of the experimental eggs introduced outside the nest-cup of the hole-nester spotless starling Sturnus unicolor and the study of the retrieval of these eggs. Ultraviolet-reflecting eggs (controls) were more frequently retrieved to the nest-cup than non-reflecting (-UV) eggs. These results were not due to '-UV' eggs being recognized by starlings as parasitic because when a parasitic egg is detected, starlings removed it from the nest-box. Therefore, these results are consistent with the hypothesis that UV egg colours are designed to provide highly detectable targets for parent birds in dark nest environments.

Animals↗

PubMed2001

Frustrated total reflection: the double-prism revisited.

Geometrical optics prohibits any penetration of light into an optically rarer medium in the case of total reflection. When sandwiching, however, the rarer medium between optically denser media, a transmitted beam can be observed in the third medium. The experiment is often realized by a double-prism arrangement [1]; the effect is called frustrated total reflection due to the enforced transmission. Amazingly, the reflected and transmitted beams are shifted with respect to geometrical optics as conjectured by Newton [2] and experimentally confirmed by Goos-Hänchen 250 years later [3]. However, inconsistent results on the spatial shifts have been reported [4-7]. Here we report on measurements of the Goos-Hänchen shift in frustrated total reflection with microwaves. We found an unexpected influence of the beamwidth and angle of incidence on the shift. Our results are not in agreement with both previous experiments [6,7] and theoretical predictions [8-10]. The topic of frustrated total reflection is important for both fundamental research and applications [11-13].

Journal Article↗

PubMed2004

Quantum reflection times for attractive potential tails.

When a wave packet with a narrow momentum distribution is quantum reflected in a purely attractive potential proportional to -1/r(alpha), alpha>2, it generally experiences a time gain compared to a free particle reflected at r=0; for alpha=3 and very low energies there are large time delays. In quantum reflection of an atomic beam by a surface, such a time gain (delay) represents an apparent plane of reflection which is shifted in front of (behind) the surface. The quantum reflected wave is always delayed with respect to the classical particle accelerated in the attractive potential.

Journal Article↗

PubMed2004

Quantum reflection from a solid surface at normal incidence.

We observed quantum reflection of ultracold atoms from the attractive potential of a solid surface. Extremely dilute Bose-Einstein condensates of 23Na, with peak density 10(11)-10(12) atoms/cm(3), confined in a weak gravitomagnetic trap were normally incident on a silicon surface. Reflection probabilities of up to 20% were observed for incident velocities of 1-8 mm/s. The velocity dependence agrees qualitatively with the prediction for quantum reflection from the attractive Casimir-Polder potential. Atoms confined in a harmonic trap divided in half by a solid surface exhibited extended lifetime due to quantum reflection from the surface, implying a reflection probability above 50%.

Journal Article↗

PubMed2005

Anomalous quantum reflection of Bose-Einstein condensates from a silicon surface: the role of dynamical excitations.

We investigate the effect of interatomic interactions on the quantum-mechanical reflection of Bose-Einstein condensates from regions of rapid potential variation. The reflection process depends critically on the density and incident velocity of the condensate. For low densities and high velocities, the atom cloud has almost the same form before and after reflection. Conversely, at high densities and low velocities, the reflection process generates solitons and vortex rings that fragment the condensate. We show that this fragmentation can explain the anomalously low reflection probabilities recently measured for low-velocity condensates incident on a silicon surface.

Journal Article↗

PubMed1991

Phytochrome-mediated detection of changes in reflected light.

Measurements of phytochrome photoequilibria and photoconversion rates in vivo, in seedlings of Cucurbita pepo L. exposed to light in growth chambers, indicate that significant changes in the state of phytochrome can be brought about by changes in the quality and quantity of the light reflected from the walls of the growth chambers. The changes in reflected light, although large, were small in terms of the total radiation (direct light from the lamps plus wall-reflected light) to which the seedlings were exposed. The conditions used were approximate simulations of direct and reflected sunlight conditions in the natural environment. Keeping in mind the limitations imposed by the approximation of the simulations, the results from this study are consistent with the hypothesis that, in the natural environment, a plant might be capable of detecting the presence of nearby plants, before being shaded by them, through the phytochrome-mediated perception of changes in reflected light.

Journal Article↗

PubMed2000

Resonant X-ray diffraction: 'forbidden' Bragg reflections induced by thermal vibrations and point defects

In general, the local atomic environment becomes less symmetric owing to point defects and thermal vibrations of atoms in crystals. It is shown that, as a result of this phenomenon, an additional anisotropy of the resonant scattering factors can occur and the forbidden Bragg reflections can be excited near absorption edges. Examples of crystals are presented (Ge, K2CrO4, C-15 type) where such thermal-motion-induced (TMI) and point-defect-induced (PDI) reflections can be observed. The tensor structure factors of both types of reflection are computed. Owing to their resonant character, the PDI reflections allow both impurity atoms and host atoms of different types to be studied separately. The considered phenomena can provide a very sensitive method to study point defects because only the atoms distorted by defects produce contributions to the PDI reflections.

Journal Article↗

PubMed2005

Polarization anisotropy of X-ray atomic factors and 'forbidden' resonant reflections.

Symmetry and physical aspects of 'forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of 'forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local ;chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed.

Anisotropy↗

PubMed1999

Estimating unobserved reflection intensities in Laue diffraction by the maximum-entropy method.

In protein crystallography, the use of low-resolution reflections is important in defining the molecular mask and polypeptide backbone. However, in Laue data collection, the loss of low-resolution reflection data (>2dmin) can be as high as 40-50%, even after the deconvolution of multiples. To estimate the reflection intensities that are not recorded in data collection, a new method is presented based on maximizing the entropy of the Patterson function subject to the constraints imposed by the intensities of the observed reflections. The method has been tested with Laue diffraction data from hen egg-white lysozyme. All unobserved reflections within 5 A resolution were estimated, and their inclusion in the electron-density-map calculation significantly improved the connectivity. This method could also be applied to improve the completeness of monochromatic data.

Animals↗