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PubMed2002

Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate.

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is a critical parameter that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate. The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient, and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes five times larger than those of the well-known quartz NSPUDT orientation (Euler angles: 0 degrees 132.75 degrees 25 degrees) can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter- and higher-bandwidth devices due to: the increased electromechanical coupling coefficient; the higher reflection coefficient; and the lower phase velocities; while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low-loss, high-performance consumer and communications SAW designs, such as NSPUDT filters, resonator-based filters, and other devices that can benefit from a high metal strip reflectivity.

Journal Article↗

PubMed2002

The low frequency reflection characteristics of the fundamental antisymmetric Lamb wave a0 from a rectangular notch in a plate.

An analysis of the reflection of the fundamental Lamb mode a0 from surface-breaking rectangular notches in isotropic plates is presented. The results are obtained from finite element time domain simulations together with experimental measurements. Good agreement is found between the simulations and the measurements. Results are shown for a range of notch widths and depths, including the special case of a crack, defined as a zero-width notch. The reflection coefficient, when plotted as a function of the notch width, exhibits a cosinusoidal periodic shape, and this is explained by interference between the separate reflections from the start and the end of the notch. The reflection coefficient, when plotted as a function of notch depth, shows that in general the reflection increases with both frequency and notch depth, but the shapes of the functions are complex and there are some surprising features. An analysis of the reflection from cracks using the S-parameter scattering approach and some simplified descriptions of the crack-opening behavior yields physical explanations of the nature of these reflection functions. It is found that opening of the crack can be described adequately by a quasistatic assumption only when the crack is small, and in other cases a ray theory approach is more representative. The reflection function is shown to be a result of contributions from both the axial stress and the shear stress in the wave, and the relative importance of these varies with the crack depth and the frequency.

Journal Article↗

PubMed1999

The influence of early reflections on the identification and lateralization of vowels.

Sound coming directly from a source is often accompanied by reflections arriving from different directions. However, the "precedence effect" occurs when listeners judge such a source's direction: information in the direct, first-arriving sound tends to govern the direction heard for the overall sound. This paper asks whether the spectral envelope of the direct sound has a similar, dominant influence on the spectral envelope perceived for the whole sound. A continuum between two vowels was produced and then a "two-part" filter distorted each step. The beginning of this filter's unit-sample response simulated a direct sound with no distortion of the spectral envelope. The second part simulated a reflection pattern that distorted the spectral envelope. The reflections' frequency response was designed to give the spectral envelope of one of the continuum's end-points to the other end-point. Listeners' identifications showed that the reflections in two-part filters had a substantial influence because sounds tended to be identified as the positive vowel of the reflection pattern. This effect was not reduced when the interaural delays of the reflections and the direct sound were substantially different. Also, when the reflections were caused to precede the direct sound, the effects were much the same. By contrast, in measurements of lateralization the precedence effect was obtained. Here, the lateral position of the whole sound was largely governed by the interaural delay of the direct sound, and was hardly affected by the interaural delay of the reflections.

Humans↗

PubMed1993

Repeated reflection of waves in the systemic arterial system.

Traditional analysis of pulse-wave propagation and reflection in the arterial system treats measured pressure and flow waves as the sum of a single forward wave (traveling away from the heart) and a single backward wave (traveling toward the heart). The purpose of this study was to develop a more general wave reflection theory that allows repeated reflection of these waves. The arterial system was modeled as a uniform viscoelastic tube terminating in a complex load with reflections occurring at the tube load interface and the heart tube interface. The resulting framework considers the forward wave to be the sum of an initial wave plus a series of antegrade waves. Similarly, the backward wave is the sum of a series of retrograde waves. This repeated reflection theory contains within it the traditional forward/backward wave reflection analysis as a special case. In addition, the individual antegrade and retrograde waves, at the tube entrance, are shown to be independent of the tube length. Aortic pressure and flow data, from dog experiments, were used to illustrate the phenomenon of repeated reflections. Alteration of the arterial system loading conditions, brought about through pharmacological intervention, affected the number and morphology of repeated waves. These results are compared with those found in traditional forward/backward reflection analysis.

Animals↗

PubMed1996

Method for determining distribution of reflection sites in the arterial system.

We developed a new method to determine the location and importance of reflection sites in the arterial system. The method is based on the decomposition of the aortic pressure wave into its forward and backward components, and it provides the reflection profile of the arterial system as a wave reflection site amplitude versus distance from the heart. The reflection profile can be seen as the response of the arterial system to a pressure delta pulse where reflections upstream from the measurement location have been eliminated. The method was successfully tested on a simple model loaded with a pure resistor, a two-element windkessel, and a bifurcating tube system. It was then applied to the aortic pressure and flow signals measured in six mongrel dogs whose aorta was occluded at different levels. The profiles obtained from measurements at control showed two main reflection regions, one located in the vicinity (0.1-0.2 m) of the heart and the other located in the region of the iliac bifurcation. All occlusions, even the most distant one at the iliac bifurcation, could be identified in both amplitude (amount of reflections) and distance from the heart. The spatial resolution of the profiles was approximately 0.1 m as a result of the limited power spectrum contained in the arterial pulse, and the identification of reflection sites decreased rapidly with the distance.

Animals↗

PubMed1992

Increased systolic pressure in chronic uremia. Role of arterial wave reflections.

To assess the role of arterial wave reflections in the mechanism of systolic hypertension and altered pulsatile arterial dynamics in patients with end-stage renal disease (ESRD), 79 ESRD patients were compared with 73 age-matched control subjects with normal renal function and similar mean blood pressure. Wave reflections were investigated from the carotid pulse contour recorded by applanation tonometry using a Millar micromanometer-tipped probe. Wave reflections were quantified as the ratio (augmentation index, %) of the height of the late systolic peak to the total height of carotid pulse wave. Travel time of the reflected wave was timed from the foot of the pressure wave to the foot of the late systolic peak. Systolic and pulse pressure were increased in ESRD patients (p less than 0.001) and was not attributable to differences in left ventricular ejection pattern. The augmentation index was increased in ESRD patients (23.2 +/- 15.0 versus 9.8 +/- 15.6%; p less than 0.001) in association with a shorter travel time of reflected wave (109 +/- 24 versus 131 +/- 30 msec; p less than 0.001). Multiple regression analysis showed two principal factors associated (p less than 0.001) with the increase in augmentation index and shortened travel time of reflected wave: increased aortic pulse wave velocity and smaller stature with shorter body height in ESRD patients. The study points to the role of arterial wave reflections in the mechanisms producing alterations in pulsatile arterial dynamics in ESRD and is the first, through the mechanisms of early wave reflections, to show in humans that the increase in systolic and pulse pressures is associated with lesser body size.

Adult↗

PubMed1982

Pulse wave reflection: can it explain the differences between systemic and pulmonary pressure and flow waves? A study in dogs.

We have studied the effect of changes in pulse wave reflection on the configurations of pressure and flow in systemic and pulmonary circulation. Electromagnetic flow transducers, atrial catheters, and pacing leads were implanted in 10 dogs. In four animals, the flow transducer was placed on the pulmonary artery, in another four on the ascending aorta, and in two additional dogs on both vessels. One week later, ascending aortic and/or pulmonary artery flow and pressure (catheter tip manometer) were measured under general anesthesia (Nembutal, 30 mg/kg, iv). When the pulmonary circulation was studied (six dogs), measurements were made before and during serotonin infusion (0.5-0.75 mg/min). When the systemic circulation was studied (six dogs), measurements were made before and during nitroprusside infusion (50-200 micrograms/min). To quantify the arterial load, we calculated pulmonary and systemic input impedances. To estimate the amount of reflection, we used a reflection index which we defined as the amplitude ratio of reflected and forward wave. Nitroprusside decreased total peripheral resistance, increased total arterial compliance, and decreased the reflection index; similarity between aortic pressure and flow wave shapes increased, and they looked more like their pulmonary counterparts. Serotonin increased pulmonary vascular resistance, decreased pulmonary arterial compliance, and increased the reflection index. Resemblance of pressure and flow waves decreased. The differences in wave shapes can thus be explained by the amount of reflection: the less reflection the more pressure and flow resemble each other.

Animals↗

PubMed1991

Two arterial effective reflecting sites may appear as one to the heart.

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase of mean aortic pressure. A broad range of aortic pressure amplitudes and features was obtained. These waveshapes were classified into four groups. Under basal conditions, cases for which a prominent diastolic fluctuation was present (n = 8) were grouped in A. Cases for which this fluctuation was absent (n = 2) were grouped in B. Groups C (n = 4) and D (n = 3) included cases that, under vasoconstricted conditions, did or did not display, respectively, a diastolic fluctuation in pressure. Arterial T-tube model parameters were estimated by simultaneously fitting the model to both ascending and descending aortic flow with aortic pressure as input. A good fit was obtained in any case considered. After parameter estimation, forward and reflected waves and impedance patterns at the entrance of head circulation (head and upper limbs) and body circulation (trunk and lower limbs) as well as their merger in the ascending aorta were determined. T-tube input impedance compared well with impedance data points obtained from the ratio of corresponding harmonics of ascending aortic pressure and flow. In some cases (group A), modulus and phase spectra displayed two distinct minima, in the range from 0 to 10 Hz. In some other circumstances, these minima were less distinct (groups B and C) and could even appear as one (group D). Whether one or two minima appeared in the ascending aortic impedance spectra at low frequency and whether a prominent diastolic fluctuation did or did not appear in aortic pressure, pressure and flow waveshapes proximal to the heart were explained by the presence of two effective reflecting sites in the systemic circulation. In group B, a diastolic fluctuation in pressure was absent despite the fact that head-end and body-end reflected waves were distinct. This happened because body-end reflected waves peaked corresponding to a minimum of the head-end reflected wave. In group D, a diastolic fluctuation in aortic pressure was absent because the body-end reflected wave moved into systole and superimposed on the head-end reflected wave. This superimposition was due to increased pulse wave velocity in the body transmission path as a result of decreased arterial distensibility.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

Narrow-waveband reflectance ratios for remote estimation of nitrogen status in cotton.

Tailoring nitrogen (N) fertilizer applications to cotton (Gossypium hirsutum L.) in response to leaf N status may optimize N use efficiency and reduce off-site effects of excessive fertilizer use. This study compared leaf and canopy reflectance within the 350 to 950 nm range in order to identify reflectance ratios sensitive to leaf chlorophyll (Chl), and hence N status, in cotton. Plants were grown outdoors in large pots using half-strength Hoagland's (control) solution until some three-row plots received a restricted supply of N. Treatments comprised control, 20% of control N at first flower bud (square) onward; 0 and 20% of control N at first flower onward; and 0% of control N at fruit-filling onward. Despite leaf N values ranging from 51 to 19 g kg-1 across treatments and sampling dates, a weak correlation was obtained between Chl and N (r2 = 0.32, df = 70). In general, N stress led to increased reflectance at 695 +/- 2.5 nm (R695) and decreased reflectance at R410, and changes in leaf N were best correlated with either R695 or R755 in leaves and either R410 or R700 in canopies. The strongest associations between leaf constituent and canopy reflectance ratio were Chl vs. R415/R695 (r2 = 0.72), carotenoids vs. R415/R685 (r2 = 0.79), and N vs. R415/R710 (r2 = 0.70). The R415 measure appears to be a more stable spectral feature under N stress, as compared with more pronounced changes along the reflectance red edge (690-730 nm). Multiple regression identified a three-waveband canopy reflectance model that explained 80% of the variability in leaf N. Results indicate that remote sensing of N status in cotton is feasible using narrow-waveband reflectance ratios that involve the violet or blue region of the spectrum (400 to 450 nm) and the more commonly featured red-edge region.

Chlorophyll↗

PubMed2000

A model for facilitation of critical reflective practice: Part I--Introductory discussion and explanation of the phases followed to construct the model.

The purpose of this inquiry was to construct a model for facilitation of critical reflective practice, based on thorough analysis of the main concepts (critical thinking and reflection), related viewpoints, models and theories; and the data gathered and analyzed during, the naturalistic inquiry. The constructed model evolved from empirical observations, intuitive insights of the inquirer and from deductions combining ideas from several fields of inquiry. The model for facilitation of critical reflective practice postualates that practitioners have the inherent potential to change from auto-pilot practice to critical reflective practice. The purpose of the model is the facilitation of heightened awareness of the self, to enable health care professionals to consciously meet community needs and expectations. The desired outcome is transformative intellectuals who will strive to empower others to become critical reflective learners and practitioners themselves. The process followed during the construction of the model and the constructed model will be discussed in three (3) articles, namely: A model for facilitation of critical reflective practice: Part I--Introductory discussion and explanation of the phases followed to construct the model. A model for facilitation of critical reflective practice: Part II--Conceptual analysis within the context of constructing the model. A model for facilitation of critical reflective practice: Part III--Description of the model.

Attitude of Health Personnel↗

PubMed2002

[Reflectivity of broad-leaved Korean pine forest in growing season on Changbai Mountain].

The hourly reflectivity of broad-leaved Korean pine forest on Changbai Mountain from 22 May to 14 October 2001 was calculated based on total solar radiation and reflect radiation. The results showed that: the reflectivity of the forest was related to solar altitude. It was generally high just after sunrise or before sunset, but was relatively stable as solar altitude was higher than 30 degrees. The diurnal curves of reflectivity took U shape. The reflectivity of the forest was also related to sky conditions. In clear days, the U shape was quite clear. In scattered days, the reflectivity just after sunrise and before sunset was not as high as in the clear days, and the U shaped curve was shallow. In overcast days, the reflectivity fluctuated. In terms of dynamic variation in the measured period, the reflectivity was relatively high in early June, decreased a little in late June, kept stable from July to September, and dropped gradually in the first half of October. The variation was related to the phenology of the forest canopy.

Acer↗

PubMed1988

Design and evaluation of a new reflectance pulse oximeter sensor.

The design and construction of a new optical reflectance sensor suitable for noninvasive monitoring of arterial hemoglobin oxygen saturation with a pulse oximeter is described. The reflectance sensor was interfaced to a Datascope ACCUSAT pulse oximeter that was specially adapted for this study to perform as a reflectance oximeter. We evaluated the reflectance sensor in a group of 10 healthy adult volunteers. SpO2 obtained from the forehead with the reflectance pulse oximeter and SpO2 obtained from a finger sensor that was connected to a standard ACCUSAT transmittance pulse oximeter were compared simultaneously to arterial blood samples analyzed by an IL 282 CO-Oximeter. The equation for the best fitted linear regression line between the reflectance SpO2 and HbO2 values obtained from the reference IL 282 CO-Oximeter in the range between 62 and 100% was: SpO2 (%) = 4.78 +/- 0.96 (IL); n = 110. The regression analysis revealed a high degree of correlation (r = 0.98) and a relatively small standard error of the estimate (SEE = 1.82%). The mean and standard deviations for the difference between the reflectance SpO2 and IL 282 measurements was 1.38 and 1.85%, respectively. This study demonstrates the ability to acquire accurate SpO2 from the forehead using a reflectance sensor and a pulse oximeter.

Adult↗

PubMed1986

A new method to study glutathione adduct formation in periportal and pericentral regions of the liver lobule by micro-reflectance spectrophotometry.

A method was developed to measure the formation of glutathione adducts of 1-chloro-2,4-dinitrobenzene (CDNB) and 2,4-dichloro-1-nitrobenzene (DCNB) in periportal and pericentral regions of the liver lobule in the isolated perfused rat liver by surface reflectance spectrophotometry. Conjugates of DCNB and CDNB are released from livers of normal and phenobarbital-treated rats during perfusion in either the anterograde or the retrograde direction at maximal rates around 13-15 mumol/g/hr. The formation of S-(1-chloro-4-nitrophenyl)-glutathione and S-(2,4-dinitrophenyl)-glutathione by the liver decreased the amount of 366-nm light reflected from the liver surface detected with a large-tipped (2 mm) fiberoptic light guide. Initial rates of decrease in reflected light correlated highly with maximal rates of conjugate formation by the liver. Subsequently, micro-light guides were placed on periportal and pericentral regions of the liver lobule. Rates of glutathione adduct formation were calculated from the proportion of the total change in rate of reflected 366-nm light which occurred in each region and the overall rate of product formation by the liver. Changes in the reflectance signal require reduced glutathione (GSH) and were shown to originate from intracellular conjugate formation and not from adducts in the bile canaliculus. Livers from normal rats produced conjugated products from DCNB (100 microM) at maximal rates of 14 and 15 mumol/g/hr in periportal and pericentral regions of the liver lobule, respectively. With CDNB as substrate, changes in reflected light at 366 nm were detected nearly exclusively in periportal regions of the lobule in livers from normal rats. In sharp contrast, CDNB and DCNB were conjugated exclusively in periportal regions of the lobule at rates of 21-22 mumol/g/hr in livers from phenobarbital-treated rats (i.e., the reflectance signal was not altered by these substrates in pericentral areas). When CDNB and DCNB were infused into livers from phenobarbital-treated rats perfused in the retrograde direction, decreases in reflected light at 366 nm were detected initially in pericentral areas followed in about 12 min by changes in periportal regions. Maximal rates of adduct formation in both regions reached 25 mumol/g/hr during perfusion in the retrograde direction. Thus, pericentral regions indeed possess the capacity to conjugate both CDNB and DCNB. When glutathione synthesis was inhibited with L-buthionine sulfoximine treatment (6 mmol/kg), which partially depletes GSH, CDNB was conjugated in both periportal and pericentral regions of the liver lobule in livers from phenobarbital-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Reflection and absorption of millimeter waves by thin absorbing films.

Reflection, transmission, and absorption of mm-waves by thin absorbing films were determined at two therapeutic frequencies: 42. 25 and 53.57 GHz. Thin filter strips saturated with distilled water or an alcohol-water solution were used as absorbing samples of different thicknesses. The dependence of the power reflection coefficient R(d) on film thickness (d) was not monotonic. R(d) passed through a pronounced maximum before reaching its steady-state level [R(infinity)]. Similarly, absorption, A(d), passed two maximums with one minimum between them, before reaching its steady-state level [A(infinity)]. At 42.25 GHz, A(d) was compared with absorption in a semi-infinite water medium at a depth d. When d < 0.3 mm, absorption by the film increased: at d = 0.1 mm the absorption ratio for the thin layer sample and the semi-infinite medium was 3.2, while at d = 0.05 mm it increased up to 5.8. Calculations based on Fresnel equations for flat thin layers adequately described the dependence of the reflection, transmission, and absorption on d and allowed the determination of the refractive index (n), dielectric constant (epsilon), and penetration depth (delta) of the absorbing medium for various frequencies. For water samples, epsilon was found to be 12.4-19.3j, delta = 0.49 mm at 42.25 GHz, and epsilon = 9.0-19.5j, delta = 0.36 mm at 53.57 GHz. The calculated power density distribution within the film was strongly dependent on d. The measurements and calculations have shown that the reflection and absorption of mm-waves by thin absorbing layers can significantly differ from the reflection and absorption in similar semi-infinite media. The difference in reflection, absorption, and power density distribution in films, as compared to semi-infinite media, are caused by multiple internal reflections from the film boundaries. That is why, when using thin phantoms and thin biological samples, the specifics of the interaction of mm-waves with thin films should be taken into account.

Absorption↗

PubMed1980

Skin reflectance relationships with temperature and skinfolds.

Skin reflectance measurements were taken with six filters at a site on the medial aspect of the upper arm (underarm) prior to and following topical application of a cold compress. Skinfolds were measured at the underarm and triceps sites. The experiment was designed to test for effects of skin surface temperature and subcutaneous fat variations on skin color as determined by reflectometry. Topical cold-induced erythema of the skin produced marked declines in % reflectance at the shorter visible wavelengths over the range of violet, blue, and green, and only slight declines in % reflectance at the longer visible wavelengths (red range). This is consistent with the observation from past work that there is little hemoglobin absorptance at the red end of the visible spectrum. A positive relationship between the change in % reflectance following topical cold application and underarm skinfold was recorded. Hence, the thickeness of fat deposits may contribute to variation in skin reflectance. Since only large temperature differences influenced skin reflectance measurements, the need is not great for fieldworkers to control for surface temperature at the underarm site during skin reflectance survey.

Adipose Tissue↗

PubMed1991

Measurement of mechanical properties of bone material in vitro by ultrasound reflection: methodology and comparison with ultrasound transmission.

An ultrasound reflection technique was designed and implemented to study the mechanical properties of bone material. The technique uses the fact that an ultrasound beam produced in water undergoes total internal reflection off a bone sample at a critical angle formally related to the velocity of a pressure wave in bone. When the plane of scattering is rotated around the normal to the sample surface, the critical angle varies with a periodic dependence dictated by the intrinsic symmetry of the bone structure at the point being examined. Most current measurements of sound velocity are made using transmission techniques. A double-blind intercomparison between this technique and a transmission technique, which was previously validated against tensile mechanical testing, was performed for samples of isotropic materials and of human cortical bone. Strong correlations were found for both sets of samples. For the isotropic materials the velocities were approximately equal, but for bone they were on average 11% higher in reflection than in transmission. This was the result both of the higher frequency employed in reflection (3.5 rather than 2.25 MHz) and of the different effects of sample imperfections on the two measurements. In particular, the reflection technique used in this work studied the surface of the sample, but the ultrasound beam in the transmission method propagated through its interior. In assessing the mechanical properties of bone specimens by ultrasound, the reflection technique samples a discrete bone surface element and the transmission method analyzes the entire volume of the specimen. Thus the reflection technique may yield a measure of the mechanical property of bone trabeculae that is largely unaffected by the mass of the entire specimen, but mass and the structural density of the specimen affect the transmission method.

Biomechanical Phenomena↗

PubMed1983

Adaptations for reflection of bioluminescent light in the gas bladder of Leiognathus equulus (Perciformes: Leiognathidae).

The gas bladder of leiognathid fishes functions not only in buoyancy but also in reflection of bioluminescent light from the circumesophageal light organ. Purine distribution, quality (guanine/hypoxanthine ratio), and concentration, as the basis for reflectivity, were assayed enzymatically for different portions of the gas bladder lining of the common leiognathid, Leiognathus equulus (Forskal). For highly reflective areas, the percentage of tissue wet mass and dry mass represented by purine was also determined. The results indicate that total purine content in the reflective areas of the leiognathid bladder was significantly higher than values determined for other similar, shallow water fishes; instead, purine content in these reflective areas was similar to that known for very deep-dwelling fishes, in which heavy purine deposition is correlated with high pressures and high oxygen concentrations in the bladder. In addition, the results show that differential purine distribution within the bladder correlates strikingly with the path of bioluminescent light. The dorsal bladder lining, the primary site of incident luminescence, had extremely high purine concentrations (averaging 2.80 mg/cm2), whereas the secondary reflective surfaces, the lateral (1.81 mg/cm2) and ventral (1.22 mg/cm2), portions, although high in purine content, had concentrations significantly lower than the dorsum. Areas through which light is transmitted, the light organ-bladder interface (0.09 mg/cm2) and the posterior region (0.19 mg/cm2), were greatly reduced in purine content. The enhancement of purine in the reflective portions of the bladder and the correlation of the differential distribution of purines with the path of light indicate that the L. equulus gas bladder is exquisitely adapted to function as a reflector of bioluminescent light.

Air Sacs↗

PubMed2000

Noninvasive determination of hemoglobin and hematocrit using a temperature-controlled localized reflectance tissue photometer.

We performed visible/near-infrared optical measurements on the forearm of human subjects. We conducted four studies: one study using a commercial diffuse reflectance spectrometer, and three studies using a breadboard temperature-controlled localized reflectance tissue photometer. Calibration relationships were established between skin reflectance signal and either the reference blood hemoglobin (Hb) concentration or the hematocrit values (Hct). Prediction results were expressed as the prediction correlation coefficient (r(p)) and the standard error for cross-validation prediction (CV-SEP). Using diffuse reflectance measurement, r(p) = 0. 8, CV-SEP = 0.9 g/dL for Hb and r(p) = 0.7, CV-SEP = 3.3% for Hct (n = 40). In a localized reflectance study involving calculating the absorption and scattering coefficients and including effect of change of skin temperature in the calibration model, the best prediction results were r(p) = 0.9, CV-SEP = 0.8 g/dL for Hb and r(p) = 0.8, CV-SEP = 3% for Hct (n = 26). In a second localized reflectance study on a population having diverse skin colors at 34 degrees C, the optimal model led to r(p) = 0.8, CV-SEP = 0.9 g/dL for Hb and r(p) = 0.9, CV-SEP = 2.1% for Hct (n = 28) using the localized reflectance values without deducing the absorption and scattering coefficients. Improvement in the correlation was more noticeable for Hct than for the case of Hb. The photometer was used to screen prospective blood donors with low Hb concentration. It was possible to predict anemic subjects in the limited prospective blood donor population.

Calibration↗