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At least 217 records · Page 12Linked to original sources
PubMed1987

Multidimensional stopped-flow photometry monitoring initial processes of platelet activation.

A group of initial processes in platelet activation, consisting of a platelet shape change, an intracellular calcium mobilization, a calcium efflux, and a membrane fluidity (mobility) change, has been examined in rabbit platelets by a multidimensional stopped-flow method with light scattering, light transmission, and fluorescence measurements. It was found that a 90 degrees light scattering change and internal calcium release (monitored in terms of chlortetracycline fluorescence) take place after a short lag (5 s at 25 degrees C and 2 s at 37 degrees C) following activation by thrombin. The duration of the lag was the same in both cases. During the initial lag period, a rapid increase in platelet membrane fluidity (mobility) was observed by the use of pyrene excimer fluorescence. These results suggest that the intracellular calcium mobilization and the shape change are triggered by the same rate-determining step, and increase in membrane mobility may play some role in the initial stage of platelet activation before intracellular calcium mobilization occurs.

Animals↗
PubMed2005

Spectral absorbance and spatial distribution of macular pigment using heterochromatic flicker photometry.

PURPOSE: The validity of the heterochromatic flicker photometric (HFP) technique for measuring macular pigment (MP) was assessed by evaluating the spatial density and spectral absorption curves of normal subjects. METHODS: Standard Maxwellian view optics were used to measure MP spatial density and spectral absorption curves. Four subjects with normal color vision and one protanope were tested. All of the subjects were experienced psychophysical observers. RESULTS: Spatial density profiles for all subjects were nearly symmetric. The width of the spatial distribution, at half maximal density, averaged 0.70 degrees (standard deviation = 0.15). A first-order exponential decay with eccentricity described the distribution profile well (average r = 0.95). The shape of the spectral absorption curves matched an ex vivo template closely at wavelengths greater than approximately 430 nm. Stimulus size did not influence the derived spectral curves. CONCLUSION: Based on data from this study and others, the HFP method appears to be a valid method for measuring MP density in subjects without retinal disease.

Absorption↗
PubMed1991

Formation of oiliness and sebum output--comparison of a lipid-absorbant and occlusive-tape method with photometry.

Sebum output and the development of oiliness formation were studied in 24 acne-prone volunteers. Sebutape and photometric measurement by the Sebumeter were compared. Tapes were taken 1, 2 and 3 h after degreasing. Tapes were scored, and light transmission was measured by a special densitometric device. Sebumeter recordings were performed after 3 h. Densitometric evaluation of tapes was accurate with a high correlation to scoring. Sebutape and Sebumeter assessments correlated. However, in some individuals the tape method overestimated the sebum output. Right-left comparison indicated that the tape method was less reproducible, particularly after longer sampling periods. It is suggested that Sebutape, due to water occlusion and temperature insulation during the sampling period, interferes with sebum droplet formation and spreading. However, such systematic interference may be advantageous since sweating and heat are important clinical prerequisites in the formation of oiliness. Thus, it is suggested that the Sebutape is a specialized method for the determination of 'oiliness', the very last phase of sebum output, in which sebum droplets spread over the skin surface. The tape is not automatically comparable to other methods for determining sebum output from the follicular reservoir.

Acne Vulgaris↗
PubMed1981

Improvement in microscope photometry by voltage to frequency conversion: analogue measurement and digital processing.

A system for digital measurement of microscope photometric signals, based on Voltage to Frequency Conversion (VFC) and suitable for automatic data processing, has been devised. Advantages and disadvantages are illustrated with special emphasis on the comparison between photocurrent measuring and photon counting techniques. A statistical analysis of the results allows the calibration of VFC net counts versus detected photons. A biological application is reported; this shows the suitability of the system even to low light levels.

Animals↗
PubMed1983

Evaluation and interpretation of grain density autoradiographs by reflectance photometry.

The tritium content of nervous tissue sections is calculated from grain-density of autoradiograph without loss in anatomical information. The calculation is not based on determination of (expected) grain numbers but on photometric measurements (SKphot), interpreted as the result of the function of exposure time (T) and incorporated activity (beta): SKphot = f(T, beta). As experimental radiation standards homologous material (optic nerve preparations) with different activities determined by liquid scintillation counting has been used. Exposure times between 12 h and 28 weeks for these preparations with known radioactivities yielded a set of curves (nomogram) relating photometric values of exposure times. At any given exposure time the knowledge of photometric readings and related radioactivities within that set of curves enabled the development of a function covering all photometer readings within the range of the nomogram. Thus, any photometric reading could be correlated to the corresponding radioactivity. Such a function has been applied for the transformation of photometric values obtained from particular brain-section areas exposed for 16 weeks. Since the results are given in Bq, they may be related and, if necessary, corrected to results obtained by other tritium detection methods. Terminology used in the text: experimental radiation source = experimental standards prepared from optic nerve sections; standard radiation source = polymer reference source.

Animals↗
PubMed1995

Notes on the apparent discordance of pulse oximetry and multi-wavelength haemoglobin photometry.

Multi-wavelength photometers, blood gas analysers and pulse oximeters are widely used to measure various oxygen-related quantities. The definitions of these quantities are not always correct. This paper gives insight in the various definitions for oxygen quantities. Furthermore, the possible influences of dyshaemoglobins and fetal haemoglobin on the accuracy of pulse oximetry are discussed. As pulse oximeters are constructed for the determination of arterial oxygen saturation, they should be validated with sample oxygen saturation values and not with the oxyhaemoglobin fraction. The influence of carboxyhaemoglobin is insubstantial over an oxygen saturation range of 0% to 100%. Through the presence of methaemoglobin, pulse oximetry will give an underestimation above 70% and an overestimation below 70% oxygen saturation. The influence of fetal haemoglobin is insignificant in the neonatal use of pulse oximetry, in the range of 75% to 100% arterial oxygen saturation. However, a pulse oximeter underestimates the arterial oxygen saturation at the 25% level with 5%, if the pulse oximeter has been calibrated in human adults. Such a low level of arterial oxygen saturation can be present in the fetus during labor.

Adult↗
PubMed1976

Estimation of B- and T-lymphocytes in lymphoid tissue by means of photometry and 51Cr labelled marker erythrocytes.

Some new techniques for estimating B- and T-lymphocytes in lymphoid tissue are introduced. The density of marker erythrocytes on closed chamber incubated sections was estimated by the light transmission in relation to the number of the respective lymphocyte subpopulation, measured on suspensions of eluted lymphocytes. Using 51Cr labelled marker erythrocytes, the number of adsorbed marker erythrocytes per lymphocyte could be estimated from the gamma-irradiation of the section. The number of lymphocytes in the section was determined by the amount of protein in the section compared with the protein amount of a tissue specimen of known wet weight and known lymphocyte content. Furthermore, the number of adsorbed marker erythrocytes per rosette in suspensions of eluted lymphocytes was estimated by means of radioactively labelled marker erythrocytes.

Appendicitis↗
PubMed1981

Rapid screening for bacteriuria by light scatter photometry (Autobac): a collaborative study.

A total of 2,720 urine specimens from three laboratories were evaluated by Autobac (Pfizer Diagnostics) and were compared with simultaneous colony counts for evidence of bacteriuria. Of 599 specimens with a colony count of greater than or equal to 10(5) colony-forming units per ml, 93.8% were detected within 6 h. This detection rate increased to 97% of 447 positive urine specimens when only specimens from patients not on antimicrobials were evaluated. The majority (77.9%) of positive specimens were detected as early as 3 h. Those specimens with greater than or equal to 10(5) colony-forming units per ml, which were negative by Autobac at 6 h, included organisms which are frequently considered to be contaminants (diphtheroids, lactobacilli, alpha and gamma streptococci, yeasts, and Staphylococcus epidermidis), or were from patients who were being treated with antimicrobial agents. Of 2,121 urine specimens with colony counts of less than 10(5), 98.1% were correctly determined to be negative by Autobac at 3 h. This percentage decreased to 86.0 at 6 h. The majority of these false-positive specimens were those with colony counts of 10(4) to 10(5) colony-forming units per ml. There appeared to be no major difference in results from the three laboratories or among the four lots of broth used in this study.

Anti-Bacterial Agents↗
PubMed1966

Use of silicon photovoltaic cells to provide a second channel in flame emission photometry.

Sodium and potassium may be measured simultaneously, using a modified Eppendorf flame photometer. After automatic sampling and dilution of the plasma, the potassium content is measured, using the existing Eppendorf optical and photomultiplier system. The sodium emission is measured by three silicon photovoltaic cells mounted behind an interference filter for sodium, sited on the atomiser casing. The outputs from the photomultiplier and from the silicon cells are recorded by two sensitive recorders. Sixty samples an hour may be estimated, using only 0.12 ml. plasma. Reproducibility tests showed a coefficient of variation of 0.4%.

Photometry↗