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Heart Microcirculation
Published in John H. Barker, Gary L. Anderson, Michael D. Menger, Clinically Applied Microcirculation Research, 2019
Macromolecular permeability can be quantified in the isolated perfused venules with FITC-labeled tracers by measuring the ratio of the transmural flux of the tracer per unit surface area at different transmural solute concentrations.20 With the use of an “optical window” from a video photometer positioned over the vessels on the monitor, the fluorescence intensity from the window is measured (Figure 4). In each measurement, the isolated vessel is first perfused with nonfluorescent perfusate through the outer inflow pipette to establish a baseline intensity. The vessel lumen is then rapidly filled with fluorochromes by switching the perfusion to the inner inflow pipette, which produces a step increase and, subsequently, a gradual increase in the fluorescence intensity. There is a step decrease of intensity when the fluorochromes are washed out by switching the perfusion to the outer inflow pipette. The apparent solute permeability coefficient (P) is calculated by the equation P = (1/ΔIf)(dIf/dt)o(r/2), where ΔIf is the step increase in fluorescence intensity, (dIf/dt)o is the initial rate of increase in intensity as solutes diffuse out of the vessel and into the extravascular space, and r is the vessel radius.
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Published in Anton Sebastian, A Dictionary of the History of Medicine, 2018
Microchemistry Technique for measuring concentration of chemicals in small samples of biological fluids was introduced around 1910. The photometer, an instrument which utilized a photocell linked to a sensitive microammeter, for analysis of the chemical constituents in small samples of blood and urine, was invented by G.E. Davis and C. Sheard of America in 1927. A photoelectric hemoglobinometer was developed by Sheard and A.H. Sanford in 1928.
Modelling and analysis of skin pigmentation
Published in Ahmad Fadzil Mohamad Hani, Dileep Kumar, Optical Imaging for Biomedical and Clinical Applications, 2017
Ahmad Fadzil Mohamad Hani, Hermawan Nugroho, Norashikin Shamsudin, Suraiya H. Hussein
A spectrophotometer is a combination of a spectrometer and a photometer (Figure 4.28). Spectrometer refers to a light radiation system and photometer is a photon conversion system into an electrical (digital) signal. In a spectrophotometer, a prism or similar optical equipment is located between spectrometer and photometer and used to disperse the re-emitted light from the skin into numerous bands (Figure 3.8).
Evaluation of Pupillometric Parameters in Patients with COVID-19
Published in Ocular Immunology and Inflammation, 2023
Yücel Öztürk, Merve Beyza Yıldız, Rüveyde Bolaç
The measurement was performed based on Prakash et al.’s method16 in a completely dark room with a pupillometer as the only light source. After five minutes of dark adaptation, the measurement was conducted by the device’s protocol in the following order: illuminations were 0.4, 4.0 and 40 lux for scotopic, mesopic, photopic measurements respectively. The photometer was used to confirm the lighting settings. The patient was asked not to look at the LED source to prevent the accommodation effect. During the measurement, the subjects opened their both eyes. For each illumination setting, the right eye was examined first, followed by the left eye. Dynamic pupillometry was performed at last. Capture in dynamic pupillometry began when the annular disc was fully illuminated (500 lux). The illumination was turned off when the capture has started. We were able to monitor pupil dilatation and pupil size from the photopic to the non-light condition.
Platelet Function Assays for the Diagnosis of Aspirin Resistance
Published in Platelets, 2022
Nameer Van Oosterom, Michael Barras, Neil Cottrell, Robert Bird
LTA utilizes a sample of platelet-rich plasma to measure the change in light transmission through the sample while aggregation occurs. This aggregation is in response to an exogenous agonist which is added to the sample, such as AA, adenosine diphosphate (ADP), or collagen [3]. When the agonist is added, it is expected that the sample becomes clearer as the platelets aggregate and precipitate, allowing greater transmission of light [18]. The use of a photometer measures the transmittance of light through the sample between 0% and 100%, where 0% is the maximal optical density of platelet-rich plasma, and 100% is zero optical density indicating no free platelets in the plasma [18]. The results are then displayed graphically through a time versus percentage of aggregation curve (Figure 2). Often the single sample uses different agonists at varying concentrations to obtain different information on platelet function [18]. LTA is considered to be the gold standard assay to assess platelet function. When AA is used as the agonist, it has high specificity as it targets TxA2 synthesis via COX; the pathway inhibited by aspirin [26].
Bagolini filter bars: an analysis of light transmittance and their use in a pediatric population
Published in Strabismus, 2019
On one occasion, each filter on each bar was measured for percentage light transmittance. This was performed in a dark room at The University of Sheffield, by first measuring the luminance level of the same ophthalmoscope (with a single layer of Blenderm tape over the light source) when it was 33 cm from a spot photometer (Sekonic Dual Spot F Model L-778). Following each measurement with the ophthalmoscope, a filter was placed directly in front of the photometer and the luminance level on the photometer was recorded. The process of measuring the luminance of the ophthalmoscope with and without a filter was repeated three times for each filter on each bar and a mean luminance level was calculated in each situation. By dividing the mean luminance level for each filter by the mean luminance level without each filter and multiplying by 100, the mean percentage light transmittance was calculated.