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Biomedical subjects

G Kwant

Publications and source records attributed to G Kwant.

6 recordsLinked to original sources
PubMed1979

Spectrophotometric determination of oxygen saturation of blood independent of the presence of indocyanine green.

The strong absorbance of indocyanine green in a broad band around lambda = 800 nm invalidates the usual spectrophotometric two-wavelength methods for measuring oxygen saturation operating in the red and near infrared region. By proper wavelength selection, however, the effect of the dye can be eliminated. With the two-wavelength method utilising lambda = 660 and 860 nm oxygen saturation is measured virtually independent of the presence of indocyanine green.

Animals↗
PubMed1978

A fiberoptic reflection oximeter.

A catheter tip oximeter is described consisting of a cardiac catheter containing optical fibers, and incandescent light source, a light detection unit and a processing unit. Half of the optical fibers guide the light to the blood at the tip of the catheter, the other half the backscattered (reflected) light to the detection unit. The detection unit contains a dichroic mirror, transmitting most of the light with lambda less than 800 nm and reflecting most of the light with lambda greater than 900 nm, thus splitting the light into two beams. These pass through interference filters with nominal wavelengths of 640 and 920 nm respectively, and are focused on silicium barrier layer photocells. The photocell signals are amplified and fed into a divider giving the ratio of measuring (R640) and compensating (R920) photocell output. The relationship between log R640/R920 and oxygen saturation is represented by a slightly curved line. The relation may be linearized by subtracting a constant voltage from the divided output before taking the logarithm. The slope of the calibration line is dependent on the total haemoglobin concentration. Nonetheless an average calibration line can be used between 70 and 100% oxygen saturation. For 78 measurements of pig blood samples in this range (haemoglobin concentration between 96 and 161 g.1(-1)), the standard deviation of the difference between the fiberoptic oximeter and a Radiometer OSM1 oxygen saturation meter was 1.9% saturation, for 152 samples over the entire saturation range the standard deviation of the difference was 3.1% saturation. The influence of the flow velocity of blood on the light reflection depends on wavelength as well as on oxygen saturation. Therefore, complete compensation for the flow effect is not possible by simple means.

Animals↗
PubMed1976

A new reference method for the determination of the oxygen content of blood.

To be able to determine the slight differences between the theoretical and the actual O2-binding capacity of human haemoglobin, a highly accurate method has been developed for measuring the O2 content of blood samples. It is an adaptation of an established O2 determination in organic microanalysis. The bound O2 of the blood is set free by conversion of HbO2 to Hi, and the O2 stripped from the blood is converted to CO by contact with granular carbon at 1120 degrees C. The CO is then converted to CO2 using CuO at 300 degrees C and the CO2 titrated in a solution of BaCl2, using NaOH of known strength. The measuring system was checked by analysis of 36 samples of air, yielding an O2 content of 20.93 +/- 0.06%. The coefficient of variation calculated from 62 duplicate determinations of samples of human blood was 0.65%.

Autoanalysis↗
PubMed1976

Light-absorbing properties, stability, and spectral stabilization of indocyanine green.

The absorption spectrum of indocyanine green depends on the nature of the solvent medium and on the dye concentration. Binding to plasma proteins causes the principal peaks in the absorption spectrum to shift about 25 nm toward the higher wavelengths. The much greater influence on the spectrum of the dye concentration results from progressive aggregate formation with increasing concentration. Indocyanine green solutions therefore do not follow Lambert-Beer's law above 15 mg-I-1 (in plasma). Indocyanine green solutions in plasma and concentrated (1,000 mg-I-1) solutions in distilled water are stable for at least 4 h. In long-term experiments the optical density of indocyanine green solutions in plasma as well as in distilled water generally diminishes, even in the dark. On the 7th day a new absorption maximum starts to appear at gamma=900 nm, possibly caused by further aggregate formation leading to much larger particles. Spectral stabilization after injection of a concentrated solution into the blood is most rapid when the dye is dissolved in distilled water. Spectral stabilization slows down with decreasing temperature. As rapid spectral stabilization is essential in quantitative dye dilution studies, the practice of adding a albumin and/or isotonic saline solution to the injectate should be discontinued. When a 10 g-1(-1) aqueous solution of indocyanine green is used, spectral stabilization takes less than 1.5 a (at 37 degrees C), which is sufficiently fast for almost any application.

Blood↗