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A new method for the spectrophotometric determination of Evans Blue in plasma is presented. The method is based on the precipitation of the non-albumin fraction of the plasma proteins with polyethylene glycol, in order to eliminate the variable background absorption of plasma at the wavelength of maximum absorbance of Evans Blue. The accuracy and precision of the method is excellent: at an Evans Blue concentration in plasma of 5 mg · 1 the coefficient of variation of the method is < 1 %. Five different procedures currently in use for the calculation of the plasma volume from the amount of indicator injected and the concentration at zero time (c 0 ) were compared. Extrapolation to zero time of the early part (10 to 60 min) of the log concentration vs time curve turned out to be the best method for the calculation of c 0 , and hence yields the best estimate of the plasma volume. Eine verbesserte Methode fur die Bestimmung des Plasmavolumens mit Evans BlueZusammenfassung: Eine neue Methode für die spektrophotometrische Bestimmung von Evans Blue wird beschrieben. Sie beruht auf der Fällung der Nicht-Albumin-Fraktion der Plasmaproteine mit Polyethylenglycol, um die variierende Untergrundabsorption von Plasma bei der Wellenlänge des Absorptionsmaximums von Evans Blue zu eliminieren. Richtigkeit und Genauigkeit der Methode sind hervorragend: bei einer Evans Blue-Konzentration von 5 mg/1 Plasma ist der Variationskoeffizient der Methode < 1%. Fünf verschiedene Verfahren, die gegenwärtig zur Ermittlung des Plasmavolumens aus der Menge an injiziertem Indikator und der Konzentration zum Zeitpunkt t = 0 (c 0 ) Verwendung finden, wurden verglichen. Extrapolation des frühen Teils (10-60 min) der log Konzentration gegen Zeit-Kurve auf die Zeit t = 0 erwies sich als die beste Methode für die Ermittlung von c 0 und ergibt deshalb den besten Wert für das Plasmavolumen.

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The determination of D2) in biological fluids by means of infrared spectrometry was reinvestigated. When the temperature of a solution, containing D2O in the range from natural abundance to 5 ml . 1-1 increases, its absorbance decreases and the wavenumber of maximum absorption shifts to a higher value. Both changes are linearly related to the change in temperature. Storage for 17 d in either glass or polyethylene tubes does not affect the D2O concentration. Purification of biological fluids by vacuum-sublimation removes all substances which also absorb at the O-D vibration band and the recovery of D2O from plasma and urine is complete. The partition ratio of D2O between plasma water and red cell water equals unity, and the same holds for plasma water and urine water over a wide range of urine flows and osmolalities. The arterial and urinary disappearance curves of D2O, measured over several days, both permit the calculation of the total amount of body water (Vbw), the daily water turn-over (F) and the half-time of water in the body (t1

The suitability of ferocyanide as an indicator for the measurement of extracellular fluid volume was tested. Added ferrocyanide could be recovered completely from urine, plasma and blood. In in vitro experiments ferrocyanide did not penetrate into erythrocytes, nor did it adhere to the red cell membrane. In gel filtration and electrophoresis experiments binding of ferrocyanide to plasma proteins could not be demonstrated. In in vivo experiments on dogs, the urinary recovery of intravenously administered ferrocyanide was 98.9 +/- 2.1% (n = 14). The partition ratio of ferrocyanide between lymph water and plasma water was 0.99 +/- 0.02 (n = 20). Ferrocyanide could not be detected in cerebrospinal fluid or red cells of dogs after administration by intravenous infusion. No untoward effects of the infused ferrocyanide were observed during or after the experiments. In nephrectomized dogs ferrocyanide reached its ultimate distribution volume 2 hrs after intravenous administration of a single dose and remained constant for up to 10 hrs. The average distribution volume was 224 +/- 17 ml-kg-1 body mass (n = 6). In intact dogs continuously infused with indicator, ferrocyanide also reached its ultimate distribution volume in 2 hrs and remained constant thereafter for up to 7 hrs after the start of the infusion. The average distribution volume was 237 +/- 27 ml-kg-1 body mass (n = 14). It is concluded that ferrocyanide fulfils the requirements to be met by an indicator for the measurement of the extracellular volume, and is well suited for repeated determinations of the extracellular fluid volume in one and the same experiment.