No abstract

In up to six different sides along the body axis during tilting manoeuvres, volume shifts into or out off superficial tissues were followed with a newly developed miniature plethysmograph. It was possible to localize a region where no or only minor volume changes during the tilt table experiments occurred. This region is identical with the Hydrostatic Indifferent Point (HIP) being localized below the apex of the heart in the upper third of abdominal vena cava. Above the HIP fluid is drained out off the tissues during assumption of upright posture whereas below the HIP fluid volume is pooled. The volume changes occurred in two phases. Within the first 5 s in the cephalad parts of the body a rapid decrease occurred, thereafter the volume remained unchanged or even increased; below the HIP within the first 5 s a large volume increase was followed by a slow continuous volume increment. The functional peculiarities of the low pressure system as a whole were visible studying only superficial shell tissues of the body with the non invasive miniature plethysmographic technique.

With an ultrasonic method tissue layer thickness was measured in man in circumscribed superficial tissue areas where the underlaying bone provided good backwall echos. In a 5 mm tissue layer changes of +/- 0.2% could be reliably detected. Knowing the height of the tissue cylinder between the surface of the skin and the bone allowed to calculate the tissue volume. The ultrasonic probes could therefore serve as miniature plethysmograph. Several probes were attached in the frontal region, sternum, along the vertebral column and along the tibia simultaneously. Changes of the volume content of the superficial shell tissues were induced by orthostasis, water immersion and heat exposure. It was possible to assess quantitatively the volume shifts into or out of the superficial tissues. During orthostasis 166 ml of fluid left the superficial tissues of the cephalad parts of the body and 164 ml could be traced in the dependent parts. Heat exposure was followed by a pooling 140 ml in the tissues studied. The most pronounced tissue volume changes were observed in the forehead region during heat exposure.

The reliability of the mechanical oscillator technique (MOT) for blood and plasma mass density measurements on small samples is quantified in this paper. Sources of measurement errors that can reduce both the accuracy and precision of density determinations include storage of plasma samples, inhomogeneity of blood samples, and density reading before adequate temperature equilibration. Measurements on fractions from identical samples and repeated samplings from test subjects under steady-state conditions revealed a 10(-2) g/l reproducibility of density readings. The mean plasma density (PD) readings did not change significantly after up to 1-wk storage at +4 degrees C or up to 2 mo storage at -20 degrees C. The variability of the PD findings increased with storage time and were generally higher with storage at -20 degrees C, compared with +4 degrees C. Densitometers of different sizes were used to evaluate rheological influences on blood density (BD) readings. Linear correlations between PD and plasma protein concentration, between BD and blood hemoglobin concentration, and between erythrocyte density and mean corpuscular hemoglobin concentration were significant (P less than 0.001). Rapid density measurements with up to 10(-2) g/l reliability on small (less than 0.1 ml) volumes of biological fluids and continuous blood densitometry can be performed with use of the MOT.

Zusammenfassung: Zwischen der Dichte und dem Eiweißgehalt von Serum besteht eine seit langem bekannte, lineare Beziehung. Mit einem neuen Verfahren zur Messung der Dichte, der sogenannten Biegeschwingermethode, gelingt es, diese Beziehung zur Messung der Gesamteiweißkonzentration im Serum zu nützen. Die Methode beruht auf der Bestimmung der Resonanzfrequenz eines mit einer Probe gefüllten, gläsernen, U-förmigen Biegeschwingers. Aus der Verstimmung der Resonanzfrequenz durch die Masse des an der Schwingung teilnehmenden, konstanten Volumens der Probe wird die Dichte bzw. die Eiweißkonzentration berechnet. Trotz der geringen Spezifität der Methode ist der Einfluß von Störsubstanzen wie Glucose, Harnstoffoder Triglyceriden auch bei stark pathologischen Verhältnissen gering. Einfachheit, Schnelligkeit und hohe Genauigkeit in der Dichtebestimmung machen die Biegeschwingermethode zu einem für das Routinelabor empfehlenswerten Verfahren. Determination of the serum protein concentration based on the measurement of density by the mechanical oscillator techniqueSummary: A linear relation is well established between the density and protein concentration of the serum. The measurement of protein concentration by a new technique for the determination of the absolute density, the mechanical osciDator technique, was investigated .The method is based on the determination of the resonant frequency of a mechanical bending-type, U-shaped glass tube oscillator filled with the sample. The shift in the resonant frequency of the oscillator caused by the mass of the defined volume of the sample taking part in the vibration can be used to calculate the density or protein concentration of the sample. In spite of the low specifity of the method, the interference of substances like glucose, urea or triglycerides is small. Simplicity and rapid results of high accuracy recommend the mechanical oscillator technique for the routine laboratory.