Physiological measurement in circulation research. A review on the biological application of a new method.

We have recently introduced a new technique for the continuous recording of blood density based on the so-called mechanical oscillator principle. The availability of this technique makes a discussion of the diagnostic meaning of the blood density--defined as mass per unit volume--and its variations under certain conditions worthwhile. In this study, the use of the density dilution method for the determination of distribution volumes of different injected solutions will be discussed. The influence of temperature and of certain artifacts like acceleration forces in the density measuring device has to be considered and may be used for certain additional diagnostic purposes, like the determination of erythrocyte sedimentation velocity. Some most interesting observations are related to the marked influence that fluid shift between extravascular compartments and the intravascular compartment has on blood density. Here, particularly, the effect of the intravenous injection of hypertonic solutions will be discussed. These injections lead to an osmotic fluid shift towards the blood which, in a very characteristic way, reduces blood density and plasma density. A simple model for the description of this reaction is presented. Furthermore, reactions of the blood density to hemorrhage, to different vasoactive substances, and to orthostatic load will be discussed.