AJP - Heart and Circulatory Physiology, Vol 244, Issue 5 726-H729, Copyright © 1983 by American Physiological Society
An intravascular protein osmometer
J. W. Henson and R. A. Brace
Our purpose was to develop an intravascular osmometer for measuring the
colloid (i.e., protein) osmotic pressure (COP) of circulating blood. A
semipermeable hollow fiber from a Cordis Dow artificial kidney (C-DAK 4000)
was attached to polyethylene tubing on one end, filled with saline, and
sealed at the other end. This was small enough to be inserted into the
vasculature of research animals. Protein osmotic pressure plus hydrostatic
pressure was measured by a Statham pressure transducer attached to the
hollow fiber. Simultaneously, a second catheter and transducer was used to
measure hydrostatic pressure, which was subtracted from the pressure
measured from the fiber with an on-line computer. The system was documented
by a variety of tests. The colloid osmotic pressure vs. albumin
concentration curve determined with the fiber is identical to the curve
determined by standard membrane osmometry. The time constant for 2- and
8-cm fibers was 2.6 +/- 0.6 and 1.5 +/- 0.5 (+/- SD) min, respectively. The
reflection coefficient (+/- SD) of the fiber for NaCl is 0.042 +/- 0.019 (n
= 38); COP measured at varying temperatures (absolute scale) changed
linearly as expected from COP = nCRT (i.e., van't Hoff's law). Finally,
hollow-fiber osmometers were inserted into femoral veins of dogs and sheep,
and blood COP was continuously recorded during osmotic manipulations. In
conclusion, we attempted to develop and document a simple method for
continuous measurement of intravascular colloid osmotic pressure.
