A Self‐Recording Electronic Osmometer for Quick, Direct Measurement of Colloid Osmotic Pressure in Small Samples¹

Abstract

A self‐recording electronic osmometer for clinico‐physiological use is described. It is a further development of an osmometer described earlier by the author. It is based on the passive counter‐pressure principle and as such representing a return to the principle that was first applied in osmotic pressure measurements. The general principles for the measuring of osmotic pressure and the special requirements to be fulfilled if quick performance is to be obtained are discussed. The importance of the diffusion phenomena in this context has been emphasized and experimentally elucidated. The sample of plasma or serum which is required, is from 0.02 to 0.1 ml. Ten to 15 measurements can be performed per hour. The confidence limits for one measurement are ± 0.5 mm Hg. at the 5% level. Commercially available cellulose membranes are used. No stopcocks are employed. Stainless steel is used for all parts in contact with membrane and sample. The possible usefulness of the osmometer for investigation of the reflection coefficient of permeating particles and for testing membranes is pointed out. Also the possible use in investigations of active trans port problems in connection with organic membranes is hinted at. Finally it is mentioned that the red blood cells under certain circumstances will influence the osmotic pressure.

Development of an Apparatus to Measure Plasma Colloid Osmotic Pressure Mounted on the Extracorporeal Hemodialysis Circuit.

“…It can be measured by using a semipermeable membrane that is impermeable to the plasma protein but permeable to the other components of blood plasma (Morissette 1977). There are two types of apparatus for measurement of plasma colloid osmotic pressure; one is membrane type developed by Hansen (1961) and the other is needle type developed by Kakiuchi et al (1979). These conventional apparatus require a blood sample set in them.…”

Relation Between Trans‐synovial Flow and Plasma Osmotic Pressure, With an Estimation of the Albumin Reflection Coefficient in the Rabbit Knee

“…COP was measured on 200,l plasma samples at room temperature (20-24°C) using an electronic, thermally insulated osmometer calibrated by a water column (Hansen, 1961). Three changes of sample were used to prevent dilution by reference fluid.…”

Starling pressures in the human arm and their alteration in postmastectomy oedema.

“…Colloid osmotic pressure measurements A lagged electronic membrane osmometer (Hansen, 1961) was fitted with a special enclosed head to reduce minimum loading volume to 10 /al and minimize evaporation (Bates, Levick & Mortimer, 1991b). The Gould P23XL transducer was calibrated by a water column (O to -100 cmH20).…”