Hinghofer-Szalkay H

Volume and density changes of biological fluids with temperature

J Appl Physiol. 1985; 59: 1686-9

• Physiologisches Institut der Karl-Franzens-Universitaet, Graz, Austria; and Space Physiology Branch, NASA-Ames Research Center, Moffett Field, California, USA

Purpose: High-precision (10^-5 g/ml) mass density measurements on human blood, plasma, plasma ultrafiltrate (using PM-10 membranes), and erythrocyte concentrate samples were performed with the mechanical oscillator technique.

Measurement temperatures varied between 4 and 48 deg C and were accurate to ±1x10^-2 K. The coefficient of thermal expansion (beta), defined as relative volume change with temperature, was calculated.

Results: It was shown that

1. beta increases with temperature in these fluid samples over the entire temperature range investigated;
2. the magnitude of this increase declines with increasing temperature, becoming independent of density above 40 deg C; and
3. the beta of the intracellular fluid has about twice the value of the beta for extracellular fluid at low (4-10 deg C) temperatures but is equal for both fluids at >40 deg C.

Conclusion: The mechanical oscillator technique provides data with an accuracy sufficient to perform precise (10^-5 K) calculations of beta of small volumes of biological fluids. The coefficient of thermal expansion increases with density at temperatures below 40 deg C but is independent of density above 40 deg C.

Density of a red cell (RC) and an ultrafiltrate (UF) sample at low (A) and high (B) temperatures. Note different density scales.

Coefficient of thermal expansion as function of sample density at 5 (A), 25 (B), and 45 degrees Celsius (C). No significant correlation existed at 45 deg C.

A: Coefficient of thermal expansion as function of temperature. B: Increase of beta with density, determined as in above figure, between 5 and 47 deg C. C: Volume expansion of erythrocytes (RC) and ultrafiltrate (UF) from 4 to 48 deg C; curve was calculated from data in (A).

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