Relation Between Blood Resistivity and Hematocrit in Fresh Human Fetal Blood


Summary: This study determined the relation between hematocrit and resistivity of fetal blood and compared it with values obtained in similar studies on adult blood. Both exponential and Maxwell-Frick-estimated relationships were calculated and compared. The results indicate that there is no significant difference between resistivity in adult and fetal blood. The best relation between blood resistivity and fetal hematocrit is obtained by using the Maxwell-Frick estimated curve calculated in the following manner:

ρ = 53.0(1 + χ · h)/(1 - h)


χ = 1.2

h = H/100 (H = hematocrit).

Speculation: Hematocrit varies over a wide range during the newborn period. Accurate knowledge of resistivity-hematocrit relationships over the entire hematocrit range is essential whenever blood resistivities are to be estimated from hematocrit values. This study reveals that a better correlation is obtained when using the Maxwell-Frick model instead of the ordinary exponential model. Thus, a tool is offered to improve the accuracy of the impedance cardiography method in newborns.

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Correspondence to Kenneth Sandberg.

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Sandberg, K., Sjöqvist, B. & Olsson, T. Relation Between Blood Resistivity and Hematocrit in Fresh Human Fetal Blood. Pediatr Res 15, 964–966 (1981).

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  • blood resistivity
  • hematocrit
  • impedance cardiography
  • Maxwell Frick equation

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