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What Is the Conductivity of Blood?

The conductivity of blood is a measure of how well it carries electric current. Its inverse property, resistivity, is a measure of how well it resists electric current. Because conductivity and resistivity have a inverse proportion relationship, knowing one value means knowing the other. Health care providers will measure conductivity for many reasons, such as treating a stroke victim, but the numerical value of the reading varies with several factors, such as hematocrit, concentration of red blood cells; concentration of electrolytes, liquids that conduct electricity due to the presence of dissolved ions within them; and blood-flow rate.

  1. Hematocrit

    • Hematocrit is the proportion, by volume, of the blood that consists of red blood cells. Its value varies by demographics like age and sex. According to the Mayo Clinic, the normal range is 38.8 to 50 percent for men and 34.9 to 44.5 percent for women. A higher hematocrit value creates a higher resistivity or a lower conductivity.

    Plasma

    • Other than red blood cells, plasma is the majority of whole blood. As a liquid with ions suspended in it, plasma is more conductive than red blood cells. Therefore, the more plasma by volume, the more conductivity, which is an inverse relation to the hematocrit.

    Electrolytes

    • The concentration of electrolytes in blood will affect its conductivity. The more electrolytes, the higher the conductivity. The concentration is determined by one or more ion measurements, with sodium being of the greatest interest since it is the primary electrolyte in plasma.

    Erythrocyte and Flow

    • Erythrocytes or red blood cells have low conductivity. Erythrocytes are concave on both sides to help with the diffusion of oxygen and carbon dioxide, their surfaces are resistant to electric current, and their orientation affects blood conductivity. At low frequencies of electric current, the erythrocytes align with the flow, reducing their cross sections and increasing the conductivity of blood in the direction of flow.

    Common Values

    • According to a study by S. N. Mohapatra, Kate L. Costeloe and D. W. Hill, published in Intensive Care Medicine in 1977, a traditional value of resistivity assumed for an average hematocrit is 150 ohm-centimeters. Conductivity is then the inverse, which is 0.00667 siemens per centimeter or 0.667 siemens per meter.

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