Mellander, S. and R. F. Rushmer. Venous blood flow recorded with an isothermal flowmeter. An isothermal flowmeter has been developed for recording of steady blood flow such as occurs in veins. The flow recording element consists of a fine heating coil enclosing a thermistor mounted on the tip of a catheter. The sensing element is held in the center of a vessel by five fine spring wires which also hold the dimensions of the vessel at a known constant size during recording. Heat is dissipated from the coil by blood flowing past the heating element. If the temperature of the thermistor is maintained at a constant level slightly above the blood temperature, the heat production in the heating coil has been found to be linear with blood flow over the range of flow met with in large blood vessels. The maximum error was found to be & 5 per cent of full scale deflection. Changes in venous flow can be measured at a single site or the catheter can be advanced along venous channels, sampling blood flow at various positions. The distribution of the blood flow into the inferior caval vein from various vascular beds has been investigated in dogs. Refinements in the design are being performed to make the isothermal flowmeter suitable to clinical studies, if possible.
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Mellander et al. (1960) studied this question.