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| Typical Number in Hospital: 1 | Cost Bands: 4 | References: 6 |
Electrical impedance measurements are used in a number of medical devices, including a type of limb plethysmograph, a skin resistance meter for relaxation control, and a breathing or apnoea monitor. Electrical impedance changes between electrodes at the neck and waist, can relate to the movements of blood. The electrodes take the form of four strips of metal foil, two at the neck and two around the waist. The outer pair of electrodes are fed with a constant electrical current at high frequency (e.g. 100 [u]A at 100 kHz) and the inner pair are connected to an amplifier and phase sensitive detector, and any necessary computing apparatus.
Experimental work suggests good accuracy of cardiac output calculation by this method as compared to dye dilution, and Fick methods. However, the devices have not gained wide acceptance.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details