ELFA is based on the patented concept of quantitative CO2 rebreathing
ELFA
a new way to measure
FRC (Functional Residual Capacity) and CO (Cardiac Output)
noninvasively, quickly and inexpensively
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The patented* measuring principle :
Allow rebreathing through an external deadspace with precisely known volume and measure the resulting rise in the end-expiratory carbon dioxide concentration. From the shape of the increasing concentration, both FRC and CO can be deduced. See the schematic illustration below. The starting slope "A" determines FRC and the height of the plateau "B" determines CO.
In order to obtain FRC and CO as shown above a known amount of carbon dioxide must be rebreathed in each breath. The amount can be calculated by having a precisely known deadspace volume and by determining the average concentration of CO2 in that volume.
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The illustration below shows how this can be implemented by retaining within the deadspace, only the last part of the exhaled air and by measuring the CO2 concentration in the deadspace at a point that divides the deadspace volume in two equal parts. In this way the concentration measured in that point will be representative of the average concentration in the whole of the deadspace.
