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Abstract

A method and apparatus for measuring the concentration of an analyte of interest, e.g. glucose, in blood non-invasively, i.e., without penetrating the skin or obtaining a biological sample from the body of a patient. The method and apparatus uses a plurality of measurement channels with appropriate wavelengths of interest to control variations of signal and to separate the contribution of the analyte of interest from those of interfering compounds. The method and apparatus of this invention can also be adapted to allow a portion of a body part to be engorged with blood to bring about greater accuracy in optical measurements. In the method of this invention, at least two similar, but not identical, measurements are made concurrently. For example, at least two measurements can be made with similar, but not identical, wavelengths of electromagnetic radiation. The two wavelengths should not be overlapping to allow maximum non-identity. By making measurements concurrently, each measurement channel in the system experiences variations as they occur substantially simultaneously in all channels. By selecting one of the channels as a reference channel and by normalizing the optical measurements of the other channels to this reference channel, the variations common to all channels are eliminated. Removing these common variations from the optical measurements by normalization, such as by calculating ratios of the measurement of each of the measuring channels to that of the reference channel, will allow the actual changes of the signal for a specific analyte of interest to be measured.

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First Claim