Self-emission noninvasive infrared spectrophotometer with body temperature compensation

摘要

A method and apparatus for monitoring glucose, ethyl alcohol and other blood constituents in a noninvasive manner. The measurements are made by monitoring infrared absorption of the desired blood constituent in the long infrared wavelength range where the blood constituent has a strong and distinguishable absorption spectrum. The long wavelength infrared energy emitted by the person as heat is monitored and the infrared absorption of particular constituents in the blood (such as glucose or blood alcohol) is measured at characteristic infrared absorption wavelengths for those constituents. The measurements are preferably synchronized with systole and diastole of the cardiac cycle so that the signal contribution caused by veins and tissues (which do not pulse) may be cancelled when a ratio of the detected signals is taken. On the other hand, if no synchronization is provided, the spectrophotometer may measure the arterial, venous and tissue constituent concentrations simultaneously, which may be desired in some circumstances. The internal "blackbody" energy level of an infrared emissions source such as a vascularized appendage prior to glucose absorption is measured and used to compensate temperature dependent effects in the concentration calculation. The internal energy level is then ratioed to the actual measured energy and used to compute the percentage of energy absorbed by the glucose. Discontinuities in the ratio are eliminated by converting the absorption measurements from voltages to watts.