The present invention performs its operation by the combination of the following features. First and second beams of a wavelength subjected to a change in absorbance due to a change in oxygen saturation of hemoglobin in blood of tissue of aliving body, third and fourth beams of another wavelength not subjected to any change in absorbance, and fifth and sixth beams of a further wavelength subjected to a relatively small change in absorbance due to changes in a quantity of hemoglobin andoxygen saturation, are applied to the tissue of the body, and light receiving means receives the first to sixth beams reflected from the tissue of the body. Intensities of the respective outputs of the light receiving means are evaluated and, based on apredetermined function, the quantity of hemoglobin in the tissue is calculated and the result of the calculation is outputted.
Consequently, the present invention makes it possible to avoid various problems encountered in the conventional non-invasive type oximeters, such as the ability of measuring in a body part where a pulsation component does not exist, measurementslimited only to oxygen saturation in an artery, noise due to sway or vibration of a sensor, and the ability of measuring without an optical cuvette because of an optical transmission method. Accordingly, the oximeter of the present invention is capableof evaluating lung functions, heart functions, the state of oxygen supplied to tissue, and other data in examinations of anesthesiology, dermatology, pediatrics etc., and is also capable of continuously monitoring conditions of a patient for a longperiod.
In a preferred embodiment of the present invention, a calibration mode and a measurement mode can be selected and when the calibration mode is selected, a voltage to be applied to light source means is set so that the intensity of light emittedfrom the light source means is within a predetermined range.
According to the above-mentioned preferred embodiment of the present invention, the intensity of light emitted from the light source means is calibrated prior to measurement and a quantity of hemoglobin in the tissue of the body can be measuredmore accurately.
In another preferred embodiment of the present invention, assuming that intensities of the first, second, third, fourth, fifth and sixth beams reflected from the tissue are P1, P2, P3, P4, P5 and P6, the quantity of hemoglobin in the tissue iscalculated by:
where C1, C2 and C3 are correction values.
In addition, in a further preferred embodiment of the present invention, the light source means is formed by first to sixth light sources emitting the first to sixth beams, respectively, and the first, third and fifth light sources are located atpositions distant from the center of the light receiving means by a predetermined distance d1, while the second, fourth and sixth light sources are located at positions distant from the center of the light receiving means by a predetermined distance d2,with a relation of d1<d2 being maintained.
In another aspect of the present invention, first and second beams of a wavelength subjected to a change in absorbance due to a change in oxygen saturation of hemoglobin in the blood of the tissue of a living body, third and fourth beams ofanother wavelength not subjected to any change in absorbance, and fifth and sixth beams of a further wavelength subjected to a relatively small change in absorbance due to a change in oxygen saturation are applied to the tissue of the body and the firstto sixth beams relected therefrom are detected, whereby intensities of the respective beams are evaluated and the oxygen saturation of the tissue is evaluated based on a predetermined function.
Consequently, according to this aspect of the invention, it becomes possible to measure the oxygen saturation in a body part not containing a pulsation component, which could not be measured in a conventional apparatus.
These objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
