A noninvasive optical oximeter for measuring oxygen saturation of arterial blood. A sample of blood is illuminated with light at two different wavelengths. Light reflected by the blood is sensed by a photodetector and an output signal is created in response thereto. The output signal is processed to form a quotient representing the AC components of the reflected light at each wavelength. The oxygen saturation of the blood is calculated by correlating this quotient with an oxygen saturation reference curve uniquely representative of the blood oxygen saturation characteristics of a particular individual. The reference curve used in the preferred embodiment of the invention is calibrated in a two-step process which minimizes the effects of calibration errors. A first oxygen saturation reference curve is calculated which is based on a linear relationship between the ratio of the AC components of the reflected light. This curve is then used to calibrate a second reference curve based on a linear ratio of the squared values of the AC components of the reflected light. Once the second reference curve has been properly calibrated, it is used for all subsequent measurements of oxygen saturation.
Systems and methods for non-invasive material analysis are disclosed in which a material (e.g., a liquid such as blood) is illuminated at a plurality of discrete wavelengths. Measurements of the intensity of reflected light at such wavelengths are taken, and an analysis of reflection ratios for various wavelengths is performed. Changes in the reflection ratios can be correlated with specific material properties such as the concentration of analytes (e.g., oxygen content, glucose levels, cholesterol or drugs in a subject's circulatory system).
Biochemical components and changes in the components are measured by directing light of several wavelengths into a body at one location, sensing light at the wavelengths emerging from the body at a plurality of distances from the one location, and ascertaining biochemical component characteristics in the body as a function of variations, with respect to distance, of the logarithm of the ratio of the light sensed to the light directed into the body. The variations with respect to distance are in the form of the derivative and square of the derivatives of the logarithm.
Light components are radiated into a blood vessel from light-emitting diodes (17, 18) for emitting light components having different wavelengths through an optical fiber. Bight components reflected by the blood upon radiation into the blood vessel are received by a photo transistor (19) to detect their reflected light intensities. For example, a minimum value of the reflected light intensity of the light component from the light-emitting diode (18) is obtained from the reflected light intensities detected within a predetermined period of time. A measurement value is calculated using this minimum value and a minimum value of the reflected light intensity of the light component from the corresponding light-emitting diode (17).
An apparatus of and method for measuring arterial blood oxygen saturation at a particular tissue level of interest. Visible and near infrared radiation are emitted into a patient at the measurement site using two different wavelengths. Detection at two different detection sites permits rejection of oxygen saturation at undesired tissue levels.
A method for determining the content of chemical constituents in a biological tissue medium includes providing a probe comprising a light source and a plurality of photodetector strips circumferentially arranged around the light source. A wavelength for the illumination of the light source is selected and the photodetector strips are illuminated at the selected wavelength. Voltage readings are then taken for each photodetector strip. After taking the readings, the probe is placed on a surface of the tissue medium and the medium is illuminated at the selected wavelength. Voltage readings are again taken at each photodetector strip. The voltage readings taken from the tissue medium are then adjusted by dividing these readings by the initial voltage readings for each photodetector strip. A logarithm is taken for the adjusted voltage readings as a function of the separation distance between each photodetector strip and the light source. The values from the logarithmic function may be filtered according to a formula in which a smoothing approximation is utilized. A theoretical model is used to determine the flux of photons incident on each of the photodetector strips. Parameters are used to minimize the mean squared error or other error function when comparing the model values to the measured values.
