Surgery – Truss – Pad
Patent
1995-09-19
1997-10-14
Cohen, Lee S.
Surgery
Truss
Pad
356 41, A61B 500
Patent
active
056761414
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for making in vivo measurements of blood constituent concentrations. More specifically, a method and apparatus are described wherein hemoglobin oxygen saturation may be measured using a pulse oximeter which directs light of two or more wavelengths into living tissue and then measures the attenuation of the resultant absorbed and scattered light to determine the level of hemoglobin oxygen saturation.
It is well known that hemoglobin oxygen saturation, i.e., blood oxygenation level, can be determined by measuring the attenuation of light energy when passed through a blood sample, either in vivo or in vitro. In the bloodstream, hemoglobin loosely combines with oxygen to form oxyhemoglobin in order to transport oxygen to various body tissues where it then can be released. In vivo optical measurement of blood oxygenation level relies on the fact that, because the light absorption properties of hemoglobin and oxyhemoglobin differ, the degree to which a given blood sample attenuates light energy is directly related to the concentration of oxygen in the sample. For example, hemoglobin transmits considerably less visible red light (i.e., light having wavelengths from 620-720 nanometers (nm)) than does oxyhemoglobin. Therefore, blood with high oxygen concentrations will transmit more visible red light than will blood with low oxygen concentrations.
To provide sufficient warning of the onset of hypoxemia, a pulse oximeter must be capable of accurate and continuous real-time measurement of patient hemoglobin oxygen saturation. Oximeters have been developed which employ pulsed light sources in combination with photosensors to measure light intensities transmitted through patient tissue. Light emitting diodes (LEDs) are often used for light sources to produce, for example, visible red light and infrared radiation. In some devices, the LEDs are serially pulsed to produce an interleaved signal stream which is detected by a photosensor. The signal stream might consist of visible red light, infrared radiation, and ambient radiation interleaved in any desired manner. Such oximeters usually include a photoelectric probe and an electronic processor. The photoelectric probe, which houses the light sources and the photosensors, is positioned on a patient so that light can either be directed through the tissue (forward scattering), or reflected from the tissue (back scattering), before being detected by the photosensors. The photoelectric probe is typically mounted on the patient's finger or ear.
An electronic processor is used in conjunction with the photoelectric probe for controlling power to the light sources, measuring the amplitude of light signals from the photosensor, determining the degree to which light is attenuated by the tissue, and providing readouts of blood oxygenation levels. A pulse oximeter of this general type is disclosed in commonly assigned U.S. Pat. No. 4,621,643 to New, Jr., et al., the entire specification of which is incorporated herein by reference.
For effective, continuous, real-time monitoring of blood oxygenation levels, the operation of a pulse oximeter must be as automated as possible. For example, during surgery anesthesiologists need current, accurate, in vivo information on oxygenation levels over an extended period of time. In such situations, it is preferable that this information be available with little or no need for manual adjustment of oximeter equipment so that attention is not diverted from higher priority tasks.
Automated operation of pulse oximeters has been achieved through the use of controllers and control circuitry such as embodied in, for example, a central processing unit (CPU). CPUs have not only been used for the calculation and display of blood oxygenation levels, but also for a variety of other tasks, including data acquisition, adjustment of transmitted light intensity levels, controlling the chopping rate of the LEDs, adjustment of circuitry gains for measuring light intensities, and con
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Cohen Lee S.
Nellcor Puritan Bennett Incorporated
Winakur Eric F.
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