Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
1996-03-06
2001-06-26
Dvorak, Linda C. M. (Department: 3739)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S323000
Reexamination Certificate
active
06253097
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of medical monitoring instruments such as pulse oximeters. The invention uses vertical cavity surface emitting laser diodes (VCSELs) as the light sources. The VCSELs are located either in: (1) the probe itself, (2) the connector to the probe, or (3) the monitor box connected with an optical fiber to the probe.
PROBLEM
It is a problem in the field of medical monitoring instruments to manufacture a monitoring instrument that satisfies a number of diverse and sometimes contradictory requirements. It is important that the monitoring instrument be simple to use, in that it conforms to a variety of patients who differ in size and shape. The probe must be securely affixable to the patient, such as on a patient's appendage, without requiring complex structures or elements that can irritate the patient. In addition, in order to reduce the risk of infection and contamination, the probe is built to be disposable so that the probe is used one or more times with the patient and then destroyed. In some cases the probe must also be inexpensive so that it can be disposable after use and yet the patient must be shielded from any potentially dangerous electrical signals or heat produced by the probe. The probe must also reliably and accurately perform the required measurements. The probe, cable and monitoring instrument are all subject to a hostile operating environment and must be manufactured to be rugged to survive rough handling and the presence of highly reactive fluids. The probe must therefore maintain the required measurement accuracy, be rugged to withstand the hostile environment, be safe for attachment to the patient and yet be inexpensive since it is often a disposable element. To achieve these goals, compromises are typically made, although the accuracy of the measurements tends to be of paramount importance.
In the specific field of photoplethysmography, the light beams that are generated by the probe must be of sufficient intensity to illuminate the perfused tissue and also be of constant wavelength, since the light absorption of the monitored analyte varies as a function of wavelength. Light emitting diodes (LEDs) that produce light beams at red and infrared wavelengths are typically used in the probe for this purpose. The production of an intense beam of light must be balanced with the requirement that the probe does not operate at a significantly elevated temperature, which would cause irritation to the patient's skin. A complicating factor is that the light emitting diodes are mounted in the probe module, and are juxtaposed to the patient's skin. The light emitting diodes are therefore subject to significant temperature fluctuations and the corresponding changes in wavelength output by the light emitting diodes, which causes a measurable source of error in the measurements that are taken by the monitor device.
It is preferable in photoplethysmographic systems to use laser diodes, which produce a beam of substantially monochromatic light similar to or exceeding the light power available from light emitting diodes that are typically used in photoplethysmography. The difficulty with laser diodes currently available is that their cost prevents them from being used in a disposable probe. Placement of the laser diode in the monitoring instrument necessitates the use of one or more fiber optic strands in the cable that interconnects the disposable probe with the monitoring instrument. The cable in a hospital environment typically suffers rough handling and the life of the fiber optic strands in the connector cable can be fairly limited, thereby increasing the effective cost of the disposable probe since the cable must be replaced on a fairly frequent basis.
Thus, there presently does not exist a monitoring instrument that can fully satisfy this plurality of diverse requirements in a manner that does not compromise the performance of the monitoring instrument.
SOLUTION
The above describe problems resolved and a technical advance achieved in the field of medical monitoring instruments by the apparatus of the present invention which makes use of a monochromatic light source, in the form of a plurality of surface emitting laser devices, to produce a plurality of high intensity substantially monochromatic beams of light. In the preferred embodiment of the invention disclosed herein, the monitoring instrument and probe comprise an arterial blood monitoring instrument, such as a pulse oximeter instrument which noninvasively monitors blood analytes in the patient. The use of monochromatic light improves the accuracy of the measurements and simplifies the calibration process.
The light source is an array of surface emitting laser devices, each of which outputs a substantially monochromatic beam of light of substantially circular cross section. The preferred embodiment of this apparatus places the laser diodes in the connector at the distal end of the cable proximate to the disposable portion of the probe to thereby implement an instrumented connectorized laser diode probe cable. Placement of the light source at the point of contact on the patient and using surface emitting laser devices, the light beam can directly irradiate the perfused tissue and the probe can be constructed to be more lightweight, conformable and inexpensive. This architecture eliminates the need for fiber optic strands in the cable yet provides the benefits of laser diode light generation over the presently used light emitting diodes. Furthermore, the potentially disposable section of the probe can be a minimalistic design since all the expensive active elements are located in the cable connector. The disposable section of the probe simply consists of the apparatus required to affix the probe to the patient's appendage and the mating portion of the connector that interconnects with the cable and a photodetector. An alternative embodiment of the invention places the surface emitting laser diodes in the probe itself, rather than in the connector, thereby simplifying the connector implementation and making the surface emitting laser diodes an integral element in the probe. Another alternative embodiment of the invention places the surface emitting laser diodes in the monitoring instrument itself and transmits the generated beams of light to the potentially disposable segment of the probe via a cable.
This basic probe architecture with the light source detached from the probe, and using surface emitting laser diodes, overcomes the problems inherent in existing probes and also is architected for ease of reliable and accurate manufacture. The probe generates a constrained light path, can be less expensive than existing probes and uses improved packaging with fewer conductors required to connect the probe with the monitor. This monitor and probe architecture therefore represents a significant advance in the technology of medical monitoring instruments.
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Aronow Kurt A.
Pologe Jonas A.
Datex-Ohmeda Inc.
Dvorak Linda C. M.
Gibson Roy
Marsh & Fischmann & Breyfogle LLP
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