Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Patent
1997-02-24
1999-04-06
Peffley, Michael
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
A61B 500
Patent
active
058910255
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Pulse oximetry is a process for measuring arterial oxygen ration. It can be employed in principle in all pulsatile (systolic-diastolic blood pressure) perfused tissues of all species.
Description of the Related Art
Pulse oximetry has been employed clinically with great success for many years. It is no longer possible to imagine operating theaters, intensive care stations, emergency rooms, ambulances, obstetrics wards, etc. without it. Its success rests on its simple operation, the reliable indication and the uncomplicated interpretation of the indicated values.
Pulse oximetry has, until this day, not been available for use as an indicator during delivery. This is remarkable, because oxygen saturation is an essential piece of information for the birth helper, problems relating to oxygen condition, and indicators (16% Germany, 20% Europe, 25-33% USA). order to make this process available for use during delivery. An author of the present patent application has been awarded a pioneer patent for transmission pulse oximetry on unborn fetuses during birth.
During the development of pulse oximetry for assistance in delivery, a particular difficulty has become apparent: calibration. By this, we refer to the achievement of a correlation between the fetal oxygen saturation indicated by the pulse oximeter and the actual arterial oxygen saturation found in the blood of the fetus. Calibration becomes particularly difficult in the fetal area because the fetus already has, or can have, a physiologically very low oxygen saturation. One must thus be able to calibrate, among other things, for very low arterial oxygen saturation levels, which are not reconcilable with those of normal living organisms (be they human or animal), at least not in all situations, in which the brain is included in the low arterial oxygen saturation levels. This does not apply when, for example, a body part, such as an arm, is temporarily isolated for calibration/validation, that is, has a circulation rate differing from the rest of the body which is in correspondence with that of the brain. The fetus is equipped, for this physiological oxygen poor condition, with a special hemoglobin variant, the fetal hemoglobin (HbF). It exhibits a left-biased oxygen binding curve, and thus has a particularly high affinity for oxygen and makes possible therewith even under physiologically non-optimal conditions (prolonged phases of oxygen bonding with oxygen which makes oxygen ultimately available to the fetal tissue.
Because all pulse oximeters available on the market must be calibrated by the manufacturer, a number of methods have been developed and described in the literature. The calibration over a great oxygen saturation range, as is necessary for the fetal situation, provides, however, a particular requirement or demand on the manufacturer of the respective devices, which cannot be overcome with known methods.
The state of the art describes various calibration methods:
1) Calibration on voluntary subjects: carbon dioxide), of which the oxygen partial pressure is stepwise lowered in defined steps from normal values to hypoxic values. After an equilibration is achieved between the oxygen partial pressure in the gas mixture and in the blood, blood samples are taken, from which the oxygen saturation in the arterial blood is determined and at the same time, that is, at the moment the blood is withdrawn, the measured value Omega (see below) is measured with the pulse oximeter to be calibrated. This calibration is thus developed by obtaining as many solid measured values as possible, for which both the oxygen saturation as well as the Omega value is known.
A table or curve is then input into the device, that is, the software of the device, which makes it possible to determine at any measured Omega the corresponding oxygen saturation (Severinghaus/San Francisco: Pulse Oximetry, Springer Verlag, 1986).
2) Another method comprises photometricaly measuring the pulsatile arterial blood in an artificial construct instead of in a living tissu
REFERENCES:
patent: 4834532 (1989-05-01), Yount
patent: 4968137 (1990-11-01), Yount
patent: 5111817 (1992-05-01), Clark et al.
patent: 5278627 (1994-01-01), Aoyagi et al.
Buschmann Johannes P.
Falkowski Reinhold
Peffley Michael
Winakur Eric F.
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