Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2001-01-17
2003-03-04
Walberg, Teresa (Department: 3742)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S324000, C600S340000, C600S301000, C600S484000, C600S529000
Reexamination Certificate
active
06529752
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of pulse oximeters and methods for monitoring the occurrences of a patient's sleep disorder breathing events. More particularly, this invention relates to a device and method for monitoring oxygen desaturations in a subject's arterial blood flow (oximetry) as a result of sleep apnea events and other respiratory disturbances, and counting the number of these events that occur during a prescribed period.
2. Description of the Related Art
The diagnosis of a patient's sleep disorders typically involves an analysis of the patient's breathing disturbances during his or her sleep. These breathing disturbances are defined by the American Sleep Disorder Association and the American Sleep Apnea Association as being sleep “apnea” if the disordered breathing is a pause that lasts ten or more seconds. They are further identified as: (1) Central Apnea—cessation of airflow (upper airway—oral and nasal) and respiratory effort (amplitude of chest movement during breathing); (2) Obstructive Apnea—cessation of airflow with continuation of respiratory effort; (3) Hypopnea—decrease in airflow from baseline (typically one-third to one-half or more) with continuation of normal or decreased levels of respiratory effort; and (4) Cheyne-Stokes Breathing—a breathing pattern that characteristically shows cyclical breathing with progressively decreasing breathing to a shallow level followed by progressively increasing breathing in a decrescendo-crescendo pattern. During the shallow breathing period the decreases may be severe enough to be clear central hypopneas or apneas which last for several seconds. Such apnea events may occur hundreds of times during the sleep period and may lead to severe sleep disruptions and frequent awakenings.
The analysis and diagnosis of respiratory sleep pathologies currently involve a comprehensive testing method utilizing polysomnography (PSG). This procedure involves a full night testing in a medical sleep laboratory to monitor the temporal variations in the amplitude of the patient's sleep-impacted, physiological parameters, including: a continuous measure of the level of oxygen saturation in the arterial blood flow (SpO2), heart rate, upper respiratory airflow, thorax and abdomen respiration efforts, electroencephalograms (EEG; electrical activity of the brain), electro-oculogram (EOG; electrical activity related to movement of the eyes), and electromyograms (EMG; electrical activity of a muscle). The PSG testing procedures are expensive as they are typically conducted in clinical settings by trained PSG technicians.
Current PSG equipment used for sleep testing share common, less-than-desirable features: (1) their use is expensive, since the equipment itself is expensive and a technician usually must be involved for its set-up and disconnection, plus the data collected must be subjectively analyzed by highly trained, sleep professionals, and (2) the recording devices require patients to be outfitted with tethered sensors for connection to bulky body monitors, computers or consoles such as a polygraph, thus, their size and weight does not allow the patient to be ambulatory, which can be essential for the evaluation of treatment efficiency and compliance.
Although PSG testing is the standard method establish for testing sleep disordered patients, there is strong evidence that measurements of the level of oxygen saturation in a subject's arterial blood flow (SpO2) alone is useful for assessing a patient's sleep-related, breathing disturbances. A compilation of several recent studies, which observed over seven thousand patients suspected or diagnosed with sleep apnea, reported typical oxygen levels decreases of anywhere form 2% to 4% for hypopneas (Note: The average oxygen saturation (profusion) baseline, measured at the finger of a subject, typically ranges from 92% to 98%). Some patients with central or obstructive apneas have been noted to experience arterial blood oxygen saturation decreases greater than 30%.
Oxygen desaturation events of ten seconds or longer duration and having a oxygen level decrease of 3% or more would appear to be a viable means for diagnosing the occurrence of a sleep hypopnea. See FIG.
1
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Such measurements of the level of oxygen saturation in a subject's arterial blood flow (SpO2) are typically made with commercially-available pulse oximeters. Pulse oximetry has previously been described in many U.S. Patents, including U.S. Pat. Nos. 4,407,290, 4,266,554, 4,086,915, 3,998,550, and 3,704,706.
As blood is pulsed through the lungs by the heart action, a certain percentage of the deoxyhemoglobin, RHb, picks up oxygen so as to become oxyhemoglobin, HbO2. From the lungs, the blood passes through the arterial system until it reaches the capillaries at which point a portion of the HbO2 gives up its oxygen to support the life processes in the adjoining cells.
By medical definition, the oxygen saturation level is the percentage of HbO2 over the total hemoglobin; therefore, SpO2=HbO2/(RHb+HbO2). A person can lose consciousness or suffer permanent brain damage if the person's oxygen saturation value falls to very low levels for extended periods of time. Because of the importance of the oxygen saturation value, it has been referred to as the fifth vital sign.
An oximeter determines the blood's saturation value by analyzing the change in color of the blood. When radiant energy passes through a liquid, certain wavelengths may be selectively absorbed by particles which are dissolved therein. For a given path length that the light traverses through the liquid, Beer's Law (the Beer-Lambert or Bouguer-Beer relation) indicates that the relative reduction in radiation power at a given wavelength is an inverse logarithmic function of the concentration of the solute in the liquid that absorbs that wavelength.
For a solution of oxygenated human hemoglobin, the absorption maximum is at a wavelength of about 640 nanometers (red), therefore, instruments that measure absorption at this wavelength are capable of delivering clinically useful information as to the oxyhemoglobin levels.
In general, noninvasive methods for measuring oxygen saturation in arterial blood utilize the relative difference between the electromagnetic radiation absorption coefficient of deoxyhemoglobin, RHh, and that of oxyhemoglobin, HbO2. It is well known that deoxyhemoglobin molecules absorb more red light than oxyhemoglobin molecules, and that absorption of infrared electromagnetic radiation is not affected by the presence of oxygen in the hemoglobin molecules. Thus, both RHb and HbO2 absorb electromagnetic radiation having a wavelength in the infrared region to approximately the same degree. However, in the visible region, the light absorption coefficient for RHb is quite different from the light absorption coefficient of HbO2 because RHb absorbs significantly more light in the visible spectrum than HbO2.
In the practice of pulse oximetry techniques, the oxygen saturation of hemoglobin in intravascular blood is determined by: (1) alternately illuminating a volume of intravascular blood with electromagnetic radiation of two or more selected wavelengths (e.g., a red wavelength and an infrared wavelength), (2) detecting the time-varying electromagnetic radiation intensity transmitted through or reflected back by the intravascular blood for each of the wavelengths, and (3) calculating oxygen saturation values for the patient's blood by applying the Lambert-Beer transmittance law to the detected transmitted or reflected electromagnetic radiation intensities at the selected wavelengths.
Today's conventional pulse oximeters generally are complex, table-top consoles or handheld devices. They are commercially available from many sources, including: Nonin (#8500 model), HealthDyne (#920M), Vitalog (#VX4), Novametrix (#510/511), Allied Healthcare (#3520), Criticare Systems (#5040), Lifecare International (SpotChek+),
Allen Richard P.
Krausman David T.
Dahbour Fadi H.
Guffey Larry J.
Walberg Teresa
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