Surgery – Diagnostic testing – Respiratory
Reexamination Certificate
2002-02-22
2004-03-23
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Respiratory
C600S324000
Reexamination Certificate
active
06709402
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to medical diagnostic instruments and, more specifically, to the field of photoplethysmography and using a plethysmographic system to monitor secondary physiological processes based on a plethysmographic signal.
BACKGROUND OF THE INVENTION
During many medical procedures, especially surgical procedures, it is desirable to monitor the functioning of a patient's cardiopulmonary system (i.e., the heart and lungs) to determine a patient's current condition. Various methods for measuring physiological functioning of the cardiopulmonary system exist. Lung functioning may be monitored through the frequency of a patient's respiration using, for example, respiration sensors based on thermistors placed in the respiratory path in front of the mouth and/or nose or breathing belts applied around the chest and abdomen for mechanical pulmonary monitoring. Additionally, a patient's heart may also be monitored during a given procedure. Again, numerous methods exist for monitoring a patient's heart rate from manually checking with a stethoscope to the use of pressure transducers applied to the skin. A disadvantage of such cardiopulmonary measurement methods is that a measurable respiratory movement and/or heart rate is by no means a sign of effective cardiopulmonary operation. For example, in cases where there are obstructions in the respiratory pathway or uncoordinated, out of phase chest and abdominal respiration, a patient may be breathing and their heart may be beating, but oxygen is not being efficiently transferred to their bloodstream. Therefore, it is often desirable to monitor a patient's blood oxygen saturation levels to assure that effective cardiopulmonary functioning is occurring.
Blood oxygen saturation (SpO
2
) levels of a patient's arterial blood may be monitored using a pulse oximeter, which typically measures the absorption of red and infra red light applied to a patient's tissue by oxygenated hemoglobin and deoxygenated hemoglobin in the blood. Pulse oximeters commonly comprise a sensor that is releaseably attached to a patient's appendage, such as a finger, ear lobe or nasal septum, for a given medical procedure. The sensor typically includes a detector and at least one red light source and one infrared light source that may be focused on or through a patient's tissue. The detector detects the light that reflects from or passes through the patient's tissue. This light detector, typically a photodetector, produces what is termed a “plethysmographic signal” indicative of the light attenuation caused by the absorption, reflection and/or diffusion due to the tissue on which the light is directed. This measured absorption data from the plethysmographic signal allows for the determination of the relative concentration of de-oxyhemoglobin (RHb) and oxyhemoglobin (HbO
2
) and, therefore, (SpO
2
) levels, since de-oxyhemoglobin absorbs more light than oxyhemoglobin in the red band and oxyhemoglobin absorbs more light than de-oxyhemoglobin in the infrared band, and since the absorption relationship of the two analytes in the red and infrared bands are known. See, for example, U.S. Pat. Nos. 5,934,277 and 5,842,979.
As may be appreciated, in order to accurately monitor a patient's cardiopulmonary functioning, it is often necessary to use a combination of three separate monitors, a pulse oximeter, a respiratory monitor and a heart rate monitor.
SUMMARY OF THE INVENTION
A primary objective of the present invention is to use plethysmographic signals to monitor a secondary physiological process of the patient such as respiration or heart rate.
A related objective is to use optical signals to monitor a patient's respiration rate.
A further related objective is using multi-channel optical signals transmitted through a patient's tissue to monitor respiration rate.
Another objective is using plethysmographic signals obtained during a given time period to monitor both blood oxygenation and respiration rate.
A further objective of the present invention is to provide a practical algorithm for monitoring variations in a blood analyte composition that are indicative of a patient's respiration.
In accordance with the above objectives, the inventor has recognized that the signals produced by various monitoring devices for monitoring physiological processes of the human body typically include minor variations which are indicative of a secondary physiological processes. In particular, the inventor has recognized that plethysmographic signals contain two components of interest which each may contain minor variations indicative of secondary processes occurring in and/or affecting the cardiopulmonary system. The first component of interest is a low frequency or substantially invariant component in relation to the time increments considered for blood oxygen saturation calculations, sometimes termed the “DC component,” which generally corresponds to the attenuation related to the non-pulsatile volume of the perfused tissue and other matter that affects the transmitted plethysmographic signal. The second component sometimes termed the “AC component,” generally corresponds to the change in attenuation due to the pulsation of the blood. In general, the AC component represents a varying wave form which corresponds in frequency to that of the heartbeat. In contrast, the DC component is a more steady baseline component, since the effective volume of the tissue under investigation varies little or at a low frequency if the variations caused by the pulsation of the heart are excluded from consideration. However, the inventor has recognized that the DC component does vary over a low frequency and small amplitude and that this variation in the DC component is generally attributable to changes in the monitored tissue caused by spill-over effects of various physiological processes of the body including cardiopulmonary processes. Finally, the inventor has recognized that by determining what causes a particular variation in the DC component of the plethysmographic signal it may be possible to monitor a secondary physiological process such as respiration in addition to blood oxygen levels while using a pulse oximeter. Additionally, the inventor has realized the advantages of being able to supply additional physiological information regarding a patient's health during a medical procedure while reducing the number of monitors attached to the patient.
One or more of the above objectives and additional advantages are indeed realized by the present invention where, in one aspect, an apparatus is disclosed to monitor at least one secondary physiological process through variations caused by that physiological process in at least a portion of an optical signal used to calculate a value related to blood oxygenation levels. The apparatus comprises one or more emitters for controllably emitting at least first and second wavelengths of electromagnetic radiation onto or through a portion of living tissue and a detector for detecting signals relative to the transmitted first and second wavelengths of electromagnetic radiation passing through or being reflected from the tissue. The detector is further operable to produce at least a first detector output signal indicative of the electromagnetic radiation passing through or reflected from the tissue. The apparatus also includes a processor which is operative to produce a first output value related to blood oxygen levels of the tissue through a mathematical computation using at least a portion of the detector signal corresponding to each wavelength of electromagnetic radiation applied to the tissue. Further, the processor is able to monitor this first output related to the tissue's blood oxygen levels over a predetermined period to identify variations therein that are indicative of a secondary physiological process. Finally, the processor generates a second output signal indicative of the secondary physiological process.
As will be appreciated,
Datex-Ohmeda Inc.
Marsh & Fischmann & Breyfogle LLP
Winakur Eric F.
LandOfFree
Apparatus and method for monitoring respiration with a pulse... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for monitoring respiration with a pulse..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for monitoring respiration with a pulse... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3266004