Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-05-26
2002-09-10
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S330000, C600S336000, C600S322000
Reexamination Certificate
active
06449501
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to pulse oximetry devices and methods. More particularly, the invention is concerned with a pulse oximetry system that provides enhanced signal quality information to the operator via signal sonification, in order to improve monitoring accuracy and availability.
BACKGROUND
Pulse oximeters are well known in the art. Typically, such devices comprise a sensor with light emitting device(s) and associated photodetector(s), attached to a monitoring device performing signal acquisition, analysis, and display/print functions. One particular example of a pulse oximeter is described in U.S. Pat. No. 5,842,981.
The signals acquired from a pulse oximeter are proportional to the tranmissivity of the biological tissues at the sensor. When visualized as photoplethysmographic waveforms, pulsations are visible occurring in synchrony with the heart rate. These pulsations result from the increased absorption of light occurring during passage of blood through the arterial system. Because the arterial pulsation is the result of systole in the heart, this rapid increase in absorption (decrease in detected light intensity) is referred to herein as the systolic phase of the signal. The intervening time between systolic phases, characterized by a relatively gradual decrease in absorption, is herein referred to as the diastolic phase. By choosing appropriate wavelengths of light, the plurality of oximetry signals can be interpreted to yield the percentage of saturation of the hemoglobin molecules with oxygen (SpO
2
). In the prior art, red and infrared pulsatile amplitudes, scaled by their respective mean light intensities, are combined in a ratiometric equation to yield a ratio related to SpO
2
.
The pulsatility of the photoplethysmographic waveform is very distinctive, resembling an inverted arterial blood pressure waveform even to the extent that a dichotic notch is often visible. (This similarity is commonly emphasized by inverting the photoplethysmographic waveform.) Like the arterial pressure waveform, the oximetry signals represent the hemodynamic activity of the cardiovascular system, rather than electrical activity of the heart like an ECG. Hence oximeters often provide a means of signal visualization to convey signal quality as well as physiological information (such as the pulse rate and rhythmicity).
Successful physiological monitoring, including pulse oximetry, depends upon acquisition of usable signals from the sensor(s). One problem associated with pulse oximetry is that signal quality can be highly dependent upon sensor placement and the condition of the underlying tissue. This problem is relatively worse in reflectance mode pulse oximetry, wherein signals are typically of lower intensity.
Reflectance pulse oximetry appears, however, to be the only viable method for in utero fetal pulse oximetry. The sensor is inserted into the uterus of a mother to noninvasively monitor the condition of a fetus, a mother, and a placenta. One particular example of a sensor designed for fetal pulse oximetry is described in U.S. Pat. No. 5,425,362. The sensor placement is made through the birth canal to reach a monitoring position on the fetus. This process and its outcome are difficult to satisfactorily visualize, even utilizing intrauterine imaging technologies such as ultrasound. Thus, fetal pulse oximetry represents a challenging scenario for signal acquisition in medical monitoring.
Clinical experience with fetal pulse oximetry bears this out. A recent study looking at 164 cases in which fetal oxygen saturation could be measured found that reliable signals were available only 64.7% of the time during the first stage of labor, and even less during the second stage of labor (Goffmet et al, 1997). Other studies have reported still lower availability. This percentage of monitoring availability is much less than experienced in clinical practice when using pulse oximetry in adults or even neonates, indicating the difficulty of fetal oxygen saturation monitoring and the need for further improvement.
Thus, it is important to provide the clinician assistance in assessing the efficacy of sensor placement by indirect means, but commercially available systems have failed to satisfy this requirement. The prior art suggests several possible solutions.
In one prior art fetal oximetry sensor, described in U.S. Pat. No. 5,247,932, electrical impedance is monitored near the sensor's active components to detect whether the sensor is in contact with tissue. If both electrodes are bathed in amniotic fluid, the impedance is lower than when one electrode is in contact with wet tissue. A high impedance interface, however, does not guarantee that the tissue site is suitable for pulse oximetry, i.e., adequately perfused and free of interfering material. Nor does impedance measurement alone tell whether the signal quality will be better or worse than that of another site with similar interface impedance, or even if the site is on the fetus and not the mother.
Audio pulse tone generation has been employed in prior art pulse oximeters, an early example of which was described in U.S. Pat. No. 4,653,498. The prior art devices generate a simple tone for each identified pulse. In a further enhancement revealed in the patent, the tone pitch is proportional to the oxygen saturation level. Although useful for providing pulse rate and oxygen saturation trend information, this technique is inadequate for signal quality representation.
Sonification is the field of study dealing with the expression of information as humanly perceptible sound patterns. The human auditory system is highly sophisticated, featuring impressive dynamic range and parallel processing of many narrow sub-bands of the audible frequency range. This makes the audio medium ideal for expressing information that may contain subtle, time-varying features. Sonification has been suggested as a means of conveying more physiological information to the operator of a medical device, as described in U.S. Pat. No. 5,730,140. That patent teaches that the prior art in pulse tone generation (as cited above) suffers from the limitation of “quantization”. That is, the complex, continuous signals acquired from the sensor have been reduced to artificial, simplistic beeps, with a drastic loss of information. The present invention seeks to avoid the information loss inherent in quantization.
The type of quantized pulse tone generation revealed in the prior art is dependent upon successful completion of a chain of algorithmic operations directed at accurately identifying pulsatile events in the input signals. With variations in design and implementation, analogous steps are performed in all pulse oximeters. The purpose of this signal filtering, pulse detection, and ratiometric computation is to obtain the pulse rate and oxygen saturation values, updating them on a relatively frequent basis (ideally, every pulse). These algorithms are generally tuned to rigorously avoid false positive pulse identification, as might occur during conditions of poor signal quality, since false pulses could result in erroneous pulse rate and/or oxygen saturation readings. Therefore, any condition compromising signal quality is likely to result in silence or merely a sporadic audio signal, without helping to discriminate the reason for the signal quality problem (movement, poor perfusion, low illumination level, etc.).
There remains a need for a pulse oximeter providing continuous signal quality information to the operator with rapid response to changing conditions at the sensor-tissue interface and little time delay. Such signal quality information would preferably be conveyed to the operator without requiring full attention to a visual display. That is, the operator should be capable of perceiving the signal quality information even while concurrently attending to the patient or manipulating the sensor. Preferably, the signal quality information would guide the operator during sensor adjustments intended to improve signal quality, that is, con
Kremer Matthew
OB Scientific, Inc.
Reinhart Boerner Van Deuren S.C.
Winakur Eric F.
LandOfFree
Pulse oximeter with signal sonification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pulse oximeter with signal sonification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulse oximeter with signal sonification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2887106