The invention relates generally to pulse oximeter, and more particularly to, a method and system for reducing effects of cross talks in a pulse oximeter.
Pulse oximetry is at present the standard of care for the continuous monitoring of arterial oxygen saturation (SpO2). Pulse oximeters provide instantaneous in-vivo measurements of arterial oxygenation, and thereby provide early warning of arterial hypoxemia, for example. A conventional pulse oximeter comprises a probe including at least two LED emitters and a photo detector to detect the lights. The probe is connected to a patient's finger tip or to the ear lobe. The light from the emitters is passed through the tissue and the photo detector detects the light and, based on the transmitted and received light, light absorption by the tissue is evaluated.
The accuracy of the pulse oximeter is determined by several factors. An important factor affecting the accuracy of a pulse oximeter is the direct electrical crosstalk between the circuitry driving the LEDs and the circuitry receiving the signal from the photo detector. Due to crosstalk of this type, non-optical signal components may superimpose on the signal received and thus cause erroneous oxygen saturation readings. This problem does not exist with conventional pulse oximeters using wide pulses, where power consumption is not a major concern.
But in the case of portable oximeters, especially battery operated oximeters, the power consumption is a major concern and the pulse width cannot be increased beyond a certain level. Lower power consumption calls for narrower pulses for driving the LEDs, the narrower pulses being more vulnerable to this type of crosstalk. The problem is further aggravated if the tissue of the patient is thicker than normal, whereby the signal received from the photo diode detector is weaker than normal.
Further the cross talk generated within a pulse oximeter depends on topology of the circuitry driving the LEDs and the circuitry receiving detect signal from the photodiode detector and the topology of the cable that connects the detector with the circuitry receiving detect signal or the cable that connects or feeds the drive signal for driving the LED emitters in the pulse oximeter. The cross talk generated may vary based on the configuration of the cable or the probe used. Since the probes are manufactured by different manufactures, the allowable cross talk limit, noise etc may vary. Thus even though many of the pulse oximeters today are configured to accept different types of probes, manufactured by different manufactures, special attention needs to be given in addressing effects of cross talks generated by these probes.
Thus there exists a need to provide an improved low power pulse oximeter, wherein the effect of cross talk is configured to be a minimum.
The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification.
One embodiment of the present invention provides a method for reducing effects of cross talk in a pulse oximeter. The method includes: setting an initial pulse width and pulse rate for an LED drive signal; measuring a cross talk generated within the pulse oximeter; and minimizing the pulse width of the LED drive signal with reference to the cross talk.
In another embodiment, a pulse oximetry method is described. The method includes: setting initial pulse width and pulse rate for an LED drive signal; obtaining cross talk generated within the pulse oximeter; comparing value of the cross talk with a threshold value; adjusting the duty cycle of the LED drive signal upon detecting cross talk value as below the threshold value; and initiating the measurement of oxygenation once the pulse width is adjusted to a desirable value.
In yet another embodiment, a method of monitoring arterial oxygen saturation (SpO2) using a plurality of light emitters and at least one detector is disclosed. The method includes: initiating monitoring of the oxygenation using an emitter drive signal having preset initial characteristics; obtaining cross talk generated within the pulse oximeter; determining an error value generated in the measurement of oxygenation due to the cross talk; comparing the error value with a threshold value; adjusting the duty cycle of the emitter drive signal until the error value is below the threshold value; and identifying the arterial oxygen saturation (SpO2).
In yet another embodiment, a method of configuring a pulse oximeter to adapt multiple probes is disclosed. The method includes: selecting at least one probe from a plurality of probes; activating the selected probe by a drive signal having preset initial characteristics; accessing value of cross talk generated within the pulse oximeter in relation to the selected probe; obtaining a threshold value of permissible cross talk for the selected probe; and minimizing duty cycle of the drive signal in reference to the cross talk generated due to the probe, the duty cycle being minimized until the cross talk reaches the threshold value.
In yet another embodiment, a pulse oximeter is disclosed. The system comprises: at least one probe including at least two emitters configured to emit radiations in different wavelengths and at least one detector to receive radiations; a drive unit for providing drive signal to the emitters, the drive signal configured to have preset initial characteristics; a cross talk identifier configured to identify electrical cross talk synchronous with the drive signal, generated within the pulse oximeter; and a processor configured to adjust duty cycle of the drive signal in reference to the cross talk.
Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken as limiting the scope of the invention.
Various embodiments of the present invention provide a method of reducing the effects of cross talk in a pulse oximeter. The invention addresses the electrical cross talks generated within the pulse oximeter.
In an embodiment, the invention facilitates a method of controlling the power consumption in a pulse oximeter. The power consumption is minimal, when the pulse width of the drive signal is minimum. However if the pulse width is minimal, the cross talk will adversely affect the accuracy of oxygenation measurement. Thus an optimum value of duty cycle needs to be derived where the effect of cross talk is minimum on the oxygenation measurement, but still the pulse oximeter is power efficient.
In an embodiment, the invention suggests a method of varying duty cycle of a drive signal in a pulse oximeter system in real time, even while the system monitors the oxygenation.
In an embodiment, with reference to the cross talk, the duty cycle of the detector signal is modified to avoid the effect of cross talk in the oxygenation measurement.
The term “cross talk” referred to in the specification refers to electrical cross talk generated within the pulse oximeter due to the various power coupling such as resistive, inductive, capacitive etc. The cross talk may occur due to the various cables involved in the pulse oximetry system. Mainly the cross talk due to the cable that carries drive signal from a drive unit to the LEDs in the probe and another cable that carries the detecting signal from the detector located inside the probe to an amplifier.
At step 120, cross talk generated within the pulse oximeter is measured. Different mechanism such as using a leakage resistor, changing the amplitude of the drive signal in a fixed pattern etc may be used in measuring the cross talk. The cross talk measurement need not be limited to the examples mentioned; the system may use any technique for measuring the cross talk. In an embodiment, the electrical cross talk synchronous with the LED drive signal is measured. The electrical cross talk could be due to at least one of capacitive, resistive or inductive power coupling from the driving signal to the detect signal or in the drive signal due to the cable topology. The cross talk caused by resistive, captive or inductive power coupling may be measured together or separately. Further the cross talk could be measured before measurement of the oxygenation level, based on some standard values or could be measured during the arterial oxygen saturation (SpO2).
At step 130, the pulse width is minimized with reference to the cross talk. For each probe used in monitoring the oxygenation, there is a threshold value indicating the allowable cross talk level. The measured cross talk is compared with the threshold value and, based on the same, pulse width of the drive signal is minimized. The pulse width is increased until the cross talk remains within the threshold value. The reduction in pulse width will reduce the power consumption as well.
In an example, an error signal may be generated from the measured oxygenation signal. This error signal could be compared with a standard threshold value that indicates the allowable error limit and if the error value is within the threshold value, the pulse width may be minimized. By minimizing the pulse width, while monitoring the cross talk, will ensure a power efficient method with the cross talk having least impact on the measurement.
In an example, the pulse width of detect signal that is detected by the detector may be adjusted to reduce the impact of cross talks on the measurement of oxygenation. The pulse width of the detect signal is varied based on the cross talk. The pulse width may be increased to delay the sampling of the detect signal. This facilitates the cross talk to die off before sampling of the detect signal.
In an embodiment, based on the measured cross talk, the pulse rate or frequency of the drive signal may be modified or adjusted. This adjustment will also assist in reducing the impact of cross talk.
In an example, there could be multiple probes used with a pulse oximeter system. These multiple probes include different probes manufactured by different manufacturers. Thus, different probes may have different threshold allowable cross talk levels and based on the same pulse width of the corresponding drive signal may be adjusted.
In an example, the pulse width of the emitter drive signal may be adjusted in real time. From the measured oxygenation level, the error in the measurement due to the cross talk is calculated in real time and, based on the comparison result, the pulse width of the emitter drive signal is adjusted.
If different types of cross talk, noise or any other possible errors by a probe are detected, their values may be obtained and compared individually with their corresponding threshold values. Based on the comparison result, the pulse width of the drive signal or detect signal may be adjusted accordingly.
The photo detector 514 detects the light that comes out of the tissue and the signal detected by the detector 514, the detect signal, is passed to an amplifier 530 for amplifying the detect signal. A cable carries the detect signal to the amplifier 530. There exist a resistive, inductive, capacitive cross talk (illustrated in
The amplifier 530 feeds the detect signal to a sampling mechanism 580, wherein the detect signal is sampled to identify the arterial oxygen saturation (SpO2). In an example, sampling of the detect signal is delayed based on the cross talk. The duty cycle of the detect signal may be increased or the sampling of the detect signal may be delayed so that the cross talk can die off or dissipate before sampling the detect signal.
The advantages of various embodiments of the invention include improving the performance of a pulse oximeter. The effect of cross talk in the arterial oxygen saturation (SpO2) measurement can be reduced or minimized. Also embodiments of the invention suggest a method of reducing power consumption of the pulse oximeters.
Thus various embodiments of the invention describe a method and system for reducing the effect of cross talk in a pulse oximeter. Another aspect of the invention suggests a method of reducing the power consumption of pulse oximeters.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
Exemplary embodiments are described above in detail. The assemblies and methods are not limited to the specific embodiments described herein, but rather, components of each assembly and/or method may be utilized independently and separately from other components described herein. Further the steps involved in the workflow need not follow the sequence in which there are illustrated in figures and all the steps in the work flow need not be performed necessarily to complete the method.
While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention as set forth in the following claims.
This application is related to commonly assigned U.S. Pat. No. 6,963,767 B2, granted on Nov. 8, 2005 to Rantala, et al. and entitled “Pulse Oximeter”, which is herein incorporated by reference in its entirety.