Patent Application
20170319142
Not Applicable
Not Applicable
This invention relates to optical measurement methods used in medical instrumentation.
Optical detection is a method used to monitor a number of factors in humans and animals. It consists of shining a light source on a portion of the body, detecting the transmitted or reflected light then analyzing the resulting data to determine levels of the factor of interest or monitor changes which can determine pulse. Measurements while the body is in motion such as in medical transport or during activities such as exercise are of growing interest. Problems with the technique are encountered when the motion causes changes in the optical path changes in the detected signal often to the point of obscuring the desired signal. Minor changes in the optical path can cause large effects in the optical signal. Detection of the pulse during exercise is a common application. Separation of the pulse signal from the exercise signal can be very difficult particularly if the exercise is rhythmic such as running and if the pace is in the same range as typical pulse. Current state of the art uses accelerometers to detect the motion. While the signal provided by the accelerometer does indicate the motion of the body, it may or may not indicate any change in the optical signal so is not of much value as a correction signal. If a signal representing the change in the optical signal due to motion is available it can be mathematically reduced from the optical signal through the use of an adaptive algorithm.
There are a number of optical detection methods currently used for monitoring. Pulse Oximetry is an optical method used to detect the pulse and the oxygenation level of the blood. It is done by shining infrared and red light either through the skin or reflected from the skin and detecting and calculating the ratio between the two. Carbon Monoxide is detected the same manor but using a different wavelength where the Carbon Monoxide preferentially absorbs light. Glucose level detection is another use as are others.
In addition to the transmittance and reflectance measurement methods Photoacoustic and Raman spectroscopy are optical methods that can also be used and can benefit from motion artifact reduction. Photoacoustic uses a pulsed source which when it is absorbed by a compound, heats it slightly causing an expansion which causes a sound which can be detected Raman is similar to reflection only it detects emitted light, which has been sifted slightly from the source wavelength. The optical elements are comprised of sources and detectors. With the different techniques the source can vary from one to several LEDs, or a laser, a lens or fiber optic which is providing the source light to the body. The detectors can be one or several optical detectors, a lens or fiber optics or a microphone for Photoacoustic.
To reduce the motion artifacts from the optical signal, a noise cancellation algorithm such as an adaptive filter is used.
We have found that measurement of the force between the optical sensors and the body produces a signal, which correlates to the variation in the optical path, which contributes to artifacts or noise.
Measurement of force can be performed in a number of ways. One method is through the use of thin film sensors. Thin film force sensors are composed of a number of layers or flexible material usually plastic, which surround an active layer which response to changes in force by changing its resistance. Thin film sensors because of their small size and flexibility are useful for this device, but other measurement methods such as inductive, capacitive and magnetic can be used.
Location of the force sensor can varied in a number ways as long as it is physically connected, if not physically touching, the optical elements and the body so it is able to monitor the change in force of the optical elements on the body being testing. One example is implemented by using a thin film force sensor located under the optical source and detector utilizing a sensor that transmits the wavelength of light for the analysis or simply has holes where needed for light passage. Another method is to mount the source and detector on the force sensor. In a system such as watch or armband, the sensor could be mounted on the band opposite of the optical sensor or monitoring the band tension. Further enhancements are to incorporate the force sensor into the same chip as the source leds and detector.
The problem with an accelerometer used by a number of systems is that the signal does not necessarily correlate with the undesired changes in the optical signal because it is only the change in the optical path or body part monitored with relationship to the sensor that is of interested, i.e. if both are accelerated together the optical response will not change but the accelerometer does.
An electronics module located near the optical sensor and the force sensor collects data from each simultaneously or interleaved so they are monitoring at the same time. The data can be fully processed by this module to reduce noise and calculate and display resulting values such as pulse or Oxygen levels. This module can be implemented as a circuit comprised of individual components, or a microprocessor or a combination of the two. The data may be partially processed locally or not at all and simply transmitted to another system such as a smart phone, via bluetooth, or WIFI where further processing is done and results displayed.
Other embodiments include moving the sensor to other locations that can provide a good noise signal caused by motion this could be on the other side of the body or the force sensor could be integrated in the band and be monitoring the tension of the band.
In addition to noise cancellation, it is anticipated the force signal can be used as a start signal to collect data only when the sensor is in contact with the skin. The force signal can be further analyzed to detect pulse directly, or to indicate exercise parameters such as pace. Other variations include the application of several force sensors such as once associated with the optical source and another with the optical detector in cases where the two a some distance apart.
The invention improves optical measurements methods used on humans and animals that may be in motion by using an integrated force sensor to provide a noise signal, which is used mathematically to reduce the artifacts in the signal, caused by subject motion.
The present invention uses a force sensor to detect changes in the force between the optical sensors and the skin being measured where we have found there is a direct correlation between the optical signal artifacts and the force signal.
In this configuration, which can be applied to the body like a watch or an armband, the optical sensor 5 and light source/s 4 are mounted on a thin film force sensor 3 and the entire package is held to the body by a band 1 (shown cut away). The Source 5 and Sensor 4 monitor the blood in the body 6. An electronics module which includes the source and the sensor like the MAX30100 from Maxim Integrated San Jose, Calif. can be used and mounted on a thin-film sensor such as the FSR400 from Interlink Electronics, Inc, Westlake Village. Data is collected on a microprocessor such as an ARM 1pc1768 from NXP Semiconductors Netherlands B.V. Eindhoven The Netherlands.
This application claims the benefit of PPA Ser. No. 62/156,661 filed May 4, 2015 by the present inventor
