Patent Application
20170020420
This application claims priority to Korean Application No. 10-2015-0102695, filed Jul. 20, 2015, and Korean Application No. 10-2016-0023632, filed Feb. 26, 2016. The applications are incorporated herein by reference.
The present invention relates to methods, apparatuses and non-transitory computer-readable recording media for measuring photoplethysmography signals.
Due to recent rapid progress in science and technology, the quality of life of all mankind is being enhanced and medical environment has changed a great deal. In the past, once a medical image was taken by means such as X-ray, CT, fMRI or the like, it would take several hours or days to be able to interpret the image.
However, a picture archive communication system (PACS) has been introduced to enable a medical image to be taken and then transmitted to a monitor screen of a radiology specialist for prompt interpretation. Further, medical equipment for ubiquitous healthcare are wide spread so that patient-performed self-checks on blood glucose and blood pressure are feasible at anytime and anywhere out of hospital, and diabetic or hypertensive patients use the equipment at their home and/or office. Particularly, in the case of hypertension, which is one of the principal causes of various diseases and whose prevalence rate is increasing, there is a need for a system for consistent measurement and real-time notification of blood pressure, and various types of studies associated therewith are being attempted.
Meanwhile, biological information such as an electrocardiogram, heart rate, body temperature, oxygen saturation level, electromyogram, sweat gland activity, sweat rate, and respiratory rate is obtained on the basis of biosignals respectively acquired from two or more contacts on a human body (not necessarily adjoining each other physically), and thus a technique for properly processing and measuring the biosignals acquired from the contacts on the body is required to obtain biological information.
Photoplethysmography (PPG) signals are significantly utilized in measuring a variety of biological information on cardiac functions, including blood oxygen saturation levels (SpO2). According to conventional PPG signal measurement techniques that have been used so far, there are technical constraints such as a need for a shielding structure for preventing errors caused by external light sources.
As a technique for measuring a blood oxygen saturation level (SpO2) using PPG signals, it is possible to sense visible light (e.g., red light, green light, etc.) and infrared light reflected from a human body and calculate an oxygen saturation level on the basis of PPG signals, each corresponding to the sensed visible light and infrared light. The technique is based on a principle that light absorptivity of oxyhemoglobin (HBO2) in blood is greater for infrared light than for visible light.
The brightness (i.e., illuminance) of light sensed by the light receiver 110 needs to be constantly maintained in order to accurately measure PPG signals (and an oxygen saturation level). In order to address this problem, a shielding structure has been employed in the prior art to shield the parts where light is irradiated and sensed from the external light source. According to the prior art, this causes spatial constraints requiring the shield structure to contain all of the components including the light emitter for irradiating light and the light receiver for sensing light, which causes the size of the measurement apparatus to become excessively large due to the shielding structure.
Therefore, a technique for accurately measuring PPG signals (and an oxygen saturation level) in a situation in which brightness of ambient light is not constant due to external light sources is desirable.
Provided herein are methods, apparatuses, and non-transitory computer-readable recording media for accurately measuring photoplethysmography (PPG) signals in a situation in which brightness of ambient light is not constant due to external light sources, by irradiating light of a first wavelength range and light of a second wavelength range onto a body part of a user through a first filter and a second filter, respectively; sensing light of the first wavelength range entering through the first filter and light of the second wavelength range entering through the second filter, respectively; measuring a first illuminance of the light of the first wavelength range entering through the first filter and a second illuminance of the light of the second wavelength range entering through the second filter, respectively; generating a first PPG signal corresponding to the sensed light of the first wavelength range and a second PPG signal corresponding to the sensed light of the second wavelength range; and when a difference between a predetermined reference illuminance and at least one of the first and second measured illuminances is not less than a predetermined level, correcting at least one of the first and second PPG signals with reference to a relative relationship between the predetermined reference illuminance and at least one of the first and second measured illuminances.
According to one exemplary embodiment, there is provided a method for measuring photoplethysmography (PPG) signals, including the steps of: irradiating light of a first wavelength range and light of a second wavelength range onto a body part of a user, respectively; sensing light of the first wavelength range entering through a first filter and light of the second wavelength range entering through a second filter, respectively, and measuring a first illuminance of the light of the first wavelength range entering through the first filter and a second illuminance of the light of the second wavelength range entering through the second filter, respectively; generating a first PPG signal corresponding to the sensed light of the first wavelength range and a second PPG signal corresponding to the sensed light of the second wavelength range; and when a difference between a predetermined reference illuminance and at least one of the first and second measured illuminances is not less than a predetermined level, correcting at least one of the first and second PPG signals with reference to a relative relationship between the predetermined reference illuminance and at least one of the first and second measured illuminances.
According to another aspect of the invention, there is provided an apparatus for measuring photoplethysmography
(PPG) signals, comprising: a first light emitter and a second light emitter configured to irradiate light of a first wavelength range and light of a second wavelength range onto a body part of a user, respectively; a first light receiver and a second light receiver configured to sense light of the first wavelength range entering through a first filter and light of the second wavelength range entering through a second filter, respectively; a first illuminance sensor and a second illuminance sensor configured to measure a first illuminance of the light of the first wavelength range entering through the first filter and a second illuminance of the light of the second wavelength range entering through the second filter, respectively; and a calculator configured to generate a first PPG signal corresponding to the sensed light of the first wavelength range and a second PPG signal corresponding to the sensed light of the second wavelength range, and when a difference between a predetermined reference illuminance and at least one of the first and second measured illuminances is not less than a predetermined level, configured to correct at least one of the first and second PPG signals with reference to a relative relationship between the predetermined reference illuminance and at least one of the first and second measured illuminances.
In addition, there are further provided other methods and apparatuses to implement the invention, as well as non-transitory computer-readable recording media having stored thereon computer programs for executing the methods.
According to the invention, PPG signals may be accurately measured even in a situation in which brightness of ambient light is not constant due to external light sources.
According to the invention, accuracy of a variety of biological information derivable from PPG signals may be improved.
According to the invention, a signal corresponding to sensed light may be adaptively corrected on the basis of a measured illuminance, thereby preventing spatial constraints caused by a conventional shielding structure and allowing a PPG signal measurement apparatus to be easily installed in a wearable device having a small size and limited shape.
In the following detailed description of the present invention, references are made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different from each other, are not necessarily mutually exclusive. For example, specific shapes, structures and characteristics described herein may be implemented as modified from one embodiment to another without departing from the spirit and scope of the invention. Furthermore, it shall be understood that the locations and/or arrangements of individual elements within each of the disclosed embodiments may also be modified without departing from the spirit and scope of the invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the invention, if properly described, is limited only by the appended claims together with all equivalents thereof. In the drawings, like reference numerals refer to the same or similar functions throughout the several views.
Although one or more exemplary embodiments are described as using a plurality of units to perform the exemplary processes, it is understood that the exemplary processes can also be performed by one or plurality of modules. Additionally, it is understood that the term controller/control unit refers to a hardware device that includes a memory and a processor. The memory is configured to store the modules and the processor is specifically configured to execute said modules to perform one or more processes which are described further below. Any units described herein can be devices and/or structures that are configured to perform the stated functions. Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
An entire system for measuring photoplethysmography (PPG) signals according to one embodiment will be discussed in detail below.
As shown in
First, the communication network 100 according to one embodiment can be implemented regardless of communication modality such as wired and wireless communications, and can be constructed from a variety of communication networks, such as local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs). The communication network 100 described herein can include known short-range wireless communication networks such as Wi-Fi, Wi-Fi Direct, LTE Direct, and Bluetooth. However, the communication network 100 is not necessarily limited thereto, and may at least partially include known wired/wireless data communication networks, known telephone networks, or known wired/wireless television communication networks.
Next, the PPG signal measurement apparatus 200 according to one embodiment can function to accurately measure PPG signals in a situation in which brightness of ambient light is not constant due to external light sources, by irradiating light of a first wavelength range and light of a second wavelength range onto a body part of a user through a first filter and a second filter, respectively; sensing light of the first wavelength range entering through the first filter and light of the second wavelength range entering through the second filter, respectively; measuring a first illuminance of the light of the first wavelength range entering through the first filter and a second illuminance of the light of the second wavelength range entering through the second filter, respectively; generating a first PPG signal corresponding to the sensed light of the first wavelength range and a second PPG signal corresponding to the sensed light of the second wavelength range; and when a difference between a predetermined reference illuminance and at least one of the first and second measured illuminances is not less than a predetermined level, correcting at least one of the first and second PPG signals with reference to a relative relationship between the predetermined reference illuminance and at least one of the first and second measured illuminances.
The functions of the PPG signal measurement apparatus 200 will be discussed in more detail below. Meanwhile, although the PPG signal measurement apparatus 200 has been described as above, the above description is illustrative and it will be apparent to those skilled in the art that at least some of the functions or components required for the PPG signal measurement apparatus 200 can be implemented or included in the device 300, as necessary.
Lastly, the device 300 according to one embodiment is digital equipment that can function to connect to and then communicate with the PPG signal measurement apparatus 200, and any type of digital equipment having a memory means and a microprocessor for computing capabilities can be adopted as the device 300. The device 300 can be a wearable device such as a smart glass, a smart watch, a smart band, a smart ring, and/or a smart necklace, or can be a device such as a smart phone, a smart pad, a desktop computer, a notebook computer, a workstation, a personal digital assistant (PDA), a web pad, and/or a mobile phone. According to one embodiment, the device 300 can include a sensing means, such as one or more sensors, for acquiring a biosignal from a human body, and a display means, such as one or more displays, for providing biological information to a user.
In addition, according to one embodiment, the device 300 can further include an application program for performing the functions provided herein. The application can reside in the device 300 in the form of a program module. The nature of the program module can be generally similar to those of a calculator 250, a communicator 260, and a controller 270 of the PPG signal measurement apparatus 200 to be described below. Here, at least a part of the application can be replaced with a hardware and/or firmware device that can perform substantially equal or equivalent functions, as necessary.
Hereinafter, the internal configuration of the PPG signal measurement apparatus 200 configured in part to implement some or all of the functions of the respective components thereof will be discussed.
Referring to
First, according to one embodiment, the light emitter 210 can function to irradiate light of a first wavelength range and light of a second wavelength range onto a body part (e.g., a finger, wrist, etc.) of a user for which measurement is to be carried out. Specifically, the light emitter 210 according to one embodiment can include a first light emitter 211 for emitting light of the first wavelength range and a second light emitter 212 for emitting light of the second wavelength range, and can consist of light emitting diodes (LEDs) for generating the light of the first wavelength range or the light of the second wavelength range according to a predetermined cycle. For example, the light of the first wavelength range can include visible light of a wavelength range of about 490 nm to 780 nm, and the light of the second wavelength range can include infrared light of a wavelength range of about 800 nm to 980 nm.
Further, according to one embodiment, the light of the first wavelength range and the light of the second wavelength range emitted from the light emitter 210 can be irradiated onto the body part of the user through the first filter 241 and the second filter 242, respectively. Here, the first and second filters 241 and 242 can consist of filters for selectively transmitting the light of the first wavelength range and the light of the second wavelength range, respectively.
Next, according to one embodiment of the invention, the light receiver 220 can function to sense light of the first wavelength range and light of the second wavelength range, respectively. Specifically, the light receiver 220 according to one embodiment can include a first light receiver 221 for sensing light of the first wavelength range and a second light receiver 222 for sensing light of the second wavelength range, and can include photodiodes for sensing the light of the first wavelength range or the light of the second wavelength range. According to one embodiment, the light sensed by the light receiver 220 can include the light irradiated by the light emitter 210 and reflected from the body part of the user and ambient light irradiated from external light sources.
Further, according to one embodiment, the light of the first wavelength range and the light of the second wavelength range sensed by the light receiver 220 can enter through the first and second filters 241 and 242, respectively. As described above, the first and second filters 241 and 242 may consist of filters for selectively transmitting the light of the first wavelength range and the light of the second wavelength range, respectively.
Next, according to one embodiment, the illuminance sensor 230 can function to measure a first illuminance of the light of the first wavelength range entering through the first filter 241 and a second illuminance of the light of the second wavelength range entering through the second filter 242, respectively. Specifically, the illuminance sensor 230 according to one embodiment can include a first illuminance sensor 231 for sensing the first illuminance and a second illuminance sensor 232 for sensing the second illuminance, and the first and second illuminance sensors 231 and 232 can be disposed around the first and second light receivers 221 and 222, respectively.
Next, according to one embodiment, the calculator 250 can function to generate a first PPG signal corresponding to the light of the first wavelength range and a second PPG signal corresponding to the light of the second wavelength range.
Further, according to one embodiment, when the difference between a predetermined reference illuminance and at least one of the first and second measured illuminances is not less than a predetermined level, the calculator 250 can function to correct at least one of the first and second PPG signals with reference to a relative relationship between the predetermined reference illuminance and at least one of the first and second measured illuminances.
Specifically, the calculator 250 according to one embodiment can perform correction to scale the intensity of at least one of the first and second PPG signals on the basis of the relative ratio of at least one of the first and second measured illuminances and the predetermined reference illuminance. For example, when the first illuminance measured by the first illuminance sensor 231 is about 2,000 lux and the predetermined reference illuminance is about 1,000 lux, then the intensity of the first PPG signal corresponding to the light of the first wavelength range sensed by the first light receiver 221 can be scaled by about ½. For another example, when the second illuminance measured by the second illuminance sensor 232 is about 2,000 lux and the predetermined reference illuminance is about 1,000 lux, then the intensity of the second PPG signal corresponding to the light of the second wavelength range sensed by the second light receiver 222 can be scaled by about ⅓.
PPG signals can thus be accurately measured in a situation in which brightness of ambient light is not constant due to external light sources, without employing a conventional shielding structure causing spatial constraints and consequently making accurate measurement easier, simpler, and less expensive.
Further, according to one embodiment, the calculator 250 may function to calculate a blood oxygen saturation level in the body part of the user with reference to the first and second PPG signals corrected as above.
Specifically, the calculator 250 according to one embodiment can calculate the oxygen saturation level on the basis of a model for oxygen saturation level calculation, which is applicable when the illuminance of the sensed light matches the predetermined reference illuminance. The first and second PPG signals whose intensities are adaptively corrected on the basis of a predetermined reference illuminance as described above can be applied right to the model for oxygen saturation level calculation, and thus the calculator 250 according to one embodiment can calculate the oxygen saturation level with reference to the first and second PPG signals corrected as above and the model for oxygen saturation level calculation.
For example, the model for oxygen saturation level calculation according to one embodiment can be a model for calculating oxygen content of hemoglobin in blood on the basis of the difference between AC components of the first PPG signal (i.e., the signal corresponding to red light) and the second PPG signal (i.e., the signal corresponding to infrared light) corrected as above. However, it is noted that the model for oxygen saturation level calculation is not limited thereto, and can be changed without limitation as long as the objects discussed above can be achieved.
Referring to
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Next, the communicator 260 according to one embodiment can function to enable the PPG signal measurement apparatus 200 to communicate with an external device.
Lastly, the controller 270 according to one embodiment can function to control data flow among the light emitter 210, the light receiver 220, the illuminance sensor 230, the filter 240, the calculator 250, and the communicator 260. That is, the controller 270 can control inbound data flow or data flow among the respective components of the PPG signal measurement apparatus 200, such that the light emitter 210, the light receiver 220, the illuminance sensor 230, the filter 240, the calculator 250, and the communicator 260 can carry out their particular functions, respectively.
The embodiments as described above can be implemented in the form of program instructions that can be executed by various computer components, and can be stored on a non-transitory computer-readable recording medium. The non-transitory computer-readable recording medium can include program instructions, data files, data structures and the like, separately or in combination. The program instructions stored on the non-transitory computer-readable recording medium can be specially designed and configured for the present invention and/or can be known and available to those skilled in the computer software field. Examples of the non-transitory computer-readable recording medium include the following: magnetic media such as hard disks, floppy disks and magnetic tapes; optical media such as compact disk-read only memory (CD-ROM) and digital versatile disks (DVDs); magneto-optical media such as floptical disks; and hardware devices such as read-only memory (ROM), random access memory (RAM) and flash memory, which are specially configured to store and execute program instructions. Examples of the program instructions include not only machine language codes created by a compiler or the like, but also high-level language codes that can be executed by a computer using an interpreter or the like. The above hardware devices can be configured to operate as one or more software modules to perform the processes of the present invention, and vice versa.
Although the present invention has been described in terms of specific items such as detailed elements as well as the limited embodiments and the drawings, they are only provided to help more general understanding of the invention, and the present invention is not limited to the above embodiments. It will be appreciated by those skilled in the art to which the present invention pertains that various modifications and changes can be made from the above description.
Therefore, the scope of the present invention is not limited to the above-described embodiments, and the entire scope of the appended claims and their equivalents will fall within the scope and spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0102695 | Jul 2015 | KR | national |
| 10-2016-0023632 | Feb 2016 | KR | national |
