The present disclosure provides systems and methods to measure pulse and blood oxygen saturation in living tissue using pulse oximetry with an ambient light source.
Photoplethysmography (PPG), which is a non-invasive optical technique of detecting blood volume changes in tissue, uses a light source with a light spectrum that can penetrate the tissue, and a light detector that can sense that light. Signal obtained from PPG can provide vital information about the subject including physiological signs (e.g. heart rate, respiration, blood pressure, etc.), vascular condition and heart or cardiovascular variability.
When PPG signals can be obtained from two specific portions of the light spectrum, oxygen saturation, SpO2, can be estimated by taking a ratiometric measurement of the two signals. This is possible by taking advantage of the different light absorption characteristics of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) at the two light spectrum. Pulse oximetry, a method to obtain SpO2 is a safe and inexpensive way of measuring oxygen saturation as well as other vital signs mentioned above, and is widely used in clinical use.
Pulse oximeters traditionally consist of light-emitting diodes (LEDs) and photodiodes (PDs) which can operate at two different wavelength spectrum. The two spectrum can either be green and red, or red and near-infrared (NIR), where the acceptable spectrum range is given (in nanometers) by 470<green<550, 620<red<690, and 740<NIR<950. Preferably, overlap between the two spectrum should be minimized for better accuracy in oxygen saturation calculation. Usually, a photodiode that can sense broad range of spectrum is selected and combined with two LEDs which can provide two different localized light spectrum. Most oximeters have been designed in this two LEDs, one PD (2L1P) setup. With this scheme, the photodiode itself cannot distinguish the wavelength of the incoming light. The two LEDs must operate in turn at a given frequency where the photodiode is synchronized accordingly, and the wavelength of the light detected corresponds to that of the synchronized LED. This method needs an ambient light calibration scheme in order to reduce the effect of ambient light to the signal. In addition, the operation of LEDs accounts for significant amount of the power consumed by the pulse oximeter and numerous approaches have been suggested to reduce the power consumed by the LEDs, such as reducing the duty ratio or intermittently turning off the LEDs. A one LED and two PDs (1L2P) concept of detecting changes in the tissue oxygenation was also previously demonstrated. This scheme uses a wide spectrum LED which has both red and NIR components and relies on PDs with filters to distinguish the spectrum. Although the two PDs that were used had non-negligible spectrum overlap which limits their usage in cases where precise measurements are required, relative variation in the tissue oxygenation was successfully observed. Also, this concept can bring improvement in the pulse oximeter design, in that there is only one LED to operate. Nonetheless, for both 2L1P and 1L2P schemes, the fact that LEDs are needed, and that they will drain power remains the same. Also, the LEDs need to be controlled by a LED driver which will require additional components in the front end and hence add complexity to the system.
Systems and methods for performing pulse oximetry may be performed with no controlled sources such as LEDs needed. The systems and methods herein may utilize ambient light as a light source, and use spectrally-selective sensors such as spectrally-selective organic photodiodes (OPDs). In certain embodiments, flexible and/or stretchable electronics may be used.
Flexible and stretchable electronics are well suited for wearable sensing and medical monitoring applications, in that they form conformal contact with human body. This provides better SNR compared to rigid electronics, and also allows them to be easily integrated into garments or accessories. Pulse oximetry can also benefit from using flexible optoelectronics. When optoelectronics are well-conformed to the skin, quality of the acquired signal can be greatly enhanced. The use of flexible organic PDs (OPDs) for PPG measurements have been shown to reduce noise current from ambient light considerably. OPDs also demonstrate other advantages such as light weight, decreased fabrication complexity, and mechanical flexibility. These are all useful characteristics of components for wearable and portable applications, which makes OPD an ideal candidate.
One of the distinguished traits that organic absorbers possess is that their spectral sensitivities are relatively narrow, compared to inorganic counterparts. For example, silicon photodiodes are broadband and require carefully designed rigid band-pass filters in order to have good spectral selectivity. Most organic materials are blind in the infrared region and have partial absorption in the visible spectrum. This means that they inherently possess spectral cutoff within or near the visible spectrum, which can be utilized to realize spectral selectivity.
Prior art pulse oximeters that have been presented have operated using one or two LEDs, depending on which scheme was used; 1L2P or 2L1P.
According to various embodiments, pulse oximetry may be performed with no controlled LEDs needed, utilizing ambient light as a light source, and using two spectrally-selective OPDs (e.g., 0L2P) absorbing in red and green or red and NIR wavelengths. Organic absorbers are selected so that the fabricated OPDs will be able to sense green, red, and NIR. In some embodiments, bulk heterojunction blends of poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) with [6,6]-phenyl C70-butyric acid methyl ester (PCBM70), or poly(3-hexylthiophene) (P3HT) with (O-IDTBR) are used. The OPDs are flexible and compatible with roll-to-roll printing techniques. In some embodiments, these OPDs are combined with appropriate flexible filters that allow the OPDs to become spectrally selective OPDs (ss-OPDs), e.g., to sense green, red or NIR regions with minimum spectral overlap. Using ss-OPDs, it is possible to obtain PPG signals from various ambient lights sources, including sources such as the Sun, or broadband fluorescent, LED and incandescent light sources. For example, in an embodiment, two different ss-OPDs may be used together to perform pulse oximetry under the Sun in the outdoors. In certain embodiments, this system can be integrated into a glove form factor using a wireless data transmission.
According to an embodiment, a heart rate measuring device which can conduct photoplethysmography (PPG) measurements under broadband light is provided that includes a photodiode which has spectrally sensitive sensitivity to a visible wavelength or an infrared wavelength, or both, that penetrate in to skin and reach a pulsating vein.
According to another embodiment, a heart rate measuring device which can conduct photoplethysmography (PPG) measurements under broadband light is provided that consists essentially of: a) a single photodiode that has sensitivity in or to both a first visible light wavelength and a second visible light wavelength, or the first visible light wavelength and an infrared light wavelength, which wavelengths penetrate into the skin and reach a pulsating vein; or b) a first photodiode that has sensitivity in or to the first visible light wavelength, and a second photodiode that has sensitivity in the second visible light wavelength or the infrared wavelength.
According to an embodiment, an oximeter device (e.g., pulse oximeter device) for conducting pulse oximetry measurements using broadband light is provided that includes a first spectrally-selective photodiode (ss-PD) which can sense only red light wavelengths wherein the extinction coefficient ratio of oxy- and deoxy-hemoglobins (εHb/εHbO2) has a value larger than 6; and a second ss-PD which can sense incoming only green light wavelengths, or only NIR wavelengths, wherein the extinction coefficient ratio of oxy- and deoxy-hemoglobins has a value smaller than 2 or 3, respectively.
According to another embodiment, a pulse oximeter device for conducting PPG measurements using broadband light is provided that includes a first spectrally-selective organic photodiode (ss-OPD) comprising a first spectral filter overlaying a sensing region of a first organic photodiode (OPD), wherein the first OPD absorbs/detects light in a first wavelength range including visible wavelengths up to but not including NIR wavelengths, and the first spectral filter only transmits light having wavelengths including and greater than red wavelengths; and a second ss-OPD comprising a second spectral filter overlaying a sensing region of a second OPD, wherein the second OPD absorbs/detects light in a second wavelength range including green wavelengths or NIR wavelengths, and the second spectral filter only transmits light having green wavelengths or light having a wavelength of greater than red wavelengths.
In certain aspects, the pulse oximeter device further includes a flexible substrate, wherein the first ss-OPD and the second ss-OPD are disposed on the flexible substrate. In certain aspects, the first OPD comprises PCDTBT:PCBM70 and the second OPD comprises PCDTBT:PCBM70 or P3HT:O-IDTBR. In certain aspects, the first OPD absorbs/detects light in the first wavelength range including visible wavelengths up to about 700 nm, and wherein the first spectral filter only transmits light having a wavelength greater than about 590 nm. In certain aspects, the second OPD absorbs/detects light in the second wavelength range including visible wavelengths up to about 700 nm, and wherein the second spectral filter only transmits light in a wavelength range of from about 490 nm to about 570 nm. In certain aspects, the second OPD absorbs/detects light in the second wavelength range including wavelengths above about 700 nm up to about 800 nm, and wherein the second spectral filter only transmits light having a wavelength of greater than about 700 nm.
According to yet a further embodiment, a pulse oximeter device for conducting PPG measurements using broadband light is provided that includes a first organic photodiode (OPD) having a first sensing region, the first OPD absorbs/detects light in a first wavelength range including visible wavelengths up to but not including NIR wavelengths; a first optical filter disposed proximal to the first sensing region, the first optical filter transmitting only light having wavelengths including and above red wavelengths; a second OPD having a second sensing region the second OPD absorbs/detects light in a second wavelength range including green wavelengths or NIR wavelengths; and a second optical filter disposed proximal to the second sensing region, the second optical filter transmitting only light including green or only light having a wavelength of greater than red wavelengths. In certain aspects, the first OPD comprises PCDTBT:PCBM70 and the second OPD comprises PCDTBT:PCBM70 or P3HT:O-IDTBR.
According to still a further embodiment, a pulse oximeter device for conducting PPG measurements using broadband light is provided that includes a first organic photodiode (OPD) having a first sensing region, the first OPD absorbs/detects light in a first wavelength range including visible wavelengths up to about 700 nm; a first optical filter disposed proximal to the first sensing region, the first optical filter transmitting light having a wavelength of greater than about 590 nm; a second OPD having a second sensing region, the second OPD absorbs/detects light in a second wavelength range including visible wavelengths and NIR wavelengths greater than 700 nm, e.g., up to about 800 nm or greater; and a second optical filter disposed proximal to the second sensing region, the second optical filter transmitting only light in a wavelength range of from about 490 nm to about 570 nm, or only light having a wavelength of greater than about 700 nm. In certain aspects, the first OPD comprises PCDTBT:PCBM70 and the second OPD comprises PCDTBT:PCBM70 or P3HT:O-IDTBR.
According to another embodiment. a pulse oximeter device for conducting PPG measurements using broadband light is provided that includes a first organic photodiode (OPD) having a first sensing region, the first OPD absorbs/detects light in a first wavelength range including visible wavelengths up to about 700 nm; a first optical filter disposed proximal to the first sensing region, the first optical filter transmitting only light having a wavelength of greater than about 590 nm; a second OPD having a second sensing region, the second OPD absorbs/detects light in a second wavelength range including visible wavelengths; and a second optical filter disposed proximal to the second sensing region, the second optical filter transmitting light only in a wavelength range of from about 490 nm to about 570 nm. In certain aspects, the first OPD comprises PCDTBT:PCBM70 and the second OPD comprises PCDTBT:PCBM70.
According to still a further embodiment, a pulse oximeter device for conducting PPG measurements using broadband light is provided that includes a first organic photodiode (OPD) having a first sensing region, the first OPD absorbs/detects light in a first wavelength range including visible wavelengths up to about 700 nm; a first optical filter disposed proximal to the first sensing region, the first optical filter transmitting only light having a wavelength of greater than about 590 nm; a second OPD having a second sensing region the second OPD absorbs/detects light in a second wavelength range including NIR wavelengths; and a second optical filter disposed proximal to the second sensing region, the second optical filter transmitting only light having a wavelength of greater than about 700 nm. In certain aspects, the first OPD comprises PCDTBT:PCBM70 and the second OPD comprises P3HT:O-IDTBR.
According to another embodiment, method of performing PPG measurements using any pulse oximeter device embodiment herein is provided. The method typically includes positioning the pulse oximeter device on a region of interest of a human user; and exposing the pulse oximeter device to broadband light. In certain aspects, exposing includes irradiating with a broadband light source selected from the group consisting of a fluorescent lamp, an incandescent lamp, and one or more LEDs. In certain aspects, the exposing includes exposing the pulse oximeter device to sunlight.
In certain aspects, the pulse oximeter device elements are arranged on a flexible substrate. In certain aspects, the flexible substrate comprises polyethylene napthalate (PEN) or other flexible polymer or non-polymer material.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
The present disclosure provides systems and methods to measure pulse and blood oxygen saturation in tissue using pulse oximetry with an ambient light source. In certain aspects, the pulse oximeters according to various embodiments advantageously do not require and do not include a light source such as an LED, thereby reducing complexity and reducing power consumption.
In order to achieve green, red and NIR ss-OPDs (referred to as Green, Red and NIR sensors henceforth), organic photoactive layers and filters are carefully paired by considering their optical characteristics in
To verify that the OPDs can take PPG measurements using an ambient light source, PPG signals from various ambient light sources were recorded using the sensors. As shown in
Pulse oximetry was performed under the actual Sun in the outdoors. As was previously mentioned, pulse oximetry can be done either in green and red or red and NIR spectrum. One of the two combinations are placed on a volunteer's index finger and the readings of each sensor are recorded.
Pulse Oximetry with Varying Oxygen Saturation
In order to test if the present embodiments can readily detect changes in the oxygen saturation of the body, an altitude simulator is used, which changes the oxygen concentration of the air that the volunteer breathes in through a facemask. The volunteer's oxygen concentration will change accordingly which is picked up by a commercially available finger pulse oximeter probe and the present sensor embodiments under a solar simulator. The readings collected by the prior art oximeter probe are presented in
Two spectrally selective OPDs without any programmed light source were used to perform pulse oximetry under ambient light conditions. The ss-OPDs were fabricated by combining OPDs with appropriate filters, which made it possible to obtain green, red and NIR sensitive sensors. These sensors were first tested individually under various ambient light conditions, such as the Sun, fluorescent, LED, or incandescent light, to obtain PPG signals. As a result, it was shown that with proper sensor combinations, it is possible to perform pulse oximetry under all of the ambient light sources that were tested. We took our system outdoors and used two possible combinations, Green+Red and Red+NIR sensors to perform pulse oximetry under the actual Sun. Then our system was used to track changes in the oxygen concentration which was varied by an altitude simulator, value of which was crossed checked by a commercially available pulse oximeter finger probe. The sensors used in our system are compatible with inexpensive large-area production and flexible which will allow healthcare products to be more conformable and affordable. The pulse oximeter with no controlled LEDs is a new concept which can simplify the design of future pulse oximeters, reduce the power consumed by driving the LEDs, make the overall system to be lighter and most of all significantly lower the cost of pulse oximeters.
U.S. Patent Application Publication No. 2017/0156651 A1, which is incorporated herein by reference, discloses various aspects of PPG measurements, including reflectance-based measurements, as well as useful PPG device materials. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Various embodiments are described herein. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments to be practiced otherwise than as specifically described herein. Accordingly, this specification includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
This patent application claims priority to International Patent Application No. PCT/US2020/013496, entitled, “PULSE OXIMETRY USING AMBIENT LIGHT,” filed Jan. 14, 2020, and to U.S. Provisional Patent Application No. 62/792,112, entitled “PULSE OXIMETRY USING AMBIENT LIGHT,” filed Jan. 14, 2019, which are both incorporated herein by reference.
This invention was made with Government support under Grant Numbers EEC-1160494 and EECS-1202189 awarded by the National Science Foundation. The Government has certain rights in this invention.
Number | Date | Country | |
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62792112 | Jan 2019 | US |
Number | Date | Country | |
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Parent | PCT/US2020/013496 | Jan 2020 | US |
Child | 17373345 | US |