Systems and methods for measuring biological metrics and blood vessel geometry using a multiple optical path photoplethysmography device
Inventors
Afanasiev, Andrei • Miller, Forrest • Honore, Francis • Flannery, Anthony
Assignees
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Publication Number
US-11937906-B2
Publication Date
2024-03-26
Expiration Date
Abstract
Systems and methods for monitoring blood flow metrics using a patch of a flexible substrate configured to attach to an area of skin over a blood vessel. The patch includes a plurality of light sources arranged on the substrate to form a matrix and a row of photodetectors disposed on the substrate substantially in parallel with the rows of LEDs. The patch includes an optical signal interface configured to drive each light source and to input an intensity signal at one of the photodetectors. The intensity signals are used to determine AC and DC components corresponding to each optical path. AC to DC component ratios are calculated for each optical path and used to determine ratio-of-ratio values. At least a subset of the ratio-of-ratio values are used to determine a biological metric or a cross-sectional area of the blood vessel.
Core Innovation
A flexible patch is configured to attach to an area of skin over a blood vessel. An arrangement of LEDs on the substrate forms an R×C matrix, and a row of C photodetectors is disposed substantially in parallel with R rows of LEDs extending to form C columns substantially co-linear with each photodetector. An optical signal interface on the substrate drives each LED for an on-period and inputs an optical signal at one of the photodetectors during the on-period to receive an intensity measurement for an optical path, OP_rc, formed by LEDs in rows r=1 to R in columns c=1 to C and the photodetector receiving the optical signal.
A processing system determines an AC component, I_rc,AC, and a DC component, I_rc,DC, as a function of a plurality of intensity measurements, I_rc, for each optical path, OP_rc, over a period of time. For each optical path, the processing system determines an AC-to-DC component ratio, R_(r,c)=I_(rc,AC)/I_(rc,DC). The processing system further determines a plurality of ratio-of-ratios, RoR values, by dividing a first plurality of selected AC-to-DC component ratios by a second plurality of selected AC to DC component ratios and uses at least a subset of the RoR values to determine a biological metric.
The system determines the plurality of RoRs by dividing AC to DC component ratios in each row of AC to DC component ratios corresponding to the optical paths for a nearest LED row nearest to the row of photodetectors, with nearest/further row relationships defined across the array. In a further embodiment, the biological metric is hematocrit concentration, Hct, determined using Hct=F(RoR′), where F correlates a range of RoR values to a range of hematocrit concentration values based on reference hematocrit concentrations determined from a plurality of reference RoR values measured using a reference hematocrit measurement system, and RoR′ is at least a subset of RoR values. In another embodiment, infrared LEDs and red LEDs are arranged adjacent in the R×C matrix to form independent IR and red optical paths, and oxygen saturation is determined by processing red and IR AC-to-DC component ratios, forming composite ratio-of-ratios by dividing until all red and IR AC-to-DC components are incorporated, determining RoR values from selected composite ratio-of-ratios, and using at least a subset of those RoR values to determine a biological metric.
Claims Coverage
The provided excerpt includes four independent claims: clm-00001, clm-00002, clm-00003, and clm-00009. Across these independent claims, the core claim structure includes an R×C LED matrix with parallel photodetectors, time-based optical intensity measurements for multiple optical paths, computation of AC/DC components and AC-to-DC ratios, formation of ratio-of-ratios (RoR), and use of at least a subset of RoR values to determine a biological metric; additional claim-specific restrictions further define how RoRs are computed and which biological metric (hematocrit concentration or oxygen saturation) and wavelength structure are used.
R×C LED matrix with parallel photodetector row and optical paths
A patch of a flexible substrate configured to attach to an area of skin over a blood vessel; a plurality of LEDs arranged on the substrate to form a R×C matrix and a row of C photodetectors disposed on the substrate substantially in parallel with R rows of LEDs extending to form C columns substantially co-linear with each photodetector; an optical signal interface mounted on the substrate and configured to drive each LED for an on-period and to input an optical signal at one of the photodetectors during the on-period to receive an intensity measurement for an optical path, OP_rc.
AC/DC decomposition and ratio-of-ratios to determine a biological metric
Determine an AC component, I_rc,AC, and a DC component, I_rc,DC, as a function of a plurality of intensity measurements, I_rc, for each optical path, OP_rc, over a period of time; determine an AC-to-DC component ratio, R_(r,c)=I_(rc,AC)/I_(rc,DC), for each optical path; determine a plurality of ratio-of-ratios, RoR values, by dividing a first plurality of selected AC-to-DC component ratios by a second plurality of selected AC to DC component ratios; using at least a subset of the RoR values to determine a biological metric.
Nearest LED row RoR division across photodetector rows
Determine the plurality of RoRs by dividing AC to DC component ratios in each row of AC to DC component ratios corresponding to the optical paths for a nearest LED row nearest to the row of photodetectors.
RoR computation across nearest and further LED rows by sequential row relationships
Determine the plurality of RoRs by dividing AC to DC component ratios in a row of AC to DC component ratios corresponding to the optical paths for a nearest LED row nearest to the row of photodetectors by themselves, and dividing AC to DC component ratios in each row starting with a second row by AC to DC component ratios in a next further row of AC to DC component ratios.
Hematocrit via IR RoR transfer function
The plurality of LEDs is a plurality of infrared (IR) LEDs emitting infrared light; using at least the subset of RoR values to determine the biological metric is hematocrit concentration, Hct, determined using Hct=F(RoR′), where F is a transfer function that correlates a range of RoR values to a range of hematocrit concentration values based on reference hematocrit concentrations determined from a plurality of reference RoR values measured using a reference hematocrit measurement system, and where RoR′ is at least a subset of RoR values.
IR and red adjacent LEDs with composite RoR processing for oxygen saturation
The plurality of LEDs is a plurality of infrared (IR) LEDs for emitting light at a first wavelength in the infrared, the system further including a plurality of red LEDs for emitting light at a second wavelength in the red; each of the plurality of red LEDs is arranged adjacent to each of the plurality of IR LEDs in the R×C matrix; the optical signal interface is configured to drive each IR LED and each red LED independently to form independent IR and red optical paths, OP_IR,r,c and OP_red,r,c; and the processing system is configured to measure an oxygen saturation metric by receiving red and IR intensity measurements for the optical paths, determining red and IR AC and DC components, determining red and IR AC-to-DC component ratios, determining a plurality of composite ratio-of-ratios by dividing each of either red or IR AC-to-DC component ratios by each of either IR or red AC-to-DC component ratios until all of the red and IR AC to DC components are incorporated, determining a plurality of ratio-of-ratios, RoR values, by dividing a first plurality of selected composite ratio-of-ratios by a second plurality of selected composite ratio-of-ratios, and using at least a subset of the RoR values to determine a biological metric.
Across the independent claims, the invention centers on a wearable flexible patch with an R×C LED matrix and parallel photodetector row to obtain multiple optical path intensity measurements, compute AC and DC components, form AC-to-DC ratios, construct ratio-of-ratios (RoR) from selected ratios, and use at least a subset of RoR values to determine a biological metric. Specific claim embodiments further constrain RoR construction across nearest/further rows, map RoR subsets to hematocrit concentration using a transfer function with reference measurements, and use adjacent IR and red LED optical paths to compute oxygen saturation via composite ratio-of-ratios processing.
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