WO2021211636A1 - System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors - Google Patents
System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors Download PDFInfo
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Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/024—Detecting, measuring or recording pulse rate or heart rate
- A61B5/02416—Detecting, measuring or recording pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/024—Detecting, measuring or recording pulse rate or heart rate
- A61B5/02438—Detecting, measuring or recording pulse rate or heart rate with portable devices, e.g. worn by the patient
-
- A—HUMAN NECESSITIES
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/024—Detecting, measuring or recording pulse rate or heart rate
- A61B5/0245—Detecting, measuring or recording pulse rate or heart rate by using sensing means generating electric signals, i.e. ECG signals
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- A—HUMAN NECESSITIES
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
- A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
- A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
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- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/25—Bioelectric electrodes therefor
- A61B5/251—Means for maintaining electrode contact with the body
- A61B5/256—Wearable electrodes, e.g. having straps or bands
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- A—HUMAN NECESSITIES
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/25—Bioelectric electrodes therefor
- A61B5/279—Bioelectric electrodes therefor specially adapted for particular uses
- A61B5/28—Bioelectric electrodes therefor specially adapted for particular uses for electrocardiography [ECG]
- A61B5/282—Holders for multiple electrodes
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/316—Modalities, i.e. specific diagnostic methods
- A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
- A61B5/346—Analysis of electrocardiograms
- A61B5/349—Detecting specific parameters of the electrocardiograph cycle
- A61B5/352—Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
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- A—HUMAN NECESSITIES
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- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
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Definitions
- Patent Application Serial number 17/135,936 entitled SYSTEMS FOR SYNCHRONIZING DIFFERENT DEVICES TO A CARDIAC CYCLE AND FOR GENERATING PULSE WAVEFORMS FROM SYNCHRONIZED ECG AND PPG SYSTEMS, filed December 28, 2020, the entire disclosures of which are incorporated herein by reference in their entireties for all purposes.
- the present system relates to cardiac sensing systems using combined electrocardiographic (EKG) and photoplethysmographic (PPG) sensing systems.
- EKG electrocardiographic
- PPG photoplethysmographic
- Venous hemoglobin oxygenation in health is often greater than 80%. While this may seem surprising, this high level of oxygenation represents a metabolic reserve that the body can dip into even though a deep breath has not been taken in the last few seconds. In states of stress that reserve will be whittled away; as such venous saturation is clinically useful as it provides a measure of the body’s oxygen reserve. Currently this can only be obtained via an invasive venous blood gas measurement. Venous oxygen saturation and serum lactate are both used to measure a patient’s degree of metabolic reserve and stress, as venous saturation is depressed in times of metabolic stress. Serum lactate will rise when tissues are not receiving sufficient oxygen to meet the metabolic needs, and the tissues turn to anaerobic use of glucose.
- the present system determines venous oxygen saturation in a system that comprises: (a) a device positionable against a person’s skin; (b) at least one PPG sensor mounted on the device for measuring the person’s PPG signal at multiple wavelengths of light; (c) a plurality of electrodes for measuring the person’s EKG signal; (d) a computer logic system for receiving and analyzing the PPG signal and the EKG signal, wherein the computer logic system further comprises: (i) a system for identifying cardiac cycles in the EKG signal; (ii) a system for segmenting the PPG signal into a series of PPG signal segments based upon features in the identified cardiac cycles, (iii) a system for sorting the PPG signal segments into a plurality of bins, each bin based upon durations of prior R-to-R cardiac cycles and current R-to-R cardiac cycles, (iv) a system for generating a composite signal for each of the plurality of bins, and (v) a system for measuring a person
- the present system for measuring a person’s venous oxygen saturation selects preferred bins from which the composite signals are used when calculating the person’s venous oxygen saturation, and the preferred bins correspond to the bins having the largest number of PPG signal segments therein and/or the largest difference between current and prior R-to-R values.
- a composite signal may be generated for each bin by summing or averaging the PPG signal segments in the bin.
- the composite signal may be used to generate a composite Signal Prime Over Signal (SPOS) which is the derivative of the composite signal normalized by the composite signal itself.
- SPOS Signal Prime Over Signal
- a system for calculating arterial oxygen saturation by comparing composite SPOS signals measured at different wavelengths of light may be included.
- the system for generating a composite signal for each of the plurality of bins comprises a system for removing aberrant PPG signal segments from the calculation of the composite signal, for example, by iteratively re-calculating the composite signal, by: comparing a SPOS of each of the PPG signal segments used to calculate a composite signal against the SPOS of the calculated composite signal, removing outlier PPG signal segments, re-calculating the composite signal with the outlier PPG signal segments removed, and repeating the iteration until there are no more outlier PPG signal segments.
- the present system is a hand- held device with the at least one PPG sensor mounted thereon and a plurality of electrode wires extending therefrom or mounted thereon.
- the present system may be positioned within a strap or band disposed around the person’s chest or limb with at least one PPG sensor and the plurality of electrodes are disposed within the strap or band.
- the present system may be disposed in a patch with the at least one PPG sensor and at least one of the plurality of electrodes positioned therein.
- Systems are also provided for data transmission. The present system provides information regarding the metabolic reserve/stress of a given patient, inexpensively and non-invasively.
- FIG. 1 shows the system top-level flow diagram for estimating venous saturation, wherein the hemoglobin saturation of arterial blood is obtained from the main-pulse region of a composite PPG signal shape (101), i.e. the region of greatest slope change, and a separate estimation of venous blood hemoglobin oxygenation is obtained using only end-pulse signal maxima/arterial pulse minima (102). The two results are then compared to determine how much oxygen reserve is apparent.
- the key to this analysis is understanding that the dynamics of the “tissue sandwich”, through which the PPG signal is filtered, changes slightly at the end of the pulse. This seen in FIG. 2.
- the curve 201 is an experimentally obtained arterial waveform, derived from a composite IR PPG signal. As one can see, the waveform is incredibly clean, the result of intelligent similar pulse averaging over a number of minutes. The salient point is that, were the arterial pulse descent from the peak (or “roll-off’) a simple exponential, or even a steady decline, the curve would not result in the “hump” seen prior to the pulse minimum just prior to the onset of the next pulse (202).
- Line 302 shows the arterial pulse sampled via standard oximetry, through which LED signal (301) sampling occurs.
- Line 303 is the resultant PPG signal.
- Point 304 shows a signal maxima/pulse minima.
- FIG. 3B shows the different sampling done in end- pulse/signal maxima oximetry.
- Line 306 shows the arterial pulse, through which LED signal (305) sampling occurs, though only at end-pulse, signal maxima.
- Line 307 is the resultant PPG signal with such sampling.
- FIG. 4A Further depiction of the structure being measured at arterial end-pulse can be seen in FIG. 4.
- FIG. 4A the arteriole/capillary/venule structure is shown as an hourglass.
- an hourglass representing the arteriole/capillary/venule structure measured in reflective oximetry is dominated by the maximally oxygenated, pre-capillary arteriole blood (401).
- FIG. 4B gives another representation of the structure, with the structure measured in reflective oximetry is shown as a shaded area (403).
- FIGS. 5A and 5B showing changes between the sampling points (the R-to-R duration) as linear, and how the PPG signal may change.
- Area 501 shows the end-pulse arterial (pre-capillary) blood, and area 502 the end-pulse venous (post- capillary) blood; area 503 is the fixed elements of the structure (largely connective tissue).
- LED sampling through the structure at end-pul se/signal maxima (504) before and after long pulses yields PPG signals 505 and 506, separated by time 507 (R-to-R duration).
- FIG. 5A LED sampling through the structure at end-pul se/signal maxima (504) before and after long pulses yields PPG signals 505 and 506, separated by time 507 (R-to-R duration).
- the present system uses combined electrocardiography (EKG) and photoplethysmography (PPG) signals (PPG is also commonly referred to as oximetry and the two terms will be used interchangeably throughout this specification).
- EKG electrocardiography
- PPG photoplethysmography
- the former senses voltage produced by heart muscle contraction, and the latter measures light absorbed by tissues. Changes in PPG signal reflect changes in blood volume and measurement at different wavelengths allows determination of oxygen saturation.
- the present system allows different insight than is currently available using hand-held, portable PPG systems/devices.
- the combination of EKG and PPG signals in this system utilize Pulse Wave Transit Time (or PWTT), and PPG Signal Prime Over Signal (SPOS) curves.
- PWTT Pulse Wave Transit Time
- SPOS PPG Signal Prime Over Signal
- PWTT is the period of time taken between a heartbeat as measured by the onset of the QRS complex and the time at which the blood from the aorta reaches an extremity or other body part, as determined by the negative spike generated in the SPOS curve, also described as the derivative of the LED signal divided by the signal.
- Else of the signal derivative to determine the change in a LED signal heralding the arrival of an arterial pulse has been described in U.S. Patent 10,213,123, assigned to MocaCare Corporation of Palo Alto, California, however use of the signal prime over signal (SPOS) allows for greater insight, as it normalizes each wavelength signal and thus allows for comparisons between different wavelength SPOS curves.
- SPOS signal prime over signal
- Improved arterial oxygen saturation estimation is then generated by this system from an SPOS curve using a composite sum/average of similar pulses, with the added ability to generate oxygen saturation for selected segments of the cardiac cycle, specifically end-pulse oximetry.
- Prior (n-1) EKG R-to-R duration using R-wave peaks are calculated, as are Current (n) R-to-R duration, PWTT, and SPOS. These are all used by the present system to determine similarity of oximetry pulses, with similar pulses summed/averaged to form composite pulses, then comparing differing composite pulses to gain cardiovascular insight.
- Reduced PWTT corresponds to greater pulse wave velocity, though the greater velocity does not indicate better pump function. This is because the aortic bulb acts as a “mechanical capacitor”, allowing metered delivery of arterial pulse volume. However, having obtained the PWTT for any given monitoring point on the body, this metric remains relatively stable and changes only gradually barring a sudden change in cardiovascular state (e.g. sudden change in heart rhythm such as onset of atrial fibrillation with rapid ventricular response). PWTT therefore provides a means by which to ensure accurate further data collection and analysis. This allows more reliable extraction of additional information from the combination of signals, and removal/minimization of introduced noise. Measurement of absorption of light (per Beer-Lambert law) has the form and the signal prime over signal (SPOS) of the measurement will be:
- the LED signals in plethysmography have the form: and describe the composition of the blood and generally change slowly. Therefore, these two terms are constants across time for the duration of our sampling. (These terms will be explained in greater detail herein).
- Hb x fractional composition of blood of various types of hemoglobin.
- the Sum of fractional components of different types of hemoglobin 1.0
- EKG noise Any recording of EKG, or oximetry signals, or their interaction, will have physiologic variability, as well as noise. Management of EKG noise have established protocols that have been built up over 100 years. Conditioning of oximetry signals do not have as long a history. Physiologic oximetry variability can occur from changes in venous flow (due to volitional movement, or passive movement from repositioning, or inflation/deflation of a blood pressure cuff/sphygmomanometer, etc.), respiration causing changes in intra-thoracic pressure with resultant change in blood volume return to the heart, or beat-to-beat duration variability.
- Noise, or non-physiologic variability can also occur from a range of possibilities, from variation in the surface pressure and angle of application of the detector, to ambient light infection of signal collection, to DC drift of the detection circuit. Whatever the specific source of variation, without an intelligent approach to the signals, one cannot tell physiologic variability apart from non- physiologic variability (introduced noise).
- FIG. 1 is a top-level flow diagram of the operation of the present system.
- FIG. 2 shows a PPG signal filtered through a “tissue sandwich”, showing slight changes at the end of the pulse.
- FIG. 3 A is an illustration of LED sampling for standard PPG arterial hemoglobin oximetry.
- FIG. 3B is an illustration of end-pulse/signal maxima sampling.
- FIG. 4A illustrates arteriole/capillary/venule structure is shown as an hourglass.
- FIG. 4B corresponds to FIG. 4A, with the structure measured in reflective oximetry.
- FIG. 5 A illustrates LED sampling through the structure of FIGS. 4A and 4B at end-pul se/signal maxima before and after long pulses.
- FIG. 5B illustrates LED sampling through the structure of FIGS. 4A and 4B at end-pul se/signal maxima before and after short pulses.
- FIG. 6 shows the process of R- wave peak refinement used to generate tOn.
- FIG. 7 shows the nomenclature and data structures used in the description of the present system.
- FIG. 8 also shows the nomenclature and data structures used in the description of the present system.
- FIG. 9 is an exemplary illustration of various physical components of the present system.
- FIGS. 10A to 10D show various views of a hand-held embodiment of the present system, having PPG and EKG sensors mounted thereon or attached thereto.
- FIG. 11 is a is a cut-away view of a portion of the device of FIGS. 10A to 10D, showing an optical waveguide adjacent to a PPG sensor.
- FIG. 12A is an illustration of the system of FIGS. 10A to 11 collecting PPG signals from a person’s fingers.
- FIG. 12B is an illustration of the system of FIGS. 10A to 11 collecting PPG signals from the outside of a person’s arm.
- FIG. 13 is a is an illustration of EKG and PPG signals measured over time and generated SPOS signals corresponding thereto.
- FIG. 14 is a is an illustration of one-sided Gaussian fitting.
- FIG. 15 illustrates the time relationship of the end-pulse/pre-pulse area of interest relative to the SPOS negative spike fitting window.
- FIG. 16 illustrates a time-correlated comparison of EKG and PPG signals showing the relationships in creation of two-beat dependencies, showing current and prior “R-to-R”.
- FIG. 17A illustrates the number of pulses in each bin for a run of a patient with normal sinus rhythm.
- FIG. 17B illustrates filling of the Current R-to-R versus Prior R-to-R matrix for purposes of determining end-pulse oximetry (the greatest difference in R-to-R duration), and the “fail-back” or second tier bin choices using intermediate bins providing PPG signal maxima differences allowing for venous oxygen saturation estimation.
- FIG. 18 is a top-level block diagram for the end-pulse/venous oxygen saturation calculation.
- FIG. 19 is a is an exemplary algorithm for preparing Pulse Data Sets in accordance with the present system.
- FIG. 20 illustrates the derivation of the Pulse Wave Transit Time (PWTT).
- FIG. 21 shows the calculation of end-pulse/venous oxygen saturation.
- FIG. 22 illustrates an exemplary embodiment of the present system disposed in a chest strap.
- FIG. 23 is a is a sectional view through the patient corresponding to FIG. 22.
- FIG. 24 illustrates an exemplary embodiment of the present system incorporating a bicep strap with an electrode extending therefrom.
- FIG. 25 is a is a sectional view through the patient corresponding to FIG. 24.
- the central element of the system is the identification and manipulation of PPG signals on the basis of Prior R-to-R and CurrentR-to-R duration.
- the system generates composite pulses from similar pulses.
- FIG. 6 shows the process of R-wave peak refinement used to generate tOn.
- the example shows how the algorithm has determined the polarity of this collection to be negative (wires reversed), and thus the R-wave to be negative.
- the tOn of the R-wave peak is found using polynomial fitting (602) to EKG datapoints (601) and interpolation, then used to define a Pulse Data Set.
- the t0n time point is then used to define a Pulse Data Set with the PPG signals of multiple wavelengths (here red, infrared, and green).
- Stored with the PPG signal are the values for the prior R-to-R, and current R-to-R durations, the derived signals for Signal Prime over Signal (SPOS) for each wavelength, and the Pulse Wave Transit Time (PWTT) for each wavelength. Note the first PPG signal maxima (701) and the second PPG signal maxima (702).
- SPOS Signal Prime over Signal
- PWTT Pul
- FIG. 8 shows the structure of the Composite Pulse Data Set, constructed from a group of Pulse Data Sets on the basis of a defined criteria (e.g. similar prior R-to-R, or current R-to-R duration). Note how the PPG waveforms are of duration longer than a single cardiac cycle, and are long enough to assure capture of both the first (801) and second PPG signal maxima (802).
- a defined criteria e.g. similar prior R-to-R, or current R-to-R duration
- FIGS. 9-11 show a preferred device implementation of the system.
- the device block diagram shows the elements of the device/system, with multiple wavelength LEDs (901) and a photodiode detector (902), and EKG input from electrodes (903) applied to the left and right chest (or left and right upper extremities.
- signals are then fed to a processing unit (904) carrying out “on-chip” logic that then generates Composite Pulse Data Sets from raw signal.
- the Composite Pulse Data Sets are then communicated via either wireless or direct cable connection to an “off-device” display/computing unit (905) that provides the user with the final end-pulse oxygenation, arterial main-pulse oxygenation, and resulting venous saturation estimation with more graphical options (such as changes over time).
- an “off-device” display/computing unit (905) that provides the user with the final end-pulse oxygenation, arterial main-pulse oxygenation, and resulting venous saturation estimation with more graphical options (such as changes over time).
- the processing unit simply coordinates communication of raw ECG and PPG signal data to the external computing/display device which handles all aspects of the hydration level estimation logic.
- all aspects of hydration level estimation are carried out by the processing unit, including rendering of graphics and reporting of oxygen saturation.
- the external computing/display device provides only the display function.
- FIGS. 10A-D show various view of the PPG collection device.
- 1001 shows the optical waveguide (in front of LEDs and detector);
- 1002 shows optional incorporated EKG electrodes;
- 1003 shows plug-in connector sites for EKG lead wires to adhesive EKG electrodes (on right and left chest).
- FIG 11 shows detail of the PPG head, with an optical waveguide (1101) that abuts the LEDs and detector (1102) on the interior of the device.
- the optical waveguide allows for collection of PPG signals at sites other than the finger.
- FIGS. 12A and 12B depict the device in use collecting PPG signals from the finger (FIG. 12A), and the outside of the upper arm (FIG. 12B).
- the PPG measurement end of the device is applied to the skin in a stable fashion so that PPG measurement can be taken over the course of 1-2 minutes or more.
- EKG electrodes are applied to the left and right sides of the torso (or upper extremities) and connected to the plug-ins on the smaller end of the device.
- PPG and EKG signals are collected.
- PPG waveform selection is performed to screen out aberrant beats considerably different than the majority of pulses, such as premature ventricular contraction beats, an example where the cardiac contraction does change appreciably from the beat prior.
- FIG. 13 shows: EKG signal (1301); EKGR-wave peak (1302); PPG signal segments (contained within Pulse Data Sets) (1303, 1304, 1305); SPOS signals (contained within Pulse Data Sets) (1306, 1307, 1308); PWTT using SPOS (also contained within Pulse Data Sets)
- the present method and system of intelligent pulse averaging counters the effect of drift in “K” (seen in equation 1), related to absorption from fixed elements in the tissue being analyzed. With averaging, some pulses will have an upward drift in K, some will have a downward drift, leaving the averaged pulse with more options for data point comparisons across the composite pulse width.
- SPOS generates similar shaped curves for the LED signals for the different wavelengths, magnitude differing only by a multiplier that is the for the specific wavelength.
- the present system includes the two novel approaches of examining the SPOS signal in the region of the “negative spike” to determine:
- any such fitting can be applied to one wavelength to yield a fitted curve. Fitting to another wavelength only requires finding the magnitude needed to best fit that curve. For example, if f(t) best fits the infrared LED SPOS, then “A” needed to best fit A*f(t) to the SPOS for the red LED signal yields the arterial oxygen saturation just as with the equation 1.
- the difference with the standard formulation is that this fitting is based on many more time points (up to 50 at slower heart rates) than the two (maximum and minimum) used in the standard formulation.
- FIG. 14 shows this concept using a one-sided Gaussian derivative fitting.
- Curve 1401 are the datapoints of a collected Composite IR SPOS signal with a fitting window 1402 selecting out the negative SPOS “spike”.
- Curve 1403 shows the datapoints for the window in an expanded plot, also showing the one-sided Gaussian derivative fitted curve 1404.
- the interval of the fitting window selected represents a unique period wherein a single dominant and coherent physiologic event - the contraction of the left ventricle during the time of an open aortic valve - is clearly separate from other confounding physiologic features. This allows for extraction of parameters, which can then be applied to the entire PPG sensor pulse waveform.
- the interval just preceding this fitting window for the “negative spike” of the SPOS represents yet another unique interval, as described in the summary of the physiology above.
- FIG. 15 shows the time relationship of the end-pulse/pre-pulse area of interest relative to the SPOS negative spike fitting window.
- Time 1501 identifies the end-pulse point; region 1502 shows the excess SPOS PPG above expected linear or exponential “rolloff’ (the shaded region of FIG. 15 corresponds to the shaded region of FIG. 2).
- Region 1503 identifies the window of the negative SPOS “spike” used to estimate arterial hemoglobin oxygen saturation fraction
- 2-beat complex selection for a longer train of pulses in atrial fibrillation is shown in FIG. 16.
- Signal from a two-electrode, single lead EKG (curve 1601) is plotted in temporal alignment with an infrared (IR) LED PPG signal (curve 1602).
- IR infrared
- the infrared wavelength has relatively equivalent absorption from venous and arterial blood, this is the wavelength shown and used to select pulses for further analysis.
- composite pulse construction can be taken from one pulse minima/signal maxima all the way through to the next pulse minima/signal maxima.
- FIG. 16 shows the top/bottom alignment of EKG (1601) and PPG signals (1602) showing the steps in the of generation of a composite PPG wave for purposes of venous oxygen saturation derivation.
- the above EKG (1601) signal shows a series of pulses labeled A through I. Each of these pulses has a different duration, though some are closer in duration than others.
- 2-beat dependency ties together two successive beats, with key features being the R-to-R duration of the first beat, and the PPG signal of the second beat. This is a dependency (1603) as depicted in the bracket tying together the R-to-R duration of beat “B” (1604) and the PPG signal (1605) of beat “C”. Additionally important in this analysis is the current R-to-R duration, which for this complex is the R-to-R duration of pulse “C” (1606). Notable with the bracketed complex 1603 is a paring of a long n-1 R-to-R followed by a short n R-to-R.
- Pulses B and C are analyzed together, with the R-to-R duration of B and R-to-R duration of C putting this 2-beat complex in the long n-1 R-to-R/short n R-to-R “bin”.
- pulses C and D are considered together, with the R-to-R duration of C and R-to-R duration of D putting this 2- beat complex in the short n-1 R-to-R/long n R-to-R “bin”.
- pulses D and E are considered together, with the R-to-R duration of D and R-to-R duration of E putting this 2-beat complex in the long n-1 R-to-R/intermediate n R-to-R “bin”.
- pulses E and F are considered together, with the R-to-R duration of E and R-to-R duration of F putting this 2-beat complex in the intermediate n-1 R-to-R/short n R-to-R “bin”.
- pulses F and G are considered together, with the R-to-R duration of F and R-to-R duration of G putting this 2-beat complex in the short n-1 R- to-R/long n R-to-R “bin”.
- pulses G and H are considered together, with the R-to-R duration of G and R-to-R duration of H putting this 2-beat complex in the long n-1 R-to- R/intermediate n R-to-R “bin”.
- FIG. 17A shows the number of pulses in each bin for a run of a patient with normal sinus rhythm. Note how the diagonal corresponding to the same n-1 and n R-to-R durations are most populated and the short-long and long-short bins are the least populated.
- 17B shows the preferential filling of the Current R-to-R versus Prior R-to-R matrix (1701) for purposes of determining end-pulse oximetry (the greatest difference in R-to-R duration), and the “fail-back” or second tier bin choices using intermediate bins (1702) providing PPG signal maxima differences allowing for venous oxygen saturation estimation.
- R-wave peak refinement of pulse “n” is done with curve fitting and interpolation (1801) prior to determining the prior (n-1) and current (n) R-to-R duration; then prior (n-1) and current (n) R- to-R durations for Pulse Data Set “n” are incorporated into Pulse Data Set “n” (1802).
- PPG signals are gathered, and a process of outlier rejection is carried out (including but not limited to data determined to be corrupted using accelerometer input, as well as cross-checking with multiple LED PPG sensors, 1803).
- the Pulse Data Set is considered together with all available prior Pulse Data Sets and their PPG signals (each of which is associated with a prior (n-1) R-to-R duration and current (n) R-to-R duration).
- Available Pulse Data Sets are then sorted into a 3 by 3 bin matrix of Prior R-to-R and Current R-to-R, each of which are considered and deemed to be short, intermediate, or long duration (1804).
- Dynamic boundary adjustment is used to ensure relatively equal numbers across bins, to the extent possible: normal sinus rhythm yields few Pulse Data Sets available for bins off the diagonal of short-short, intermediate-intermediate, and long-long (see FIG. 17).
- the optimal bins are selected, e.g. those bins containing the largest number of Pulse Data Sets and those that reveal the biggest changes in signal maxima (1805). With the optimal bins established, and initial Composite Pulse Data Set is formed by adding together the corresponding PPG signals of each wavelength for each Pulse Data Set in the bin (1808).
- a pruning loop is carried out for each bin to weed out Pulse Data Sets with noisy or otherwise aberrant PPG signals (1806) that made it through the coarser outlier rejection.
- the PWTT for the wavelength is compared against the PWTT for the wavelength for the Composite Pulse Data Set (aggregate of all the pulses). If the PWTT of two of the current three wavelengths (red, green, IR) are within 15% of the PWTT of the Composite Pulse Data Set, the Pulse Data Set is left in the composite.
- FIG. 20 shows the derivation of the Pulse Wave Transit Time (PWTT). This is done using the Signal Prime Over Signal (SPOS(t)) curve for each wavelength PPG signal(t), together with interpolation and (negative) peak refinement.
- SPOS(t) Signal Prime Over Signal
- the calculation of end-pulse/venous oxygen saturation then proceeds as shown in FIG. 21.
- the venous oxygen saturation calculation follows the derivation shown in Appendix B using 2- point composite signals composed of PPG signal maxima corresponding to incongruent R-to-R duration from 2-beat complexes (1807). The results are averaged and the venous fractional oxygen saturation is reported (1809).
- FIG. 22 illustrates use of a chest strap (2201) across the chest, with incorporated electrodes (2202) contacting the left and right chest, and LED device with detector (2203).
- FIG 23 illustrates cross section of a chest strap (2301) across the chest, with incorporated electrodes (2302) contacting the left and right chest, and LED device with detector (2303).
- FIG. 24 illustrates use of a bicep strap (2401), with incorporated electrode (2402) and LED device with detector (2403).
- a second electrode piggybacks off existing telemetry wiring (2404).
- FIG 25 illustrates cross section of a bicep strap (2501), with incorporated electrode (2502) and LED device with detector (2503).
- a second electrode piggybacks off existing telemetry wiring (2504).
- a chest or arm strap or band provides a normal force on the LED of the PPG sensor to get a good signal off the chest wall.
- optional “traction” may also be provided on the inside of the strap, similar to the silicone / adhesive bead that is found on the inside of standard bike shorts to keep the legs from riding up.
- Circulatory shock causes inadequate oxygen delivery, resulting in mitochondrial hypoxia.
- energy metabolism becomes dependent on anaerobic glycolysis.
- Anaerobic glycolysis sharply increases the production of cellular lactate, and then blood levels.
- the blood lactate concentration varies in proportion to the ongoing deficit in tissue oxygenation.
- the ability of the patient to clear blood lactate indicates restoration of oxygen delivery with resuscitation. Studies have shown that a lactate clearance of 10% or more predicts survival from septic shock.
- APPENDIX B Venous Hemoglobin Saturation Calculation
- delta arterial blood gamma* delta volume
- delta venous blood (1 -gamma)* delta volume Where gamma is somewhere between 1 and 0.5.
- HbO2 Done at two or more different wavelengths (e.g. red, infrared, though not exclusive to these), one can solve for HbO2, given that the only unknowns are HbO2 and dVolume(t)/dt. Note that at each wavelength is known from analyses done elsewhere in the system description.
Abstract
Description
Claims
Priority Applications (10)
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AU2021255871A AU2021255871B2 (en) | 2019-12-30 | 2021-04-13 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated EKG and PPG sensors |
KR1020237036508A KR20230151085A (en) | 2019-12-30 | 2021-04-13 | System and Method of Measuring Venous Oxygen Saturation Using Intelligent Pulse Averaging With Integrated EKG and PPG Sensors |
EP21788382.6A EP4135573A4 (en) | 2019-12-30 | 2021-04-13 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors |
BR112022020839A BR112022020839A2 (en) | 2019-12-30 | 2021-04-13 | VENOUS OXYGEN SATURATION MEASUREMENT SYSTEM AND METHOD USING INTELLIGENT PULSE AVERAGE WITH INTEGRATED ECG AND PPG SENSORS |
KR1020227035775A KR102595127B1 (en) | 2019-12-30 | 2021-04-13 | System and method for measuring venous oxygen saturation using intelligent pulse averaging with integrated EKG and PPG sensors |
CA3177643A CA3177643A1 (en) | 2020-04-14 | 2021-04-13 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors |
JP2022562720A JP7345681B2 (en) | 2019-12-30 | 2021-04-13 | System and method for measuring venous oxygen saturation using intelligent pulse averaging with integrated EKG and PPG sensors |
MX2022012886A MX2022012886A (en) | 2019-12-30 | 2021-04-13 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors. |
AU2023202053A AU2023202053A1 (en) | 2019-12-30 | 2023-04-04 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors |
JP2023142748A JP2023159456A (en) | 2019-12-30 | 2023-09-04 | System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated ekg and ppg sensors |
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US63/067,147 | 2020-08-18 | ||
US17/135,936 US20210275110A1 (en) | 2019-12-30 | 2020-12-28 | Systems For Synchronizing Different Devices To A Cardiac Cycle And For Generating Pulse Waveforms From Synchronized ECG and PPG Systems |
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US20130066176A1 (en) * | 2011-09-09 | 2013-03-14 | Nellcor Puritan Bennett Ireland | Venous oxygen saturation systems and methods |
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US10478075B2 (en) * | 2013-10-25 | 2019-11-19 | Qualcomm Incorporated | System and method for obtaining bodily function measurements using a mobile device |
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