# US 11,896,405 B2 · System and method of measuring venous oxygen saturation using intelligent pulse averaging with integrated EKG and PPG sensors

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- Number: US 11,896,405 B2
- Document ID: US11896405B2
- Status: Granted
- Kind: B2
- Application number: 17/229,759
- Filed: 2021-04-13
- Published: 2021-10-14
- Granted: 2024-02-13
- Earliest claimed: 2020-04-14
- Assignees: Hemocept Inc.
- Applicants: Hemocept Inc.
- Inventors: Eric Raman; Kevin Peterson; Iain Hueton
- Web page: https://patentgrep.com/patent/US11896405B2

## CPC

- A61B 5/7285: {for synchronizing or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal}
- A61B 5/004: {adapted for image acquisition of a particular organ or body part (A61B5/0082 takes precedence; arrangements for optical scanning A61B5/0062)}
- A61B 5/0006: {ECG or EEG signals}
- A61B 5/0036: {including treatment, e.g., using an implantable medical device, ablating, ventilating}
- A61B 5/024: Measuring pulse rate or heart rate
- A61B 5/0205: Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
- A61B 5/14: {Devices for taking samples of blood (hypodermic syringes A61M5/00); Measuring characteristics of blood in vivo, e.g. gas concentration within the blood, pH-value of blood (measuring of blood pressure A61B5/02; non-radiation detecting or locating of foreign bodies in blood A61B5/06)}
- A61B 5/14552: {Details of sensors specially adapted therefor}
- A61B 5/282: Holders for multiple electrodes (for introduction into the body A61B5/287)
- A61B 5/349: Detecting specific parameters of the electrocardiograph cycle
- A61B 5/366: Detecting abnormal QRS complex, e.g. widening
- A61B 5/4839: {combined with drug delivery}
- A61B 5/6823: {Trunk, e.g., chest, back, abdomen, hip}
- A61B 5/6831: {Straps, bands or harnesses}
- A61B 5/6833: {Adhesive patches}
- G16H 40/63: for local operation
- A61B 5/0245: by using sensing means generating electric signals, {i.e. ECG signals}
- A61B 5/02427: {Details of sensor}
- A61B 2560/0223: of calibration, e.g. protocols for calibrating sensors
- A61B 2562/146: for optical coupling
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA

## Abstract

A system using combined electrocardiography (EKG) and photoplethysmography (PPG) sensing, to determine venous oxygen saturation is described. The system uses averaging of similar pulses based on Prior (or n−1) R-to-R pulse wave duration, and current (or n) R-to-R pulse wave duration for evaluation of the metabolic reserve and/or stress of the patient.

## Claims

### Claim 1

A system for determining venous oxygen saturation, comprising:
(a) a device positionable against skin of a person;
(b) at least one PPG sensor mounted on the device for measuring a PPG signal of the person at multiple wavelengths of light;
(c) a plurality of electrodes for measuring an EKG signal of the person;
(d) a computer logic system for receiving and analyzing the PPG signal and the EKG signal,
wherein the computer logic is configured to:
identify cardiac cycles in the EKG signal;
segment the PPG signal into a series of PPG signal segments based upon features in the identified cardiac cycles,
sort the PPG signal segments into a plurality of bins based upon a similarity in durations of prior R-to-R cardiac cycles and a similarity in durations of current R-to-R cardiac cycles,
generate a composite signal for each of the plurality of bins,
generate a composite Signal Prime Over Signal (SPOS) for each of the composite signals by calculating a derivative of the composite signal and normalizing the derivative of the composite signal by the composite signal itself,
measure venous oxygen saturation of the person by:
(a) calculating arterial oxygen saturation by comparing the composite SPOS signals measured at different wavelengths of light,
(b) sub-sampling composite signals at two consecutive signal maxima measured at different wavelengths of light, and
(c) comparing the sub-sampled composite SPOS signals measured at different wavelengths of light to the calculated arterial oxygen saturation to determine venous oxygen saturation, and
output to a display device an indication of the determined venous oxygen saturation to enable noninvasive monitoring of cardiac conditions.

### Claim 2 (depends on 1)

The system of claim 1, wherein to measure venous oxygen saturation of the person, the computer logic system is configured to select preferred bins from which the composite signals are used when determining the venous oxygen saturation.

### Claim 3 (depends on 2)

The system of claim 2, wherein the preferred bins correspond to the bins having the largest number of PPG signal segments therein.

### Claim 4 (depends on 3)

The system of claim 3, wherein the preferred bins correspond to the bins having the largest difference between current and prior R-to-R values.

### Claim 5 (depends on 1)

The system of claim 1, wherein to generate the composite signal for each of the plurality of bins, the computer logic system is configured to sum or average the PPG signal segments in the bin.

### Claim 6 (depends on 1)

The system of claim 1, wherein to generate the composite signal for each of the plurality of bins, the computer logic system is configured to remove aberrant PPG signal segments from the calculation of the composite signal.

### Claim 7 (depends on 6)

The system of claim 6, wherein to remove aberrant PPG signal segments from the calculation of the composite signal, the computer logic system is configured to iteratively recalculate 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.

### Claim 8 (depends on 1)

The system of claim 1, wherein the device is a hand-held device with the at least one PPG sensor mounted thereon and a plurality of electrode wires extending therefrom.

### Claim 9 (depends on 8)

The system of claim 8, wherein the device is a hand-held device with the at least one PPG sensor mounted thereon and at least one of the plurality of electrodes mounted thereon.

### Claim 10 (depends on 8)

The system of claim 8, wherein an optical waveguide is interposed between the at least one PPG sensor on the device and the skin of the person.

### Claim 11 (depends on 1)

The system of claim 1, wherein the device is positioned within a strap or band disposed around a chest or limb of the person such that the at least one PPG sensor and the plurality of electrodes are disposed within the strap or band disposed around the chest or limb of the person.

### Claim 12 (depends on 1)

The system of claim 1, wherein the device is a patch with the at least one PPG sensor and at least one of the plurality of electrodes positioned therein.

### Claim 13 (depends on 1)

The system of claim 1, wherein the computer logic system is positioned within the device such that the composite signals are generated within the device, and wherein the device comprises:
a data transmission system for transmitting one or both of:
the composite signals to a remote computer system for analysis, or measured PPG and EKG signals to a remote computer system for analysis.

### Claim 14

A system for determining venous oxygen saturation, comprising:
(a) a device positionable against skin of a person;
(b) at least one PPG sensor mounted on the device for measuring a PPG signal of the person at multiple wavelengths of light;
(c) a plurality of electrodes for measuring an EKG signal of the person;
(d) a computer logic system for receiving and analyzing the PPG signal and the EKG signal,
wherein the computer logic system is configured to:
identify cardiac cycles in the EKG signal;
segment the PPG signal into a series of PPG signal segments based upon features in the identified cardiac cycles,
sort the PPG signal segments into a plurality of bins based upon a similarity in durations of prior R-to-R cardiac cycles and a similarity in durations of current R-to-R cardiac cycles,
generate a composite signal for each of the plurality of bins by summing or averaging the PPG signal segments in the bin, and
generate composite Signal Prime Over Signal (SPOS) for each of the composite signals by calculating a derivative of the composite signal and normalizing the derivative of the composite signal by the composite signal itself, and
measure venous oxygen saturation of the person by:
(a) calculating arterial oxygen saturation by comparing the composite SPOS signals measured at different wavelengths of light,
(b) sub-sampling composite signals at two consecutive signal maxima measured at different wavelengths of light, and
(c) comparing the sub-sampled composite signals measured at different wavelengths of light to the calculated arterial oxygen saturation to determine venous oxygen saturation.

### Claim 15

A system for determining venous oxygen saturation, comprising:
(a) a device positionable against skin of a person;
(b) at least one PPG sensor mounted on the device for measuring a PPG signal of the person at multiple wavelengths of light;
(c) a plurality of electrodes for measuring an EKG signal of the person;
(d) a computer logic system for receiving and analyzing the PPG signal and the EKG signal,
wherein the computer logic system is configured to:
identify cardiac cycles in the EKG signal;
segment the PPG signal into a series of PPG signal segments based upon features in the identified cardiac cycles,
sort the PPG signal segments into a plurality of bins based upon a similarity in durations of prior R-to-R cardiac cycles and a similarity in durations of current R-to-R cardiac cycles,
generate a composite signal for each of the plurality of bins comprising a system for removing aberrant PPG signal segments from the calculation of the composite signal 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, and measure a person's venous oxygen saturation by:
(a) calculating arterial oxygen saturation by comparing composite signals measured at different wavelengths of light,
(b) sub-sampling composite signals at two consecutive signal maxima measured at different wavelengths of light, and
(c) comparing the sub-sampled composite signals measured at different wavelengths of light to the calculated arterial oxygen saturation to determine venous oxygen saturation.