Device and method for determining vital signs of a subject

• US 10,478,078 B2
• Filed: 11/28/2014
• Issued: 11/19/2019
• Est. Priority Date: 12/12/2013
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: De Haan, Gerard
• Primary Examiner(s): Kahelin, Michael W
• Application Number:
  US15/102,649
• Publication Number:
  US 20160302679A1
• Time in Patent Office: 1,817 Days
• CPC Class Codes: A61B 5/0077 Devices for viewing the surface of the body, e.g. camera, magnifying lens
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

The present invention relates to a Device for determining vital signs of a subject comprising an interface (22) for receiving a periodic photoplethysmographic, PPG, signal obtained from a subject (14) by a PPG measurement, a signal partitioning unit (24) for partitioning the PPG signal in time into a plurality of PPG sub-signals covering a half period or an integer multiple of a half period, a normalizing unit (26) for normalizing the PPG signal in advance of the partitioning and/or the PPG sub-signals in time and/or amplitude, a signal combination unit (28) for combining a number of normalized PPG sub-signals to obtain a combined PPG sub-signal, and a vital sign processor (30) for deriving a desired vital sign from the PPG signal, one or more combined PPG sub-signals or an enhanced PPG signal obtained by consecutively arranging a number of combined PPG sub-signals.

Claims

1. A device for determining vital signs of a subject comprising:

a controller with a memory that stores instructions;

a processor that executes the instructions, wherein, when executed by processor, the instructions cause the controller to execute a process comprising;

receiving a periodic photoplethysmographic (PPG) signal obtained from a subject by a PPG measurement;

partitioning the PPG signal in time into a plurality of PPG sub-signals respectively covering a half period of the PPG signal;

normalizing in time and/or amplitude the PPG signal in advance of the partitioning and/or the PPG sub-signals to obtain normalized PPG sub-signals;

combining the normalized PPG sub-signals to obtain one or more combined PPG sub-signals; and

deriving a desired vital sign of the subject from the one or more combined PPG sub-signals or an enhanced PPG signal obtained by consecutively arranging a plurality of the combined PPG sub-signals.

2. The device as claimed in claim 1, wherein said combining further comprises consecutively arranging the combined PPG sub-signals according to a chronological order of the normalized PPG sub-signals, from which they have been obtained.

3. The device as claimed in claim 1, wherein said combining further comprises combining a predetermined number of consecutive normalized PPG sub-signals arranged within a time window to obtain a combined PPG sub-signal, wherein the time window is shifted in time for each combined PPG sub-signal.

4. The device as claimed in claim 1, wherein the partitioning further comprises detecting zero-crossings and/or extrema of the PPG signal, and using the detected zero-crossings and/or extrema for partitioning the PPG signal.

5. The device as claimed in claim 1, wherein said normalizing the PPG signal in advance of the partitioning further comprises:

detecting extrema of the PPG signal, fitting a first curve through detected peaks and a second curve through detected valleys;

subtracting a momentary average value of the first and second curves from a momentary signal value of the PPG signal; and

dividing a momentary resulting value by a momentary difference value of the first and second curves to obtain a normalized signal value of the PPG signal.

6. The device as claimed in claim 1, wherein said normalizing further comprises repeating the normalizing until a stop condition is met or normalized signal value obtained from the normalizations converge.

7. The device as claimed in claim 1, wherein said combining further comprises generating an average, a weighted average or a trimmed mean of two or more normalized PPG sub-signals.

8. The device as claimed in claim 1, wherein said combining further comprises generating a weighted average or a trimmed mean of two or more normalized PPG sub-signals, wherein the weight for weighting normalized PPG sub-signals decreases with a time-distance to a current time interval.

9. The device as claimed in claim 1, further comprising a filter for low-pass or band-pass filtering the received PPG signal, wherein the filtered PPG signal is used for subsequent processing.

10. The device as claimed in claim 1, wherein said combining further comprises scaling the period of the combined PPG sub-signals in time to match the period of a current time interval and to consecutively arrange a number of the scaled combined PPG sub-signals to obtain the enhanced PPG signal.

11. The device as claimed in claim 1, further comprising a high frequency (HF) boosting filter for boosting of high-frequency harmonics in the PPG sub-signals and/or the enhanced PPG signal, wherein said filtered PPG signal is used for subsequent processing.

12. The device as claimed in claim 1, further comprising

an imaging unit for acquiring image frames of a subject, and the process further comprises:

deriving a PPG signal from a skin portion of the subject shown in the image frames and for providing the PPG signals to an interface.

13. The device as claimed in claim 1, further comprising a PPG sensor for acquiring PPG signals from a PPG measurement at a skin portion of the subject and for providing the PPG signals to a interface.

14. A method for determining vital signs of a subject, the method comprising:

receiving a periodic photoplethysmographic (PPG) signal obtained from the subject by a PPG measurement;

partitioning the PPG signal in time into a plurality of PPG sub-signals respectively covering a half period of the PPG signal;

normalizing in time and/or amplitude the PPG signal in advance of the partitioning and/or the PPG sub-signals to obtain normalized PPG sub-signals;

combining the normalized PPG sub-signals to obtain one or more combined PPG sub-signal; and

deriving a desired vital sign from the one or more combined PPG sub-signals or an enhanced PPG signal obtained by consecutively arranging a plurality of the combined PPG sub-signals.

15. A non-transitory computer-readable medium storing a computer program executable on a computer processor, which when executed by the computer processor cause a computer to carry out the steps of the method as claimed in claim 14.