Assessing a subject's circulatory system

• US 20100125214A1
• Filed: 11/17/2009
• Published: 05/20/2010
• Est. Priority Date: 11/17/2008
• Status: Active Grant

• Current Assignee: Dialog Devices Limited
• Original Assignee: Dialog Devices Limited
• Inventors: Brown, Jeevanjot, Crabtree, Vincent
• Granted Patent: US 8,491,486 B2
• Time in Patent Office: Days
• US Class Current: 600/504
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography

Abstract

An apparatus including an input interface configured to provide signals from at least two sensors for at least two postures including: signals, dependent upon blood presence, from a first sensor when a subject is in a first posture; signals, dependent upon blood presence, from the first sensor when the subject is in a second posture; signals, dependent upon blood presence, from a second sensor when the subject is in the first posture; and signals, dependent upon blood presence. from the second sensor when the subject is in the second posture; and processing circuitry configured to determine and output a metric by combining, according to pre-defined calibration data the provided signals.

Claims

I_We. I/We claim:

1. An apparatus comprising:

an input interface configured to provide signals from at least two sensors for at least two postures including;

signals, dependent upon blood presence, from a first sensor when a subject is in a first posture;

signals, dependent upon blood presence, from the first sensor when the subject is in a second posture;

signals, dependent upon blood presence, from a second sensor when the subject is in the first posture; and

signals, dependent upon blood presence. from the second sensor when the subject is in the second posture; and

processing circuitry configured to determine and output a metric by combining, according to pre-defined calibration data the provided signals.

2. An apparatus as claimed in claim 1, wherein the signals, for each combination of sensor and posture, comprises at least one logarithm of detected light intensity.

3. An apparatus as claimed in claim 1, wherein the signals, for each combination of sensor and posture, include separately a time varying component of detected light intensity and a quasi static component of detected light intensity.

4. An apparatus as claimed in claim 1, wherein the signals, for each combination of sensor and posture, include separately a logarithm of a time varying component of detected light intensity and a logarithm of a quasi static component of the detected light intensity.

5. An apparatus as claimed in claim 1, wherein the signals, for each combination of sensor and posture, include a signal based upon a light intensity signal detected at an optical reflectance sensor and a signal based upon a light intensity signal detected at an optical transmission sensor.

6. An apparatus as claimed in claim 1, wherein the signals, for each combination of sensor and posture, include a signal based upon a light intensity signal detected at a first wavelength but not at a second wavelength and a signal based upon a light intensity signal detected at least the second wavelength but not the first wavelength.

7. An apparatus as claimed in claim 1, wherein the calibration data is used to assess divergence of the provided signals from an expected average of a statistical model of expected signals to produce the metric.

8. An apparatus as claimed in claim 1, wherein the calibration data defines a non-linear combination of the signals.

9. An apparatus as claimed in claim 1, wherein the calibration data is predetermined using machine learning.

10. An apparatus as claimed in claim 1, configured to emulate an artificial neural network comprising a plurality of nodes each of which has associated weights for inputs to the node, wherein the calibration data provides said weights.

11. An apparatus as claimed in claim 1, further comprising a memory storing multiple sets of calibration data comprising a set of calibration data for each of a plurality of predetermined standard sequences of different body postures.

12. An apparatus as claimed in claim 1, wherein at least one of the sensors provide signals from optical reflection detectors

13. An apparatus as claimed in claim 1, wherein a change from the first posture to the second posture is expected to cause a local, as opposed to systemic, circulatory reaction

14. An apparatus as claimed in claim 1, wherein a change from the first posture to the second posture causes, for the subject, a relative vertical displacement with respect to the subject'"'"'s heart of a subject'"'"'s peripheral limb of without relative vertical displacement with respect to the subject'"'"'s heart of the subject'"'"'s head.

15. An apparatus as claimed in claim 14, wherein at least the first sensor is on the limb.

16. An apparatus as claimed in claim 1, wherein a change from the first posture to the second posture is expected to cause a systemic circulatory reaction.

17. An apparatus as claimed in claim 1, wherein a change from the first posture to the second posture causes, for the subject, a relative vertical displacement with respect to the subject'"'"'s heart of the subject'"'"'s head.

18. An apparatus as claimed in claim 17, wherein at least the first sensor is on the subject'"'"'s head.

19. An apparatus as claimed in claim 18, wherein the first sensor provides signals from an optical transmission sensor.

20. An apparatus as claimed in claim 1, wherein the metric records a divergence of the signals from an expected pattern of signals that characterize an expected response of a normalized circulation system to the predetermined sequence of first and second postures.

21. A system comprising:

an apparatus as claimed in claim 1; and

at least a first sensor and a second sensor.

22. A system as claimed in claim 21, wherein the first sensor is at a first location and the second sensor is at a second, different, location.

23. A system as claimed in claim 21, wherein the first sensor detects light at a first wavelength but not at a second wavelength and the second sensor detects light at the second wavelength but not at the first wavelength.

24. A system as claimed in claim 21, wherein the first sensor is a reflectance sensor and is attached without clamping using an opaque adhesive collar that closely circumscribes the reflectance sensor.

25. A system as claimed in claim 21, wherein the first sensor and second sensor are attached to a flexible substrate comprising interconnects that are connectable to the apparatus via an interface, wherein a portion of the flexible substrate, underlying one or more of the interconnects, has a manufactured structural weakness and wherein, in use, the portion of the flexible substrate having the structural weakness connects with the interface which retains the substrate against removal such that on attempted removal of the flexible substrate from the interface the manufactured structural weakness breaks the one or more interconnects.

26. A system as claimed in claim 25, wherein the interface additionally detaches a portion of the flexible substrate to reveal an indicator.

27. A system as claimed in claim 21, wherein the first sensor and second sensor are attached to a flexible substrate for application to a subject and are connectable to the processing circuitry via a first set of interconnects embedded in the flexible substrate, wherein an ordering of the interconnects embedded in the substrate is dependent upon whether the flexible substrate is for use on a right limb or a left limb and wherein the ordering of the interconnects embedded in the substrate, in use, is indicative to the processing circuitry of whether the flexible substrate is applied to a right limb of the subject or a left limb of the subject.

28. A system as claimed in claim 21, wherein the first sensor and second sensor are attached to a first side of a flexible reversible substrate and are connectable to the processing circuitry via a first set of interconnects on the first side of the flexible substrate and wherein a third sensor and a fourth sensor are attached to a second side of the flexible substrate and are connectable to the processing circuitry via a second set of interconnects on the second side of the flexible substrate, wherein an ordering of the first set of interconnects across the first side of the flexible interconnect, when the first side of the flexible substrate is upwards facing, is different to an ordering of the second set of interconnects across the first side of the flexible substrate when the second side of the flexible substrate is upwards facing thereby enabling the processing circuitry to determine which side of the reversible flexible substrate is operational.

29. A system as claimed in claim 21, wherein first signals detected by the first sensor are processed to produce parallel signals that have different frequency components before combination at the processing circuitry and wherein second signals detected by the second sensor are processed to produce parallel signals that have different frequency components before combination by the processing circuitry.

31. A method comprising:

attaching optical sensors to a subject;

connecting the optical sensors to an apparatus as claimed in claim 1;

moving the subject through a predetermined ordered sequence of different postures including the first and second postures.

32. A method as claimed in claim 31, wherein the optical sensors are attached by attaching a disposable flexible substrate to the subject.

33. A method as claimed in claim 32, wherein the disposable flexible substrate is attached to a limb and comprises at least one optical reflectance sensor.

34. A method as claimed in claim 33, wherein the flexible substrate is attached using adhesive only and without the use of a clamping force.

35. A method as claimed in claim 32, wherein the disposable flexible substrate is attached to a subject'"'"'s head and comprises at least one optical transmission sensor.

30. A system for assessing a subject'"'"'s blood circulation

a first detector configured to detect signals dependent upon blood presence when the subject is in a first posture and when the subject is in a second posture;

at least one other detector configured to detect signals dependent upon blood presence when the subject is in the first posture and when the subject is in the second posture; and

processing circuitry configured to determine a metric by combining the detected signals from the first and second detectors for the first and second postures according to calibration data.