Methods and devices for vascular plethysmography via modulation of source intensity

• US 6,731,967 B1
• Filed: 07/16/2001
• Issued: 05/04/2004
• Est. Priority Date: 07/16/2001
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Turcott, Robert
• Primary Examiner(s): Bennett, Henry
• Assistant Examiner(s): Dahbour, Fadi H.
• Application Number:
  US09/907,349
• Time in Patent Office: 1,023 Days
• Field of Search: 600/407, 600/474, 600/478, 600/479, 600/480, 600/485, 600/486, 600/493, 600/500, 600/501, 600/502, 600/503, 600/504, 600/507, 600/508, 600/472, 600/473, 600/475, 600/476, 600/477, 600/428, 128/898
• US Class Current: 600/407
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light

Abstract

A time-varying modulating signal is used as a plethysmography signal, rather than a time-varying detected optical power. The time-varying detected optical power is used (e.g., in a feedback loop) to adjust the source intensity. Light is transmitted from a light source, wherein an intensity of the transmitted light is based on a light control signal. A portion of the light transmitted from the light source is received at a light detector, the portion having an associated detected light intensity. A feedback signal is produced based the portion of light received at the light detector, the feedback signal indicative of the detected light intensity. The feedback signal is compared to a reference signal to produce a comparison signal. The light control signal is then adjusted based on the comparison signal, wherein at least one of the comparison signal and the light control signal is representative of volume changes in blood vessels.

Claims

1. For use in a medical device including a light source and a light detector, a method for monitoring volume changes in blood vessels, comprising the following steps:

(a) transmitting light from the light source, wherein an intensity of the transmitted light is based on a light control signal;

(b) receiving, at the light detector, a portion of the light transmitted from the light source, the portion having an associated detected light intensity;

(c) producing a feedback signal based on the portion of light received at the light detector, the feedback signal indicative of the detected light intensity;

(d) comparing the feedback signal to a reference signal to produce a comparison signal; and

(e) adjusting the light control signal based on the comparison signal,

wherein at least one of the comparison signal and the light control signal is representative of volume changes in blood vessels.

2. The method of claim 1, further comprising the steps of:

converting the comparison signal from a voltage signal to a current signal, the light control signal comprising the current signal; and

driving the light source based on the current signal.

3. The method of claim 2, further comprising the steps of:

producing a further voltage signal that is proportional to the current signal, the further voltage signal representative of volume changes in blood vessels; and

measuring the further voltage signal to thereby monitor volume changes in blood vessels.

4. The method of claim 1, wherein step (e) comprises adjusting the light control signal to thereby keep the detected light intensity of the portion of light received at the light detector relatively constant.

5. The method of claim 4, wherein step (e) comprises adjusting an amplitude of the light control signal to thereby keep the detected light intensity of the portion of light received at the light detector relatively constant.

6. The method of claim 4, wherein step (e) comprises adjusting a frequency of the light control signal to thereby keep the detected light intensity of the portion of light received at the light detector relatively constant.

7. The method of claim 4, wherein step (e) comprises adjusting pulse widths of the light control signal to thereby keep the detected light intensity of the portion of light received at the light detector relatively constant.

8. The method of claim 1, wherein step (e) comprises adjusting the light control signal to minimize a difference between the feedback signal and the reference signal.

9. The method of claim 8, wherein step (e) comprises adjusting an amplitude of the light control signal to minimize a difference between the feedback signal and the reference signal.

10. The method of claim 8, wherein step (e) comprises adjusting a frequency of the light control signal to minimize a difference between the feedback signal and the reference signal.

11. The method of claim 8, wherein step (e) comprises adjusting a pulse width of the light control signal to minimize a difference between the feedback signal and the reference signal.

12. The method of claim 1, wherein step (c) comprises the steps of:

(c.1) adjusting a current signal based on the portion of light received at the light detector; and

(c.2) converting the current signal to a voltage signal, wherein the feedback signal comprises the voltage signal.

13. The method of claim 1, wherein:

the light control signal comprises a digital signal; and

the light source comprises a plurality of LEDs, each of which is turned on or off based on the digital signal.

14. The method of claim 13, wherein step (e) comprises adjusting the digital signal to minimize a difference between the feedback signal and the reference signal.

15. The method of claim 13, wherein step (e) comprises adjusting the digital signal to thereby keep the detected light intensity of the portion of light received at the light source relatively constant.

16. For use in a medical device including a light detector and a light source that transmits light of at least two different wavelengths, a method for monitoring volume changes in blood vessels, comprising the following steps:

(a) transmitting light having a first wavelength and light having a second wavelength from the light source, wherein an intensity of the transmitted light is based on a first light control signal and a second light control signal;

(b) receiving, at the light detector, a portion of the light having the first wavelength and a portion of the light having the second wavelength transmitted from the light source, each portion having an associated detected light intensity;

(c) producing a first feedback signal based on the portion of light having the first wavelength, and a second feedback signal based on the portion of light having the second wavelength, each feedback signal indicative of the associated detected light intensity;

(d) comparing the first feedback signal to a reference signal to produce a first comparison signal, and the second feedback signal to a reference signal to produce a second comparison signal; and

(e) adjusting the first and second light control signals, respectively, based on the first and second comparison signals,

wherein the first and second comparison signals are representative of volume changes in blood vessels.

17. The method of claim 16, wherein the first wavelength is within the red visible light spectrum, and the second wavelength is within the infrared or near infrared light spectrum.

18. The method of claim 17, further comprising the step of:

(g) producing first and second plethysmography information signals that are respectively proportional to the transmitted light having the first wavelength and the transmitted light having the second wavelength; and

(h) calculating blood oxygenation levels based on the first and second plethysmography information signals.

19. A device for monitoring volume changes in blood vessels, comprising:

a light controller to produce a light control signal;

a light source to transmit light based on the light control signal, wherein an intensity of the transmitted light is based on the light control signal;

a light detector to

receive a portion of the light transmitted from the light source, the portion having an associated detected light intensity, and

produce a feedback signal based on the portion of light received at the light detector, the feedback signal indicative of the detected light intensity; and

a comparator to compare the feedback signal to a reference signal to produce a comparison signal,

wherein the light controller adjusts the light control signal based on the comparison signal, at least one of the comparison signal and the light control signal being representative of volume changes in blood vessels.

20. The device of claim 19, further comprising a transistor to convert the comparison signal from a voltage signal to a current signal that drives the light source, wherein the light control signal comprises the current signal.

21. The device of claim 20, further comprising a resistor to produce a further voltage signal proportional to the current signal, wherein the further voltage signal is representative of volume changes in blood vessels.

22. The device of claim 19, wherein the light controller adjusts an amplitude of light control signal based on the comparison signal.

23. The device of claim 19, wherein the light control signal comprises a pulse train, and wherein the light controller adjusts a frequency of the pulse train based on the comparison signal.

24. The device of claim 19, wherein the light controller further comprises:

a monostable multivibrator (MMV);

a register to store a value and increment or decrement the value based on the comparison signal when the register receives a pulse from the MMV;

a countdown timer to receive the value stored in the register when the countdown timer receives a pulse from the MMV, and to output a trigger pulse after counting from the value down to zero,

wherein the MMV produces a pulse having a substantially constant amplitude and pulse width when the MMV receives a trigger pulse from the countdown timer, and

wherein the MMV produces a plurality of the pulses having substantially constant amplitude and pulse width, the plurality of the pulses having a variable frequency based on the comparison signal, wherein the light control signal comprises the plurality of pulses having the variable frequency.

25. The device of claim 24, wherein the countdown timer receives a plurality of values from the register over time, the plurality of values representative of volume changes in blood vessels.

26. The device of claim 19, wherein the light control signal comprises a pulse train, and wherein the light controller adjusts pulse widths of the pulse train based on the comparison signal.

27. The device of claim 19, wherein the light controller adjusts the light control signal more than once per heart beat.

28. The device of claim 19, wherein the light controller further comprises:

a pulse means for producing a train of trigger pulses having a substantially constant frequency;

a comparator that compares the feedback signal to a reference signal to produce a comparison signal;

a register to store a value and increment or decrement the value based on the comparison signal when the register receives a trigger pulse from the pulse means; and

a countdown timer to receive the value stored in the register when the countdown timer receives a trigger pulse from the pulse means, wherein the count down timer outputs a pulse after counting from the value down to zero, the countdown timer thereby producing a plurality of pulses each having a pulse width proportional to the comparison signal.

29. The device of claim 28, wherein the countdown timer receives a plurality of values from the register over time, the plurality of values representative of volume changes in blood vessels.

30. The device of claim 19, wherein:

the light control signal comprises a digital signal; and

the light source comprises a plurality of LEDs, each of which is turned on or off based on the digital signal.

31. The device of claim 19, wherein the light source comprises a plurality of LEDs, and wherein the light controller further comprises:

a pulse means for producing a train of trigger pulses having a substantially constant frequency;

a register to increment or decrement a stored value based on the comparison signal when the register receives a trigger pulse from the pulse means;

wherein the register outputs the value as a digital signal when the enable pin is activated by a trigger pulse of the pulse means; and

wherein each of the plurality of LEDs is independently turned on or off based on the digital signal when the LEDs receive a trigger pulse from the pulse means.

32. The device of claim 19, wherein the light source and the light detector are arranged in a transmission configuration.

33. The device of claim 32, wherein the light source and the light detector are arranged such that a human appendage can be placed between the light source and the light detector.

34. The device of claim 19, wherein the light source and the light detector are arranged in a reflection configuration.

35. The device of claim 34, wherein the light source and the light detector are located relatively adjacent to one another.

36. The device of claim 35, wherein the light source and the light detector are arranged such that a human appendage can be placed upon the light source and the light detector.

37. The device of claim 35, wherein the light source, the light controller, and the light detector are incorporated into an implantable device.

38. The device of claim 19, further comprising:

a means for determining volume changes in blood vessels based on at least one of the comparison signal and the light control signal.

39. A device for monitoring volume changes in blood vessels, comprising:

a light controller to produce a light control signal based on a first light control signal and a second light control signal;

a light source to transmit light having a first wavelength and light having a second wavelength based on the light control signal, wherein an intensity of the transmitted light is based on the first and second light control signals;

a light detector to

receive a portion of the light having the first wavelength and a portion of the light having the second wavelength transmitted from the light source, each portion having an associated detected light intensity, and

produce a first feedback signal based on the portion of light having the first wavelength and a second feedback signal based on the portion of the light having the second wavelength, each feedback signal indicative of the associated detected light intensity;

a first comparator to compare the first feedback signal to a reference signal to produce a first comparison signal; and

a second comparator to compare the second feedback signal to a reference signal to produce a second comparison signal,

wherein the light controller adjusts the light control signal based on the first and second comparison signals, the first and second comparison signals being representative of volume changes in blood vessels.

40. The device of claim 39, wherein the light sources comprises:

a first light emitting diode (LED) that transmits the light having the first wavelength; and

a second LED that transmits the light having the second wavelength.

41. The device of claim 40, wherein the first wavelength is within the red visible light spectrum, and the second wavelength is within the infrared or near infrared light spectrum.

42. The device of claim 41, further comprising:

means for producing first and second plethysmography information signals that are respectively proportional to the transmitted light having the first wavelength and the transmitted light having the second wavelength; and

means for calculating blood oxygenation levels based on the first and second plethysmography information signals.

43. An implantable device for monitoring volume changes in blood vessels, comprising:

a light source to transmit light;

a light detector to receive a portion of the light transmitted from the light source, the portion having an associated detected light intensity;

a light controller to adjust an intensity of the transmitted light based on the detected light intensity; and

a means for determining volume changes in blood vessels based on a signal produced by the light controller, the signal being proportional to the intensity of the transmitted light.

44. The device of claim 43, wherein the light source and the light detector are located adjacent to one another on the housing of the implantable device.

45. The device of claim 43, wherein the light source and the light detector are located adjacent to one another on the header of the implantable device.

46. The device of claim 43, wherein the implatable device includes a housing having an optically transparent window, and wherein the light source and the light detector are located adjacent to one another within the housing such that the transmitted light is directed through the window and the received portion of the transmitted light is received through the window.

47. The device of claim 43, wherein the means for determining determines volume changes in blood vessels more than once per heart beat.

48. The device of claim 43, wherein the means for determining determines volume changes in blood vessels at least twenty times per heart beat.