High sensitivity noise immune stethoscope

• US 20070165872A1
• Filed: 11/15/2006
• Published: 07/19/2007
• Est. Priority Date: 11/15/2005
• Status: Active Grant

• Current Assignee: Active Signal Technologies, Inc
• Original Assignee: Active Signal Technologies, Inc
• Inventors: Bridger, Keith, Sewell, John, Lutian, Joseph, Kohlhafer, Dennis, Strite, Richard, Cooke, Arthur
• Granted Patent: US 8,265,291 B2
• Time in Patent Office: Days
• US Class Current: 381/67
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R

Abstract

A physiological sensing stethoscope suitable for use in high-noise environments is disclosed. The stethoscope is designed to be substantially matched to the mechanical impedance of monitored physiological activity and substantially mismatched to the mechanical impedance of air-coupled acoustic activity. One embodiment of the stethoscope utilizes a passive acoustic system. Another embodiment utilizes an active Doppler system. The passive and active systems can be combined in one stethoscope enabling switching from a passive mode to an active mode suitable for use in very high-noise environments. The stethoscope is suitable for use in environments having an ambient background noise of 100 dBA and higher. The passive includes a head having a housing, a flexural disc mounted with the housing, and an electromechanical stack positioned between the housing and the flexural disc in contact with the skin of a patient. The active system detects Doppler shifts using a high-frequency transmitter and receiver.

Claims

1. A stethoscope, comprising:

a housing comprising an inner cavity;

a flexural disc mounted on the housing structured and arranged to deflect based upon physiological activity of a patient; and

an electromechanical stack positioned at least partially within the inner cavity mechanically coupled between the housing and the flexural disc which generates an electrical signal upon deflection of the flexural disc.

2. The stethoscope of claim 1, wherein the inner cavity of the housing comprises a longitudinal axis and the longitudinal axis is substantially perpendicular to a plane defined by the flexural disc.

3. The stethoscope of claim 2, wherein the electromechanical stack is longest in a dimension substantially collinear with the longitudinal axis.

4. The stethoscope of claim 2, wherein the electromechanical stack has a poled direction and the poled direction is substantially collinear with the longitudinal axis.

5. The stethoscope of claim 2, wherein deflection of the flexural disc towards the inner cavity of the housing causes compression of the electromechanical stack substantially along the longitudinal axis.

6. The stethoscope of claim 1, wherein the electromechanical stack comprises a piezoelectric material and/or a magnetostrictive material.

7. The stethoscope of claim 1, wherein the electromechanical stack comprises at least one of piezoelectric lead zirconate titanate, quartz crystal, lithium niobates, barium titanate, lead titanate, meta-lead niobate, lead magnesium niobate, polyvinylidene di-fluoride, and/or Terfenol-D.

8. The stethoscope of claim 1, wherein the electromechanical stack is monolithic or comprises a plurality of plates.

9. The stethoscope of claim 8, wherein the electromechanical stack comprises a first plate comprising a first material and a second plate comprising a second material.

10. The stethoscope of claim 1, further comprising a moveable piston positioned between the electromechanical stack and the flexural disc movable along a longitudinal direction of the housing.

11. The stethoscope of claim 10, wherein the moveable piston comprises a contact ridge extending from a bottom surface of the moveable piston, the contact ridge circumferentially located near a periphery of the moveable piston and engaging the flexural disc having an edge, the edge in communication with the housing, whereby movement of the flexural disc in the longitudinal direction generates a smaller movement of the moveable piston in the longitudinal direction.

12. The stethoscope of claim 1, further including a potting compound layer adjacent the flexural disc.

13. The stethoscope of claim 12, wherein the potting compound layer includes a protrusion extending away from the flexural disc.

14. The stethoscope of claim 1, wherein the housing has a mass greater than 100 grams.

15. The stethoscope of claim 1, wherein the housing is greater than 75 percent by weight of the stethoscope.

16. The stethoscope of claim 1, wherein the flexural disc is in direct contact with a patient.

17. The stethoscope of claim 1, wherein a potting compound layer is adhered to the flexural disc and in direct contact with the patient.

18. A stethoscope, comprising:

a housing;

an electromechanical stack positioned within the housing; and

means for mechanically amplifying physiological signals in communication with the electromechanical stack.

19. The stethoscope of claim 18, wherein the means for amplifying physiological signals include a flexural disc is in communication with the housing.

20. The stethoscope of claim 19, wherein the means for amplifying physiological signals further include a moveable piston positioned between the electromechanical stack and the flexural disc.

21. The stethoscope of claim 20, wherein the moveable piston includes a contact ridge extending toward the flexural disc.

22. The stethoscope of claim 21, wherein the moveable piston is in pressing contact with the electromechanical stack.

23. The stethoscope of claim 18, wherein the means for amplifying physiological signals generates an amplified signal that is distinguishable over ambient noise of at least 90 dBA.

24. The stethoscope of claim 18, wherein the electromechanical stack comprises a piezoelectric material and/or a magnetostrictive material.

25. The stethoscope of claim 18, wherein the electromechanical stack is monolithic or comprises a plurality of plates.

26. The stethoscope of claim 25, wherein the electromechanical stack comprises a first plate comprising a first piezoelectric material and a second plate comprising a second piezoelectric material.

27. A stethoscope, comprising:

a housing having an interior and a longitudinal axis;

a transducer capable of converting mechanical energy into an electrical signal positioned within the housing, wherein the transducer has a longest dimension substantially collinear with the longitudinal axis;

means for mechanically amplifying forces exerted by physiological activity in communication with the transducer; and

means for amplifying the electrical signal of the transducer.

28. The stethoscope of claim 27, wherein the transducer comprises a piezoelectric material.

29. The stethoscope of claim 27, wherein the amplifying means comprises a preamplifier and volume control.

30. The stethoscope of claim 27, wherein the amplifying means comprises an audio amplifier and a power amplifier.

31. The stethoscope of claim 30, wherein the power amplifier is a Class D power amplifier designed to provide up to one watt of output power.

32. The stethoscope of claim 27, further comprising batteries for powering the amplifying means, the batteries contained within the housing.

33. A stethoscope, comprising:

a housing;

a passive system incorporated into the housing, the passive system comprising an acoustic transducer;

an active system incorporated into the housing, the active system comprising a transmitter an a receiver; and

a switch in communication with the passive system and the active system, the switch able to select the passive system or active system.

34. The stethoscope of claim 33, wherein the acoustic transducer is an electromechanical stack.

35. The stethoscope of claim 33, wherein the acoustic transducer comprises at least one of piezoelectric lead zirconate titanate, quartz crystal, lithium niobates, barium titanate, lead titanate, meta-lead niobate, lead magnesium niobate, polyvinylidene di-fluoride, and/or Terfenol-D.

36. The stethoscope of claim 33, wherein the transmitter generates high frequency signals which are reflected from an object thereby creating reflected high frequency signals having a frequency shift dependent on the motion of the object, wherein the receiver detects the reflected high frequency signals and converts the high frequency signal into an electrical signal.

37. The stethoscope of claim 33, wherein the passive system is capable of detecting breathing and heartbeat of a patient with ambient noise levels above 85 dBA.

38. The stethoscope of claim 33, wherein the active system is capable of detecting breathing and heartbeat of a patient at ambient noise levels greater than 95 dBA.

39. The stethoscope of claim 33, wherein the active system is capable of detecting breathing and heartbeat of a patient at ambient noise levels up to at least 110 dBA.

40. The stethoscope of claim 33, wherein the switch is manually operable.

41. The stethoscope of claim 33, wherein the housing has a forward side and a rear side, wherein the passive system and active system are both oriented to receive input from the forward side.

42. The stethoscope of claim 33, further comprising an electronics box including a power supply, control logic, an audio switching circuit, a power amplifier and the switch.

43. A stethoscope capable of use in a high amplitude ambient noise environment, comprising:

a housing;

an active system incorporated into the housing, the active system comprising a transmitter and a receiver for sending and receiving high frequency signals to and from a patient exposed to the high amplitude ambient noise environment; and

a signal conditioner for reducing or eliminating unwanted signals selected from the high amplitude ambient noise and/or other spurious signals.

44. The stethoscope of claim 43, wherein the signal conditioner comprises a front end which receives the high frequency signals from a patient and wherein the front end comprises a demodulator.

45. The stethoscope of claim 44, wherein the high frequency signal is of a selected frequency and the demodulator comprises a bandpass filter set to pass only the high frequency signal within +/−

1.0 percent of the selected frequency of the high frequency signal.

46. The stethoscope of claim 44, further comprising a bandpass filter following the demodulator which excludes demodulated signals outside an audible range.

47. The stethoscope of claim 46, wherein the audible range is restricted to about 40 Hz to about 500 Hz.

48. The stethoscope of claim 46, further comprising an amplifier to strengthen the demodulated and filtered signal and a user adjusted gain control.

49. The stethoscope of claim 43, where the high frequency signal is in the ultrasound range.

50. A method for detecting physiological activity in a high amplitude ambient noise environment comprising:

transmitting a high frequency signal into a patient;

receiving a reflected signal;

demodulating the reflected signal;

filtering the demodulated signal; and

transmitting the filtered and demodulatedsignal to an earpiece.

51. The method of claim 50, further comprising amplifying the demodulated and filtered signal prior to the transmission to the earpiece.

52. The method of claim 51, further comprising adjusting the gain of the amplified signal prior to the transmission to the earpiece.