Single diaphragm pressure-balanced telemetric pressure sensing system

• US 4,281,666 A
• Filed: 04/13/1978
• Issued: 08/04/1981
• Est. Priority Date: 06/21/1976
• Status: Expired due to Term

• Current Assignee: Eric R. Cosman
• Original Assignee: Eric R. Cosman
• Inventors: Cosman, Eric R.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/895,953
• Time in Patent Office: 1,209 Days
• Field of Search: 128/673, 128/675, 128/748, 128/660, 73/701, 73/708, 73/716-719, 73/722
• US Class Current: 600/561
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/031 Intracranial pressure
• CPC Class Codes: A61M 27/006 Cerebrospinal drainage; Accessories therefor, e.g. valves

Abstract

A differential pressure sensing device is fully implanted in the body of a patient to monitor internal pressure such as intracranial pressure. A movable element in the sensor communicates on one side with the internal pressure to be measured and on the other side with an external pressure which is applied by an external pressurizer-control system and which is communicated to the sensor through the intact skin. An imbalance of the two opposing pressures causes a displacement of the movable element which changes a physical characteristic of the sensor, such as the resonant frequency of a tuned L-C circuit. This change is detected outside the body by an external detection system, such as a frequency swept radio frequency oscillator. The external pressure is varied until the external detector senses that the pressures are balanced on the movable element, at which point the external pressure equals the internal pressure, and the former is measured and read out.

Claims

1. An in vivo differential pressure sensor adapted for implantation beneath the skin in the living body for in vivo calibration after implantation, said sensor comprising:

(a) a housing having means defining an opening therein;

(b) a single flexible diaphragm means which extends across the housing opening and is secured with respect to said housing, said single flexible diaphragm means having a first and a second side, at least a portion of said first side comprising at least a portion of the exterior surface of said sensor, said housing and said single flexible diaphragm means being adapted so that, when said sensor is implanted beneath the skin, the exterior surface of said single flexible diaphragm means is positioned to be adjacent to and facing an interior portion of skin whereby said exterior surface portion of said single flexible diaphragm means is in mechanical pressure communication with the skin and whereby pressures external to the body can be communicated mechanically across the skin to said single flexible diaphragm means;

(c) means allowing the second side of said single flexible diaphragm means to be in contact with and in mechanical pressure communication with a bodily medium, the pressure of which is to be sensed when said sensor is implanted in the living body, so that changes in the difference of pressures on said two sides of said single flexible diaphragm means cause a motion of at least a portion of said single flexible diaphragm means

(d) means connected to said housing for contacting the single flexible diaphragm means for a predetermined relationship between the pressures on said single flexible diaphragm means thereby defining a mechanical contact reference position of said single flexible diaphragm means with respect to said housing for a predetermined relationship between the pressures on said single flexible diaphragm means; and

,

(e) means having a preselected parameter that is detectable by detection apparatus located outside the living body, said means having a preselected parameter being at least in part cooperatively connected to and movable with said single flexible diaphragm means so that preselected parameter will change with movement of said single flexible diaphragm means, said parameter being detectable at least when said single flexible diaphram means is substantially at said mechanical contact reference position and said parameter changing upon at least a displacement of at least;

(i) a portion of said single flexible diaphragm means from said mechnical contact reference position or (ii) displacements of at least a portion of said single flexible diaphragm means with respect to said housing;

whereby when said sensor is implanted beneath the skin said single flexible diaphragm means can be driven to said mechanical contact reference position by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined at said mechanical contact reference position after implantation and whereby the magnitude of the external pressure applied to the skin that is required to drive said single flexible diaphragm means to said mechanical contact reference position is a function of the pressure in said bodily medium.

2. The sensor of claim 1 wherein said means allowing said second side of said single flexible diaphragm means to contact a second bodily medium comprises a through opening in said housing, with said single flexible diaphragm means extending across said through opening and being secured with respect to said housing.

3. An in vivo differential pressure sensor adapted for implantation beneath the skin in the living body and sensing the pressure of a bodily fluid and adapted for in vivo calibration after implantation, said sensor comprising:

(a) a housing;

(b) a single flexible diaphragm means which is fluid pressure sealed with respect to said housing and having a first and a second side with at least a portion of said first side comprising at least a portion of the exterior surface of said sensor and being positioned so that after implantation, said portion of said first side is in mechanical pressure communication with the skin and whereby pressures external to the body can be communicated mechanically across the skin to said single flexible diaphragm means, said single flexible diaphragm means and said housing together defining a chamber such that the second side of said single flexible diaphragm means communicates mechanically with pressure inside said chamber so that changes in the difference in pressures on said two sides of said single flexible diaphragm means causes a motion of at least a portion of said single flexible diaphragm means;

(c) inlet means to said chamber allowing the entrance of a bodily fluid from an internal bodily region to the inside of said chamber, thereby providing a fluid pressure communication between said internal bodily region and the inside of said chamber when said sensor is implanted in the living body, and enabling that a change in the pressure in said internal bodily region will cause a movement of at least a portion of said single flexible diaphragm means with respect to said housing;

(d) contact means connected to said housing for contacting the single flexible diaphragm means for a predetermined relationship between the pressures on said single flexible diaphragm means thereby defining a mechanical contact reference position of said single flexible diaphragm means with respect to said housing at a predetermined relationship between said pressures on said single flexible diaphragm means;

(e) means having a preselected parameter that is detectable by detection apparatus located outside the living body, said means having a preselected parameter being at least in part cooperatively connected to and movable with said single flexible diaphragm means so that said preselected parameter will change with movement of said single flexible diaphragm means, said parameter being detectable at least when said single flexible diaphragm means is at said mechanical contact reference position and said parameter changing upon at least;

(i) a displacement of at least a portion of said single flexible diaphragm means from said mechanical contact reference position or (ii) displacements of at least a portion of said single flexible diaphragm means with respect to said housing;

whereby when said sensor is implanted beneath the skin, said single flexible diaphragm means can be driven to said mechanical contact reference position by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined at said mechanical contact reference position by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined at said mechanical contact reference position after implantation, and whereby the magnitude of the external pressure applied to the skin required to drive said single flexible diaphragm means to said mechanical contact reference position is a function of the pressure in said internal bodily region.

4. The apparatus of claim 3 wherein said housing has an opening in its walls and is fluid pressure sealed with respect to said housing so that said single flexible diaphragm means defines part of the exterior surface of said sensor.

5. The apparatus of claim 3 wherein said contact means comprises a mechanical stop means which stops the motion of said movable portion of said single flexible diaphragm means with respect to said housing at said predetermined pressure relationship.

6. The apparatus of claim 3 wherein said contact means includes electrode contacts that change their electrical condition at a reference position of said single flexible diaphragm means relative to said housing, and said means having a detectable parameter includes circuit means within said sensor and cooperative with said electrode contact whereby the change in electrical condition of said electrode contacts produces a characteristics response of said circuit that is detectable by apparatus outside said living body.

7. The apparatus of claim 3 wherein said contact means is so adapted that said mechanical contact reference position corresponds to the balance of said pressures on opposite sides of said single flexible diaphragm means.

8. The apparatus of claim 3 wherein said inlet means comprises a tube.

9. The apparatus of claim 3 wherein the locus of points where said single flexible diaphragm means is fluid pressure sealed to said housing defines a perimeter which lies substantially in a plane, and wherein said single flexible diaphragm means is at least partially in coplanar geometry with respect to said plane for said predetermined pressure relationship.

10. The apparatus of claim 3 wherein said means having a preselected, detectable parameter comprises electronic circuit means, said parameter being a characteristic response parameter of said circuit means which is detectable by electromagnetic coupling to electronic apparatus means located external to said living body.

11. The apparatus of claim 10 wherein said electronic circuit means includes an inductor and further comprises a magnetic material that is cooperatively connected to said single flexible diaphragm means and which which moves relative to the inductor with at least a portion of said single flexible diaphragm means, such movement producing a displacement of said magnetic material relative to said inductor thereby varying the inductance of said inductor.

12. The apparatus of claim 10 wherein said electronic circuit means includes an inductor and further comprises a conductive material that is cooperatively connected to said single flexible diaphragm means and which moves relative to the inductor with at least a portion of said single flexible diaphragm means, such movement producing a displacement of said conductive material relative to said inductor thereby varying the inductance of said inductor.

13. The apparatus of claim 10 wherein said electronic circuit means comprises a resonant electrical circuit which includes a coil and a capacitor.

14. The apparatus of claim 13 wherein said coil is fixed with respect to said housing.

15. The apparatus of claim 13 further comprising means for varying the capacitance of said capacitor in response to said displacement of at least a portion of said single flexible diaphragm means.

16. The apparatus of claim 13 wherein said resonant electrical circuit is a parallel resonant circuit and wherein said preselected detectable parameter is the resonant frequency of said resonant circuit.

17. The apparatus of claim 3 wherein said single flexible diaphragm means is spring loaded with respect to said housing.

18. The apparatus of claim 3 and further comprising an outlet means which permits the exit of fluid from the interior of said chamber.

19. The apparatus of claim 18 wherein said inlet and outlet means include tubes.

20. The apparatus of claim 18 further comprising a fluid shunt valve means interposed in series with at least one of said inlet or said outlet means for regulating the flow of said bodily fluid from said second bodily region.

21. The apparatus of claim 18 further comprising a fluid shunt valve means which is mounted in part of said single flexible diaphragm means and in part on said housing so that at least a portion of said single flexible diaphragm means displaces under changes in said pressures on either side of said single flexible diaphragm means, there will result a change in the opening of said fluid shunt valve means so as to change the flow regulation of said bodily fluid.

22. The apparatus of claim 3 wherein the part of said means having a preselected, detectable parameter that is cooperatively connected to said single flexible diaphragm means is at least a part of said single flexible diaphragm means.

23. The sensor of claim 3 wherein said means having a preselected, detectable parameter comprises a scatterer of ultrasonic radiation.

24. An in vivo differential pressure sensor adapted for implantation in the living body and adapted for in vivo calibration after implantation and sensing the pressure of a bodily fluid, said sensor comprising;

(a) a housing having means defining an opening therein;

(b) a single flexible diaphragm means extending over the end of the housing opening and being fluid pressure sealed with respect to said housing, said single flexible diaphragm means forming part of the exterior surface of the sensor whereby when said sensor is implanted beneath the skin, said single flexible diaphragm means is adjacent to and in pressure communication with the skin and whereby pressure external to the body applied to the skin is mechanically communicated to said single flexible diaphragm means, said single flexible diaphragm means and said housing forming a chamber with said single flexible diaphragm means communicating on one side with pressure inside the chamber and on the other side with pressure external to the sensor and adjacent to said single flexible diaphragm means;

(c) inlet means to said chamber allowing the entrance of a bodily fluid from an internal bodily region to the inside of said chamber and thereby proving fluid pressure communication between said internal bodily region and said single flexible diaphragm so that a change in the difference of pressures on said single flexible diaphragm means will produce a movement of a portion of said single flexible diaphragm means with respect to said housing;

(d) a magnetic material that is connected to and thus moves with said single flexible diaphragm means;

(e) a parallel resonant circuit means comprising an inductor and a capacitor that are mounted within said housing so that the inductance of said inductor and thus the resonant frequency of said resonant circuit is varied in accordance with the position of the magnetic material relative to the inductor, said resonant frequency being detectable by apparatus external to the living body;

(f) a mechanical stop for said single flexible diaphragm means against said housing when the pressure external to said sensor on said single flexible diaphragm means is equal to or greater than the pressure in said chamber whereby, when said sensor is implanted beneath the skin, said single flexible diaphgram means can be driven to said mechanical stop by a pressure applied externally to the skin and said resonant frequency can be determined at said mechanical stop after implantation and whereby the magnitude of the external pressure applied to the skin required to drive said single flexible diaphragm means to said mechanical stop is a measure of the pressure of said bodily fluid.

25. The sensor of claim 24 and further comprising an outlet means for allowing said bodily fluid to flow out of said chamber, the outlet means including a tubing.

26. The sensor of claim 25 and further comprising a fluid shunt valve means in series arrangement with at least one of said inlet or said outlet means so as to regulate the flow of said bodily fluid.

27. The sensor of claim 25 and further comprising a fluid reservoir in series with at least one of said inlet or said outlet means.

28. An in vivo differential pressure sensor adapted for implantation in the living body and adapted for in vivo calibration after implantation and sensing the pressure of a bodily fluid, said sensor comprising:

(a) a housing having means defining an opening therein;

(b) a single flexible diaphragm means extending over the end of the housing opening and being fluid pressure sealed with respect to said housing, said single flexible diaphragm means forming part of the exterior surface of the sensor whereby when said sensor is implanted beneath the skin said single flexible diaphragm means is adjacent to and in pressure communication with the skin and whereby pressure external to the body applied to the skin is mechanically communicated to said single flexible diaphragm means, said single flexible diaphragm means and said housing forming a chamber with said single flexible diaphragm means communicating on one side with pressure inside said chamber and on the other side with pressure external to said sensor and adjacent to said single flexible diaphragm means;

(c) inlet means to said chamber allowing the entrance of a bodily fluid from an internal bodily region to the inside of said chamber and thereby proving fluid pressure communication between said internal bodily region and said single flexible diaphragm means so that a change in the difference of pressure or said single flexible diaphragm means will produce a movement of a portion of said flexible diaphragm means with respect to said housing;

(d) a conductive material that is connected to and thus moves with said single flexible diaphragm means;

(e) a parallel resonant circuit means comprising an inductor and a capacitor that are mounted within said housing so that the inductance of said inductor and thus the resonant frequency of said resonant circuit is varied in accordance with the postion of the conductive material relative to the inductor, said resonant frequency being detectable by apparatus external to the living body;

(f) a mechanical stop for said single flexible diaphragm means against said housing when pressure external to said sensor on said single flexible diaphragm means is equal to or greater than the pressure in said chamber whereby, when said sensor is implanted beneath the skin, said single flexible diaphragm means can be driven to said mechanical stop by a pressure applied externally to the skin and said resonant frequency be determined at said mechanical stop after implantation and whereby the magnitude of the external pressure applied to the skin required to drive said single flexible diaphragm means to said mechanical stop is a measure of pressure of said bodily fluid.

29. The sensor of claim 28 and further comprising an outlet means for allowing said bodily fluid to flow out of said chamber, the outlet means including a tubing.

30. The sensor of claim 28 and further comprising a fluid shunt valve means in series arrangement with at least one of said inlet or said outlet means so as to regulate the flow of said bodily fluid.

31. The sensor of claim 28 and further comprising a fluid reservoir in series with either said inlet or said outlet means.

32. An in vivo pressure detecting system comprising in combination:

(a) a differential pressure sensor adapted for implantation in a living body and for in vivo calibration after implantation, said sensor comprising;

(1) a housing having means defining an opening therein;

(2) a single flexible diaphragm means which extends across the housing opening and is secured with respect to said housing, said single flexible diaphragm means having a first and a second side, at least a portion of said first side comprising at least a portion of the exterior surface of said sensor, said housing and said single flexible diaphragm means being adapted so that when said sensor is implanted beneath the skin, the exterior surface of said single flexible diaphragm means is positioned to be adjacent to and facing an interior portion of skin whereby said exterior surface portion of said single flexible diaphragm means is in mechanical pressure communication with the skin and whereby pressures external to the body can be communicated mechanically across the skin to said single flexible diaphragm means;

(3) means allowing the second side of said single flexible diaphragm means to be in contact, and thereby in pressure communication with a bodily medium the pressure of which is to be sensed when said sensor is implanted in the living body, so that changes in the difference in pressures on said two sides of said flexible diaphragm means cause motion of at least a portion of said single flexible diaphragm means with respect to said housing;

(4) means connected to said housing for contacting the single flexible diaphragm means for a predetermined relationship between the pressures on said single flexible diaphragm means thereby defining a mechanical contact reference position of said single flexible diaphragm means with respect to said housing for a predetermined relationship between said pressures on said single flexible diaphragm means;

(5) means having a preselected parameter that is detectable by detection apparatus located outside the living body, said means having a preselected parameter being at least in part cooperatively connected to and movable with said single flexible diaphragm means so that said preselected parameter will change with movement of said single flexible diaphragm means, said parameter being detectable at least when said single flexible diaphragm means is substantially at said mechanical contact reference position and said parameter changing upon at least;

(i) a displacement of at least a portion of said single flexible diaphragm means from said mechanical contact reference position or (ii) displacement of at least a portion of said single flexible diaphragm means with respect to said housing;

whereby when said sensor is implanted beneath the skin said single flexible diaphragm means can be driven to said mechanical contact reference position by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined at said mechanical contact reference position after implantation and whereby the magnitude of the external pressure applied to the skin required to drive said single flexible diaphragm means to said mechanical contact reference position is a function of the pressure in said bodily medium;

(b) a controllable pressure source means adapted to be located external to the living body and in cooperative relation with the living body and said single flexible diaphragm means for establishing said predetermined pressure relationship; and

,

(c) means for detecting said preselected parameter and the value of said preselected parameter at said mechanical contact reference position and any variation therefrom when said sensor is implanted in a living body, said detecting means being adapted to be located external to the living body and in cooperative relation with the living body and said sensor and without any connection to said sensor which requires a break in the skin of the living body.

33. The system of claim 32 wherein at least a portion of said controllable pressure source means and said sensor parameter detecting means comprise an integral unit.

34. An in vivo pressure detecting system comprising in combination:

(a) an in vivo differential pressure sensor adapted for implantation beneath the skin in the living body and sensing the pressure of a bodily fluid, and adapted for in vivo calibration after implantation, said sensor comprising;

(1) a housing;

(2) a single flexible diaphragm means which is fluid pressure sealed with respect to said housing and has a first and a second side with at least a portion of said first side comprising at least a portion of the exterior surface of said sensor and being positioned so that after implantation, said portion of said first side is in mechanical pressure communication with the skin and whereby pressures external to the body can be communicated mechanically across the skin to said single flexible diaphragm means, said single flexible diaphragm means and said housing together defining a chamber such that the second side of said single flexible diaphragm means communicates mechanically with pressure inside said chamber so that changes in the difference in pressures on said two sides of said single flexible diaphragm means cause a motion of at least a portion of said single flexible diaphragm means;

(3) inlet means to said chamber allowing the entrance of a bodily fluid from an internal bodily region to the inside of said chamber when said sensor is implanted in the living body, thereby providing a fluid pressure communication between said internal bodily region and the inside of said chamber when said sensor is implanted in the living body, and enabling that a change in pressure will cause a movement of at least a portion of said single flexible diaphragm means with respect to said housing;

(4) contact means connected to said housing for contacting the single flexible diaphragm means for a predetermined relationship between the pressures on said single flexible diaphragm means thereby defining a mechanical contact reference position of said single flexible diaphragm means with respect to said housing at a predetermined relationship between said pressures on said single flexible diaphragm means;

(5) means having a preselected parameter that is detectable by detection apparatus located outside the living body, said means having a preselected parameter being at least in part cooperatively connected to and movable with said single flexible diaphragm means so that said preselected parameter will change with movement of said single flexible diaphragm means, said preselected parameter being detectable at least when said single flexible diaphragm means is at said mechanical contact reference position and said parameter changing upon at least;

(i) a displacement of at least a portion of said single flexible diaphragm means from said mechanical contact reference position or (ii) displacement of at least a portion of said single flexible diaphragm means with respect to said housing;

whereby when said sensor is implanted beneath the skin said single flexible diaphragm means can be driven to said mechanical contact reference position by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined at said mechanical contact reference position after implantation and whereby the magnitude of the external pressure applied to the skin required to drive said single flexible diaphragm means to said mechanical contact reference position is a function of the pressure of said bodily fluid;

(b) a controllable pressure source means adapted to be located external to the living body and in cooperative relation with the living body and said single flexible diaphragm means for establishing said predetermined pressure relationship; and

,

(c) means for detecting said preselected parameter and the value of the parameter at said mechanical contact reference position and any variation therefrom when said sensor is implanted in a living body, said detecting means being adapted to be located external to the living body and in cooperative relation with the livig body and said sensor and without any connection to said sensor which requires a break in the skin of the living body.

35. The system of claim 34 wherein at least a portion of said controllable pressure sources means and said sensor parameter detecting means comprise an integral unit.

36. An in vivo differential pressure sensor adapted for implantation in the living body, said sensor comprising:

(a) a housing having means defining an opening extending therethrough;

(b) a single flexible diaphragm means extending across said housing opening and secured to said housing, said single flexible diaphragm means communicating with pressures in two separate regions external to the sensor that are separated by the single flexible diaphragm means with the pressure in one of the regions being an internal bodily pressure when the sensor is implanted in a living body so that opposite sides of said single flexible diaphragm means are in contact with and in mechanical pressure communication with two bodily media that are separated by said single flexible diaphragm means;

(c) contact means connected to said housing for contacting the single flexible diaphragm means for a predetermined relationship between the pressure on said single flexible diaphragm means thereby defining a mechanical contact reference position of said single flexible diaphragm means with respect to said housing for a predetermined pressure relationship in said regions; and

,

(d) means having a preselected, detectable parameter that changes upon at least a displacement from said mechanical contact reference position of said single flexible diaphragm means upon a change from said predetermined pressure relationship.

37. An in vivo differential pressure sensor adapted for in vivo calibration after implantation, said sensor comprising:

(a) a housing which defines a chamber therein, at least a portion of the wall of said housing being flexible so that changes in the pressures inside said chamber and outside said housing will cause movement of said flexible portion of said housing wall, said housing being adapted so that, when implanted beneath the skin in the living body, said flexible portion of said housing wall can be placed in mechanical pressure communication with an interior portion of skin and whereby pressures external to the body can be communicated mechanically across the skin to said flexible portion of said housing wall;

(b) inlet means to said chamber allowing the entrance into said chamber of a bodily fluid, the pressure of which is to be measured when the sensor is implanted in the body;

(c) stop means within said housing adapted to make contact with, and thereby stop the movement of, said flexible portion of said housing wall for a predetermined pressure relationship between pressures inside said chamber and outside said housing;

(d) means within said housing having a preselected parameter that is detectable by apparatus outside the living body, said means having a preselected parameter being at least in part cooperatively connected to said flexible portion of said housing wall so that said preselected parameter will change with the movement of said flexible portion of housing wall, the preselected parameter being detectable at least when said flexible portion of the wall is in contact with said stop means and said parameter changing upon at least a movement of said flexible portion of wall away from said stop means, whereby when said sensor is implanted beneath the skin, said flexible portion of wall can be driven to contact said stop means by a pressure external to the living body applied to the skin adjacent to said sensor and said preselected parameter can be determined when said flexible portion of the wall is in contact with said stop means after implantation, and whereby the magnitude of the external pressure applied to the skin required to drive said flexible portion of wall to contact said stop means is a function of the pressure in said internal bodily region.

38. The sensor of claim 37 wherein said means having a preselected parameter comprises electronic circuit means with said preselected parameter being a characteristic response parameter of said electronic circuit means which is detectable by electromagnetic coupling to the electronic apparatus located external to said living body.

39. The sensor of claim 38 wherein said electronic circuit means is a resonant electronic circuit with an element of said resonant electronic circuit being at least in part cooperatively connected to said flexible portion of wall so that a movement of said flexible portion of wall will cause a change in said resonant frequency.

40. The sensor of claim 37 wherein said flexible portion of wall contacts said stop means when said pressure outside said housing on said flexible wall portion is equal to or greater than the pressure in said chamber.