Apparatus and method for measuring augmented osmotic pressure in a reference cavity

• US 8,539,822 B2
• Filed: 08/20/2008
• Issued: 09/24/2013
• Est. Priority Date: 08/20/2007
• Status: Active Grant

• Current Assignee: Lifecare Holdings Incorporated (Hospital Acquisition LLC)
• Original Assignee: Lifecare Holdings Incorporated (Hospital Acquisition LLC)
• Inventors: Johannessen, Erik
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): NGUYEN, HOANG T
• Application Number:
  US12/733,258
• Publication Number:
  US 20100223981A1
• Time in Patent Office: 1,861 Days
• Field of Search: 73/644.7, 422/62, 422/68.1, 422/68.13, 436/148, 600/309, 600/311, 600/316, 600/365
• US Class Current: 73/64.47
• CPC Class Codes: A61B 5/14503 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors A61B5/1459, A61B5/1464, A61B5/1473, A61B5/1482, A61B5/14865 take precedence
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement

Abstract

An apparatus and method for measuring augmented osmotic pressure in a reference cavity is provided, in which the device comprise a substrate frame (4) attached to a support structure (1) in which a plurality of transducer devices (2) are buried. An array of osmotic membranes (3) is integrated by the support structure and which acts to facilitate a trans-membrane pressure gradient as a function of the osmotic pressure change in a sealed cavity (7). The sealed cavity is formed by rigid substrate materials (5,6) in which the membranes, support structure and transducer devices only will be subject to induced stress in response to augmented osmotic pressure and thereby generate a pressure induced signal change observed from the transducer devices. The transducer devices may be arranged as piezoresistive elements, as micromechanical switches, as variable capacitive elements or as an optical light source and detector. The device can be used to monitor changes in osmotic pressure in response to a concentration change of a specified dissolved solute particle.

Claims

1. Apparatus for measuring augmented osmotic pressure in a reference cavity filled with an osmotic active solution, wherein the reference cavity is bounded on one side by an attached semi-permeable membrane coupled with at least one transducer device operable therewith, the at least one transducer device is capable of sensing any mechanical induced bulging in the semi-permeable membrane due to augmented osmotic pressure in the reference cavity, and providing a sensing measurement output consistent with the amount of augmented osmotic pressure, wherein at least one sensing element of the transducer device(s) is located along edges of the semi-permeable membrane.

2. Apparatus according to claim 1, wherein the at least one transducer device is arranged to sense induced mechanical stress in support structures or a supporting frame of the semi-permeable membrane, wherein the induced mechanical stress in the support structures or the supporting frame is mechanically transferred from the semi-permeable membrane when there is an augmentation in the osmotic pressure in the reference cavity.

3. Apparatus according to claim 2, wherein the at least one transducer device is embedded into the support structures or the supporting frame.

4. Apparatus according to claim 3, wherein the at least one transducer device comprises piezo resistive elements.

5. Apparatus according to claim 4, wherein the piezo resistive elements are arranged as a Wheatstone bridge.

6. Apparatus according to claim 5, wherein the piezo resistive elements are arranged as independent sensing elements.

7. Apparatus according to claim 3, wherein the at least one transducer element comprises at least one piezo resistive element.

8. Apparatus according to claim 3, wherein the at least one transducer element is arranged as micro electro mechanical (MEMS) switches.

9. Apparatus according to claim 3, wherein the at least one transducer element is arranged as variable capacitive elements.

10. Apparatus according to claim 1, wherein the apparatus is powered by an embedded battery.

11. Apparatus according to claim 1, wherein the apparatus is powered by radio frequency (RF) signals from an RF source outside the apparatus.

12. Apparatus according to claim 11, wherein the RF signal powering the apparatus is pulsed such that the sensing measurement output consistent with the amount of augmented osmotic pressure is transmitted as a pulsed RF signal.

13. Apparatus according to claim 12, wherein the pulsed measurement signal is received by a phase lock in amplifier located outside the apparatus.

14. Apparatus according to claim 1, wherein the sensing measurement output consistent with the amount of augmented osmotic pressure is processed by a unit located outside the apparatus.

15. Apparatus according to claim 14, wherein the unit processing measurement signals is embedded in the apparatus.

16. Apparatus according to claim 14, wherein the processing unit converts the measurement signals to an indication of a medical status of a patient implanted with the apparatus.

17. Apparatus according to claim 15, wherein the transmitted output signal is received by a display unit located outside the apparatus displaying a medical status of a patient implanted with the apparatus.

18. Apparatus according to claim 14, wherein the processing unit provides a processing of the measurement signals according to pore size of the semi-permeable membrane.

19. Apparatus according to claim 1, wherein the sensing measurement output consistent with the amount of augmented osmotic pressure is transmitted as a dimensionless measurement signal.

20. Apparatus according to claim 3, wherein the at least one transducer device comprises piezo resistive elements embedded as doped p-type or n-type resistors in a single silicon crystalline support structure.

21. Apparatus according to claim 20, wherein the piezo resistive elements are deposited as poly silicon or metal on the support structure.

22. Apparatus according to claim 1, wherein the osmotic active solution in the reference cavity has a higher osmolality than the fluids that the apparatus is intended to be used with for measurements.

23. Apparatus according to claim 1, wherein the apparatus comprises two respective reference cavities, wherein one of the cavities is used with a solid membrane measuring only rapid hydrostatic induced trans-membrane pressure gradients, and the sensing measurement output signal is subtracted with the measured rapid hydrostatic contribution.

24. Apparatus according to claim 1, wherein the reference cavity is arranged with a first channel for inserting a micro injector inserting an osmotic active solution into the reference cavity, and a second channels acting as an expansion relief when filling the reference cavity, and wherein the channels are sealed off with screws after the filling is complete, wherein one of the screws are arranged with pressure relief channels.

25. Apparatus according to claim 24, wherein the pressure relief channels are provided by letting at least one of the first or second channels comprise a square channel profile.

26. Apparatus according to claim 1, wherein the apparatus is manufactured as a disposable device.

27. Apparatus according to claim 1, wherein the apparatus is shipped in a container comprising an isotonic solution.

28. Apparatus according to claim 1, wherein the apparatus is embedded as a micro chip device.

29. Apparatus according to claim 2, wherein the support structure of the semi-permeable membrane is manufactured from one of the materials in the list comprising silicon glass, poly silicon, amorphous silicon, epitaxial grown silicon, bulk single crystalline silicon, crystalline or amorphous or polycrystalline semiconductor, ceramics and polymers.

30. Apparatus according to claim 1, wherein the semi-permeable membrane is arranged as part of an array of several membranes, each constituting at least one transducer device operable therewith.

31. Apparatus for measuring augmented osmotic pressure in a reference cavity filled with an osmotic active solution, wherein the reference cavity is bounded on one side by an attached semi-permeable membrane coupled with at least one transducer device operable therewith, the at least one transducer device is capable of sensing any mechanical induced bulging in the semi-permeable membrane due to augmented osmotic pressure in the reference cavity, and providing a sensing measurement output consistent with the amount of augmented osmotic pressure, wherein at least one sensing element of the transducer device(s) is located in areas where the induced stress from an osmotic trans-membrane pressure gradient will inflict the largest relative rate of change of displacement or induced stress in a support structure or supporting frame of the semi-permeable membrane.