Patent Application
20080011297
In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
Embodiments of the invention are directed to sensing respiratory parameters within a trachea of a body to monitor a physiologic condition. In one embodiment, a method comprises suspending a dual pressure sensor within a trachea to detect an airflow-induced pressure differential in the trachea associated with inhalation and exhalation and thereby determine a velocity of the airflow through the trachea. By tracking the velocity of the airflow over a period of time, a sensor monitor determines one or more respiratory parameters, such as a tracheal airway (or gas) pressure, a respiratory tidal volume including inspiration and exhalation volumes, as well as flow rates and other respiratory parameters. The placement of the dual pressure sensor directly in the airflow within the trachea, in combination with the structure of the dual pressure sensor, enables highly accurate measurement of these respiratory parameters.
Analyzing patterns and/or values of these respiratory parameters enables assessing various physiologic conditions, such as sleep apnea, chronic obstructive pulmonary disease (COPD), asthma, pain levels, stress, etc. In another aspect, tracking these respiratory parameters enables analyzing or assessing various aspects of lung mechanics. In another aspect, monitoring these respiratory parameters via the trans-tracheal sensing device enables assessing a physiologic response to pharmaceuticals administered to a patient or study animal, or assessing other interventions intended to alter those physiologic conditions. Accordingly, these applications and numerous other applications of monitoring physiologic conditions are produced from tracking respiratory parameters via trans-tracheal sensing.
In addition, trans-tracheal sensing via embodiments of the invention enables measuring respiratory parameters in a minimally invasive manner to provides minimal interference with normal breathing patterns. This arrangement, in turn, produces lower stress on a test subject, thereby enabling highly accurate long term stationary monitoring or ambulatory monitoring to better mimic real life conditions of a test subject. Conventional airway testing environments are relatively high stress, short term conditions that hinder test accuracy. In embodiments of the invention, longer term monitoring and direct access measurements via trans-tracheal implantation also enable capturing a more complete profile of respiratory parameters on a single test subject, thereby producing more useful test data. Conventional airway testing results are typically based indirect measurements using on average data models from several sets of test subjects.
In one embodiment, a dual pressure sensor obtains measurements via a symmetric arrangement of two substantially identical pressure sensors that provide low sensitivity to temperature and a low sensitivity to motion while accurately capturing airflow data for monitoring respiratory parameters.
In one embodiment, the dual pressure sensor is positioned within the airway of the trachea via a support arm anchored relative to a wall of the trachea. In another embodiment, the dual pressure sensor is positioned externally of the trachea with a pressure sensitive target portion positioned within the trachea. A fluid medium extends within a chamber (which also acts as a support arm) between the pressure sensitive target portion and the dual pressure sensor to transmit pressure sensed at the pressure sensitive target portion from within the trachea to the dual pressure sensor located externally of the trachea. This embodiment enables a lower profile insertion through the trachea and minimizes the amount of space that the sensor occupies within the airway of the trachea.
These embodiments and other embodiments of the invention are described and illustrated in association with
In one aspect, dual pressure sensor 24 of sensor assembly 14 is positioned adjacent an end of support arm 22 opposite from flange 20. Support arm 22 is sized and shaped for slidable insertion through wall 32 of trachea 30 via an insertion tool while flange 20 of sensor assembly 14 is configured to be secured externally relative to wall 32 of trachea 30. In one aspect, support arm 22 has a length sized to extend from flange 20, through wall 32 of trachea 30 to position dual pressure sensor 24 within airway 34 of trachea 30 to enhance accurate measurement of airflows (AI and AE). In one embodiment, dual pressure sensor 24 is positioned adjacent a central axial portion of airway 34 while in other embodiments, dual pressure sensor 24 is positioned in a non-central axial location of airway 34. Additional aspects of dual pressure sensor 24 for accurately measuring respiratory parameters are described and illustrated later in association with
In another embodiment, support arm 22 is configured with a length and a generally straight elongate shape to suspend dual pressure sensor 24 in a position within trachea 30 that is generally co-planar relative to support arm 22 and relative to flange 20 located externally of trachea 30. Accordingly, an operator need not direct sensor assembly 14 downward into trachea 30 below the point of trans-tracheal implantation. This arrangement simplifies trans-tracheal implantation of sensor assembly 14 and helps to insure positioning of the dual pressure sensor 24 within airway 34 of trachea 30. In another aspect, support arm 22 forms a resilient, semi-rigid member or a rigid member to facilitate insertion of support arm 22 through wall 32 of trachea 30 and to maintain the position of sensor 24 within trachea 30.
In one aspect, an output signal of dual pressure sensor 24 is communicated via a wired pathway 40 or wireless pathway 42 to sensing monitor 12 for processing to determine various respiratory parameters associated with inhalation and exhalation airflows within trachea 30. In another aspect, wireless communication pathway 42 between sensor assembly 14 and sensing monitor 12 enhances accurate measurements of respiratory parameters because the test subject is no longer tethered to a stationary monitoring station via wired connection, thereby enhancing the freedom of the test subject to behave more naturally during measurement of respiratory parameters.
In one embodiment, sensing monitor 12 of trans-tracheal sensing system 10 comprises controller 50 including memory 52, wireless module 56, and user interface (GUI) 58. Controller 50 controls operation of dual pressure sensor 24, which produces an output signal comprising a pressure differential 60 sensed via dual pressure sensor 24 and which is based on a first pressure 62 associated with a first pressure sensor of dual pressure sensor 24 and a second pressure 64 associated with a second pressure sensor of dual pressure sensor 24.
In one embodiment, sensing monitor 12 determines an array of respiratory parameters based on the pressure differential 60 sensed via pressure sensor 24. Accordingly, sensing monitor 12 also comprises respiratory parameters module 70, which is configured to measure and track a profile of respiratory parameters. In embodiment, respiratory parameter module 70 comprises, but is not limited to, measuring and/or tracking pressure parameter 71, velocity airflow parameter 72, inhalation parameter 73, exhalation parameter 74, volume parameter 75, time parameter 76, total parameter 77, and other respiratory parameter 78. Pressure parameter 71 generally corresponds to an airway pressure within trachea 30 such as an airway pressure during inhalation or exhalation. Velocity airflow parameter 72 comprises a velocity of airflow, which is derived from and proportional to the pressure differential 60 sensed via dual pressure sensor 24. Inhalation parameter 73 generally corresponds to parameters associated with inhalation airflows, such as the velocity airflow during inhalation. Exhalation parameter 74 generally corresponds to parameters associated with exhalation airflows, such as the velocity airflow during exhalation. Volume parameter 75 generally corresponds to volumes derived from an airflow velocity over a time period via time parameter 76, and includes but is not limited to, an inhalation volume, an exhalation volume, or total tidal volume. Total parameter 77 generally corresponds to any respiratory parameter, such as total tidal volume, determined via pressure differential 60 that incorporates both inhalation and exhalation respiratory functions.
Upon determining and tracking any one of respiratory parameters 71-77, one can determine and monitor one or more physiologic conditions about a patient or study animal in which dual pressure sensor 24 is trans-tracheally mounted.
In one embodiment, sensing monitor 12 and/or functions performed by controller 50 of sensing monitor 12 may be implemented in hardware, software, firmware, or any combination thereof. The implementation may be via a microprocessor, programmable logic device, or state machine. Additionally, components of the sensing monitor 12 may reside in software on one or more computer-readable mediums. The term computer-readable medium as used herein is defined to include any kind of memory, volatile or non-volatile, such as floppy disks, hard disks, CD-ROMs, flash memory, read-only memory (ROM), and random access memory.
Although
Accordingly, in this arrangement, sensor 24 is suspended within trachea 30 via anchor 80 secured externally of wall 30 of trachea. In addition, in this arrangement, the position of sensor assembly 14 is maintained within airway 34 of trachea 30 while migration of sensor assembly 14 relative to wall 32 of trachea 30 is prevented, thereby insuring robust mounting of sensor assembly 14 during ambulatory monitoring or long-term monitoring.
In another aspect, this arrangement avoids unnecessarily obstructing airway 34 of trachea 30 with structures other than sensor assembly 14 (including support arm 22 and dual pressure sensor 24), thereby generally maintaining the natural inhalation and exhalation airflows through trachea 30. Accordingly, in one embodiment, dual pressure sensor 24 is sized and shaped to have a first surface area A that extends transversely across airway 34 of trachea 30 that is substantially less than a second transverse cross-sectional area B of airway 24 of trachea 30. In one embodiment, the first surface area A of dual pressure sensor 24 occupies about 20% or less of the second transverse cross-sectional area B of trachea 30. In one example of a trachea 30 having a second transverse cross-sectional area B of about 0.8 to 3 cm2, the first surface area of dual pressure sensor 24 is about 0.2 cm2.
In another aspect, support arm 22 has a third surface area C that extends transversely across airway 34 of trachea 30. Accordingly, in another embodiment, a combination of the first surface area A of dual pressure sensor 24 and the third surface area C of support arm 22 together results in sensor assembly 14 occupying about 20% or less of a second transverse cross-sectional area B of airway 34 of trachea 30. In another embodiment, the combined transverse cross-sectional area of A and C is larger than 20% but presents potential hindrances to natural tracheal functioning and airflow patterns, thereby potentially diminishing accurate measurements of natural respiratory parameters.
In one aspect, dual pressure sensor 24 of sensor assembly 14 is calibrated at the time of its construction to validate its operating characteristics. In one embodiment, to account for the different tracheal diameters for different test subjects, and to the account for the actual position of dual pressure sensor 24 relative to a central portion of airway 34 of the trachea, dual pressure sensor 24 is further calibrated upon its trans-tracheal implantation by comparing measurements at dual pressure sensor 24 with other known indirect measurements of an intra-tracheal pressure via conventional sensing instruments.
In addition, the accuracy of dual pressure sensor 24 and the in-situ calibration of dual pressure sensor 24 also depends, in part, on the alignment of dual pressure sensor 24 to the airflows within trachea 30. Accordingly, in one embodiment, to insure that the pressure sensitive portions of dual pressure sensor 24 are in direct alignment with the airflows to be measured, flange 20 of sensor assembly 14 additionally includes an alignment indicia 85 to facilitate aligning dual pressure sensor 24 within trachea 30. The construction and orientation of these pressure sensitive portions of dual pressure sensor 24 are further described and illustrated in association with
In another embodiment, a magnetic mechanism releasably secures sensor assembly 14 relative to anchor 80. In particular, as illustrated in
In one aspect, anchor 90 and sensor assembly 14 (including support arm 22 and dual pressure sensor 24) are made from one or more biocompatible materials and/or are coated with one or more biocompatible coatings, such as parylene, surface treated polyurethane, silicone elastomers, polytetrafluoroethylene, etc. These biocompatible materials and/or coatings maintain the sensitivity and accuracy of dual pressure sensor 24 within a dynamic and harsh biologic environment via maximizing corrosion resistance, promoting shedding of body fluids and contaminants, as well as maximizing surface electrical passivation. Additional embodiments described later in association with
In another embodiment, as illustrated in
Using a puncture tool, an opening 39 is created in wall 32 of trachea 30 to enable insertion and secure implantation of sensor assembly 14 in the manner illustrated in
In another embodiment, a peelable introducer sheath (not shown) is additionally used with the insertion tool to insert sensor 24 and support arm 22 of sensor assembly 14 through wall 32 and into airway 24, whereupon the peelable introducer sheath is removed to leave sensor assembly 14 in place within airway 34 of trachea 30. In one aspect, a dilator is used in conjunction with the peelable introducer sheath to achieve the desired size of opening 39.
In another embodiment, a method of implanting sensor assembly comprises cutting through wall 32 of trachea 30 through one or more rings 36 when necessary to accommodate a larger size sensor assembly 14 or to employ a different surgical technique for securing sensor assembly 14 relative to wall 32 of trachea 30. In this embodiment, opening 39 is larger than that shown in
As illustrated in
As illustrated in
In one aspect, second pressure sensor 104 comprises substantially the same features and attributes as first pressure sensor 102, with like elements having like reference numerals except being designated as “B” elements. In addition, second pressure sensor 140 is oriented in an opposite direction (i.e., a mirrored relationship) relative to first pressure sensor 102 with the base 120B of second pressure sensor 104 arranged against and secured in contact with base 120A of first pressure sensor 102. This base-to-base arrangement aligns inlet 136A of first pressure sensor 102 to be in fluid communication with inlet 136B of second pressure sensor 104 so that the respective chambers 154A, 154B defined within the respective diaphragm portions 146A, 146B of first and second pressure sensors 102,104 have a common reference pressure and define a closed air volume. This common reference pressure is generally equal to the atmospheric pressure at the time that base 120A of first pressure sensor 102 is connected to and sealed relative to base 120B of second pressure sensor 104.
In addition, the base-to-base arrangement of first and second pressure sensors 102, 104 orients the diaphragm portions 146A, 146B of respective first and second pressure sensors 102,104 to face in opposite directions with first pressure sensor 102 generally facing an inhalation airflow (AI) and second pressure sensor 104 generally facing an exhalation airflow (AE). In this aspect, diaphragm portions 146A extends in a plane that is generally parallel to diaphragm portion 146B. In another aspect, each diaphragm portion 146A, 146B of the respective first and second pressure sensors 102, 104 extends transversely across the airway 34 of the trachea 30 (
In another aspect, diaphragm portion 146A of first pressure sensor 102 is mechanically independent of diaphragm portion 146B of second pressure sensor 104 to insure independent, separate measurements at each respective first and second pressure sensor 102, 104.
In another aspect, establishing a common pressure reference for both first pressure sensor 102 and second pressure sensor 104 (via the sealed base-to-base arrangement) enables dual pressure sensor 100 to sense a pressure differential via diaphragm portions 146A, 146B of the respective first pressure sensor 102 and second pressure sensor 104 based on the exposure of those oppositely oriented diaphragm portions 146A, 146B to the bidirectional airflow in trachea 30. In one aspect, upon an inhalation airflow (AI), a pressure differential is created at sensor 100 with a greater pressure exerted upon diaphragm portion 146A of first pressure sensor 102 (that directly faces the inhalation airflow AI) than upon diaphragm portion 146B of second pressure sensor 104. Likewise, in another aspect, upon an exhalation airflow (AI), a pressure differential is created at sensor 100 with a greater pressure exerted upon diaphragm portion 146B of second pressure sensor 104 (that directly faces the exhalation airflow AE) than upon diaphragm portion 146A of first pressure sensor 102. Accordingly, in one aspect, a direction of airflow is determined by which pressure sensor, either first pressure sensor 102 or second pressure sensor 104 registers the greatest magnitude of pressure.
In another aspect, given that the magnitude of the pressure differential results primarily from either a inhalation providing the dominant pressure signal on the first pressure sensor (with a negligible signal on the second pressure sensor), or from the exhalation providing a dominant pressure signal on the second pressure sensor (with a negligible signal on the first pressure sensor), the pressure differential provides a signal substantially proportional to the airway pressure exhibited during inhalation or during exhalation, respectively.
Sensing monitor 12 processes these pressure signals sensed via dual pressure sensor 100 using a pressure-velocity relationship of Bernoulli's equation in which airflow velocity is proportional to the square root of pressure, with background pressures and gravity effects being negated for this calculation. Accordingly, the pressure differential sensed via dual pressure sensor 100 yields a velocity for either an inhalation airflow (AI) or an exhalation airflow (AE). By tracking the airflow velocity, sensing monitor 12 determines one or more respiratory parameters, such as tidal volumes, airflow rates, etc for either inhalation, exhalation, or both, as previously described and illustrated in association with
In one aspect, the pressure differential at first pressure sensor 102 and/or second pressure sensor 104 is measured via a sensing circuit 300, as described in more detail later in association with
In another aspect, sensor 100 comprises a protective cover 108 that encapsulates first pressure sensor 102 and second pressure sensor 104 to seal out body fluids and other substances that would interfere with the operation of sensors 102, 104. In one aspect, protective cover 108 comprises a thin, flexible and resilient element made of a biocompatible polymer or other material that is resistant to body fluids and other body substances while not interfering with pressure sensing by first and second pressure sensors 102, 104. In one aspect, cover 108 comprises a hydrophobic material or water shedding material to prevent collection of body fluids on cover 108.
In one embodiment, as illustrated in
In one aspect, dual pressure sensor 200 is suspended within airway 34 of trachea 30 (
In one aspect, in a manner substantially the same as dual pressure sensor 100, dual pressure sensor 200 senses a pressure differential and a velocity for an inhalation airflow (AI) or exhalation airflow (AE) is determined by sensing monitor 12 (
In one embodiment, dual pressure sensor 200 comprises a cover 208 encapsulating first pressure sensor 202 and second pressure sensor 204 to shield first pressure sensor 202 and second pressure sensor 204 from interference by body fluids within airway 34 of trachea 30.
In one aspect, first sensor portion 310 and second sensor portion 312 are electrically coupled together to produce a differential signal output, which neutralizes noise because of geometrical asymmetry between the first pressure sensor 102 and second pressure sensor 104, as well as neutralizing noise because of as temperature sensitivity, gravitational sensitivity, and other noise characteristics, that are experienced by both first pressure sensor 102 and second pressure sensor 104.
In one aspect, first sensor portion 310 comprises array 171 of gauges represented as resistors 170-178 and second sensor portion 312 comprises array 181 of gauges represented as resistors 180-188, and arranged in a Wheatstone bridge configuration. In one aspect, resistor 172 of first sensor portion 310 is electrically connected to resistor 180 of second sensor portion 312 and resistor 176 of first sensor portion 310 is electrically connected to resistor 184 of second sensor portion 184. In addition, second output 332 is defend by a common node 173, extending between resistor 170 and resistor 174, and by a common node 183, extending between resistor 182 and resistor 186.
In another aspect, a first output 330 of sensing circuit 300 generally corresponds to the output of a balancing resistor 314 (e.g., a potentiometer) that is electrically coupled between common pathways 316A and 316B. Common pathway 316A extends between resistor 172 of first sensor portion 310 and resistor 180 of second sensor portion 312, while common pathway 316B extends between resistor 176 of first sensor portion 310 and resistor 184 of second sensor portion 312. The balancing resistor 314 enables calibrating the output of the respective first and second pressure sensors of a dual pressure sensor, such as first dual pressure sensor 100 (
As illustrated in
In one aspect, chamber 364A of first sensor mechanism 362 is filled with a fluid medium 374A. At one end of chamber 364A, fluid medium 374A is in communication with pressure sensitive portion 384A or 386A and at the other end of chamber 364A, fluid medium 374A is operatively coupled relative to first pressure sensor 370A. In one embodiment, fluid medium 374A comprises a viscous liquid adapted to transmit pressure changes with minimal noise components while in other embodiments, fluid medium 374A comprises air. Accordingly, in one aspect, fluid medium 374A comprises a fluorinert fluid material or similar fluid material.
In another aspect, second sensor mechanism 363 is constructed and operates in a substantially similar manner as first sensor mechanism 362, with like elements designated by like reference numerals except carrying the “B” designation (e.g. fluid medium 374B) instead of the A designation (e.g., fluid medium 374A). However, target sensing portion 380B of second sensor mechanism 363 is oriented in an opposite direction relative to target sensing portion 380A of first sensor mechanism 362. Accordingly, in this arrangement, first sensor mechanism 362 and second sensor mechanism 363 are arranged so that the target sensing portion 380A of first sensor mechanism 362 directly faces an inhalation airflow AI and the target sensing portion 380B of second sensor mechanism 364 directly faces an exhalation airflow (AE).
In one aspect, the first and second pressure sensors 370A, 370B are positioned at one end of the respective first and second sensor mechanisms 362, 363 for location externally of the wall 32 of trachea 30 while target sensing portions 380A, 380B are positioned at an opposite end of the respective sensor mechanisms 362,363 for suspension within the airway 34 of the trachea 30. Accordingly, an inhalation airflow exerted upon target sensing portion 380A is coupled to first pressure sensor 370A via fluid medium 374A and while an airflow exerted upon target sensing portion 380B is coupled to second pressure sensor 370B via fluid medium 374B.
In another aspect, first pressure sensor 370A and second pressure sensor 370B are operatively coupled together via an airway 391 to define a common reference pressure for both first pressure sensor 370A and second pressure sensor 370B, thereby enabling sensing a pressure differential between first sensor mechanism 362 and second sensor mechanism 363.
In one aspect, in a manner substantially the same as dual pressure sensors 100, 200 (of
In this arrangement, dual pressure sensor assembly 360 provides a low profile trans-tracheal sensing system because the arrangement permits maintaining the relatively larger first and second pressure sensors 370A, 370B externally of wall 32 of trachea 30 while the relatively smaller target sensing portion 380A, 380B are inserted through wall 32 of trachea 30 and suspended within airway 34 of trachea 30. Accordingly, this embodiment enables smaller incisions in trachea 30 and eases design constraints otherwise associated with miniaturizing a full sensor (e.g., dual pressure sensor 100, 200) in order to place the full-size sensor through wall 32 and within airway 34 of trachea 30. For example, in one embodiment, this smaller size arrangement enables inserting the first and second pressure sensing mechanisms 362,363 into the airway 34 of trachea 30 via a very small incision in a tissue region 38 between an adjacent pair of rings 36 of wall 32 of trachea 30.
In addition, the relatively smaller size target sensing portions 380A, 380B and chambers 364A, 364B occupy less space within airway 34 of trachea 30, thereby facilitate accurate measurements because the dual pressure sensor assembly 360 interferes less with the volume and type (e.g., laminar) of flow through airway 34 of trachea 30. For example, in one embodiment, target sensing portions 380A, 380B of dual pressure sensor assembly 360 are sized and shaped to have a first surface area (analogous to first surface area A in
In another aspect, chambers 364A, 364B of dual pressure sensor assembly 360 define a third surface area C (analogous to C in
In one embodiment, first and second sensor mechanisms 401 and 403 are arranged to have a length and a generally straight elongate shape to position target sensing portions 380A, 380B within trachea 30 to extend generally co-planar relative to the respective chambers 364A, 364B and relative to the respective pressure sensors 402, 404 located externally of the trachea 30. Accordingly, an operator need not direct sensor assembly 400 downward into trachea 30 below the point of trans-tracheal implantation. This arrangement simplifies trans-tracheal implantation of sensor assembly 400 and helps to insure positioning of the target sensing portions 380A, 380B adjacent a central axial portion of airway 34 of trachea 30.
In one embodiment, as illustrated in
As illustrated in
Second sensor mechanism 403 includes second pressure sensor 404 and in all other respects, comprises substantially the same features and attributes as first sensor mechanism 402, with like elements being represented by like reference numerals (except using the B designation instead of the A designation). Accordingly, in one aspect, second sensor mechanism 403 comprise second pressure sensor 404, fluid chamber 452B including fluid medium 445B, and target portion 380B (shown in
As illustrated in
In use, an airflow within trachea 30 exerts pressure on target portion 380A,380B (
Accordingly, dual pressure sensor 400 comprises a symmetric arrangement of substantially identical first pressure sensor 402 and second pressure sensor 404, arranged side-by-side, so that differences in pressure sensed via first pressure sensor 402 and second pressure sensor 404 are due substantially to the pressure differential resulting from a simultaneous measurement of an airflow with via two oppositely oriented pressure sensitive elements within an airway of the trachea during inhalation and exhalation airflows.
In one aspect, an airflow within trachea 30 causes a deflection in pressure sensitive target portions 380A, 380B (
Embodiments of the invention provide substantially direct and accurate measurements of respiratory parameters associated with inhalation and exhalation airflow within a trachea. These measurements are obtained directly by trans-tracheally suspending a dual pressure sensor within the airway of the trachea or indirectly by trans-tracheally suspending a pressure sensitive target portion within the airway of the trachea and then sensing a pressure change at a dual pressure sensor located externally of the trachea. In either case, a highly accurate measurement of a pressure differential associated with inhalation and exhalation airflows is obtained for use in determining and monitoring various respiratory parameters.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
