Abstract:
A sensor assembly includes a sensing element and an actuator. The sensing element measures a parameter associated with gas in an airway. The actuator actuates the sensing element to prevent contamination build up on the sensing element.

Description:
BACKGROUND 
       [0001]    Respiratory therapy systems are designed to assist a patient who has difficulty breathing or is unable to breath. In general terms, respiratory therapy systems include a ventilator, an optional humidifier including a heater plate, and a patient circuit. When a humidifier is used, the ventilator supplies gases to a humidification chamber coupled with the humidifier. Water within the humidification chamber is heated by the humidifier heater plate, which produces water vapor that humidifies gases passing through the chamber. From the chamber, humidified gases are then delivered to the patient through the breathing circuit. One or more breathing tubes of the patient circuit may be heated to maintain a desired temperature of gas (as used herein, the term “gas” can comprise a single type of gas (e.g., oxygen) or a mixture of multiple types of gases (e.g., a mixture of helium and oxygen) within the one or more breathing tubes. 
         [0002]    Current respiratory therapy systems (either with or without a humidifier), utilize one or more sensors to measure various parameters associated with gas in the systems. Quantitative measurement of parameters acquired from one or more sensors are used to control the systems output to a desirable set point. Example parameters may include relative humidity, temperature, flow, pressure, etc. The one or more sensors are positioned within an airway of the patient circuit and are integrated with a sensing element to measure parameters. During the coarse of delivering the humidified gases, within the airway of the breathing tubes, the integrated sensing element of the sensor(s) can be subjected to contamination due to introduction of various particles (e.g., water, salt, aerosolized medicine). The accumulation of contamination on the sensing element over time can cause incorrect measurements, ultimately resulting in improper operation and/or failure of the respiratory therapy system. For example, a safety critical feedback sensor, once subjected to contamination, can produce a signal that is drastically higher or lower in relation to a controlled system output set point, resulting in potentially unsafe output of the system (e.g., incorrect medication dosage, elevated temperature, lower temperature, etc.). 
         [0003]    In general, contamination accumulation may occur from residual water and particulates that forms a film on the sensor/sensing element surface for the inter and/or intra respiratory therapy session. For example, residual water on the sensor, after a therapy session, dries off, leaving a film of water marks, salt residue, etc. on a sensor surface. This film can impede the sensing capability of the sensor. For example, a capacitive membrane sensor absorbs and releases water relative to an environmental humidity. The change in capacitance produces electrical signals proportional to a calibrated voltage (or current) threshold. The accumulation of residual contamination can shift the signal threshold and could result in erroneous and/or erratic operation of a control system output. 
         [0004]    When using an integrated relative humidity/temperature sensor, failure of the sensor can be especially prevalent when exposed to residual contamination accumulated over time, either intra-therapy (during use) or post therapy session (after use or many uses). In particular, residual contamination can cause output of a sensing element to shift (or fail) from calibrated values resulting in dangerously high outputs, which can compromise patient safety. For example, contamination on a surface of the sensor (e.g., a capacitive or resistive membrane) can result in incorrect delivery of elevated gas temperatures for an extended period of time to the patient. This situation can be undesirable and potentially cause damage to epidermal cells of the patient. 
       SUMMARY 
       [0005]    Aspects of the present disclosure relate to a sensor assembly for positioning in an airway of a patient circuit to measure at least one parameter associated with gas (e.g., comprised of a single gas or a mixture of multiple gases) in the airway. The sensor assembly includes a sensing element mechanically coupled to an actuator. During use, the actuator actuates the sensing element. In one aspect, the sensor assembly is part of a respiratory therapy system, including the sensing element and actuator. The sensor assembly is positioned within an airway of the respiratory therapy system to measure a parameter. In yet another aspect, a method for improving reliability, repeatability and accuracy of dosage during a respiratory therapy session to a patient is disclosed. The method includes positioning a sensor assembly within an airway and actuating the sensor assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of a respiratory humidification system employing a sensor assembly. 
           [0007]      FIG. 2  is a schematic diagram of a sensor assembly positioned within a patient airway. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIG. 1  is a schematic view of a respiratory humidification system  10  including a ventilator  12 , humidifier  14  having a humidification chamber  16  and a patient circuit  18 . It is worth noting that system  10  is one exemplary environment for concepts presented herein. For example, other forms of respiratory therapy can be used with concepts presented herein such as a CPAP (Continuous Positive Airway Pressure) system, invasive system, non-invasive system or other system that may add or remove one or more of the components of system  10 . 
         [0009]    In the embodiment illustrated, ventilator  12  supplies gases to humidification chamber  16  through an initial tube  20 . Humidifier  14  heats water within the chamber  16  which is then output to patient circuit  18 . Patient circuit  18  includes an inspiratory breathing tube (or limb)  22 , a Y-connector  24  and an expiratory breathing tube (or limb)  26 . In alternative embodiments, for example in a CPAP system, the Y-connector  24  and/or expiratory conduit  26  can be eliminated. In other embodiments, humidification chamber  16  can be eliminated. During use, inspiratory tube  22  transmits humidified gases from chamber  16  to a patient through a Y-connector  24 . The Y-connector  24  can be selectively coupled to a patient interface such as an endotracheal tube. Other patient interfaces can include masks, nasal prongs, etc. After breathing in the humidified gases, the patient can exhale, transmitting exhaled gases through expiratory tube  26  back to ventilator  12 . Liquid solution is supplied to the chamber  16  from a source  28 , which, in one embodiment comprises a bag of liquid solution (e.g., water) coupled to chamber  16 . 
         [0010]    Inspiratory tube  22  and expiratory tube  26  include heating elements (e.g. wires)  30  and  32 , respectively, positioned therein that, when heated, maintains a temperature of gas in the inspiratory tube  22  and/or expiratory tube  26 . Humidifier  14  supplies electrical power to elements  30  and  32  through electrical connectors  34  and  36 , respectively. Elements  30  and  32  are generally helically shaped and selected with a desired resistance in order to heat humidified gas within tubes  22  and  26 , respectively, to a desired level. 
         [0011]    Additionally, humidifier  14  receives electrical signals from a sensor input connector  38 , interfaced with sensor assemblies  40  and  42 . Sensor assembly  40  is positioned within Y-connector  24  (and proximate the patient) whereas sensor assembly  42  is positioned within inspiratory tube  22  (and proximate humidification chamber  16 ). If desired, a second sensor input connector  44  can provide further electrical signals to humidifier  14 . Connector  44  is coupled to a sensor assembly  46  positioned within expiratory tube  26 , proximate ventilator  12 . Other sensor assemblies in various positions can further be provided. Sensor assemblies  40 ,  42 , and  46  provide one or more measurements to humidifier  14 , such as, temperature, relative humidity and/or flow information of gases within the patient circuit  18 . Humidifier  14  uses this information to control power provided to elements  30  and  32  as well as control the temperature of fluid within chamber  16 . In one example, sensor assemblies  40 ,  42 , and  46  are identical and measure relative humidity and temperature in order to provide feedback to humidifier  14  indicative of relative humidity and temperature within system  10 . In a further embodiment, information from sensor assemblies  40 ,  42  and  46  can also be provided to ventilator  12  for controlling the output of the system  10 . 
         [0012]    Sensor assemblies  40 ,  42 , and  46  are sterilized before each use and may be single use (i.e., disposable) or multi-use. In the case of reusable sensor assemblies, it is desirable to utilize reliable and efficient cleaning approaches to maintain safe and sterilized components so as to prevent contamination of patient circuit  18 . In some examples, autoclaving (which includes high temperature sterilization with pressurized steam cleaning) is one method commonly used to sterilize sensor assemblies  40 ,  42 , and  46 . However, some components within the assemblies  40 ,  42 , and  46  can not be sterilized using autoclaves as the process can damage components. Thus, other reliable cleaning methods are employed in particular situations. 
         [0013]    Independent of utilizing a single use or multiple use sensor assembly, relative humidity and temperature sensing integrated within the patient circuit  18  and in particular proximate Y-connector  24  can be beneficial to patient safety and for precise control of humidifier  14 . For example, hazard conditions such as thermal overshoots, over the limits enthalpy, energy vapor dosage over extended periods, dry chamber protection, no flow due to blockage or to excessive rainout can be monitored and controlled in a timely fashion. The percentage relative humidity information to the humidifier  14  also serves a critical feedback path for humidification dosage optimization in various therapy modes such as manual and standard modes. Other benefits include data logging of percent relative humidity vs. temperature over time, thermal overshoot tracking and direct real time polling of miscellaneous measurements within the close proximity to the patient. 
         [0014]    As provided below, the sensor assemblies  40 ,  42 , and  46  of system  10  apply high frequency oscillations to a sensing element therein so as to break away particles that contact a sensor surface. To achieve a high frequency oscillatory cycle, the sensing element is mounted to a cantilever vane capable of producing short rapid oscillations that produce shockwaves to dislodge particulates and water droplets from the sensor surface, leaving it clean to maintain reliable, accurate and repeatable sensing levels within calibrated response limits. Moreover, the oscillations can be utilized in a cleaning cycle to dry and/or remove contaminants from the sensor assemblies, for example post therapy session in an idle mode. Mechanical shockwave energy induced onto the sensor surface through oscillatory motion transforms rapidly reversing potential energy into kinetic energy creating moment of inertia to break away particulates before they become a permanent adhesion on a surface of the sensor assemblies  40 ,  42 , and  46 . 
         [0015]      FIG. 2  is a schematic, sectional view of a sensor assembly  100  positioned within an airway  102  configured to actuate for reduction of contamination build-up thereon. Sensor assembly  100  can be used in  FIG. 1  as one or more of sensor assemblies  40 ,  42  and  46 , wherein airway  102  can be inspiratory tube  22 , Y-connector  24  and/or expiratory tube  26 . Sensor assembly  100  includes an assembly housing  104 , a flexible seal  106  coupled to the assembly housing  104  and a sensing element housing  108  maintaining a sensing element  110 . Assembly housing  104  is positioned outside the airway  102 , whereas seal  106 , sensing element housing  108  and sensing element  110  are positioned within the airway  102  to receive airflow, indicated by arrow ‘A’. 
         [0016]    Assembly housing  104  maintains a plurality of electrical connectors  112  (including connectors  112   a - e ) and a mounting element comprising a beam  114  configured to couple an actuator  116  (e.g., a piezoelectric actuator) and a printed circuit board (PCB)  118  to assembly housing  104 . Connectors  112  are electrically coupled to a controller  119  that is configured to provide signals to and/or from the connectors  112 . In one embodiment, controller  119  is part of humidifier  14 , electrically coupled to connectors  112  through a cable (e.g., electrical connectors  38  and  44 ). Seal  106 , in one embodiment, is a duckbill-type seal (e.g., as used on a trocar) configured to seal the actuator  116  and PCB  118  as well as provide flexibility to deflect upon operation of actuator  116 . 
         [0017]    Sensing element  110  can be formed of a capacitive or resistive membrane to sense relative humidity of gas within airway  102  and may further include a thermal sensing element such as a resistive temperature detector (RTD) or thermistor. Suitable sensing elements can be obtained from vendors such as Honeywell and Sensirion. PCB  118  is coupled to sensing element housing  108  (e.g., through a mechanical bond) and is further electrically coupled to sensing element  110  through an electrical connector  120  (e.g., solder, pins). In one embodiment, PCB  118  also includes a liquid resistant coating  122  (e.g., formed of paralyne) to protect the PCB  118 . 
         [0018]    Connectors  112   a  and  112   e  are electrically coupled to actuator  116 . As discussed below, connectors  112   a  and  112   e  provide drive signals to actuator  116 , ultimately causing PCB  118 , sensing element housing  108  and sensing element  110  to oscillate within airway  102 . Connectors  112   b,    112   c  and  112   d  are electrically coupled to PCB  118  and sensing element  110 . Collectively, connectors  112   b - d  provide power to components on PCB  118  and sensing element  110 . Moreover, connectors  112   b - d  provide signals (e.g, to controller  119 ) indicative of measurements made by sensing element  110 . Thus, sensor assembly  100  includes at least a first connector (e.g., connectors  112   b - d ) electrically coupled to sensing element  110  and at least a second connector (e.g., connectors  112   a  and  112   e ) electrically coupled to actuator  116 . Controller  119  can include an oscillator to provide driving forces to actuator  116 , for example a voltage to generate a force within actuator  116 . 
         [0019]    Actuator  116  is configured to oscillate sensing element housing  108  so as to prevent build up of contamination on the housing  108  and/or sensing element  110 . In one embodiment, actuator  116  is an electro-mechanical transducer that possesses high motion and voltage sensitivity. As illustrated in  FIG. 2 , actuator  116  is a sandwich-like structure in which two thin piezoelectric ceramic elements  124  and  126  are bonded to a cantilevered center support vane  128  and positioned on the top and bottom of PCB  118 . Vane  128  provides mechanical integrity and built-in leverage to amplify the motion and electrical output of the piezoelectric elements  124  and  126 . In one embodiment, vane  128  forms a U-shaped channel so as to accommodate PCB  118  therein and surround PCB  118  on opposite sides. Vane  128  can be formed of various suitable materials such as brass, stainless steel, and/or an alloy, for example. 
         [0020]    Elements  124  and  126  are electrically coupled to electrical connectors  112   a  and  112   e,  respectively. When an electric drive signal is applied via connectors  112   a  and  112   e  to elements  124  and  126 , one ceramic element (e.g., element  124 ) expands laterally and the other element (e.g., element  126 ) contracts laterally. This opposing strain results in a bending or deflection of actuator  116  (thus providing deflection of sensing element  110 ) that is proportional to the voltage applied using electrical connectors  112   a  and  112   e.  Actuator  116  can generate large displacements and moderate forces at low levels of electrical drive. The resonant frequency to drive the actuator  116  is proportional to the dimensional characteristics of the piezoelectric elements  124  and  126  and serves to provide mechanical movement to PCB  118 , sensing element housing  108  and sensing element  110 . 
         [0021]    As discussed above, particulate contamination can cause sensor failures and performance degradation. By employing actuator  116  to eliminate particle accumulation on sensing element  110 , particulate contamination can be reduced. In particular, the sensor assembly  100  can be subject to high frequency oscillations introduced through actuator  116  that creates a continuous reversing potential energy, inducing an accelerated moment of inertia and kinetic energy within the particulates, thus breaking away their adhesion from the sensing element  110 . Thus, the sensor assembly  100  is left clean and clearly exposed for repeatability and accuracy of sensing desired parameters. 
         [0022]    Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.