Abstract:
A flow sensor for a medical ventilator system is disclosed herein. The flow sensor includes a valve assembly having a valve seat, and a valve flap attached to the valve seat. The valve flap is composed of an elastomeric material configured to generate a pre-load that biases the valve flap into engagement with the valve seat such that the valve assembly remains closed in the absence of an externally applied force. The flow sensor also includes a pressure transducer configure to measure a first pressure level at an upstream position relative to the valve assembly, and a second pressure level at a downstream position relative the valve assembly. The flow sensor also includes a processor configured to estimate the flow rate of a fluid passing through a medical ventilator system based on the first and second pressure levels.

Description:
FIELD OF THE INVENTION 
       [0001]    This disclosure relates generally to system and method for a flow sensor that may be implemented in a medical ventilator system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Medical ventilator systems are used to provide respiratory support to patients undergoing anesthesia and respiratory treatment whenever the patient&#39;s ability to breath is compromised. The primary function of the medical ventilator is to maintain suitable pressure and flow of gases inspired and expired by the patient. Medical ventilator operation is commonly regulated based on feedback from one or more flow sensors. The flow sensors are generally disposed within or otherwise pneumatically coupled with a breathing circuit. One problem with conventional ventilator systems is that such systems require accurate and reliable flow sensors that are expensive to manufacture. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    The above-mentioned shortcomings, disadvantages and problems are addressed herein which will be understood by reading and understanding the following specification. 
         [0004]    In an embodiment, a flow sensor for a medical ventilator system includes a valve assembly. The valve assembly includes a valve seat, and a valve flap attached to the valve seat. The valve flap is composed of an elastomeric material. The elastomeric material of the valve flap is configured to generate a pre-load that biases the valve flap into engagement with the valve seat such that the valve assembly remains closed in the absence of an externally applied force. The flow sensor also includes a pressure transducer configure to measure a first pressure level at an upstream position relative to the valve assembly, and a second pressure level at a downstream position relative the valve assembly. The flow sensor also includes a processor connected to the pressure transducer. The processor is configured to estimate the flow rate of a fluid passing through a medical ventilator system based on the first and second pressure levels. 
         [0005]    In another embodiment, a medical ventilator system includes a ventilator, a breathing circuit pneumatically coupled with the ventilator, and a flow sensor pneumatically coupled with the breathing circuit. The flow sensor includes a valve assembly comprising a valve seat, and a valve flap composed of an elastomeric material. The valve flap comprises a protrusion configured to retain the valve flap to the valve seat. The valve flap protrusion is elastically deformed during the process of attaching the valve flap to the valve seat. The elastic deformation of the valve flap protrusion generates a pre-load that biases the valve flap into engagement with the valve seat such that the valve assembly remains closed in the absence of an externally applied force. The medical ventilator system also includes a pressure transducer configure to measure a first pressure level at an upstream position relative to the valve assembly, and a second pressure level at a downstream position relative the valve assembly. The medical ventilator system also includes a processor connected to the pressure transducer. The processor is configured to estimate the flow rate of a fluid passing through the medical ventilator system based on the first and second pressure levels. 
         [0006]    In another embodiment, a method for estimating a flow rate of a fluid passing through a medical ventilator system includes providing a breathing circuit, providing a valve assembly comprising providing a valve flap composed of an elastomeric material, and assembling the valve flap to a valve seat such that the elastomeric material of the valve flap is elastically deformed during the assembly process. The elastic deformation generates a pre-load that biases the valve flap into engagement with the valve seat such that the valve assembly remains closed in the absence of an externally applied force. The method for estimating a flow rate of a fluid passing through a medical ventilator system also includes estimating a first pressure level within the breathing circuit at an upstream position relative to the valve assembly. The method for estimating a flow rate of a fluid passing through a medical ventilator system also includes estimating a second pressure level within the breathing circuit at a downstream position relative to the valve assembly. The method for estimating a flow rate of a fluid passing through a medical ventilator system also includes estimating a flow rate of a fluid passing through the breathing circuit based on the first and second pressure levels. 
         [0007]    Various other features, objects, and advantages of the invention will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram illustrating a ventilator system connected to a patient in accordance with an embodiment; 
           [0009]      FIG. 2  is a sectional isometric view illustrating a flow sensor valve assembly in the closed position in accordance with an embodiment; 
           [0010]      FIG. 3  is a sectional isometric view illustrating a flow sensor valve assembly in the open position in accordance with an embodiment; 
           [0011]      FIG. 4  is an isometric view illustrating a valve flap of the valve assembly of  FIG. 3  in accordance with an embodiment; 
           [0012]      FIG. 5  is an isometric view illustrating a valve seat of the valve assembly of  FIG. 3  in accordance with an embodiment; 
           [0013]      FIG. 6  is an exploded sectional view illustrating the valve assembly of  FIG. 3  in accordance with an embodiment; 
           [0014]      FIG. 7  is a sectional view illustrating the valve assembly of  FIG. 3  in accordance with an embodiment; and 
           [0015]      FIG. 8  is a sectional view illustrating a valve assembly in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken as limiting the scope of the invention. 
         [0017]    Referring to  FIG. 1 , a schematically illustrated ventilator system  10  is shown connected to a patient  12  in accordance with an embodiment. The ventilator system  10  includes a ventilator  14 , a breathing circuit  16 , an inspiratory flow sensor  18 , and an expiratory flow sensor  20 . The ventilator  14  includes an inspiratory connector  22 , an expiratory connector  24 , and a processor  25 . The breathing circuit  16  includes an inspiratory branch  26 , an expiratory branch  28 , a Y-connector  30 , and a patient branch  32 . 
         [0018]    The ventilator  14  is adapted to deliver breathing gasses to the patient  12 . The ventilator connectors  22 ,  24  respectively receive the inspiratory branch  26  and the expiratory branch  28 , and thereby pneumatically couple the ventilator  14  with the breathing circuit  16 . The ventilator processor  25  is operatively connected to and configured to receive data from the flow sensors  18 ,  20 . According to one embodiment, the data from the flow sensors  18 ,  20  can be implemented by the processor  25  to provide feedback on the status of the patient  12  and to facilitate ventilator  14  operation. 
         [0019]    According to the embodiment depicted in  FIG. 1 , the ventilator system  10  implements the ventilator processor  25  to convert pressure data from the flow sensors  18 ,  20  into flow rate data. Alternatively, the flow sensors  18 ,  20  may individually comprise a separate processor (not shown) configured to provide similar flow rate data in accordance with a slightly different embodiment. The inspiratory flow sensor  18  is configured to estimate the flow rate of inspiratory gasses passing through the inspiratory branch  26  of the breathing circuit  16 , and the expiratory flow sensor  20  is configured to estimate the flow rate of expiratory gasses passing through the expiratory branch  28  of the breathing circuit  16 . The flow sensors  18 ,  20  may be operatively connected to or disposed within the breathing circuit  16  as shown in  FIG. 1  and described in detail hereinafter. Alternatively, the flow sensors  18 ,  20  may be incorporated into the ventilator  14  and positioned so they remain in pneumatic communication with the breathing circuit  16 . 
         [0020]    The flow sensor  18  will now be described in more detail with the understanding that that the flow sensor  20  is generally identical. The flow sensor  18  includes a valve assembly  40  that is pneumatically coupled with a remotely located pressure transducer  42  via a high-pressure tube  44  and a low-pressure tube  46 . The pressure transducer  42  is operatively connected to the ventilator processor  25 . According to one embodiment, the valve assembly  40  is disposed within the inspiratory branch  26  of the breathing circuit  16 , and the pressure transducer  42  is disposed within the ventilator  14 . 
         [0021]    Referring now to  FIG. 2 , a sectional isometric view illustrates the flow sensor  18  partially disposed within the inspiratory branch  26  of the breathing circuit  16  (shown in  FIG. 1 ) in accordance with an embodiment.  FIG. 2  depicts the valve assembly  40  in its closed position. For purposes of this disclosure, the term fluid is defined as a substance that continually deforms or flows under an applied shear stress, and therefore includes both liquids and gases. 
         [0022]    According to the depicted embodiment, the valve assembly  40  includes a disc shape valve flap  50  that is pivotably connected to an annular valve seat  52 . The high-pressure tube  44  is pneumatically coupled with the inspiratory branch  26  on the upstream side of the valve assembly  40 , and the low-pressure tube  46  is pneumatically coupled with the inspiratory branch  26  on the downstream side of the valve assembly  40 . The pressure transducer  42  monitors the pressure differential between the pressure level in the high-pressure tube  44  and the pressure level in the low-pressure tube  46 . The flow rate of a fluid passing through the valve assembly  40  is proportional to this pressure differential and can be calculated by the ventilator processor  25  (shown in  FIG. 1 ) in a known manner. 
         [0023]    In the absence of an externally applied force (e.g., patient inspiration), the periphery of the valve flap  50  engages the annular valve seat  52  to form a circumferential seal and thereby close the valve assembly  40 . When the valve assembly  40  is closed, the pressure within the high-pressure tube  44  is generally identical to that within the low-pressure tube  46  such that the pressure differential measured by the pressure transducer  42  is zero. Accordingly, a zero pressure differential as measured by the pressure transducer  42  is indicative of zero flow rate through the inspiratory branch  26 . 
         [0024]    When the patient  12  inhales or receives a breathing gas from the ventilator  14  (shown in  FIG. 1 ), a force is exerted upon the valve flap  50  which tends to pivot the valve flap  50  away from the valve seat  52  such that valve assembly  40  opens. Referring to  FIG. 3 , valve assembly  40  is depicted in its open position which allows the transfer of fluid through the inspiratory branch  26 . The arrows  53  represent inspiratory gasses passing through the open valve assembly  40  and through the inspiratory branch  26 . It should be appreciated that the process of pivotably opening the valve assembly  40  in response to the forces generated by patient inhalation has the effect of impeding inspiratory flow. This inspiratory flow impediment generates a pressure differential across the valve assembly  40  that can be measured by the pressure transducer  42  and implemented by the ventilator processor  25  to estimate flow rate. 
         [0025]    Having described the operation of the flow sensor  18 , some of the flow sensor  18  components will now be described in more detail. Referring to  FIG. 4 , the valve flap  50  of the flow sensor  18  (shown in  FIG. 3 ) is shown in accordance with an embodiment. The valve flap  50  is preferably composed of material that can be repeatedly elastically deformed without failure such as, for example, an elastomer. The valve flap  50  includes a generally disc-shaped sealing portion  60  and one or more protrusions  62 . The valve flap  50  will hereinafter be described as including two generally identical protrusions  62  that are collectively configured to resist valve flap rotation, however it should be appreciated that other quantities and configurations may be envisioned. 
         [0026]    Referring to  FIG. 5 , the valve seat  52  of the flow sensor  18  (shown in  FIG. 3 ) is shown in accordance with an embodiment. The valve seat  52  is preferably composed of material that is inexpensive and easy to manufacture such as, for example, an injection moldable plastic. The valve seat  52  includes a seat ring  54  and a retention shoulder  55  (shown in  FIG. 6 ). The valve seat  52  defines one or more attachment apertures  56 , and a fluid flow aperture  58 . The valve seat  52  will hereinafter be described as defining two generally identical attachment apertures  56  that are each configured to receive one of the protrusions  62  (shown in  FIG. 4 ) in accordance with an embodiment, however it should be appreciated that other quantities and configurations may be envisioned. 
         [0027]      FIG. 6  is an exploded sectional view showing the valve assembly  40  components prior to assembly in accordance with an embodiment. The valve flap  50  is depicted in alignment with the valve seat  52  such that when the components come together the outer periphery of the valve flap  50  engages and forms a seal with the seat ring  54  of the valve seat  52 , and the protrusion  62  of the valve flap  50  extends at least partially through the attachment aperture  56  of the valve seat  52 .  FIG. 7  is a sectional view showing the valve assembly  40  in accordance with an embodiment. 
         [0028]    Referring now to  FIGS. 6 and 7 , the protrusion  62  includes a terminal end portion  70 , a reduced diameter portion  72 , and a tapered portion  74  formed therebetween. The interface between the tapered portion  74  and the reduced diameter portion  72  defines a flange  76 . The reduced diameter portion  72  will be described as having a length X, the terminal end portion  70  will be described as having a diameter V, and the tapered portion  74  will be defined as having a maximum diameter (i.e., as measured at the flange  76 ) of W as shown in  FIG. 6 . The tapered portion  74  is optional and may be implemented to facilitate assembly by simplifying the process of inserting the protrusion  62  through the attachment aperture  56 . 
         [0029]    The retention shoulder  55  of valve seat  52  defines a surface  80 . The retention shoulder  55  circumscribes and thereby also defines the attachment aperture  56 . The retention shoulder  55  will be described as having a width Y, and the attachment aperture  56  will be described as having a diameter Z as shown in  FIG. 6 . 
         [0030]    When the valve flap  50  is assembled to the valve seat  52 , the terminal end portion  70  of the protrusion  62  is inserted into the attachment aperture  56  of the valve seat  52 . The diameter V of the terminal end portion  70  is preferably less than the diameter Z of the attachment aperture  56  to facilitate the insertion. The maximum diameter W of the tapered portion  74  is, however, preferably greater than the diameter Z of the attachment aperture  56  such that the tapered portion  74  must be forcibly passed through the attachment aperture  56  in a manner that compresses the protrusion  62 . As previously described, the valve flap  50  may be comprised of an elastomeric material such that protrusion  62  elastically deforms during this compression and thereafter returns to its steady state configuration wherein the maximum diameter W of the tapered portion  74  exceeds that of the attachment aperture  56 . After the tapered portion  74  is inserted into and passes completely through the attachment aperture  56 , the flange  76  engages surface  80  of the retention shoulder  55  in order to secure the valve flap  50  to the valve seat  52 . 
         [0031]    According to one embodiment, the steady state length X of the reduced diameter portion  72  is less than the width Y of the retention shoulder  55  such that the reduced diameter portion  72  must be deformed or stretched during the assembly process described hereinabove. The process of deforming the protrusion  62  by stretching the reduced diameter portion  72  has the effect of generating a pre-load. This pre-load biases the valve flap  50  into engagement with the valve seat  52  such that the valve assembly  40  remains closed in the absence of an externally applied force. When an external force (e.g., from patient inspiration) is applied to the valve flap  50 , the pre-load bias can be overcome and the valve opens. Advantageously, as soon as the external force is removed, the pre-load has the effect bringing the valve flap  50  back into engagement with the valve seat  52  such that the valve assembly  40  automatically closes. 
         [0032]    The magnitude of the pre-load generated by stretching the reduced diameter portion  72  of the protrusion  62  is selectable such as, for example, by modifying the material composition; the degree to which the reduced diameter portion  74  is stretched; and/or the geometry of the protrusion  62 . It is envisioned that the magnitude of the pre-load may be selected to be large enough to consistently close the valve assembly  40  in the absence of an external force, and small enough to be overcome by a typical patient&#39;s inspiration and/or expiration. In this manner, by appropriately selecting the magnitude of the pre-load, the valve assembly  40  can be automatically opened in response to a patient&#39;s inspiration and/or expiration, and thereafter the valve assembly  40  can automatically close. 
         [0033]    While the aforementioned pre-load has been described in accordance with an embodiment as originating from the geometry and composition of the protrusions  62  (shown in  FIG. 4 ), it should be appreciated that other embodiments may generate a similar pre-load from an alternate source. As an example, an elastomeric valve flap comprising a concave or otherwise curved sealing surface (not shown) could be forcibly brought into engagement with the valve seat  52  during the assembly process such that the geometry and composition of the entire valve flap generates the pre-load. 
         [0034]    Referring to  FIG. 8 , a sectional view shows the valve assembly  90  in accordance with an alternate embodiment. Common reference numbers will be used to identify similar components from previously described embodiments. The valve assembly  90  comprises the valve flap  50  and a valve seat  92 . 
         [0035]    The valve seat  92  includes pin  94  described in detail hereinafter, but is otherwise similar to the valve seat  52  (shown in  FIG. 5 ). The pin  94  is a localized protrusion disposed in close proximity to the seat ring  54  at a radial position that is generally opposite the attachment aperture  56 . The pin  94  protrudes or extends away from the remainder of the valve seat  92  in an axial direction by an amount that is slightly greater than that of the seat ring  54 . When the valve assembly  90  is in its closed position, the pin  94  engages a discrete portion of the valve flap  50  and thereby maintains partial separation between the valve flap  50  and the seat ring  54 . By maintaining partial separation between the valve flap  50  and the seat ring  54 , surface tension attributable to moisture within the ventilator system  10  (shown in  FIG. 1 ) is less likely to interfere with valve assembly  90  operation. More precisely, the surface tension attributable to moisture is less likely to generate adhesion between the valve flap  50  and the seat ring  54  such that the valve assembly  90  becomes stuck in the closed position. 
         [0036]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.