Patent Publication Number: US-2016220780-A1

Title: Opening and closing device and respiratory assistance device

Description:
TECHNICAL FIELD 
     The present invention relates to an opening and closing device and a respiratory assistance device. 
     BACKGROUND ART 
     Respiratory assistance devices such as artificial respirators are used in medical practice. A typical respiratory assistance device includes an oxygen supply source such as an oxygen tank, an inspiratory pipe connected to the supply source, a mask attached to a tip of the inspiratory pipe, an expiratory pipe branched from the inspiratory pipe, an expiratory valve fixed to a tip of the expiratory pipe, etc. (for example, Japanese Patent Application Laid-Open Nos. Hei. 02-131765, Hei. 02-131773, Hei. 02-131774, and Hei. 05-245204). 
     Various methods such as a controlled ventilation (Controlled Ventilation) method used for a patient in the absence of spontaneous breathing (a patient under general anesthesia, during cardiopulmonary resuscitation, or in a critical condition) and an assisted ventilation (Assisted Ventilation) method in which a positive pressure (Positive Pressure) is created in an air passage in synchronization with the spontaneous breathing of a patient are employed for such respiratory assistance devices. 
     In a respiratory assistance device employing any of these methods, oxygen sent out from the oxygen tank is supplied to lungs as inspiratory air via the inspiratory pipe. The oxygen supplied to the lungs is then exhaled by the lungs as expiratory air. If the expiratory air is discharged into the expiratory pipe, a pressure in the expiratory pipe is increased. A control unit then receives a sensing signal from a pressure sensor having detected the pressure increase in the expiratory pipe and opens the expiratory valve. In this manner, the expiratory air is emitted to the outside from the expiratory pipe. 
     SUMMARY OF INVENTION 
     Technical Problem 
     A diaphragm valve has been known as an expiratory valve employed in such a respiratory assistance device. The diaphragm valve includes: a valve seat formed along a circumference of an opening of a hole through which the expiratory air passes (hereinafter referred to as an expiratory hole); and a valve element movable between a position supported by the valve seat and blocking the expiratory hole and a position away from the valve seat and opening the expiratory hole. 
     Although such a diaphragm valve is switchable between a state in which the entire expiratory hole is opened (hereinafter, referred to as an open state) and a state in which the entire expiratory hole is closed (hereinafter, referred to as a closed state), switching to a state in which part of the expiratory hole is opened, i.e., an intermediate state between the open state and the closed state is difficult to achieve. 
     The present invention has been made in view of the above problem, and it is an object of the present invention to provide an opening and closing device capable of switching among the open state, the closed state, and the intermediate state therebetween, and a respiratory assistance device including the opening and closing device. 
     Solution to Problem 
     Owing to the diligent studies by the present inventor, the above-described object can be achieved by the following means. 
     An opening and closing device of the present invention includes: a separating member having a separating surface in which a flow hole is opened; and an opening and closing mechanism for opening and closing the flow hole. The opening and closing mechanism is movable along the separating surface between a first position and a second position each having a different aperture area of the flow hole. When a direction perpendicular to a moving direction of the opening and closing mechanism is defined as a width direction, an aperture length of the flow hole in the width direction increases or decreases from the first position toward the second position. 
     Preferably, an aperture ratio of the flow hole when the opening and closing mechanism is located in the first position is smaller than that when the opening and closing mechanism is located in the second position, and a rate of change in an aperture length of the flow hole in the moving direction of the opening and closing mechanism is smaller at the first position than at the second position. 
     Preferably, a plurality of the flow holes are provided in the separating member. Moreover, the opening and closing mechanism preferably closes the plurality of the flow holes simultaneously. 
     Preferably, the opening and closing mechanism is movable among the first position, the second position, and a third position, the first position is disposed between the second position and the third position, the flow hole is closed at the first position, and the flow hole is opened at the second position and the third position. Moreover, a variation profile of the aperture length of the flow hole from the first position toward the third position is preferably different from a variation profile of the aperture length of the flow hole from the first position toward the second position. Alternatively, a variation profile of the aperture length of the flow hole from the first position toward the third position may be the same as a variation profile of the aperture length of the flow hole from the first position toward the second position. 
     A piezoelectric element for holding the opening and closing mechanism and moving the opening and closing mechanism by its deformation, and a controller for controlling the deformation of the piezoelectric element are preferably included. Moreover, a piezoelectric element and a controller for controlling deformation of the piezoelectric element are further included, and part of the piezoelectric element serves as the opening and closing mechanism. Furthermore, a travel amount of the opening and closing mechanism preferably corresponds to a level of a signal input from the controller to the piezoelectric element. 
     An aperture area adjusting member movable along the separating surface is preferably further included, and a gap through which part of the flow hole is exposed is formed between the aperture area adjusting member and the opening and closing mechanism. Moreover, the aperture area adjusting member is preferably connected to the opening and closing mechanism. 
     A respiratory assistance device of the present invention includes the above-described opening and closing device, and the separating member is formed by a mask for covering a nose or a mouth, and a communicating pipe communicated with a space formed inside the mask in a worn state. 
     Preferably, the flow hole is formed in the mask. Alternatively, the flow hole may be formed in the communicating pipe. The flow hole preferably forms an expiratory pathway through which expiratory air exhaled from the nose or the mouth passes. 
     Advantageous Effects of Invention 
     The opening and closing device of the present invention allows for switching among the open state, the closed state, and the intermediate state therebetween. Moreover, such an opening and closing device is suitable as an opening and closing device (for example, an expiratory valve) in a respiratory assistance device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of a respiratory assistance device according to a first embodiment of the present invention. 
         FIG. 2  includes perspective views illustrating the overview of an expiratory valve provided in a mask, where  FIG. 2(A)  shows a state in which the expiratory valve opens an expiratory hole, and  FIG. 2(B)  shows a state in which the expiratory valve blocks the expiratory hole. 
         FIG. 3  is a block diagram illustrating a hardware configuration of a control unit. 
         FIG. 4  is a block diagram illustrating a functional configuration of the control unit. 
         FIG. 5  is a graph showing a relationship between an input voltage V to a piezo element and a travel amount M of a tip of the expiratory valve, in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the travel amount M of the tip of the expiratory valve. 
         FIG. 6(A)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V A ,  FIG. 6(B)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V B , and  FIG. 6(C)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V C . 
         FIG. 7  is an explanatory diagram showing a relationship between moving directions of the expiratory valve and the shape of the expiratory hole. 
         FIG. 8  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 6 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 9  includes schematic diagrams illustrating exemplary control of the respiratory assistance device, where  FIG. 9(A)  shows a case where a user exhales air, and  FIG. 9(B)  shows a case where a user inhales air. 
         FIG. 10(A)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V A ,  FIG. 10(B)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V B , and  FIG. 10(C)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V C . 
         FIG. 11  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 10 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 12  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory holes, and their surroundings. 
         FIG. 13  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 12 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 14  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory holes, and their surroundings. 
         FIG. 15  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 14 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 16(A)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V A ,  FIG. 16(B)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V B , and  FIG. 16(C)  is an explanatory diagram illustrating the overview of the expiratory valve, the expiratory hole, and their surroundings when the input voltage V=V C . 
         FIG. 17  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 16 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 18(A)  is an explanatory diagram illustrating the overview of an expiratory valve in an opened state, and  FIG. 18(B)  is an explanatory diagram illustrating the overview of the expiratory valve in a blocked state. 
         FIG. 19(A)  is an explanatory diagram illustrating a state in which only an aperture area adjusting member blocks part of the expiratory hole, and  FIG. 19(B)  is an explanatory diagram illustrating a state in which each of an opening and closing mechanism and the aperture area adjusting member blocks part of the expiratory hole. 
         FIG. 20  is a graph showing a relationship between an input voltage V to the piezo element and an aperture ratio S/S MAX  of the expiratory hole in the case of  FIG. 19 , in which the horizontal axis represents the input voltage V to the piezo element, and the vertical axis represents the aperture ratio S/S MAX  of the expiratory hole. 
         FIG. 21(A)  is an explanatory diagram illustrating the overview of an expiratory valve in an opened state, and  FIG. 21(B)  is an explanatory diagram illustrating the overview of the expiratory valve in a blocked state. 
         FIG. 22  is a schematic diagram illustrating a configuration of a respiratory assistance device according to the second embodiment of the present invention. 
         FIG. 23(A)  is a cross-sectional view illustrating an exemplary configuration of a micro pump, and  FIG. 23(B)  is a graph showing pressure-flow rate lines of the micro pump. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will now be described below with reference to the accompanying drawings. 
       FIG. 1  illustrates an exemplary configuration of a respiratory assistance device  10  for medical use according to the first embodiment of the present invention. The respiratory assistance device  10  includes: a mask  13  having an expiratory hole  13   a  and an inspiratory hole  13   b;  an inspiratory pipe  12  inserted into the inspiratory hole  13   b;  a supply source  11  provided in the inspiratory pipe  12  and sending out an inspiratory gas; an air gage  14  for measuring a gas pressure in the mask  13 ; an expiratory valve  15  provided in the mask  13  and serving as an opening and closing mechanism for the expiratory hole  13   a;  a plurality of safety members  16  provided around the expiratory hole  13   a  so as to protrude toward the outer side of an expiratory pathway; and a control unit  17  for performing overall control on the entire device. The mask  13  and the expiratory valve  15  together form an opening and closing device. 
     The mask  13  is a wearable device that covers a mouth and a nose and serves as a member for separating a mouth and a nose from external space (a separating member). The inspiratory pipe  12  and the mask  13  are communicated with each other via the inspiratory hole  13   b.  An inspiratory pathway is formed by the inspiratory pipe  12 , the inspiratory hole  13   b,  and the mask  13 . The expiratory pathway is formed by the mask  13  and the expiratory hole  13   a.  Note that the mask  13  may be a wearable device that covers either a mouth or a nose. 
     The supply source  11  includes: a gas tank  19  that retains a gas such as air or oxygen in a compressed state; a regulating valve  20  for regulating a flow rate of the gas sent out from the gas tank  19 ; and a flowmeter  21  for measuring the flow rate of the gas regulated by the regulating valve  20 . The regulating valve  20  is controlled on the basis of sensing data (measured results, sensing signals) of the air gauge  14  and the flowmeter  21 . The regulating valve  20  is not limited to any particular type of valve, and may be an electric valve, an electromagnetic valve having a high response speed, or the like. The flowmeter  21  outputs the sensing data to the control unit  17 . 
     The inspiratory pipe  12  is formed by a bellows tube made of a resin. The inspiratory pipe  12  forms a space together with the mask  13  worn by a patient to serve as a pathway for the gas sent out from the supply source  11 . A gas pressure inside the inspiratory pipe  12  coincides with a gas pressure in the mask  13  worn by the patient in a steady state. The air gauge  14  outputs the sensing data to the control unit  17 . 
     As shown in  FIG. 2 , the expiratory valve  15  emits the gas in the mask  13  to the outside of the mask  13  by opening and closing the expiratory hole  13   a  in the form of a slit and functions as a check valve for preventing a back-flow of such a released gas. The plate-shaped expiratory valve  15  is a valve having a monomorph (unimorph) structure in which a piezo element (piezoelectric element)  15   a,  which is displaced according to an amount of applied voltage, is layered on a metal plate  15   b  and having a one-end supported (cantilever) structure. Furthermore, the respiratory assistance device  10  has a fixing member  22  for fixing one end of the expiratory valve  15  to the mask  13 . The fixing member  22  is provided so as to erect from an inner surface  13   f  of the mask  13 . The one end of the expiratory valve  15  is fixed to the mask  13  by the fixing member  22  with a position erecting from the inner surface  13   f.  A cantilever length of the expiratory valve  15  is preferably about 30 mm or more and about 40 mm or less. A stroke by which the expiratory valve  15  is displaced is preferably 2 mm or more and 3 mm or less. Note that the piezo element may have a both-end supported structure. 
     The piezo element  15   a  is deformable between an extended state (see  FIG. 2(A) ) and an arched state (see  FIG. 2(B) ) according to the level of an input voltage. When the piezo element  15   a  is in the arched state, a side surface  15   m  of the expiratory valve  15  is located on an aperture plane of the expiratory hole  13   a,  thus blocking the expiratory hole  13   a.  When the piezo element  15   a  is in the extended state, on the other hand, the side surface  15   m  of the expiratory valve  15  is away from the expiratory hole  13   a,  thus opening the expiratory hole  13   a  (see  FIG. 2(A) ). In this manner, the expiratory valve  15  is switchable between the state in which the expiratory hole  13   a  is opened and the state in which the expiratory hole  13   a  is blocked, by the deformation of the piezo element  15   a  along the side surface  15   m.  In this manner, the expiratory valve  15  can transition, due to the deformation of the piezo element  15   a,  between the state in which the expiratory hole  13   a  formed in the mask  13  is opened (hereinafter, referred to as a opened state) (see  FIG. 2(A) ) and the state in which the expiratory hole  13   a  is blocked by the side surface  15   m  of the expiratory valve  15  (hereinafter, referred to as a blocked state) (see  FIG. 2(B) ). Note that the side surface  15   m  of the expiratory valve  15  may slide on the inner surface  13   f  by the deformation of the piezo element  15   a  along the side surface  15   m.  Additionally, the inner surface  13   f  may be a flat surface or a curved surface. 
     As will be described later, the piezo element  15   a  is in the arched state under the application of a voltage and in the extended state without the application of a voltage.
     Note that the piezo element  15   a  may be configured to be in the extended state under the application of a voltage and in the arched state without the application of a voltage. Although the expiratory valve  15  having the monomorph structure has been discussed here, it is apparent that a bimorph structure including two piezo elements attached to each other may be employed instead.   

     Referring back to  FIG. 1 , if the expiratory hole  13   a  is covered by an object outside the mask  13 , the actuation of the expiratory valve  15  fails to secure the expiratory pathway. In view of this, it is preferable that the mask  13  be provided with the safety members  16 . The safety members  16  are formed so as to protrude from an outer surface  13   g  of the mask  13  and arranged to be dotted near the expiratory hole  13   a.  This can form a gap between the aperture plane of the expiratory hole  13   a  on the outer surface  13   g  side and the object covering the expiratory hole  13   a.  Thus, the expiratory pathway can be secured by the actuation of the expiratory valve  15 . 
     As shown in  FIG. 3 , the control unit  17  includes a CPU  24 , a first storage medium  25 , a second storage medium  26 , a third storage medium  27 , an input device  28 , a display device  29 , an input and output interface  30 , and a bus  31 . 
     The CPU  24  is what is called a central processing unit. Various programs are executed by the CPU  24  to implement various functions of the control unit  17 . The first storage medium  25  is what is called a RAM (Random Access Memory) and used as a work area of the CPU  24 . The second storage medium  26  is what is called a ROM (Read Only Memory) and stores a basic operating system executed by the CPU  24 . The third storage medium  27  is configured, for example, by a hard disk device with a built-in magnetic disk, a disk device for accommodating a CD, a DVD, or a BD, and a non-volatile semiconductor flash memory device. The third storage medium  27  stores various programs to be executed by the CPU  24 . 
     The input device  28 , which is an input key, a keyboard, or a mouse, inputs a variety of information. The display device  29 , which is a display, displays various operational states. A power supply and control signals for operating the expiratory valve  15  are input to and output from the input and output interface  30 . The input and output interface  30  further acquires data, such as a program, from an external personal computer. The bus  31  serves as wiring for integrally connecting, for example, the CPU  24 , the first storage medium  25 , the second storage medium  26 , the third storage medium  27 , the input device  28 , the display device  29 , and the input and output interface  30 , and the like to perform communication among them. 
       FIG. 4  shows a functional configuration obtained by executing a control program stored in the control unit  17  by the CPU  24 . The control unit  17  includes, as a functional configuration, a sensing unit  34 , an expiratory valve control unit  35 , and a regulating valve control unit  36 . The sensing unit  34  constantly acquires, and then transmits to the expiratory valve control unit  35 , the sensing data of the air gauge  14 . Additionally, the sensing unit  34  constantly acquires, and then transmits to the regulating valve control unit  36 , the sensing data of the air gauge  14  and the flowmeter  21 . The expiratory valve control unit  35  refers to the sensing data of the air gauge  14  and outputs a control signal based on this sensing data to the piezo element  15   a.  The regulating valve control unit  36  refers to the sensing data of the air gauge  14  and the flowmeter  21 , and outputs a control signal based on this sensing data to the regulating valve  20 . In this manner, a predetermined flow rate value can be obtained. 
     The details of the expiratory valve  15  and the expiratory hole  13   a  will be described next. 
     As shown in  FIG. 5 , a travel amount M of a tip  15   h  (see  FIG. 6 ) of the expiratory valve  15  is directly proportional to the level of a control signal output from the expiratory valve control unit  35 , i.e., the magnitude of an input voltage V. Therefore, the tip  15   h  of the expiratory valve  15  moves in a direction D M1  as the input voltage V increases, and moves in a direction D M2  as the input voltage V decreases. 
     If the direction perpendicular to the direction D M1  is defined as a width direction D W , a length L W  of the expiratory hole  13   a  in the width direction D W  decreases toward the direction D M1  (see  FIG. 7 ). 
     Here, if the aperture area of the expiratory hole  13   a  itself is denoted by S MAX , an area of the expiratory hole  13   a  not covered by the expiratory valve  15  (opening area) is denoted by S, and an aperture ratio of the expiratory hole  13   a  is denoted by S/S MAX , the aperture ratio of the expiratory hole  13   a  decreases non-linearly as the input voltage V increases (see  FIG. 8 ). In other words, the gradient of the graph in  FIG. 8  is in a negative value range and increases as the input voltage V increases. 
     A control example for the respiratory assistance device  10  will be described next. 
     First, if expiratory air is exhaled from a mouth or nose wearing the mask  13 , the pressure inside the mask  13  increases. If the pressure inside the mask  13  is increased, the increased value is sensed by the air gauge  14 . The sensing data is output to the control unit  17 . On the basis of the sensing data, the control unit  17  controls the expiratory valve  15 . More specifically, the control unit  17  operates the expiratory valve  15  to open the expiratory hole  13   a  as shown in  FIG. 9(A) . The expiratory air is released to the outside of the mask  13  through the expiratory hole  13   a.    
     The release of the expiratory air to the outside of the mask  13  causes the pressure inside the mask  13  to decrease. If the pressure inside the mask  13  is decreased, the decreased value is sensed by the air gauge  14 . The sensing data is output to the control unit  17 . On the basis of the sensing data, the control unit  17  controls the expiratory valve  15 . More specifically, the control unit  17  operates the expiratory valve  15  to block the expiratory hole  13   a.  This forms an enclosed space inside the mask  13 , thus enabling an inspiratory operation. 
     Subsequently, if inspiration is performed by the mouth or nose wearing the mask  13 , the pressure inside the mask  13  is decreased. If the pressure inside the mask  13  is decreased, the decreased value is sensed by the air gauge  14 . The sensing data is output to the control unit  17 . On the basis of the sensing data, the control unit  17  controls the supply source  11 . More specifically, the control unit  17  opens the regulating valve  20  to send out the gas from the gas tank  19  as the inspiratory air as shown in  FIG. 9(B) . Thereafter, the pressure inside the mask  13  is increased. If the pressure inside the mask  13  is increased, the increased value is sensed by the air gauge  14 . The sensing data is output to the control unit  17 . On the basis of the sensing data, the control unit  17  controls the supply source  11 . More specifically, the control unit  17  closes the regulating valve  20  to stop the sending out of the gas from the gas tank  19  as the inspiratory air. Thereafter, the expiratory operation and the inspiratory operation are repeated in the same manner. 
     Here, if the deformation directions of the piezo element  15   a  correspond to the direction away from the inner surface  13   f  and the direction closer to the inner surface  13   f,  such deformation directions are substantially parallel to the direction of a force generated by a pressure difference between the inside and the outside of the mask  13 . Thus, the piezo element  15   a  is easily deformed by such a force generated by a pressure difference between the inside and the outside of the mask  13 . In the respiratory assistance device  10  described above, on the other hand, the expiratory valve  15  is disposed so that the deformation directions of the piezo element  15   a  correspond to directions along the inner surface  13   f.  Thus, the deformation directions of the piezo element  15   a  are substantially perpendicular to the direction of the force generated by the pressure difference between the inside and the outside of the mask  13 . Consequently, the piezo element  15   a  is hardly deformed by such a force generated by the pressure difference between the inside and the outside of the mask  13 . In this manner, the expiratory valve  15  has rigidity enough to resist the pressure from the expiratory hole  13   a.  Moreover, since the piezo element is simply employed as the expiratory valve  15  itself, an increase in procurement cost or processing cost can be avoided. Furthermore, the expiratory valve  15  having such a structure is switchable among an intermediate state in which part of the expiratory hole  13   a  is closed as well as the opened state and the blocked state. 
     The length L W  of the expiratory hole  13   a  in the width direction D W  decreases toward the direction D M1  as shown in  FIG. 7 . Thus, the aperture ratio of the expiratory hole  13   a  can be fine-tuned more easily in a range where the expiratory hole  13   a  has a small aperture ratio than in a range where the expiratory hole  13   a  has a large aperture ratio. 
     Moreover, the expiratory valve  15  is disposed so that the deformation directions of the piezo element  15   a  correspond to the directions along the inner surface  13   f  as shown in  FIG. 2 . Thus, the fully-opened state of the expiratory hole  13   a  can be easily obtained with a smaller deformation amount of the piezo element  15   a  as compared with the case where the deformation directions of the piezo element  15   a  correspond to the direction away from the inner surface  13   f  and the direction closer to the inner surface  13   f.    
     Furthermore, since the expiratory valve  15  is configured to include the piezo element  15   a,  such an expiratory valve  15  has longer endurance, and is thus less likely to break, as compared with a case where an electromagnetic valve is employed as the expiratory valve. 
     Thus, the application of the present invention allows a patient with, for example, sleep apnea syndrome to use such a device as a home artificial respirator. 
     Moreover, the expiratory valve  15  is in the state in which the expiratory hole  13   a  is opened under no application of a voltage to the piezo element  15   a.  Thus, even when the expiratory valve  15  fails to operate due to breakdown or the like, such an expiratory valve  15  is put in the state in which the expiratory hole  13   a  is opened, thus securing the expiratory pathway. 
     Moreover, since the expiratory valve  15  is provided in the mask  13 , the expiratory valve  15  can respond to the expiratory operation quickly, thus reducing a burden on the patient. 
     Furthermore, since the expiratory valve  15  is provided inside the mask  13 , interference between the expiratory valve  15  and an object outside the mask  13  can be prevented from occurring. Note that the expiratory valve  15  may be provided on the outer surface of the mask  13 . 
     Although the length L W  of the expiratory hole  13   a  in the width direction D W  decreases toward the direction D M1  as shown in  FIG. 7  in the above-described embodiment, the present invention is not limited thereto. For example, the length L W  of the expiratory hole  13   a  in the width direction D W  may increase toward the direction D M1  as shown in  FIG. 10 . In this case, the gradient of a graph in  FIG. 11  is in a negative value range and decreases as the input voltage V increases. 
     Alternatively, a plurality of expiratory holes  13   a  with a predetermined gap therebetween in the direction D M1  or the direction D M2  may be provided in the mask  13  as shown in  FIG. 12 . In this case, the expiratory valve  15  is switchable among a state in which all of the plurality of expiratory holes  13   a  are opened, a state in which part of the plurality of expiratory holes  13   a  is closed and the remaining part thereof is opened, and a state in which all of the plurality of expiratory holes  13   a  are closed. The length L W  of each of the plurality of expiratory holes  13   a  shown in  FIG. 12  increases toward the direction D M1 . In such a case, a graph (see  FIG. 13 ) showing the relationship between the input voltage V and the aperture ratio of the expiratory hole  13   a  includes: two parts P 1  and P 3  over each of which the gradient is in a negative value range and decreases as the input voltage V increases; and a part P 2  over which the gradient is 0. The part P 2  is disposed between the part P 1  and the part P 3 . The range of the input voltage V having the part P 2  can be adjusted by the gap between the plurality of expiratory holes  13   a.    
     Although the lengths L W  of the plurality of expiratory holes  13   a  increase toward the direction D M1  in  FIG. 12 , the lengths L W  of the plurality of expiratory holes  13   a  may decrease toward the direction D M1  in the present invention. 
     Alternatively, the length L W  of one of the plurality of expiratory holes  13   a  (the expiratory hole positioned upstream in the direction D M1 ) may increase toward the direction D M1 , whereas the length L W  of the other one (the expiratory hole positioned downstream in the direction D M1 ) may decrease toward the direction D M1  (see  FIG. 14 ). In this case, a graph (see  FIG. 15 ) showing a relationship between the input voltage V and the aperture ratio of the expiratory hole  13   a  includes: a part P 1  over which the gradient is in a negative value range and decreases as the input voltage V increases; a part P 3  over which the gradient is in a negative value range and increases as the input voltage V increases; and a part P 2  disposed between the part P 1  and the part P 3 , over which the gradient is 0. 
     The accuracy of control for aperture ratios can be set individually for each predetermined voltage range by setting the shape of the expiratory hole  13   a  so that the length L W  thereof increases or decreases toward the direction D M1  as described above. 
     In the above-described embodiment, the position of the tip  15   h  to cause the opened state and the position of the tip  15   h  to cause the blocked state are arranged in this order toward the direction D M1 . However, the present invention is not limited thereto. For example, a first opening position of the tip  15   h  to cause the opened state of the expiratory hole  13   a  (V=V A , see  FIG. 16(A) ), a blocking position of the tip  15   h  to cause the blocked state of the expiratory hole  13   a  (V=V B , see  FIG. 16(B) ), and a second opening position of the tip  15   h  to cause the opened state of the expiratory hole  13   a  (V=V C , see  FIG. 16(C) ) may be arranged in this order toward the direction D M1 . Moreover, the expiratory hole  13   a  is shaped so that the length L W  thereof in the width direction D W  decreases toward the direction D M1  and increases toward the direction D M2 . Thus, the profile of change in aperture ratio when the tip  15   h  is moved from the blocking position (see  FIG. 16(B) ) to the first opening position (see  FIG. 16(A) ) is different from that when the tip  15   h  is moved from the blocking position to the second opening position (see  FIG. 16(C) ). In other words, this can yield different profiles for change in aperture ratio. Furthermore, the blocking position is set between the first opening position and the second opening position. Thus, when the tip  15   h  is at the blocking position, one of the profiles for change in aperture ratio can be selected by the input value of the input voltage V. 
     In the above-described embodiment, the expiratory hole  13   a  is shaped so as to be symmetric about an axis extending in the width direction D W . Consequently, the different profiles for change in aperture ratio can be obtained. However, the present invention is not limited thereto. The shape of the expiratory hole  13   a  may be symmetric about the axis extending in the width direction D W . In such a case, two identical profiles for change in aperture ratio can be obtained. 
     Although the opening and closing device in the above-described embodiment employs the tip  15   h  of the deformable expiratory valve  15  as an opening and closing mechanism, the present invention is not limited thereto. A valve provided to the tip  15   h  of the deformable expiratory valve  15  may be used as an opening and closing mechanism. Examples of use in such a case include the following. The opening and closing of the expiratory hole  13   a  during a normal operation are performed on the lower-voltage side, i.e., between the first opening position and the blocking position. Under an abnormal condition, i.e., when a high voltage is input due to some trouble, it is possible to open the expiratory hole  13   a.  This eliminates the risk of blocking the expiratory hole  13   a  even when a high voltage is input due to some trouble. 
     Note that the opening and closing device of the present invention may be an opening and closing device  50  as shown in  FIG. 18 . The opening and closing device  50  includes the mask  13 , a deformable member  51 , an opening and closing mechanism  52  capable of opening and closing the expiratory hole  13   a,  and an aperture area adjusting member  53  capable of adjusting the aperture area of the expiratory hole  13   a.    
     The deformable member  51  corresponds to the expiratory valve  15  shown in  FIG. 2 , for example. Referring back to  FIG. 18 , the opening and closing mechanism  52  is provided to the deformable member  51 . Thus, the opening and closing mechanism  52  can move over the expiratory hole  13   a  along the inner surface  13   f.  Furthermore, the surface of the opening and closing mechanism  52  on the inner surface  13   f  side has a shape and a size capable of covering the aperture plane of the expiratory hole  13   a.  Thus, the opening and closing mechanism  52  is movable between a state in which the expiratory hole  13   a  is opened (see  FIG. 18(A) ) and a state in which the expiratory hole  13   a  is closed (see  FIG. 18(B) ). 
     The aperture area adjusting member  53  is also movable over the expiratory hole  13   a  along the inner surface  13   f  because it is provided to the deformable member  51 . Moreover, the aperture area adjusting member  53  is apart from the opening and closing mechanism  52  by a predetermined gap G. The gap G preferably has a size just enough to cause the exposure of not all but part of the expiratory hole  13   a  (see  FIG. 19 ). 
     The function of the opening and closing device  50  will be described next. 
     As shown in  FIGS. 18 and 19 , as the input voltage V from the expiratory valve control unit  35  increases, the opening and closing device  50  sequentially switches among a state in which the entire aperture plane of the expiratory hole  13   a  is opened (see  FIG. 18(A) ), a state in which only the aperture area adjusting member  53  blocks part of the expiratory hole  13   a  (see  FIG. 19(A) ), a state in which each of the opening and closing mechanism  52  and the aperture area adjusting member  53  blocks part of the expiratory hole  13   a  (see  FIG. 19(B) ), and a state in which the entire aperture plane of the expiratory hole  13   a  is blocked (see  FIG. 18(B) ). As the input voltage V from the expiratory valve control unit  35  decreases, the opening and closing device  50  sequentially switches in the reverse order. Consequently, a graph (see  FIG. 20 ) showing a relationship between the aperture ratio of the expiratory hole  13   a  and the input voltage V includes: parts P 1  and P 3  each exhibiting a decreasing function; and a part P 2  exhibiting an increasing function. The profile for change in aperture ratio can be appropriately adjusted by the opening and closing mechanism  52 , the shape of the aperture area adjusting member  53 , the shape of the expiratory hole  13   a,  and the gap G. 
     Although the opening and closing mechanism  52  and the aperture area adjusting member  53  are spaced apart from each other in the above-described embodiment, the present invention is not limited thereto. A connecting member  55  may be used to directly connect the opening and closing mechanism  52  and the aperture area adjusting member  53  (see  FIG. 21 ). Furthermore, the opening and closing mechanism  52  and the aperture area adjusting member  53 , or the opening and closing mechanism  52 , the aperture area adjusting member  53 , and the connecting member  55  may be integrally formed. 
     Although the single deformable member  51  is used to move the opening and closing mechanism  52  and the aperture area adjusting member  53  in the above-described embodiment, the present invention is not limited thereto. One deformable member  51  may be used to move the opening and closing mechanism  52 , and another deformable member  51  may be used to move the aperture area adjusting member  53 . 
     Note that two expiratory valves  15  may be employed. One tip  15   h  thereof (see  FIG. 6 ) may be used as an opening and closing mechanism and the other tip  15   h  thereof (see  FIG. 6 ) may be used as an aperture area adjusting member. 
     Although the length L W  of the single expiratory hole  13   a  in the width direction D W  is defined as an “aperture length” in the above-described embodiment, the present invention is not limited thereto. When a plurality of expiratory holes  13   a  are provided in the mask  13 , the sum of the lengths L W  of the expiratory holes  13   a  in the width direction D W  may be defined as an “aperture length.” 
       FIG. 22  illustrates an exemplary configuration of a respiratory assistance device  70  according to a second embodiment. The respiratory assistance device  70  includes a micro pump  100  as the supply source  11  and includes only the mask  13  as an inspiratory pathway. In other words, the micro pump  100  is directly connected to the mask  13 . The micro pump proposed in Patent Literature WO 2008/069266 is used as the micro pump  100 . The micro pump  100  includes a primary blower chamber  101 , and a secondary blower chamber  102  formed outside the primary blower chamber  101  as shown in  FIG. 23(A) . 
     The primary blower chamber  101  includes a piezoelectric element  103  to serve as a vibrating source, a diaphragm  104  to which the piezoelectric element  103  is fixed; and a vibration frame  105  that forms a space together with the diaphragm  104 . The vibration frame  105  has an opening  106  for moving a fluid between the inside and the outside of the primary blower chamber  101 . The secondary blower chamber  102  has an inlet  107  on the diaphragm  104  side and an outlet  108  facing the opening  106 . 
     In the above micro pump  100 , when the piezoelectric element  103  causes the diaphragm  104  to resonate, a fluid moves between the primary blower chamber  101  and the secondary blower chamber  102 . The fluid resistance resulting from such fluid movement causes the vibration frame  105  to resonate. The resonance of the diaphragm  104  and the vibration frame  105  causes the fluid to be drawn in from the inlet  107  and causes the fluid to be discharged from the outlet  108 . 
     The micro pump  100  is suitable for use as a blower for conveying a gas and capable of conveyance without the use of a check valve. While the micro pump  100  is extremely small with a box shape having an outer dimension of about 20 mm×20 mm×2 mm, the micro pump  100  can convey air of up to about 1 L/min (under the static pressure of 0 Pa) when the input sine wave has 15 Vpp (volt peak to peak) at 26 kHz. Such a micro pump  100  can also obtain a static pressure of up to about 2 kPa (the flow rate is 0 L/min). 
     However, since a fluid is conveyed by the vibration of the diaphragm  104  caused by the piezoelectric element  103 , the micro pump  100  has naturally a limitation in the volume of a conveyable fluid. Thus, this static pressure-flow rate characteristic also exhibits a straight line as shown in  FIG. 23(B) . More specifically, in order to obtain a static pressure of about 1 kPa, for example, the flow rate is 0.5 L/min. 
     When the Vpp value of the input sine wave is changed to 10 or 20, the amplitude of the piezoelectric element  103  also changes, thus causing the flow rate and the pressure to change. In other words, when the Vpp value of the input sine wave is changed smoothly, the flow rate and the pressure can be changed smoothly. Alternatively, a change in the frequency of the input sine wave can cause the flow rate and the pressure to change. In other words, when the frequency of the input sine wave is changed smoothly, the flow rate and the pressure can be changed smoothly. Note however that the flow rate and the pressure have upper limits according to the capacity of the piezoelectric element  103  and the strength or durability of the material. The micro pump  100  is typically used at the rated Vpp and frequency. 
     Although the monomorph (unimorph) structure in which the single piezoelectric element  103  is attached to the diaphragm  104  has been discussed here, it is apparent that a bimorph structure in which two piezoelectric elements are attached to each other to increase the amount of vibration may be employed. 
     Note that the respiratory assistance device of the present invention is not limited to the above-described embodiments. It will be appreciated that various modifications are possible without departing from the scope of the present invention. Moreover, the components of the above-described embodiment may be applied to other embodiments if applicable. 
     Note that the above-described opening and closing device can be applied not only to open and close a hole through which expiratory air passes but also to open and close a hole through which a fluid (a gas or a liquid) passes as well as to open and close a hole through which a solid passes.