Abstract:
The present invention provides a small-size, small-weight, low-cost artificial respiration apparatus which can easily be used in an ordinary hospital. 
     The artificial respiration apparatus  10  includes: a positive blower  12   p  for generating a positive air pressure Ap; a negative blower  12   n  for generating a negative air pressure An; a rotary valve mechanism  54  for alternately selecting the positive pressure Ap generated by the positive blower  12   p  and the negative pressure An generated by the negative blower  12   n  and converting them into an oscillating air pressure Apn; and a diaphragm block  56  urged by the oscillating air pressure Apn from the rotary valve mechanism  54  to operate to supply air to a patient P. Use of the positive blower  12   p  and the negative blower  12   n  significantly reduces the load, enabling to use ones available on market, i.e., small-size, small-weight, low-consumption blowers.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an artificial respiration apparatus that forcibly supplies air to a patient who cannot breathe by himself/herself and that can operate so as to reduce the load on the patient when the patient spontaneously starts breathing. 
     2. Description of the Related Art 
     FIG. 5 shows a configuration of a conventional artificial respiration apparatus. Hereinafter, explanation will be given on the conventional artificial respiration apparatus with reference to FIG.  5 . 
     The conventional respiration apparatus  50  includes: a blower  52  for simultaneously generating a positive pressure Ap and a negative pressure An; a rotary valve mechanism  54  for alternately selecting the positive pressure Ap and the negative pressure An generated by the blower  52  and converting the positive and negative pressures into an oscillating air pressure Apn; and a diaphragm block  56  which is urged by the oscillating air pressure Apn from the rotary valve mechanism  54 , so as to supply air to a patient P. Moreover, the artificial respiration apparatus  50  includes: a diaphragm neutral position controller  60  for maintaining a neutral position of a diaphragm  561  of the diaphragm block  56 ; and a respiration gas port  62  for introducing the respiration gas. 
     The blower  52  has a positive pressure pipe  521  and a negative pressure pipe  522 , so that air is supplied to the blower  52  through the negative pressure pipe  522  and discharges the air through the positive pressure pipe  521 . The negative pressure pipe  522  is connected to an orifice pipe  523  communicating with the open air. The positive pressure pipe  521  is connected to an orifice pipe  524  communicating with the open air. 
     The rotary valve mechanism  54  is constituted by a rotary valve  544  having ports  541 ,  542 ,  543 , and a drive block  545  for rotating the rotary valve  544 . The drive block  545  includes a motor and a reduction gear (not depicted) so as to rotate the rotary valve  544  at 900 rpm for example. While the rotary valve  544  makes a single turn, the port  541  and the port  542  are successively made to communicate with the port  543 . The port  543  is connected to an oscillating air pressure pipe  546  for transmitting the oscillating air pressure Apn to the diaphragm block  56 . A flow control valve  547  is inserted into the oscillating air pressure pipe  546 . 
     The diaphragm block  56  includes a diaphragm  561  formed by an expandable member serving as a partition between a pressurizing chamber  562  and a pressurized chamber  563 . The pressurizing chamber  562  is connected to the oscillating air pressure pipe  546 . 
     The respiration gas port  62  is constituted by a blender  621  for mixing the open air with oxygen prepared in advance; and a humidifier  622  for humidifying the gas to be sent out from the blender  521 . The humidifier  622  is connected to a respiration gas pipe  623  for supplying to the patient P the respiration gas Ai which has passed through the humidifier. The respiration gas pipe  623  communicates with the pressurized chamber  563  and has a pressure sensor  624  provided in the vicinity of the patient P. 
     The diaphragm neutral position controller  60  includes: a diaphragm position sensor  601  for detecting a position of the diaphragm  561  of the diaphragm block  56 ; a pressure regulating valve  64  for controlling the positive pressure Ap, the negative pressure An, or the oscillating air pressure Apn; a control block  66  for controlling the pressure regulating valve  64  according to the position of the diaphragm  561  detected by the diaphragm position sensor  601 . 
     The pressure regulating valve  64  has a configuration similar to a rotary valve and is constituted by a main body  646  having ports  641  to  645  and an actuator  647  for rotating a part of the main body in normal and reverse directions. The actuator  647  is constituted by a motor and a reduction gear (not depicted) and can rotate a part of the main body  646  by a desired angle. The control block  66  is, for example, a microcomputer including a CPU, ROM, RAM, I/O interface, and the like. 
     In the artificial respiration apparatus  50 , the single blower  52  serves to generate both of the positive pressure and the negative pressure. That is, the blower  52  has a large load. On the other hand, in order to increase the ventilation amount of the artificial respiration apparatus  50 , it is most effective to increase the power of the blower  52 . However, if the power is to be increased with the single blower  52 , it becomes necessary to design a special blower having very large dimensions and weight. Such a blower is not available on market and should be prepared by a special order. 
     This has been preventing reduction in size and weight as well as cost of the conventional artificial respiration apparatus  50 . Moreover, such a large blower  52  requires a 200 V power source or a large current receptacle even if a 100 V power source can be used. This makes it difficult to use the artificial respiration apparatus  50  even in a small hospital. 
     Next, explanation will be given on the reason why the blower  52  of the artificial respiration apparatus  50  should have such a large load. A “blower” is an apparatus constituted by a motor and a fan for sucking air from the suction side and discharging the air from the discharge side. The blower  52  generates a negative pressure An by sucking air from the suction side and generates a positive pressure Ap by discharging the sucked air from the discharge side. 
     Here, for use of the positive pressure Ap, the rotary valve mechanism  54  makes the discharge side of the blower  52  communicate with the oscillating air pressure pipe  546  while closing the suction side of the blower  52 . Here, if the suction side is closed completely, it becomes impossible to obtain air for discharge. Accordingly, the suction side is connected to the orifice pipe  523  communicating with the open air. 
     On the contrary, when using the negative pressure An, the rotary valve mechanism  54  makes the discharge side of the blower  52  closed and the suction side of the blower  52  communicate with the oscillating air pressure pipe  546 . Here, if the discharge side is closed completely, the sucked air cannot be discharged. Accordingly, the discharge side is also connected to an orifice pipe  524  communicating with the open air. 
     Accordingly, when using the positive air Ap, the suction side takes in air via the orifice pipe  523 , whereas the discharge side discharges the air via the oscillating air pressure pipe  546  and simultaneously with this, the air leaks out via the orifice pipe  524 . On the contrary, when using the negative pressure An, the discharge side discharges air via the orifice pipe  524 , whereas the suction side sucks air via the oscillating air pressure pipe  546  and simultaneously with this, air flows in via the orifice pipe  523 . Thus, operation of the artificial respiration apparatus  50  is inevitably accompanied by useless air leak out and flow in. This significantly increases the load of the blower  52 . 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an artificial respiration apparatus which can realize a small size, small weight, and low production cost and can be used in small hospitals. 
     The inventors of the present invention have found that the aforementioned object can be achieved by replacing the blower generating both of a positive pressure and a negative pressure by a positive pressure blower for generating only a positive pressure in combination with a negative pressure blower for generating only a negative pressure. This can significantly reduce the load (i.e., power consumption), which in turn realizes a smaller size and weight as well as a lower cost. For example, instead of a large-size blower of a special type, ordinary two blowers are used. Such an ordinary blower is small in size and weight and is available on market, and can be used with a 100V commercial power source. 
     The present invention is based on this finding. That is, the artificial respiration apparatus according to the present invention comprises: a positive pressure generator for generating a positive air pressure; a negative pressure generator for generating a negative air pressure; an oscillating air pressure generation mechanism for alternately selecting the positive pressure generated by the positive pressure generator and the negative pressure generated by the negative pressure generator so as to convert the positive pressure and the negative pressure into an oscillating air pressure; and a diaphragm block urged by the oscillating air pressure from the oscillating air pressure generation mechanism, so as to supply a gas into a mouth of a patient. 
     Next, explanation will be given on the reason why the load is reduced when the one blower is replaced by two blowers. 
     The artificial respiration apparatus according to the present invention includes: a negative pressure blower (negative pressure generator) which sucks air at its suction side and discharging the sucked air into the open air, thus generating a negative pressure; and a positive pressure blower (positive pressure generator) which sucks air from the open air and discharges the sucked air to its discharge side, thus generating a positive pressure. 
     Here, when using the positive pressure, a rotary valve mechanism (oscillating air pressure generation mechanism) makes the discharge side of the positive pressure blower communicate with an oscillating air pressure pipe and the suction side of the negative blower closed. Here, even if the suction side of the negative pressure blower is closed completely, the positive pressure blower can suck air from the open air. Accordingly, the orifice pipe used at the suction side in the conventional respirator is not required. 
     On the contrary, when using the negative pressure, the rotary valve mechanism (oscillating air pressure generation mechanism) makes the discharge side of the positive pressure blower closed and the suction side of the negative pressure blower communicate with the oscillating air pressure pipe. Here, even if the suction side of the positive pressure blower is closed completely, the negative pressure blower can discharge air into the open air. Accordingly, the orifice pipe used at the discharge side in the conventional respirator is not required. 
     Consequently, in the artificial respiration apparatus according to the present invention, there is no useless air leak out or flow in. This can significantly reduce the blower load. For example, the conventional respirator requires a single blower of 1.35 KW, whereas the present invention requires only 0.85 KW for use of two blowers in combination. Thus, the power consumption is reduced by about 37%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a configuration of an artificial respiration apparatus according to an embodiment of the present invention. 
     FIG. 2 is a graph showing as an example, discharge characteristic of a positive pressure blower and suction characteristic of a negative pressure blower in the artificial respiration apparatus shown in FIG.  1 . 
     FIG. 3 is a cross sectional view of a pressure regulating valve used in a diaphragm neutral position controller of FIG. 1 in a state for selecting a positive pressure releasing passage and a negative pressure application passage. 
     FIG. 4 is a cross sectional view of the pressure regulating valve used in the diaphragm neutral position controller of FIG. 1 in a state for selecting a negative pressure releasing passage and a positive pressure application passage. 
     FIG. 5 shows a configuration of a conventional artificial respiration apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a configuration of an artificial respiration apparatus according to an embodiment of the present invention. FIG. 2 is a graph showing as an example, discharge characteristic of a positive pressure blower and suction characteristic of a negative pressure blower in the artificial respiration apparatus shown in FIG.  1 . Hereinafter, explanation will be given with reference to FIG.  1  and FIG.  2 . It should be noted that like components as in FIG. 5 are denoted by like reference symbols without giving any detailed explanation. 
     The artificial respiration apparatus  10  according to the present embodiment includes: a positive blower  12   p  (positive pressure generator) for generating a positive pressure Ap; a negative blower  12   n  (negative pressure generator) for generating a negative pressure An; a rotary valve mechanism  54  (oscillating air pressure generation mechanism) alternately selecting the positive pressure Ap generated by the positive blower  12   p  and the negative pressure An generated by the negative blower  12   n;  and a diaphragm block  56  urged by the oscillating air pressure Apn from the rotary valve mechanism  54  so as to supply air to the patient P. 
     The positive blower  12   p  sucks air via a filter  14  from the atmosphere and discharges the sucked air to a positive pressure pipe  521  to generate a positive pressure Ap. The filter  14  serves to remove dusts from the air to be sucked. The negative blower  12   n  sucks air from the negative pressure pipe  522  and discharges the sucked air via a silencer  16  into the atmosphere, thus generating the negative pressure An. The silencer  16  serves to reduce the sound caused by air discharge. Moreover, flow control valves  181  and  182  are provided at the suction side of the positive blower  12   p  and the discharge side of the negative blower  12   n,  respectively. 
     Moreover, as shown in FIG. 2, the discharge characteristic of the positive blower  12   p  is symmetric to the suction characteristic of the negative blower  12   n.  Accordingly, the absolute value of the positive pressure Ap is almost equal to the absolute value of the negative pressure An. Deviation of the diaphragm  561  (deviation from an average neutral position), as will be detailed later, is dissolved by a diaphragm neutral position controller  60 . As the difference between the absolute value of the positive pressure Ap and the that of the negative pressure An increases, the deviation of the diaphragm  561  becomes difficult to be dissolved by the diaphragm neutral position controller  60 . Accordingly, it is preferable that the discharge characteristic of the positive blower  12   p  be symmetric to the suction characteristic of the negative blower  12   n.    
     It should be noted that even if the positive blower  12   p  has a discharge characteristic not symmetric to the suction characteristic of the negative blower  12   n,  it is possible to make adjustment within a certain range using the diaphragm neutral position controller  60  or the flow control valves  181 ,  182 . 
     FIG.  3  and FIG. 4 are cross sectional views of a main body  646  of the pressure regulating valve  64  as an example. Hereinafter, explanation will be given with reference to FIG. 1 to FIG.  4 . 
     The main body  646  of the pressure regulating valve  64  is constituted by a fixed body  648  as an outer cylindrical member and a rotary body  649  as an inner cylindrical shape. The fixed body  648  has ports  641  to  645 . The rotary body  649  has through holes  649   a ,  649   b ,  649   c ,  749   d , a partition  649   e , and opening ends  649   f ,  649   g.    
     The port  641  is connected to a positive pressure bypass pipe  681  which communicates with the positive pressure pipe  521 . The port  642  is connected to a negative pressure bypass pipe  682  which communicates with the negative pressure pipe  522 . The port  643  is connected to an oscillating air pressure bypass pipe  683  which communicates with the oscillating air pressure pipe  546 . The ports  644  and  645  are connected to open air ports  684  and  685 , respectively. 
     The rotary body  649  is rotated by an actuator  647 . The rotary body  649 , according to its rotation angle, can select a positive pressure releasing passage  701  in combination with a negative pressure application passage  702  (FIG.  3 ); or a negative pressure releasing passage  703  in combination with a positive pressure application passage  704  (FIG.  4 ). 
     The positive pressure releasing passage  701  allows the air to flow through the positive bypass pipe  681 , the port  641 , the opening end  649   f , the through hole  649   a , the port  644 , and the orifice pipe  684  in this order. This passages lowers the absolute value of the positive pressure Ap generated by the positive blower  12   p.    
     The negative pressure application passage  702  allows the air to flow through the oscillating air pressure bypass pipe  683 , the port  643 , the through hole  649   d , the opening end  649   g,  the port  642 , and the negative pressure bypass pipe  682  in this order. This passage applies the negative pressure An generated by the negative blower  12   n,  to the oscillating air pressure Apn urging the diaphragm  561 . 
     The negative pressure releasing passage  703  allows the air to flow through the orifice pipe  685 , the port  645 , the opening end  649   g,  the port  642 , and the negative pressure bypass pipe  682  in this order. This passage lowers the absolute value of the negative pressure generated by the negative blower  12   n.    
     The positive pressure application passage  704  allows the air to flow through the positive bypass pipe  681 , the port  641 , the opening end  649   f , the through hole  649   c , the port  643 , and the oscillating air pressure bypass pipe  683  in this order. This passage applies the positive pressure Ap generated by the positive blower  12   p,  to the oscillating air pressure Apn urging the diaphragm  561 . 
     The amount of the air flowing through the respective passages can be continuously changed by rotating in jog mode the rotary body  649  using the actuator  647 . Moreover, the rotary body  649  can also be set at an angle not selecting any of the passages. 
     Description will now be directed to operation of the artificial respiration apparatus  10 . 
     The positive pressure Ap generated by the positive blower  12   p  and the negative pressure generated by the negative blower  12   n  are converted into an oscillating air pressure Apn by the rotary valve mechanism  54 . The oscillating air pressure Apn generated by the rotary valve mechanism  54  is fed to the diaphragm block  56 . In the diaphragm block  56 , the diaphragm  561  is oscillated by the cycle of the oscillating air pressure Apn, and the oscillation of the diaphragm  561  changes the pressure inside the respiration gas pipe  623 . Moreover, the respiration gas Ai is constantly supplied to the patient P. The exhaling air from the patient P is discharged via the flow control valve  607 . The flow control valve  607  in normal mode is open to a degree that the exhaling air can flow out. 
     The movement of the diaphragm  561  is detected by a diaphragm position sensor  601 , and the detected information is constantly fed as an operation information of the diaphragm  561  to the control block  66 . If this movement of the diaphragm  561  is disturbed by a spontaneous breathing of the patient, this information is immediately fed to the control block  66 , so that the control block  66  controls the flow control valve  607  to adjust the pressure inside the respiration gas pipe  623 , thus reducing the load on the patient P upon his/her spontaneous breathing. 
     If the diaphragm neutral position is deviated from the center, the reciprocal movement of the diaphragm  561  is limited to a certain degree, making incomplete the respiration operation of the artificial respiration apparatus  10 . To cope with this, the diaphragm neutral position controller  60  operates to decrease the pressure difference between the pressurizing chamber  562  and the pressurized chamber  563  within a range not disturbing operation of the diaphragm block  56 , so that the diaphragm  561  can maintain its neutral position. 
     That is, the control block  66  constantly detects deviation from an average neutral position of the diaphragm  561  according to an operation information of the diaphragm  561  obtained from the diaphragm position sensor  601 . If the average neutral position of the diaphragm  561  is deviated, the control block  66  operates as follows. 
     When the neutral position of the diaphragm  561  deflects toward the side of the patient P (rightward in FIG.  1 ), the pressure regulating valve  64  is controlled to select the positive pressure releasing passage  701  and the negative pressure application passage  702 . The positive pressure releasing passage  701  decreases the absolute value of the positive pressure Ap generated by the positive blower  12   p.  Simultaneously with this, the negative pressure application passage  702  applies the negative pressure An generated in the negative blower  12   n,  to the oscillating air pressure Apn, thus lowering the oscillating air pressure Apn. This returns the neutral position of the diaphragm  561  to its center position (leftward in FIG.  1 ). 
     On the contrary, when the neutral position of the diaphragm  561  deflects toward the positive blower  12   p  and the negative blower  12   n  (leftward in FIG.  1 ), the pressure regulating valve  64  is controlled to select the negative pressure releasing passage  703  and the positive pressure application passage  704 . The negative pressure releasing passage  703  decreases the absolute value of the negative pressure Ap generated by the negative blower  12   n.  Simultaneously with this, the positive pressure application passage  704  applies the positive pressure Ap generated in the positive blower  12   p,  to the oscillating air pressure Apn, thus increasing the oscillating air pressure Apn. This returns the neutral position of the diaphragm  561  to its center position (rightward in FIG.  1 ). 
     The time required for returning the diaphragm  561  to its center position is significantly reduced by controlling not only the positive pressure Ap but also the negative pressure An. Besides, the oscillating air pressure Apn is discharged not into the atmosphere but into the negative pressure An side or the positive pressure Ap side, so as to utilize a greater pressure difference. Thus, the time is further reduced. 
     It should be noted that the present invention is not to be limited to the aforementioned embodiment. For example, the rotary body  149  may be constructed so as to select one of the positive pressure releasing passage  201  and the negative pressure lowering passage  203 , or one of the negative pressure application passage  202  and the positive pressure application passage  204 . 
     The artificial respiration apparatus according to the present invention uses a positive pressure generator generating only a positive pressure in combination with a negative pressure generator generating only a negative pressure instead of using an air pressure generator generating both of a positive pressure and a negative pressure. This brings about following effects. 
     (1) In comparison to the conventional air pressure generator, the load of the positive pressure generator and the negative pressure generator can significantly be reduced, which in turn enables to reduce the apparatus size and weight as well as the production cost. 
     (2) Each of the positive pressure generator and the negative pressure generator can be realized by a small-size and small-weight blower or the like requiring a low power consumption, available on market. 
     (3) The positive pressure generator and the negative pressure generator are small and light. Accodingly, it is possible to provide an artificial respiration apparatus having practical dimensions and weight which can easily be handled by doctors and nurses. 
     (4) The positive pressure generator and the negative pressure generator consume a low power and accordingly, there is no need of preparing a special power source to use the artificial respiration apparatus in a small hospital. 
     (5) The positive pressure generator and the negative pressure generator are available on market without requiring a special order, and it is possible to use the artificial respiration apparatus at a low cost. 
     (6) The positive pressure generator and the negative pressure generator are independent components from each other. This facilitates maintenance operation. 
     According to another aspect of the present invention, the positive pressure generator has a discharge characteristic symmetric to a suction characteristic of the negative pressure generator. This enables to realize an ideal respiration without deviation of the neutral position of the diaphragm. 
     According to still another aspect of the present invention, each of the positive pressure generator and the negative pressure generator has at its discharge side a flow control valve. Accordingly, even if the discharge characteristic of the positive pressure generator is not symmetric to the suction characteristic of the negative pressure generator, it is possible to realize an ideal respiration having no deviation in the neutral position of the diaphragm. 
     According to yet another aspect of the present invention, a diaphragm neutral position controller is provided for maintaining the neutral position of the diaphragm. Accordingly, even if the discharge characteristic of the positive pressure generator is not symmetric to the suction characteristic of the negative pressure generator, it is possible to realize an ideal respiration having no deviation in the neutral position of the diaphragm. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristic thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     The entire disclosure of Japanese Patent Application No. 10-103741 (Filed on Mar. 31, 1998) including specification, claims, drawings and summary are incorporated herein by reference in its entirety.