Abstract:
An apparatus for supplying a breathing gas to a patient has a gas supply for generating a flow of breathable gas during an inspiration and an expiration phase of a patient breathing cycle. An inspiration line is provided having an inlet through which a flow of breathing gas from the supply can pass as well as an expiration line through which an expiration gas from the patient can flow. A flow controller is provided for selecting, during an inspiration phase, a first flow path for gas from the supply into the inlet and for selecting, during the expiration phase, a second flow path for gas from the supply in a direction across a venturi outlet of the expiration line, to enhance removal of expiration gas therefrom by venturi suction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for the supply of a breathing gas to a patient. 
     2. Description of the Prior Art 
     An apparatus, such as a ventilator or respirator, for supplying a breathing gas to a patient, in which a supply means is operated to continuously generate a flow of gas, is disclosed in European Application 0 813 883. The apparatus disclosed therein has a fan or compressor which may be continuously operated to provide a flow of a breathable gas to a flow divider. The flow divider operates to divert the gas flow either toward a patient during an inspiration phase of the patient&#39;s breathing cycle or to a recirculating system during an expiration phase, to be re-directed toward the patient in the subsequent inspiration phase. Since the supply means is operated continuously, changes in supply to the patient can be made rapidly by varying only the relatively responsive flow divider. The gas supplied by the supply means, however, is not usefully employed during the expiration phase and the energy used in powering the supply means may be considered as being wasted. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus in which gas supplied by a supply arrangement can be usefully employed during an expiration phase of a patient. 
     By providing the expiration tube with a venturi outlet and arranging for gas from the supply to pass across this outlet, preferably at an angle of 90° or less to the direction of expiration gas flow from the outlet, during an expiration phase then expiration effort expended by the patient can be reduced. 
     The supply, such as a compressor or fan assembly, can be operated to continuously generate a flow of breathable gas throughout the patient&#39;s breathing cycle. This has the advantage that no additional gas source need be included within the supply for supplying gas during the expiration phase. 
     A vane deflector, rotatable in the flow path of the gas from the supply, for selectively coupling the flow to the inspiration or expiration lines may be used. This provides a relatively simple and inexpensive flow controller. 
     Additionally, the supply can be operated to provide a flow greater than that required during an inspiration phase. This means that the vane need not deflect all gas flow into the inspiration line. This avoids problems, such as incorrect switching between the inspiration and the expiration phases, associated with the vane sticking against a sealing surface and also allows a less expensive vane deflector to be used since manufacturing tolerances are reduced compared to a deflector in which a complete seal must be effected. 
     The venturi outlet may be variable in size to allow control of the venturi effect and hence the expiration effort of a patient. This may be simply achieved by arranging for the vane of the vane deflector to be cooperable with the end of the expiration line to form a venturi outlet that varies as the deflector moves. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a portion of a ventilator of the present invention. 
     FIG. 2 a  shows details of the operating position of the vane of FIG. 1 during inspiration and FIG. 2 b  indicates the position during expiration. 
     FIG. 3 shows a schematic representation of an alternative embodiment of the present invention. 
     FIG. 4 shows a schematic representation of a further alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a patient ventilator which has a breathing gas supply  1  including a fan assembly  2  for providing an air flow continuously throughout the breathing cycle of a patient along a flow path defined, in part, by a delivery conduit  3  and a flow controller  4  connected to one end of the conduit  3  at an inlet  5 . The controller  4  is provided with a common inlet/outlet  6  which connects to one end of a breathing tube  7 . An opposite end of the tube  7  is connectable to a patient&#39;s airways (not shown) when the ventilator is in use and provides a flow path for inspiration gas to the airways and for expiration gas from the airways in a manner conventional in the art of patient ventilation. The flow controller  4  is also provided with an outlet  8  connected to an exhaust line  9  which is here vented to atmosphere. Thus, the flow path of gas from the fan  2  divides into two parts within the flow controller  4 ; one path leads gas from the inlet  5  to the outlet  8 ; and one path leads gas from the inlet  5  to the common inlet/outlet  6 . These paths are illustrated in FIG. 1 by the arrows. A deflector, in the form of a vane  10 , mounted on an axle  11  of a stepper motor  12  is also included as part of the flow controller  4 . The vane  10  is located in the flow path of the gas from the supply  1  that enters the controller via the inlet  5  and may be rotated to vary the division of the gas flow to the openings  6 ,  8  of the flow controller  4 . As shown in the embodiment of FIG. 1 a flow sensor  13  may be provided in the breathing tube  7  to sense gas flow therethrough and to provide the magnitude (and optionally direction) of the sensed flow as a control signal to the stepper motor  12  which then rotates the axle  11  to vary the inclination of the vane  10  and achieve a desired flow in the breathing tube  7 . Optionally, as also shown in FIG. 1, the output from the sensor  13  may also be used to provide a control signal to the supply  1 . This control signal may be used to vary the rotational speed of the fan  2  to assist in achieving the desired gas flow. 
     The controller  4  and its operation will be described in more detail with reference to the FIGS. 2 a  and  2   b  in which the reference numerals of FIG. 1 are used to identify  6  identical parts. The axle  11  is positioned part-way along the length of the vane  10  to divide the vane  10  into first and second sections  14 ,  15  as will be described below. The vane  10  and axle  11  are located in a widened mouth section  16 , of the common inlet/outlet  6 . As shown in FIG. 2 a , during an inspiration phase of the breathing cycle gas from the inlet  5  is diverted to the common inlet/outlet  6  to be subsequently inspired. To achieve this the vane  10  is rotated so that its first section  14  is arranged to provide a flow path for the gas from the inlet  5  to the common inlet/outlet  6  (as illustrated by the solid construction of vane  10  in FIG. 2 a ). If the flow of gas supplied to the inlet  5  is greater than that required for inspiration then the vane  10  need not form a complete seal against the internal wall surface of the flow controller  4 . The vane  10  is rotated sufficiently so that the first section  14  divides the gas flow between the common inlet/outlet  6  and the outlet  8  as shown, by the arrows representing the gas flow paths during an inspiration phase. 
     This excess gas flow is preferable since the first section  14  need not then be arranged to form a gas tight seal against flow of gas to the outlet  8  so reducing manufacturing tolerances; limiting the possibility of the vane  10  sticking; and speeding the response time of the vane  10  as friction is reduced. 
     During inspiration the second section  15  reduces the open area of the mouth  16  through which gas, deflected by the first section  14 , can flow without passing out of the controller  4  through the common inlet/outlet  6 . 
     At the end of the inspiration phase of a breathing cycle there is typically a pause before an expiration phase commences. In known ventilators, a positive pressure is often provided to the lungs that matches the end inspiration lung pressure. If it is desired to provide such a pressure in the ventilator of the present embodiment then the vane  10  may be rotated to a position in which the flow path is altered to provide the correct flow of gas to the common inlet/outlet  6 , as shown by the broken line representation of the vane  10 ′ in FIG. 2 a.    
     As illustrated in FIG. 2 b , during an expiration phase the vane  10  is rotated so that most or all of the gas from the inlet  5  can flow along a path directly to the outlet  8  in a direction across a venturi outlet  17  for expiration gas flowing into the controller  4  through the common inlet/outlet  6 . The gas flow paths during expiration is shown by the arrows in FIG. 2 b . The first section  14  of the vane  10  effectively prevents gas flow from the inlet  5  to the common inlet/outlet  6  and the second section  15  co-operates with an internal wall section  18  of the controller  4  to define the venturi outlet  17  within the larger mouth  16  of the common inlet/outlet  6 . The vane  10  is thus arranged so that in this position gas from of the inlet  5  passes across the outlet  17  causing expiration gas to be drawn through the outlet  17  by venturi suction. 
     Thus, it will be appreciated by those skilled in the art that the gas from the inlet  5  provides a regulation (here an enhancement) of the expiration gas flow when directed across the expiration outlet  17 . Rotation of the vane  10  so as to vary the size of the outlet  17  formed with the second section  15  of the vane  10  will vary the suction effect produced by any given flow from the outlet  5  so that the regulation of the flow of the expiration gas may be made variable in this embodiment of the present invention. 
     At the end of the expiration phase, it is common in the art of lung ventilation to provide a positive end expiratory pressure (PEEP) level in the lungs. This may be achieved in the present embodiment by rotating the vane  10  to a position as illustrated by the broken lines vane  10 ′ in which the vane deflects a part of the flow from the inlet  5  into the common inlet/outlet  6  while allowing a greater portion of the gas to flow along a path between the inlet  5  and the outlet  6 . Indeed the vane  10  may be rotated to this position at any time during the expiration phase to provide, as desired, a resistance to the passage of expiration gases from the outlet  17 . 
     An alternative embodiment of a ventilator according to the present invention is illustrated in FIG. 3 in which elements common to both FIG.  1  and FIG. 3 are given the same reference numerals. The ventilator has a gas supply  1  having a fan  2  for providing a continuous airflow throughout the breathing cycle of a patient. The fan  2  is at one end of a conduit  19  which connects to a mouth section  16  in fluid communication with a common inlet/outlet  6  and with an exhaust line  9 . A vane  10  is located within the conduit  19  proximal the mouth  16  and is mounted at one end for rotation on an axle  31  of a stepper motor  12  to divide a flow of gas from the fan  2  between a path along the exhaust line  9  and a path through the common inlet/outlet  6  and to a breathing tube (not shown) and can provide variable amounts of gas flowing along each of these paths. 
     During an expiration phase the vane  10  is rotated to lie across the mouth  16  and form a venturi outlet  17  in cooperation with an internal wall of the conduit  19  as shown in FIG.  3 . The vane  10  and the exhaust line  9  are relatively located so that when the outlet  17  is formed substantially all of the gas flow from the fan  2  can be deflected by the vane  10  across the outlet  17  and into the exhaust line  9  (as shown by the arrows in FIG.  3 ). As with the embodiment of FIG. 1, the flow of gas from the fan  2  in a direction across the outlet  17  draws in expiration gas from the breathing tube (not shown) and thereby reduces the expiration effort of the patient. 
     During an inspiration phase, the vane  10  is rotatable to unblock the common inlet/outlet  6  (as shown by the broken line representation of the vane  10 ′ in FIG. 3) so that the flow from the fan  2  is allowed to pass through the common inlet/outlet  6  and into the breathing tube  7 . By varying the degree of rotation of the vane  10  the flow of gas from the fan  2  can be divided between the two above described paths in different amounts, for example to achieve a PEEP level or to provide an end inspiration lung pressure. 
     FIG. 4 illustrates an alternative to the vane-type flow controller of FIG.  1  and FIG. 3 which also shows a further embodiment of a ventilator according to the present invention. A flow conduit  19  is connected at one end to the output of a gas supply means  1  comprising a fan  2  which is operated to provide a flow in the conduit  19  throughout the breathing cycle. Along the length of the conduit  19  are separate, spaced apart openings which respectively constitute an inlet  20  for supplying inspiration gas from the conduit  19  to a breathing tube  22  and a venturi outlet  21  through which expiration gas from the tube  22  may pass into the conduit  19 . The tube  22  is formed with a common flow conduit  23  and arms  24 ,  25  connecting the common flow conduit to the inlet  20  and the outlet  21 , respectively. 
     A known T-valve flow controller  26  is placed in the flow conduit  19  in operable connection with the outlet  20 . The valve is operable by means of a motor drive unit  27  to move between a position in which a flow path is created for gas from the supply  1  which leads some or all of that gas into the breathing tube  22  (illustrated by the arrows in FIG. 4) and a position in which a flow path is created which leads gas from the supply  1  across the outlet  21 . Preferably, one way valves  28 ,  29  are placed in the arms  24 ,  25  respectively to ensure gas flow in each of the arms  24 ,  25  in one direction only. 
     The ventilator operates as follows: during an inspiration phase, the T-valve  30  of the controller  26  is rotated so that gas from the supply means  1  can flow through the valve  30  and into the inlet  20  to provide gas for inspiration. During expiration the T-valve  30  of the controller  26  is rotated so that gas from the supply  1  can flow through the conduit  19  and across the outlet  21 . Expiration gas may then be drawn through the outlet  21  into the conduit  19  by venturi suction. 
     The above embodiments have all been described in relation to a gas supply that has a continuously rotating fan. It will, however, be appreciated by those skilled art that the invention is not restricted to this embodiment and that a ventilator may be provided using any suitable gas source that can operate to supply a gas flow for at least that part of the expiration phase during which it is desired to achieve regulation of the flow of expiration gas while still remaining within the scope of the invention. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.