Abstract:
A pressure regulator for regulating the expiratory flow in a CPAP system includes submerging a tube into a column of water. Improvements are included for adjusting the level to which the tube is submerged and for ensuring constant water level.

Description:
BACKGROUND TO THE INVENTION 
     i) Field of the Invention 
     The present invention relates to the use of a pressure regulator in conjunction with a breathing assistance apparatus, particularly though not solely, for regulating the pressure of gases supplied to a patient from a humidified Positive End Expiratory Pressure (PEEP) apparatus. 
     ii) Summary of the Prior Art 
     The use of a medical apparatus to facilitate breathing is well known in the art. The apparatus may take the form of a simple oxygen mask or tent which supplies oxygen at slightly above atmospheric pressure. Such devices merely assist a person to breath and work with the person&#39;s lungs. 
     Ventilators which operate at high frequency have been suggested in the past. There are two types of high frequency ventilators known in the art. One type, as exemplified by U.S. Pat. No. 2,918,917 (Emerson), employs a reciprocating diaphragm to vibrate a column of gas supplied to a subject. The vibration is in addition to the subject&#39;s respiration, natural or artificial, and at a much more rapid rate, for example, from 100 to more than 1500 vibrations per minute. The Emerson apparatus is primarily designed to vibrate the patient&#39;s airway and organs associated therewith, although Emerson also recognized that high frequency vibration causes the gas to diffuse more rapidly within the airway and therefore aids the breathing function. However, the Emerson is incapable of supporting the patient&#39;s full ventilation and must be used in conjunction with the patient&#39;s spontaneous breathing or with another apparatus which produces artificially induced inhalation and exhalation. 
     The second type of high frequency ventilator is the jet pulse ventilator as exemplified in U.S. Pat. No. 4,265,237 (Schwanbom et al.). The Schwanbom et al. ventilator produces high frequency, high pressure pulses of air which are capable of fully ventilating a patient. The respiration pulse enters with a pressure of 0.2 bar to 2.7 bar. This pressure is sufficient to expand the lungs during inspiration. Expiration is caused by the natural compliance of the lungs after the jet of air is stopped. Accordingly, it can be see that Schwanbom et al must rely on the compliance of the lungs in order to fully ventilate the patient. If the lung compliance is low, greater pressure must be used. Schwanbom et al also supply a source of lower pressure gas for spontaneous breathing by the patient. While such jet pulse ventilators are useful for some applications, they are not generally applicable and their use is limited mostly to experimental work. 
     An improvement on these types is disclosed in U.S. Pat. No. 4,821,709 (Jensen) a which provides high frequency oscillations in the gases supplied to a patient using a flexible diaphragm. Jensen provides a more practical method of ventilating a patient without spontaneous breathing of the patient, or the need for a separate ventilator. U.S. Pat. No. 4,646,733 (Strot et al.) proposes an apparatus for producing high frequency oscillations in gases supplied to a patient using a valve controlling the exhaled gases. 
     It would be desirable to have a simple system for providing high frequency pressure oscillations for spontaneously breathing patients particularly for non invasive forms of support, where the means level of gases provided to the patient can be adjusted. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a pressure regulator which goes some way to overcoming the above-mentioned disadvantages, or which will at least provide the healthcare industry with a useful choice. 
     Accordingly, in a first aspect, the present invention consists in a pressure regulating device for use with a breathing assistance apparatus which conveys inhalatory gas to, and removes exhalatory gas from a patient requiring breathing assistance, comprising: 
     a container which in use includes a body of liquid, having a substantially constant level in use, 
     a terminal conduit including proximate and distal ends, said proximate end adapted for connection to a breathing assistance apparatus and in use accepting exhalatory gas therefrom, and said distal end submerged in said body of liquid, 
     such that in use the mean pressure of said gas supplied to a patient is adjusted by the level to which said distal end is submerged in said body of liquid. 
     In a second aspect, the present invention consists in a breathing assistance apparatus for supplying gas to a patient to assist said patient&#39;s breathing a gas supply adapted to supply gas to said patient, an interface including a plurality of ports adapted to deliver said gas to said patient, an inhalatory conduit for conveying said gas from said gas supply to said interface, exhalatory conduit for conveying said patient&#39;s exhalations from said interface 
     a container which in use includes a body of liquid, and 
     a terminal conduit including proximate and distal ends, said proximate end adapted for connection to said exhalatory conduit and in use accepting exhalatory gas therefrom, and said distal end submerged in said body of liquid, 
     such that in use said patient is delivered a substantially constant mean pressure, said mean pressure adjusted by the level to which said distal end is submerged in said body of water. 
     In a third aspect, the present invention consists in a pressure regulating device for use with a breathing assistance apparatus which conveys inhalatory gas to, and removes exhalatory gas from a patient requiring breathing assistance, comprising: 
     a container which in use includes a body of liquid having substantially constant level in use, and 
     a terminal conduit including proximate and distal ends, said proximate end adapted for connection to a breathing assistance apparatus and accepting exhalatory gas therefrom, and said distal end submerged in said body of liquid, 
     such that in use the resultant bubbling occurring in said body of liquid produces relatively small controlled perturbations in the pressure of gas supplied to a patient. 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a typical configuration for supplying breathing assistance to a patient, 
     FIG. 2 is a plan view of the pressure regulator with the lid on according to the preferred embodiment of the present invention, 
     FIG. 3 is a side view of the pressure regulator according to the preferred embodiment of the present invention, 
     FIG. 4 is a cross-section of the pressure regulator according to the preferred embodiment of the present invention, 
     FIG. 5 is an alternative side view of the pressure regulator according to the preferred embodiment of the present invention, 
     FIG. 6 is a perspective view of the short conduit which extends into the water chamber according to the preferred embodiment of the present invention, 
     FIG. 7 is a cross-section of the complete pressure regulator according to the preferred embodiment of the present invention, and 
     FIG. 8 is a cross-section of a further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a means of producing the variations or oscillations in the pressure of gases supplied to a patient connected to a positive pressure ventilation device. By submerging the end of the exhalatory conduit into a water column the resulting bubbles generate a variation or ripple in the mean pressure of gases delivered to the patient. In doing so it also provides a simple method of varying the mean pressure of gases supplied to the patient by variation of the level to which the end of the exhalatory conduit is submerged within the water column. In order to keep the mean pressure of gases supplied to the patient constant the level of submergence of the end of the exhalatory conduit must be kept constant and an apparatus for ensuring this occurs is also disclosed. 
     Referring now to FIG. 1 in which a typical application is depicted. A humidified Positive End Expiratory Pressure (PEEP) system is shown in which a patient  119  is receiving humidified  114  and pressurised gas through a nasal mask  128  connected to an inhalatory conduit  121 . It should be understood that the present invention, however, is not limited to the delivery of PEEP gases but is also applicable to other types of gases delivery systems and may not necessarily involve humidification. Inhalatory conduit  121  is connected to the outlet  112  of a humidification chamber  110  which contains a volume of water  115 . Inspiratory conduit  121  may contain heating means or heater wires  120  which heat the walls of the conduit to ensure a constant humidity profile along the conduit and therefore reduce condensation of humidified gases within the conduit. As the volume of water  115  within humidification chamber  110  is heated  113 , water vapour begins to fill the volume of the chamber above the water&#39;s surface and is passed out of the humidification chamber  110  outlet  112  with the flow of gases (for example air) provided from a gases supply means or blower  118  which enters the chamber  110  through inlet  116 . 
     The humidified gases pass through the inhalatory conduit  121  to the mask  128  attached around the patient&#39;s  119  mouth. The excess gases then flow through the exhalatory conduit  130  to a pressure regulator  134 . 
     Pressure Regulator 
     In the preferred embodiment of the present invention the pressure regulator  134 , takes the form of discharging the flow of exhalatory gases into a chamber  204  containing a column of water  138 . The gases flowing through the exhalatory conduit  130  are discharged into the body of water  138  from short conduit  136  which extends from the expiratory conduit into the chamber  204 . This results in a bubbling effect, whereby the gases eventually exit the chamber  204  via the outlet port  152 , which can also be used to initially fill the chamber  204  with water. The outlet port  152  includes shielding to prevents liquid aerosols created by the vigorous bubbling on the surface of the water from being expelled. It will be appreciated that the short conduit  136 , could equally be integrated into the end of the expiratory conduit  130 . 
     Referring now to FIGS.  2  through to  7 , the pressure regulator  134  and associated components are seen in more detail. The exhalatory conduit ( 130 , FIG. 1) fits into the end of the short conduit  136  which in turn is attached to the lid  144  of the water chamber  204  via connector  146 . The connector  146  includes a number of resilient ridges or plastic toggles  148  which lock into annular grooves  150  in the short conduit  136  to keep it locked in a desired position during use. The chamber  204  is filled with a body of water  138  up to a predetermined level  140 . It will be appreciated that any appropriate liquid could be used instead of water. 
     It will be appreciated that for control over the mean pressure of supplied gases it is necessary to vary the level of which the short conduit  136  is submerged in the body of water  138 . Stepped variations in the pressure of gases delivered to the patient of ½ cm H 2 O each, are thought adequate for most applications, and is achieved by spacing each of the annular grooves 150½ cm apart. A contoured gripping portion  147  is provided at the end of the short conduit  136  which attaches to the exhalatory conduit  130 , to allow easy adjustment. In one embodiment, the pressure is adjustable over a range from 4-8 cm H 2 O but it will be appreciated that this can be modified to requirements. The pressure regulator according to the preferred embodiment of the present invention is shown in FIG. 7, adjusted to its highest pressure setting. The settings could be indicated by a number above each groove  150  on the short conduit  136 , which would be visible above the connector  146 . 
     Constant Water Level 
     In the preferred embodiment, the present invention is used in conjunction with a humidified PEEP respirator. As such, the exhalatory gases will have quite high levels of humidity, some at which will inevitably condense in the body of water  138  in the pressure regulator  134 . Thus, over time the volume of water in the water chamber  204  will rise and if unchecked will result in rising pressure of gases supplied to the patient and resultant adverse side effects. To ensure the water level is kept constant the water chamber  204  is provided with an overflow facility  218  also seen in FIGS. 2 to  7 . 
     Because of the vigorous bubbling occurring at the top of the body of water a simple lip over which excess liquid can flow would be ineffective and therefore some form of filtering or damping is required. In order to mitigate the effect of the vigorous bubbling near the top of the chamber  200  a main outlet port  202  from the main chamber  204  is provided at a substantially lower level than where the bubbles would normally be expected to occur. However, the bubbling also causes pressure waves throughout the body of the liquid. These pressure waves would normally be reflected through the main outlet port  202  into the levelling chamber  206  and therefore result in more water escaping than it is desired. To alleviate the effect of the pressure waves a wave shield  208  is located in an intermediate position between the upper level of the water  210  and the main outlet port  202 . This masks the outlet port  202  from the majority of the pressure waves due to the surface bubbling. 
     This effectively means that the water level in the levelling chamber  206  is relatively calm and substantially representative of the mean (as opposed to the instantaneous) water level in the main chamber  204 . The water level in the intermediate overflow chamber  206  in turn is regulated by an overflow port  212  situated on a raised adjacent platform  214 . The overflow port  212  is surrounded by a slightly cylindrical raised partition  216  in order to overcome the effect of any small remaining waves in the intermediate overflow chamber  206 . 
     The water then flows into the detachable overflow container  218  which when full may be detached in use and emptied. Both the main chamber  204  and the intermediate overflow chamber  206  are integrally injection moulded using a clear plastic. The separate overflow container  218 , is also injection moulded using a clear plastic as is the separate short conduit  136 . 
     Further Embodiments 
     It will also be appreciated that the apparatus used to vary the mean water level in the main chamber may take a number of forms. While in the preferred embodiment a slidable conduit is used, other forms such a concertina baffle or rotatable conduit, for example, would be equally applicable. It will also be appreciated further forms of the overflow facility will be possible. For example the further embodiment shown in FIG. 8, uses a thin slot  162  to pass water into a second chamber  160 , where baffles  164  smooth any variations before the overflow opening  166  into the overflow chamber  168 . 
     Advantages 
     Allows easy adjustment of the mean pressure level. 
     Allows high frequency pressure oscillations for spontaneously breathing patients. 
     Maintains constant mean pressure with low or no maintenance. 
     Disposable and cheap compared with prior art ventilators.