Abstract:
A pressure regulating device includes a housing having an inlet, a main outlet, an J an external venting outlet. An internal venting aperture is between the inlet and the external venting outlet. A valve is between the external venting outlet and the internal venting aperture. When the pressure of gases in the flow path is below a predetermined level, the valve at least partially blocks the internal venting aperture. When the pressure is above the predetermined level, the valve opens to allow at least a portion of the gases to flow from the inlet through the internal venting aperture and the external venting outlet. The valve is shaped to open in such a manner that the portion of gases flowing varies with the flow rate, such that the pressure at the main outlet is substantially constant over the flow rate range.

Description:
FIELD OF 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 Positive End Expiratory Pressure (PEEP) apparatus or for an infant resuscitation device. 
     BACKGROUND 
     At the moment of their first breath, a baby&#39;s lungs are collapsed and filled with fluid. The pressures needed to open such lungs, and keep them open, are several times that of a normal breath until the fluid is displaced and the lungs have filled with air. To generate these large pressures, the baby must have strong respiratory muscles, as well as a chemical called surfactant in their alveoli. Surfactant reduces the surface tension of the fluid within the alveoli, preventing the alveolar walls from sticking to each other, like coasters to coffee cups when there is water between them. 
     Neonates have difficulty in opening their lungs and keeping them open. Reasons for this include: 
     a) Weak respiratory muscles and low surfactant levels. This means that they cannot generate enough pressure to open the lungs and, should they be resuscitated, tire quickly with the effort of keeping open alveoli lacking in surfactant. 
     b) Underdeveloped internal tissue structure to support the alveoli. 
     c) Slower clearance of lung fluid. In very premature neonates, fluid may continue to be secreted in the alveoli even after birth. 
     d) A soft chest wall, horizontal ribs, and a flatter diaphragm contribute to reduce the inspiratory capacity. 
     e) The mixing of oxygenated and deoxygenated blood raises blood pressure in the lungs, increasing fluid movement from the blood vessels into the lung tissue. The reduced blood oxygen level starves tissue of oxygen and further weakens respiratory muscles. 
     f) Weak neck muscles and a lack of neck fat reduce upper airway stability so that collapse on inspiration may occur. 
     g) Collapsed, damaged alveoli secrete proteins that reduce surfactant function. 
     To alleviate this it is known to apply Positive End Expiratory Pressure (PEEP) during respiration, resuscitation or assisted respiration (ventilation). In applying PEEP, the neonate&#39;s upper airway and lungs are held open during expiration against a pressure that stops alveolar collapse. Lung fluid is pushed back into the circulating blood, alveolar surfactant is conserved, and a larger area of the lung participates in gas exchange with the blood. As blood oxygenation and carbon dioxide removal improves, more oxygen is delivered to growing tissues, while less oxygen and energy is consumed by respiratory muscles. In the case of resuscitation or ventilation the pressure is varied between a Peak Inspiratory Pressure (PIP) and the PEEP value until the patient/infant is breathing spontaneously. 
     In order to provide the PEEP across a range of flow rates, some method is required to regulate the pressure. It is known in the art to provide a valve near the infant, which actuates at a level of pressure (ie: the PEEP value) to allow the gases to vent externally. 
     Such valves may employ a spring-loaded valve, which in turn requires the use of high quality springs, which have been individually tested to give a high tolerance spring constant in order to ensure that it actuates at a value substantially that of the maximum safe pressure. Both the manufacture and testing of such a spring necessitates that its cost will be correspondingly high. Accordingly it would be advantageous to provide a pressure relief valve for a breathing assistance system which did not involve the use of such a high tolerance spring. 
     Also such valves are known to have substantial variation of the relief pressure with flow rate. For example as seen in  FIG. 5  the delivered pressure is shown for a range of valves. Over a given range of flow rates shown in the graph  50  of  FIG. 5 , a variable orifice valve as shown by line  52  gives a wide range of delivered pressure. An improvement on this is a prior art umbrella valve (for example the “umbrella check valve” manufactured by Vernay Laboratories Inc. shown in  FIGS. 4 a    &amp;  4   b ) which delivers a lower variation in delivered pressure, as shown by line  54 . However in all cases the variation in delivered pressure of prior art valves would desirably be reduced for this application. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a pressure regulator which goes some way to achieving the above-mentioned desiderata 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 and/or resuscitation apparatus, said apparatus supplying gases over a flow rate range to an infant or neonate requiring resuscitation and/or breathing assistance, said pressure regulating device comprising: 
     a housing including an inlet, a main outlet, and an external venting outlet, the housing defining a flow path between said inlet and said main outlet, said inlet adapted to be in fluid communication or integrated with said breathing assistance and/or resuscitation apparatus and said main outlet adapted to be in fluid communication with an infant, and an internal venting aperture between said inlet and said external venting outlet, 
     a valve member disposed within said housing, between said external venting outlet and said internal venting aperture, wherein when the pressure of gases in the flow path is below a predetermined level, said valve member at least partially blocks said internal venting aperture, said gases thereby flowing from said inlet to said main outlet, and wherein when said pressure of said gases is above said predetermined level, said valve member opens to allow at least a portion of said gases to flow from said inlet through said internal venting aperture and said venting outlet, 
     said valve member having a shape such that it will open to allow a portion of said gases flowing from said inlet through said internal venting aperture, said portion varying with said flow rate, such that the pressure at said main outlet is kept at a reasonably constant level over said range of flow provided by said resuscitation apparatus. 
     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. 
     The invention consists in the foregoing and also envisages constructions of which the following gives examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One preferred form of the present invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is a block diagram showing a typical configuration for supplying breathing assistance to a neonate in accordance with the prior art. 
         FIG. 2 a    is a sectional view of a typical layout of a pressure regulator that can be used with the apparatus of  FIG. 1 , according to the preferred embodiment of the present invention. 
         FIG. 2 b    is a perspective view of a valve member used with the pressure regulator of  FIG. 2 a   , according to the preferred embodiment of the present invention. 
         FIG. 3  is a side view showing hidden detail of the valve member of  FIG. 2 b   , according to the preferred embodiment of the present invention. 
         FIG. 4 a    is aside view showing hidden detail of a prior art umbrella valve. 
         FIG. 4 b    is a perspective view of the prior art umbrella valve of  FIG. 4   a.    
         FIG. 5  is a graph showing a comparison of the pressure ranges produced by different types of valves over a flow range of 5-15 liters/minute. 
         FIG. 6  is a sectional front elevation view of a pressure regulator according to a further embodiment of the present invention. 
         FIG. 7  is an exploded perspective view of the pressure regulator of  FIG. 6 . 
         FIG. 8  is a front elevation of a pressure regulator according to a still further embodiment of the present invention. 
         FIG. 9  is an exploded perspective view of the pressure regulator of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is a connector including a valve, for use when resuscitating an infant or neonate. The delivered pressure is varied between Peak Inspiratory Pressure (PIP) and Peak End Expiratory Pressure (PEEP) by the occlusion of a PEEP outlet on the valve. The PEEP outlet may either allow variable PEEP, by adjustment, or substantially flow independent fixed PEEP using a novel umbrella valve. In the preferred embodiment, a duck billed valve is included for suctioning of surfactant delivery during resuscitation. In the preferred embodiment, the connector is adapted for one handed use. If using the fixed PEEP valve, this avoids the need for adjustment as flow through the valve changes, and provides more effective therapy. 
     Referring now to  FIG. 1  a typical application as known in the prior art is depicted. A Positive End Expiratory Pressure (PEEP) system is shown in which an infant  119  is receiving pressurized gases through a nasal mask  128  (or endotracheal tube or other interface as are known in the art) connected to an inhalatory conduit  121 , preferably for resuscitation. Either the mask  128  or the inhalatory conduit  121  can include the pressure regulator  134  of the present invention, to control the pressure of gas delivered to the infant. The inhalatory conduit  121  is connected to the outlet of a resuscitator apparatus  115 , which is in turn connected to a flow regulator and air supply  118  (which provides gas to the resuscitator at 50 psi or thereabouts). 
     It should be understood that the present invention, however, is not limited to resuscitation, or the delivery of PEEP gases but is also applicable to other types of gas delivery systems. 
     Pressure Regulator 
     The preferred embodiment of the pressure regulator  134  of the present invention is shown in  FIGS. 2 and 3  in detail. In the preferred embodiment the regulator  134  is disposed within a mask  128  although it will be appreciated that it can be located in a separate assembly, so long as it is proximate the infant. 
     Referring particularly to  FIG. 2 a    we see a cross-sectional schematic of the preferred embodiment of the pressure regulator  134 . The pressure regulator  134  includes a housing or manifold  300  with an inlet  302  and two outlets  304 ,  306 . The first outlet  304  supplies respiratory gases to the infant. The second outlet  306  is an external orifice which, as described previously, can be used to vary pressure between PIP and PEEP. Located between the inlet  302  and the orifice  306  is an improved PEEP valve  308 . 
     The PIP is adjusted at the resuscitator  115  to a desired level. The gases delivered to the infant  119  are varied between the PIP (with orifice  306  near the infant occluded), and the PEEP (with the orifice  306  un-occluded, so that a portion of the gas from the resuscitator  115  flows through the orifice  306 ). It can be seen that resuscitation of an infant can be attempted by varying the pressure at outlet  304  between the PIP and PEEP at a normal respiratory frequency. 
     The purpose of the PEEP valve  308  is to keep the Positive End Expiratory Pressure (PEEP) at a reasonably constant level, independent of changes in the overall flow rate of gases from resuscitator  115 . 
     It is desirable for infant respiratory assistance that the PEEP value should be approximately 5 cmH 2 0, independent of the flow rate. Preferably interfaces of the type used for resuscitation need to be simple and cost effective, as these are single-use products. Also, due to the nature of this application, a valve with many small separate parts, such as a spring valve, is not a viable option. 
     In the preferred embodiment, the PEEP valve  308  is a small umbrella valve  308 , made of an elastomeric material, and positioned on a valve seat  310  as shown particularly in  FIGS. 2 a    &amp;  2   b . Valve seat  310  defines an internal venting aperture  311  which is covered and closed by the valve  308  in a closed position. Preferably the valve  308  and seat  310  are included as part of the nasal mask  128 , or as part of an endotracheal tube (not shown). As the overall flow rate is increased, the consequent increase in pressure inside the manifold  300  causes the umbrella valve flaps  312  to lift up from the valve seat  310 , thereby letting more air out from inside the manifold  300 , and therefore keeping the pressure inside the manifold  300  at a constant level. 
     The umbrella valve  308  of the present invention differs from other prior art umbrella valves in the material and dimensions, the material being Silastic liquid silicone rubber Q7-4840. The overall proportions of the umbrella valve are as shown in  FIG. 3 . In particular, comparing  FIG. 3  to the prior art valve shown in  FIGS. 4A and 4B , we see the present invention has a characteristic flap  312  which is thicker at the periphery than at the centre. The ratio of the centre thickness to the periphery thickness should be 2:3, giving the cross-sectional shape shown in  FIG. 3 . The valve  308  of the present invention includes a shaft  301 , which has a retaining flange  303 . 
     Due to the design used, the umbrella valve  308  of the present invention does not act as a ‘pop-off’ valve. Most umbrella valves such as that shown in  FIGS. 4A and 4B  are designed to open at a specific ‘cracking pressure’. The prior art valve shown in  FIGS. 4A and 4B  has a shaft  400  and flap  410 . Often prior art valves have a “cracking pressure which will increase as the flow threshold increases”. In contrast, the valve of the present invention is designed to open at a predetermined flow rate (in this specific application above 5 liters/minute) and will continue to open further as the flow rate increases, increasing the flow through the internal aperture  311 , and thus causing the pressure in the manifold  300  to remain constant as the flow from resuscitator  115  increases. Most prior art umbrella valves will open at a certain pressure level and do not open any further with an increase in flow rate. This causes the pressure in a manifold to increase as the flow from a resuscitator increases. 
     The improved characteristics of the present invention can be seen in  FIG. 5 . If using a simple variable orifice valve, if the flow rate is changed between 5 and 15 liters per minute a dramatic change in PEEP will also occur, as shown by line  52 . The PEEP range for the variable orifice valve is 13 cmH 2 O. In tests, the best result obtained from prior art umbrella valves, as shown by line  54 , was a PEEP range of 4.9 cmH 2 0 In the same tests, the best result gained from the valve of the present invention as shown by line  56  is a PEEP range of 2.8 cmH 2 O. 
     Referring to  FIG. 6  we see an alternate embodiment of the pressure regulator  134 . Located between the inlet  302  and the orifice  306  is a PEEP valve  308 , preferably the umbrella valve described previously for the preferred embodiment. Included in this alternate embodiment is an inlet  303  which includes a duck billed valve  305 , used for introducing tubes down the trachea of the infant  119 , for suctioning, delivery of surfactant etc. The duck-billed valve  305  is normally closed. 
     In this alternate embodiment, the manifold  300  is shaped to enable ease of use; and it is designed to enable one handed operation. The manifold  300  is preferably wide and short and in this embodiment, shown in  FIG. 6 , it has a generally cylindrical cross-section. At the outlet  304  to the neonate, which is connected to the manifold  300 , is a flange  301 . When the present invention is used with a mask, the flange  301  enables the operator to apply pressure, pushing the mask into position to seal the mask around the neonate&#39;s nose and mouth. The flange  301  also enables an operator to use one digit on their hand to occlude orifice  306 , in order that they can vary pressure in the manifold  300  between PIP and PEEP. The operator achieves this variation in the pressure most easily by placing their thumb and middle finger on the flange  301  at  309  and  360  and then using their index finger to seal orifice  306 . The orifice branch  321  is shown at an angle  309  to the manifold  300 . This angle  309  allows the index finger to be placed in a natural position to occlude orifice  306 . The previously described embodiment of the pressure regulator  134  operates in the same way as the embodiment described above. 
     As has already been described, new born neonates often lack surfactant in their lungs. When the present invention is used with an endotracheal tube, surfactant can be administered to a patient without the need to remove the breathing assistance apparatus from the patient. By using a syringe or similar, the operator can administer surfactant to the neonate by pushing the end of the syringe through the duck billed valve  305 , located opposite the inlet  301 , and administer the surfactant to the infant  119 . 
     The duck billed valve  305  is normally sealed against the passage of fluids, but upon insertion of a syringe, the duck-billed valve  305  opens to allow the syringe end to enter the interior of the manifold  307 . The bill, or inner end  320 , of the duck billed valve  305  seals around the end of an inserted syringe, ensuring that the manifold  300  remains sealed. The valve bills  320  is manufactured from a silicone rubber, or other suitable material as known in the art. It is known that surfactant is a viscous fluid, and therefore this method of administration is advantageous over the method of administering surfactant using multi lumen endotracheal tubes. 
     The duck billed valve  305  can also be used to suction a neonate or infant  119 , to remove airway secretions. Suctioning is performed using a catheter inserted through the duck billed valve  305 , inserting the catheter through the duck-billed valve  305 , then down the endotracheal tube. The bill  320  of the valve  305  seals around an inserted catheter so that airway pressure is maintained. The duckbilled valve  305  is retained in the manifold  300  in such a way that any instrument inserted into the valve  305  is guided directly into the top of an endotracheal tube (or alternatively, a nasal mask, or other interfaces as are known in the art), one end of the endotracheal tube fitted at the outlet  304 . 
       FIG. 8  and  FIG. 9  illustrate a further alternate embodiment of the pressure regulator  134 . The overall shape of the manifold  330  is similar to that previously described with reference to  FIG. 6 , with, in this embodiment, orifice branch  321  is replaced by an alternate orifice branch  326 . The pressure of the delivered gases is varied between PIP, with orifice  334  on branch  326  occluded, and PEEP, with the orifice  334  un-occluded. As is best shown with reference to  FIG. 9 , the manifold  330  includes a jet outlet  332  positioned between the inlet  328  and the outlet orifice  334 . The flow rate of the gases through the jet outlet  332  is controlled by a screw-on cap  324 , which is located screwed onto a thread on the end of the outlet branch  326  of the manifold  330 . The traveled distance of the screw on cap on the thread determines the restriction to the orifice  332  and therefore varies the PEEP. That is, the closer the screw on cap  324  is to the jet outlet  332 , the smaller the gas flow rate through the orifice  334 . The manifold  330  is otherwise as described for the previous embodiments.