US2427419A - Resuscitating apparatus - Google Patents

Description

Sept. 16, 1947.- c. c. RAUSCH 2,427,419

RESUSCITATING APPARATUS Filed J une 30,' 1945 3 Sheets-Sheet 2 INVENl'EIRI Sept. 16, 1947.

REYSUSCITATING Filed June so, 1945 c. c. RAUS'CH APPARATUS 3 Sheets-Sheet 3 A r I 1 Patented Sept. 16, 1947 RESUSCITATING APPARATUS Chester C. Rausch, Newtonville, Mass, assignor to Mechanical Resuscitator, Inc., New York, N. Y., a corporation of New York Application June 30, 1945, Serial No. 602,584

Claims.

This invention relates to resuscitating apparatus for producing artificial respiration in, or assisting in the natural but labored respiration of, persons suffering from asphyxiation, drowning or the like.

Apparatus of this type have heretofore been designed, having for their purpose to force a gas, commonly air and/or oxygen, into a patients lungs and to exhaust the spent gas therefrom by suction. These prior apparatus have, however, been rejected by the medical profession because their use involved an element of risk to the patients welfare. The positive and negative pressures to which human lungs are subjected during natural breathing are extremely low, their maximum being, for grown persons, in the neighborhood of +20 millimeters of mercury column on inhalation of fresh air and millimeters of mercury column on exhalation of the spent air. Insubstantially greater pressures, whether positive or negative, are harmful to human lungs, and pressures of 80 and 40 millimeters of mercury column may so damage the lungs as to prove fatal to the patient. While best results in the resuscitation of a person are obtained when the lungs are subjected to the same pressures as during natural respiration, this is not readily accomplished with the prior apparatus because even a slight deviation from their prescribed manual operation for a certain type of patient entails disproportionately large variations in pressures. There also remains the fact that these prior apparatus are a definite menace in the hands of non-skilled persons who in an emergency may becalled upon to operate them and through ignorance or well-meant, but excessive, zeal badly harm or even kill the patient. The failure of the prior apparatus to safeguard the patient from harm in consequence of their being improperly operated is due to the inadequacy of their valve mechanisms which, though designed with a view toward keeping the pressures within safe limits under all operating conditions, fail to accomplish this.

It is the primary aim and object of the present invention to provide in a resuscitating apparatus a valve mechanism which automatically and Without fail, and regardless of whether the apparatus is operated properly or improperly, controls the pressures well within safe limits so that no harm may ever come to human lungs from this source.

It is also among the objects of the present invention to so devise the valve mechanism that the same, though being unfailingly responsive to pressures well within safe limits, is nevertheless unresponsive to small, harmless pressure fluctuations so as to preserve the volume of gas for delivery to the lungs.

The foregoing and other objects of the invention, together with means whereby the latter may be carried into effect will best be understood from the following description of an illustrative embodiment shown in the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a resuscitating apparatus;

Fig. 2 is a front elevation of a resuscitating apparatus embodying the present invention;

Fig. 3 is a side elevation of the apparatus, broken away in part;

Fig. 4 is a section taken on the line 44 of Fig. 2 and showing most of the apparatus in plan view;

Fig. 5 is a section through the apparatus taken on the line 5-5 of Fig. 4;

Fig. 6 is a section taken on the line 6-45 of Figs. 4 or 5;

Fig. '7 is a section through the apparatus, taken mainly along the line of Fig. 8;

Fig. 8 is a section taken on the line 8-3 of Fig. '7;

Fig. 9 is a fragmentary section through a modified part of the apparatus.

Reference is first had to Fig. 1 for a general understanding of the resuscitating apparatus and its operation. The apparatus comprises juxtaposed pressure and suction cylinders 20 and 21 in which are mounted reciprocatory pistons 22 and 23, respectively, having rods 24 and 25, respectively, which are connected at their outer ends by a handle 26 for unitary reciprocation of said pistons 22 and 23. As will appear more fully in the course of the description, the stroke of these pistons may be varied toregulate the volume of gas to be forced into, and exhausted from, a patients lungs, this regulation being in accordance with the estimated capacity of the lungs determined by the size of the patient. The pressure cylinder 20 is provided at its lower end with an inlet 21 and an outlet 28 with which communicate conduits 29 and 36, respectively. The lower end of the suction cylinder 2| is likewise provided with an inlet 3! and an outlet 32 with which communicate conduits 33 and 34, respectively. The conduit 29 is adapted to conduct air or oxygen, or a mixture thereof, to the pressure cylinder 2|] during an outward or suction stroke of the piston 22, there being provided at one end of the conduit 29 a mixing valve 35 with which communicates a screened atmospheric air inlet 36 and an oxygen tank 3i, the valve 35 being adjustable to admit into the conduit 29 either gas alone, 01" any desired mixture thereof. In the conduit 29 is an inlet valve 32 which will open during each suction stroke of the piston 22 to admit the gas to the cylinder 2? and which will be closed at all other times. On each compression stroke of the piston 22, the gas charge in the pressure cylinder 20 is compressed and, When so compressed, opens a discharge valve 39 in the conduit 30 which remains closed during each suction stroke of said piston 22. The compressed gas then passes through an inhalation tube 40 to a mask 4! which may be of any desired design and fits over the patients face. Provided in a branch 42 of the conduit 38 is a pressure relief valve 43 of such design that it will remain closed within a range of safe pressures in the cylinder 26, and will open under a pressure which might be harmin] to the patient.

At the start of an operation of the apparatus, i. e., when the pistons 22 and 23 are initially moved outwardly after placing the mask ii over a patients face, a quantity of gas is drawn into the pressure cylinder 2!) and a partial vacuum or negative pressure isproduced in the suction cylinder 2|. The partial vacuum thus produced in the suction cylinder ii is sumcient to open an inlet valve 5 in the conduit 33 and thereby establish communication, through an exhalation tube 46, between the cylinder 2i and the mask 4| for the purpose of exhausting the patients lungs of any gas therein. The gas thus drawn into the cylinder 2| is forced from the latter and through the conduit 34 on the next inward stroke of said piston 23. The end of the conduit 34 is preferably enlarged to form a receptacle 41 for a discharge valve 43 which is closed during each suction stroke of the piston 23 to prevent the admission of atmospheric air into the cylinder 2 i, and which is opened by the pressure produced on each inward strok of the piston 23 to permit the exhaust of the waste gas from the cylinder 2|. A conduit 49, which branches from the conduit 33, contains a suction relief valve d and terminates in a screened atmospheric air inlet 5!, When the apparatus is properl functioning, i. e., when the negative pressure in the conduit 33 does not exceed a tolerable maximum during any suction strok of the piston 23, the relief valve 5d will remain closed to prevent the passage of atmospheric air into the conduit 33. However, should the negative pressure in said conduit 33, during any part of a suction stroke of the piston 23, exceed the tolerable maximum, the relief valve as will immediately be lifted from its seat and atmospheric air admitted into the conduit 33 to reduce the negative pressure therein below the tolerable maximum. Either on of the relief valves 43 or 58 will open automaticall and perform its intended function in consequence of a change in the condition of the patients lungs or in consequence of improper operation of the apparatus by the operator.

Through numerous experiments conducted with the present apparatus in an endeavor to find the positive and negative pressures best suited to simulated natural respiration, it has been found that positive pressures in the inhalation tube 40 should not exceed 20 millimeters of mercury column, while the negativ pressures in the exhalation tube 46 should not exceed 1i) millimeters of mercury column.

Referring now to Figs. 2, 3 and 5, the appaflanges til of the cylinders.

tus comprises a base 52 and a head 53 between which the cylinders 26 and El are mounted. The base 52 has secured thereto a stirrup 54 for receiving a foot of the operator when the apparatus is operated while standing on the ground or floor. The base 52 is provided with two annular recesses 59 (Fig. 5) for, receivingthe lower ends of the cylinders 28 and 2! which are preferably turned inwardly to form annular flanges 6Q. Placed in the lower ends of the cylinders are disk-like clamp members 5? which rest on gaskets 5! that are superposed on the annular The clamp members 62 are firmly drawn against the gaskets 6i, and rigidly secure the cylinders to the base 52, by means of bolts 63 which pass through the base 52 and are threadedly received by said clamp members. Fitted into the upper end of each cylinder is a closure member 6 which is secured to the head 53 by screws 65. The closure mem bers e4 ar provided with central hubs 66 which project through the head 53 and provide guide bearings for the piston rods 2 and 25. The upper ends of. the cylinders 25 and 2| are turned outwardly to provide flanges El on which the head 53 rests. The flanges El are drawn into firm engagement with the head 53 by means of screws 69 and nuts ill, the latter also forcing gaskets H against said flanges 6'! to seal off the upper ends of thecylinders. The pistons 22 and 23 are of identical construction, each including packing disks 12 which are suitably clamped to the pistons. The outer ends of the piston rods 24 and 25 are secured to the common operating handle 26 preferably in the manner shown at '13 in Fig. 5.

Prior to using the apparatus on a particular patient the volume of gas to be pumped to, and exhausted from, the lungs is first determined by the patients size and estimated lung capacity. To this end, means are provided to regulate the stroke of the pistons in accordance with the estimated lung capacity of the patient. These means comprise a dial plate (Figs, 4 and 5), secured by screws 8'! to the top of the head 53. The dial plate 68 is provided with graduations 87.2 with which are associated suitable indicia denoting the volumes and the number of strokes per minute of the pistons for different types of patients. The indicia may be impressed or inscribed on the dial plate 86, and may be grouped in accordance with the following table:

An additional graduation 82 is preferably provided on the dial plate 853 to designate a lock position in which the pistons 22 and 23, are locked in their cylinders in a manner explained hereinafter. Rotatable in an annular recess 85 in the head 53 and retained therein by the dial plate 83, is an index disk 85 (Fig. 5) through which the piston rod 24 extends centrally thereof. The index disk at carries a pointer 81 which moves past the graduations 82 when said index disk is turned. The index disk 86 further carries a spring-pressed latch 88 which is adapted to register with any one of several apertures 89 in the piston rod '24 on each suction stroke of the pistons 22 and 23 to limit the stroke to a prede- 'manent communication with the passage termined length. There are as many apertures 89 in the piston rod 24 as there are graduations 82 on the dial plate 89, and these apertures 89 are spaced longitudinally of, and arranged spirally about, the piston rod 24. In Fig. 5, the latch 88 is shown in registry with the aperture 89 which corresponds to the setting of the index disk 86 for an Average adult (Fig. 4). With the index disk 86 thus set, the latch 88 snaps, on the outward or suction stroke of the pistons, into the aperture 89' to prevent further outward movement of said pistons beyond the cylinder volume for an average adult, i. e., 100 cc. On turning the index disk 86 so that the pointer 8.1 thereof aligns with the Lock graduation 82, the latch 88 will, on the inward stroke of the pistons, register with the aperture 89 (not shown) which is nearest the handle 26, and lock the pistons in their innermost position. Preferably, the pistons 22 and 23 are thus locked in their respective cylinders when the apparatus is not in use. To ready the apparatus for use, the piston rod 24 is released from the latch 88 by withdrawing the latter from the aperture 89 in the former, and the index disk 86 is turned so as to align the pointer 81 with the graduation 82 which is most appropriate for the particular patient on which the apparatus is to be used. Only one other aperture 89 is shown in the piston rod 24 in Fig. 5, the same being longitudinally spaced and angularly displaced from the nearest aperture 89 thereabove. On turning the index disk 86 to bring the latch 88 into longitudinal alignment with the aperture 89', for instance, this bein the aperture for the longest stroke in the operation of the apparatus, the pointer 81 on the index the apertures 89 shown in Fig. 5, so that no two apertures 89 are longitudinally aligned and they are all so coordinated that, on alignment of the latch 88 with either one of these apertures 89,

the pointer 81 is adjacent the proper graduation 82 on the dial plate 89. The forward end of the latch 88 is bevelled as at 99 (Fig. 5) so that the same will never interfere with the inward strokes of the piston 23, but will stop the latter on its outward strokes on registering with any one of the apertures 89. To prevent accidental turning of the index disk 86 in any one of its set positions, the same carries a spring-urged ball 9I which is adapted to spring into suitable depressions 92 in the head 53 and yieldingly lock the index disk in these positions.

Provided in the base 52 are suitable passages which connect the pressure cylinder 29 with a nipple 95 and the previously mentioned air inlet '36 (Figs. 3 and 6), as well as with valve chambers 96 in the base 52 (Fig. 8). More particularly, the clamp member 62 in the pressure cylinder '29- is provided with a passage 91 (Fig. 5) which provides communication between the interior of said cylinder 29 and an annular chamber 98 in the base 52. The nipple 95, which is threaded into the base 52 (Fig. 6) and connected through a suitable hose connection (not shown) with the oxygen bottle 31 (Fig. 1), communicates with the chamber 98 through passages 99 to I91, inclusive (Figs. 6, 7 and 5) while the air inlet 36 is in per- (Fig. 6). The valve chambers 96 (Fig. 8) compassages I98, I99 and H9 in the base 52 (Figs. '7 and 8) and through the passage 91 in the clamp member 62' (Fig. 5). The base 52 is provided with further passages which connect the suction cylinder 2I with an inlet duct III (Fig. 8) and with the valve receptacle 41 (Fig. 5) previously mentioned in connection with Fig. 1. More particularly, the inlet duct III communicates with the suction cylinder 2| through passages H2 and H3, valve chambers H4, and passages H5 and I I8 in the base 52 (Figs. 8 and 7) and through a passage H1 in the clamp member 62" in said cylinder 2I (Fig. 5), while the valve receptacle 41 communicates with the cylinder 2| through passages II8 and H9 in the base 52 and through the passage H1 in the clamp member 6.2 (Fig. 5)

The mixing valve 35, previously mentioned in connection with Fig. 1, is contained within the base 52 (Figs. 6 and 7) in a position therein to control the flow to the pressure cylinder 29 of air from the inlet 36 and of oxygen or another suitable gas from the nipple 95. The mixing valve 35 is in the form of a plug I29, rotatable in a bore I2I in the base 52 and, provided with a peripheral port I22 (Fig. 6) which is so arranged with respect to the passages I99 and I9I that, as the plug is rotated to reduce the size of either one of these passages, the other passage is proportionately increased, or if the plug is rotated to completely shut oiT either one of these passages the other passage is completely open. However, in no event may both of the passages I99 and I9I be closed at the same time by the plug I29, there being suitable stop means provided (not shown) which limit the rotation of the plug in this respect. The valve plug I29 i provided on the outside of the base 52 with a handle I24 (Fig. '7) and with a graduated dial I25 (Fig, 3) which is associated with a pointer I26 and by meansof which the proper volume of air or mixture of air and oxygen may be regulated. A springpressed ball I21 (Fig. 7) in the base 52 is engageable with recesses I28 in the rear face of the dial I25 yieldingly to lock the latter in its set positions. Depending on the setting of the valve plug I29, air or oxygen, or a mixture thereof, passes, during a suction troke of the pistons, through the port I22 (Fig. 6) into the passage I92 and opens an inlet valve I29 in the passage I93, whereupon the gas may enter the lower end of the pressure cylinder 29 through the passages I94, I95, I98, I91 and 91 (Figs. 5 and 6). The inlet valve I29 is in the present instance in the form of a ball which normally rests on a conical seat I39 in an insert I3I in the passage I93, and is limited-in its lift by a stop I32 on a screw plug I33. This valve serves to prevent air or gas being forced back into the passage I 99 on the down stroke of the suction piston 29.

The valve chambers 96 in the base 52 (Fig. 8) communicate with a nipple I35 through passage I38, I31 and I38 in a casing I39 which is secured-to the top of the base 52 by bolts I4, there being a gasket MI interposed between said casing I39 and base 52. The nipple I35, which is screw-threaded into the passage I38, communicates with the face mask H through theinhalation tube 49 (Fig. 1).

On the inward or compression stroke of the pistons, the 'gas previously drawn into the pressure cylinder 29 is forced from the same through the passages 91 (Fig. 5), H9, I99 and I98 (Figs. 7 and 8), and opens inlet valves I45 in the valve chambers 96, whereupon th gas passes'to the 7 face mask 4|, through the passages I36, I31 and I38, thence through the nipple I35 and the inhalation tube 40. The inlet valves I45 are in the present instance in the form of balls (Fig. 8) which normally rest on conical seats I46 provided by inserts I41 in the valve chambers 96.

The lift of these valves I45 is limited by the ends I48 of a spring clip I49.

Also secured to the top of the base 52 by bolts I50 is another casing II (Fig. 8), having a passage I52 which provides communication between the inlet duct I II in the base 52 and a nipple I53 which communicates with the face mask 4| through the exhalation tube '46 (Fig. 1). A gasket I54 is interposed between the casing I5I and base 52. Air or any other gaseous content of the patients lungs is, on each outward or suction stroke of the pistons, drawn through the face mask 4| and exhalation tube 46 (Fig. 1) to the nipple I53 (Fig. 8), thence through the passages I52, III, H2 and H3 and, after opening inlet valves I55 in the valve chambers I I4, through the passages H5, H6 and 1 (Figs. 8, 7 and 5) to the interior of the suction cylinder 2|. The inlet valves I55 are in the present instance in the form of balls which normally rest on conical seats I56 provided by inserts I51 in the valve chambers H4.

On the inward stroke of the pistons, air or any other gaseous content of the patients lungs, previously drawn into the suction cylinder 2|, is forced from the latter through the passage H1, H3 and H9, and opens the outlet valve I56 to escape into the atmosphere. The outlet valve I58 is preferably ball-shaped and i restricted in its lift by a pin I59.

Provisions are made to prevent in the cylinders 20 and 2| the creation of excessive positive and negative pressures, respectively, which might be harmful to the patient. To this end, positive and negative pressure relief valve units I60 and |6| (Figs. 2 and 8) are provided on the casings I39 and I5I, respectively. The relief valve unit I60 provides a valve chamber I62 and an auxiliary cylinder I63, the former being formed by a sleeve I 64 in the casing I39 and the latter by a cylindrical liner I65 in a tubular member I66 which is screwed with its bottom end into the casing I39. Interposed between, and separating, the valve chamber I62 and auxiliary cylinder I63 is a plug I61 which serves as a guide for the stem I68 of a relief valve I69 the face I of which normally rests on a seat I1I, provided by an insert I12 in the valve chamber I62. The valve chamber I62 is vented through an opening I13. end of the tubular member I66 threadedly receives a cap I14 by means of which the liner I65, plug I61, sleeve I64 and insert I12 are retained in end-to-end engagement and firmly secured to the casing I39. A gasket I is preferably interposed between the liner |65 and cap I14. Slidable in the cylinder I63 is a plunger I16 which is retained by a nut I11 on an annular shoulder I18 of the valve stem I68 and, hence, is movable with the valve I69. Interposed between the plunger I16 and a plug I19 in the cylinder I 63 is a preloaded compression spring I80 which yieldingly urges the valve I69 against its seat "I. The plug I19 is slidable in the cylinder I63, and the compression of the spring I90 may be regulated by a set screw IBI in the cap I14. The valve stem I 68 is centrally recessed as at I82 and has a transverse passage |83 to provide communication between the passage I36 and the lower side of the cylinder I63.

The upper Should, durin any part of an inward or compression stroke of the pistons 22 and 23, the pressure of the gas in the passages I36, I31 and I38, with which the inhalation tube 40 communicates through the nipple I35, exceed What is considered a safe pressure limit of 20 mm. of mercury column, for instance, the excessive pressure acts on the face I10 of the relief valve I69 and also on the plunger I16 in the cylinder I63 and lifts said valve to provide, communication between the passage I36 and the vented valve chamber I62 until the pressure drops to the safe limit. While the pressure in the passages I36, I31 and I38 will soon drop when the relief valve I69 opens, due to the relatively large escape area between the valve seat HI and the open valve I69, the excessively compressed gas in the cylinder I63 does not as quickly escape through the relatively narrow passage I82, I83 in the valve stem I69, wherefore the cylinder I63 acts also as a dash pot for the relief valve I69 on its closure. The dash pot effect upon the relief valve I69 may even be enhanced and regulated by restricting the cross-sectional area of the recess I82 in the valve stem I69 in advance of the transverse passage I83 therein by means of an adjustable needle valve I85.

The relief valve unit |6| comprises a valve chamber I and an auxiliary cylinder I9I, the former being formed by a sleeve I02 in the casing I5I and the latter by a cylindrical liner I93 in a tubular member I94 which is screwed with its bottom end into the casing I5I. Interposed between, and separating, the valve chamber I90 and cylinder I9I is a plu I95 which serves as a guide for the stem I96 of a relief valve I91, the face I98 of which normally rests on a seat I99, provided by an insert 200 in the valve chamber I90. Threaded over the top end of the tubular member I94 is a cap 20| which retains the liner I93, plug I95, sleeve I92 and insert 200 in end-to-end engagement and firmly secures them to the casing I5I. A gasket 202 is preferably interposed between the liner I93 and cap 20L slidable in the cylinder |9| is a plunger 203 which is retained by a nut 204 on an annular shoulder 205 of the valve stem I96 and, hence, is movable together with the relief valve I91. Interposed between the plunger 203 and a plug 266 in the cylinder I 9| is a pre-loaded compression spring 261 which yieldingly urges the valve I91 against its seat I99. The plug 206 is slidable in the cylinder I9| and is adjustable therein by a set screw 208 to regulate the compression of the spring 201. The valve chamber I90 communicates through apassage 209 with the passage I 52 which, as previously explained, forms a part of the communication between the face mask 4I and the intake side of the suction cylinder 2|. The face I08 of the seated relief valve I91 is vented through a passage 2I0 and an air inlet 2| I which is preferably screened at 2I2 to prevent the entry of dust and other atmospheric impurities. The valve stem I96 is provided with a central recess 2| 3 and spaced transverse passages 2M and 2|5 which provide communication between the valve chamber I90 and the upper part of the cylinder I9 I.

Should, during any part of an outward or suction stroke of the pistons 22 and 23, the negative pressure in the passage I52, which communicates with the exhalation tube 46 through the nipple I53, exceed what is considered a safe negative pressure of 10 mm. of mercury column, for instance, the excessive negative pressure acts on the relief valve I91 as well as on the plunger 203 and lifts said relief valve from its seat, thereby establishing communication between the vent passage 2H] and the communication line between the face mask 4| and the intake side of the suction cylinder 2| until the negative pressure in said communication line drops to the safe limit.

While the negative pressure or partial vacuum in the passage I52 will soon be reduced when the relief valve I91 opens, due to the relatively large .area between the valve seat I99 and the open valve I91 through which atmospheric air may enter, atmospheric air will not as quickly pass into the cylinder I9I through the relatively narrow passage 213, 2I4, 2I5 in the valve stem I96 and reduce the negative pressure in the cylinder I9I, wherefore the latter acts also as a dash pot for the relief valve I91 on its closure. The dash pot effect upon the relief valve I91 may even be enhanced and regulated by restricting the crosssectional area of the recess 2I3 in the valve stemthe relief valve I69, with the result that the latter is as sensitive to gas pressure as a much larger valve, yet, when open, does not permit the escape of nearly as much gas as the larger valve. Hence, the provision of the plunger I16 in the auxiliary cylinder I63 not only renders the relief valve i69 far more sensitive togas'pressure than its actual size would permit, but'also permits the design of said relief valve in such small dimensions that the amount of gas delivered to a patients lungs is still adequate even when the relief valve is open in consequence of improper operation of the apparatus. Actual tests have shown that the relief valve I69 opens unfailingly at a maximum pressure in the inhalation line of the apparatus of approximately 20 mm. of mercury column and that the pressure in said line hardly increases beyond this maximum even when the piston 22 is stroked with unreasonable vigor. This maximum pressure at which the relief valve I69 opens and which is hardly exceeded in the inhalation line under'any circumstances, is quite harmless to human lungs, wherefore the apparatus may safely be used by an unskilled operator, if an emergency demands this. The small dimensions of the relief valve I69 also make for a condensed construction of the relief valve mechanism. Furthermore, the restricted Passage I82, I83 through the valve stem I68'delays the pressure build-up in the auxiliary cylinder I63 sufficiently so that harmless and often unavoidable momentary fluctuations of pressure near the maximum in the in halation line do not force the relief valve I69 open, thus avoiding any surging of the relief valve between its closed and open positions. The explained delay in the pressure build-up in the auxiliary cylinder I63 has the effect that even on a very rapid increase of the pressure in the inhalation line to and beyond the maximum the area of the relief plunger I16 exposed to the pressure is only gradually subjected to the increasing pressure, with the result that the relief valve I69 is gradually lifted from its seat to an extent sole- ,hands of an unskilled operator.

relief valve I91 between its closed and open posibecome seated lightly and quietly, thus causing hardly any wear to the relief valve over'a long period of use. The explained cushioned performance of the relief valve I69 is also inducive to gradual, rather than abrupt, changes in the pressure in the inhalation line at those times when said valve performs, thus making for an even'flow of gas to the patients lungs under all circumstances L ke advantages are secured by providing the auxiliary cylinder IOI and the plunger 203 in the negative pressure relief valve unit I6 I. Actual tests, have shown that the relief valve I91 opens unfailingly at a maximum negative pressure ,in the exhalation line of approximately 10 mm. of

mercury column, and that the negative pressure in this line hardly increases beyond this maximum even when the piston 23 is stroked with unreasonable vigor. A negative pressure of 10 mm..

of mercury column is quite harmless to human lungs, wherefore the apparatus is safe even in the Surging of the tions in consequence of harmless momentary fluctuations of the negative pressure in the exhala tion line is avoided due to the delayed negative pressure build-up in the auxiliary cylinder I9I through the restricted passage 2I3, 2M, 2I5 in the valve stem I96. The delayed negative pressure build-up in the auxiliary cylinder I 9|, and

the explained dash pot effect of the latter upon the relief valve I91 on its closure, render the performance of the latter valve as cushioned as that of the positive relief valve I69, with the result that the relief valve I91 is hardly worn over a long period of use and the flow of the spent air or liquid from the patients lungs is fairly even under all circumstances.

While the relief valves I69 and I91 are comparatively small in size and accordingly light in weight, their weight is supplemented by that of their respective plungers I16 and 203. This increase in the weight of the relief valves is advantageous inasmuch as a heavier, spring-closed valve will, when subjected to excess pressure, not suddenly surge wide open and fluctuate, but will open more gradually and be more steady when open, than a lighter valve.

Part of the force required to open either relief valve I69 or I91 may be supplied by a compression spring which acts counter to the spring that holds the valve closed. Thus, a compression spring 225 is shown in Fig. 9 which is interposed between the plug I61 and the relief plunger I16 of the positive pressure relief valve unit I60, said spring acting counter to the compression spring I99. With this modification, the force of the valve closing spring I has to be increased to compensate for the counter force from the valve-lifting spring 225.

I claim:

1. In a resuscitator having sucking and blowing cylinders, pistons and valves therefor, and

conduits connecting the cylinders with the pa tient, the combination of, a vented chamber for each of said conduits, a valve in each chamber normally yieldingly closed to shut off said chamber from the connected conduit and opened by excess pressure in the latter, a cylinder having a sealed end into which said valve extends, and a plunger slidable in said cylinder and mounted on 7 said valve, the latter having a passage providing On the other hand, 7 the explained dash-pot effect of the auxiliary cylinder I63 upon the relief valve I69 on its' permanent communication between said conduit and sealed cylinder end.

2. In a resuscitator having sucking and blowing cylinders, pistons and valves therefor, and

conduits connecting the cylinders with the patient, the combination of, a vented chamber for each of said conduits, a valve in each chamber to shut off the latter from the connected conduit when closed, a cylinder having a sealed end into which said valve extends, a plunger slidable in said cylinder and mounted on said valve, and a compression spring in said cylinder bearing with one end against said plunger to close said valve, the latter having a passage providing permanent communication between said conduit and sealed cylinder end.

3. Pressure reliefvalve mechanism as set forth in claim 2, further including another but weaker compression spring in said cylinder also bearing against said plunger and tending to open said valve.

4. In a resuscitator, having two pumps each having an inlet and an outlet, a face mask,and inhalation and exhalation conduits connecting said mask with the outlet of one pump and the inlet of the other pump, respectively, the combination of vented chambers open to said conduits, respectively, a valve in each chamber normally yieldingly closed to shut off said chamber from its respective conduit and opened by excessive pressure in the latter, two cylinders each having a sealed end into which a valve extends, and a plunger in each cylinder mounted on the valve extending thereinto, each valve having a passage providing permanent communication between the sealed end of its respective cylinder and the corresponding conduit.

5. In a resuscitator, having a pump having an inlet and an outlet, and a conduit connecting 'said inlet with a patient, the combination of a ventedchamber open at one side'to said conduit, a valve in said chamber having a stem and being normally yieldirigly closed to shut off said chamber from said conduit and opened by excessive negative pressure in the latter, a cylinder at another s'ide of said chamber into which said valve stem extends, the cylinder end most remote from said chamber being sealed, and a plunger slidable in said cylinder and mounted on said valve stem, said valve having .a passage providing permanent communication between said conduit and sealed cylinder end.

CHESTER C. RAUSCH.

REFERENCES- CITED The following references are of record in the file of this patent:

OTHER REFERENCES The Return of the Pulmotor, Y. Henderson: Science, vol. 98, No. 2556, Dec. 24, 1943, pp. 547-551.

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