MEANS FOR DISPENSING A PRE-MEASURED VOLUME OF RESPIRATING GAS

Abstract: A device for administering oxygen and other respi­ rating gases to a patient premeters and temporarily stores single dose quantities of respirating gas and dispenses each dose in synchronization with the patient's inspiratory cycle. A sensor produces a signal upon the onset of each inhalation and a single dose of gas is dispensed to the pa­ tient in immediate response to the sensor signal.

Description: Background of Invention This invention relates generally to apparatus for administering oxygen and other respirating gases to a patient. More particularly, this invention relates to means for administering oxygen or other gases to a patient on an intermittent, respiration controlled, basis. It has become common medical practice to treat patients suffering from advanced stages of chronic obstructive pulmonary diseases by administration of oxygen. Such pulmonary diseases, including chronic bronchitis, emphysema and severe asthma, are one of the fastest rising causes of death in the United States affecting probably more than ten million people. It is estimated that more than 500,000 people in the United States either are routinely receiving oxygen therapy or could benefit from it. Much of this rather expensive treatment is funded by Medicare. The devices which commonly have been used to deliver oxygen to a patient meter the oxygen flow at a fixed rate and deliver a constant stream of oxygen to the patient. Oxygen is received by the patient either through a mask which is placed over the nose and mouth or through a cannula which terminates in nares inserted into the patient's nostrils. In extreme cases, those wherein the patient either cannot breathe on his own or can breathe only with difficulty, a ventilator is often used. A ventilator provides the total respiration needs of the patient rather than providing relatively small quantities of supplemental oxygen as do many respirator systems. A ventilator typically delivers the total tidal volume to the patient through a tight-fitting mask or an endotracheal tube. One example of such a ventilator is described in the Fry patent, U.S. 4,459,982, which delivers a mixture of oxygen and air to a patient. The Fry device employs a single-acting compressor having a cylinder with a mechanically driven piston arranged to reciprocate therein to deliver gas at a flow rate required to satisfy the patient's inhalation rate. Another system for delivering the total tidal volume of respirating gas at a controlled rate to a person in respiratory difficulty is described in the Driskell et al patent U.S. 3,807,446. The device described therein consists of two chambers with each chamber divided into two sections. One section in each chamber is filled with a liquid and the liquid-filled sections of the two chambers are in fluid communication whereby liquid is displaced from one chamber section to the other. The volume of the liquid is set so the displaced volume of liquid equals the desired tidal volume of respirating gas delivered to the patient. A flow regulator is provided in the conduit connecting the two liquid filled sections and that liquid flow regulator determines the flow rate of the gas delivered to the patient. Yet another specialized device developed for use in conjunction with a respirator system is disclosed in the Bushman U.S. Patent No. 3,659,601. The Bushman device comprises a vaporizer for use in a medical respirator to supply a controlled mixture of a breathing gas and a vaporized liquid to a patient during the inspiratory period of the respirator. The device consists of two chambers having a combined volume equal to the patient's tidal volume; the volume of one chamber being adjustable relative to that of the other. One of the chambers us partially filled with a liquid, water for example, so that the gas in that chamber contacts the liquid and becomes saturated. Combining the gas volumes from the two chambers, one saturated with a liquid and the other not, provides control of the degree of liquid saturation of the gas which is then passed to the patient. It has long been recognized that providing a constant flow of oxygen to a patient results in the waste of a substantial proportion of the oxygen supply. The normal breathing cycle consists of an inhalation, an exhalation longer in duration than the inhalation, and then a pause before the next cycle. Oxygen supplied to a patient during the exhalation and pause phases of the respiratory cycle is totally wasted. Devices have been developed to conserve oxygen by regulating the oxygen flow, turning it on and off, in response to the respiratory cycle. Typical of such devices are those of Myers. U.S. Patent No. 4,054,133, and Mon, U.S. Patent No 4,381,002. Each of these patents disclose devices which sense inhalation and exhalation pressures in the nasal cavity of patient and converts those sensed pressure differentials to signals which control the flow of oxygen to a patient. Typically, oxygen flow is started upon the sensing of a negative pressure relative to atmospheric indicating the start of an inspiration period. Oxygen flow is then stopped at a second signal produced by the sensing of a positive pressure relative to atmospheric indicating the start of the expiration period. More recently, Dr. Gerald Durkan clinically observed that only the oxygen supplied during the initial part of an inspiration period was efficiently absorbed by a patient. It is that first inspired portion of oxygen which reaches the alveoli while oxygen supplied during the latter part of an inspiration period remains in non-absorbing areas such as the pharynx, trachea and bronchial tubes. Durkin concluded that supplying oxygen at a high rate, beginning at the start of inspiration but lasting only for a small portion of the inspiration period offered economic and physiologic advantages over those prior techniques which supplied oxygen during the entire inspiration period. As a result of his observations, Durkan developed a respirator system known as the Demand Oxygen Controller which is disclosed in U.S. Patent No. 4,457,303. That respirator system uses a fluidic laminar proportional amplifier to sense the start of an inspiration period. Oxygen flow to a patient is immediately started in response to the sensed inspiration. Timing means, also started in response to the sensed inspiration, stop the oxygen flow after a preset period of time which is shorter than is the inspiration period. As a result, oxygen is supplied to a patient only during the effective, early stages of an inspiration resulting in an oxygen savings of as much as 70% as compared to a continuous flow administration. All of these prior art techniques have one property in common. All determine or control the volume of oxygen (or other respirating gas) delivered to the patient over a respiratory cycle by controlling both the rate at which oxygen is allowed to flow and the time or duration of oxygen flow for each respiratory cycle. Both Myers and Mon teach the starting of oxygen flow upon sensing the beginning of an inspiration and the stopping of oxygen flow upon the sensing of an expiration. Durkin teaches the starting of oxygen flow upon sensing the beginning of an inspiration and stops oxygen flow at the end of a time period which is independent from, and shorter than, the inspiration period. Those prior art devices which connect a rate metered supply of oxygen to a cannula for a predetermined time to effect the desired dose delivery all have the disadvantage that both the rate and duration of flow must be precisely controlled if the dose is to be accurately measured and dispensed. Because of the small quantities of oxygen required per dose (typically about 33cc measured at standard temperature and pressure), it is difficult and expensive on a production basis to provide for the degree of accuracy of flow rate and of timing required to ensure a safe dose efficiently delivered for each breath. An improved and simplified way to dispense an oxygen dose in synchronization with a patient's respiratory cycle provides clear advantages in this art. The Summary of the Invention An apparatus for administering volumetrically metered doses of oxygen or other respirating gases to a patient in synchronization with the respiratory cycle of a patient operates by sensing the onset of an inhalation, generating a signal in response to the sensed inhalation, and using that signal to cause a premeasured volume of the respirating gas to be dispensed from a displacing means. The displacing means used comprises a double acting piston within a cylinder, the volume displaced by piston movement from one end of the cylinder to the other being that of a prescribed single dose quantity of respirating gas. The cylinder is arranged with valve means operating in response to a signal representative of the onset of an inhalation to connect the cylinder ends alternately to a source of respirating gas and to a conduit carrying gas doses to the patient. Gas at source pressure, typically 1.4 kg/cm2 or greater, entering at one end of the cylinder drives the piston to the other cylinder end forcing a single dose quantity of gas out of the cylinder for delivery to the patient while simultaneously storing another single dose quantity of gas at the source-driven end of the cylinder. A subsequent signal indicative of the onset of another inspiration reverses the valve position causing gas at source pressure to enter the cylinder at its other end forcing the stored gas dose out of the cylinder for delivery to the patient while storing yet another gas dose. Delivery of gas doses to the patient is completed during the early stage of an inspiration thus obtaining maximum physiologic advantage to the patient. Description of the Drawings Specific embodiments of the invention are illustrated in the drawings in which: Figure 1 depicts in partial section an embodiment of the invention which employs a double-acting piston as the gas dispensing means; Figure 1A illustrates one means for changing the unit dose of gas delivered by the dispensing means of Figure 7; and Figure 2 schematically depicts a control circuit useful in the embodiment of Figure 7. Description and Discussion of the Invention Various embodiments of this invention will be described and discussed in detail with reference to the drawing figures in which like reference numerals refer to the same component or part illustrated in different figures. Figure 1 depicts an embodiment of the gas supply apparatus of this invention which employs a double-acting piston as the gas dispensing means. In this embodiment, displacer 21 comprises a closed cylinder 90, shown in section, and having at least one removable end cover 91. Disposed within cylinder 90 is piston 92 which is free to reciprocate back and forth from one end of cylinder 90 to the other as is shown by the arrows. Piston 92 preferably has sealing rings 93 or other means to minimize gas leakage or blow-by between the piston and cylinder walls. It is short in length as compared to the length of cylinder 90 and preferably is of low weight construction. The piston and cylinder are sized relative to each other so that the free space or volume, within the cylinder with the piston present is equal to the unit dose of oxygen or other respirating gas which it is desired to administer to a patient at each breath. The size of a unit dose may be changed by removing end cap 91 from cylinder 90 and replacing piston 92 with a similar piston but of either shorter or longer length. This has the advantage of preventing the patient from changing the prescription without the physician's knowledge. As is shown in the drawing, there are provided two, three-way, two position valves, 95 and 96, ganged together by connecting means 97. Valve 95 includes a common port 95a and two option ports 95b and 95c. Likewise, valve 96 includes common port 96a and option ports 96b and 96c. Common port 95a of valve 95 communicates via line 22 with the interior of cylinder 90 at one end thereof while common port 96a of valve 96 communicates via line 22a with the interior of cylinder 90 at the other end thereof. Respirating gas supply line 23 branches upstream of the valves with one branch 23 communicating with option port 95b of valve 95 and the other branch 23a communicating with option port 96c of valve 96. Cannula 26 also branches downstream of the valves with one branch 26 connecting to option port 95c of valve 95 and the other branch 26a connecting to option port 96b of valve 96. Control circuit 31 is arranged to receive a signal from sensor 28 via transmitting means 30 upon the detection by sensor 28 of the onset of an inhalation. Upon being triggered by a signal received from sensor 28, the control circuit 31 acting through power circuit 32 causes valves 95 and 96 to move from one position to the other position. Each dose of oxygen must be delivered in synchronization with the patient's inspiratory cycle. To accomplish that synchronous delivery necessarily requires an extremely sensitive and fast responding sensor 28 which is operably connected to cannula 26 by means of line 29 so that, for example, it may monitor and respond to slight changes of pressure occurring in the nasal cavity of the patient. Exemplary sensors meeting those requirements and known in the prior art include a spring-loaded diaphragm sensor as shown by Myers in U.S. Patent No. 4,054,133 and fluidic devices employing laminar proportional amplifiers as shown by Mon in U.S. Patent No. 4,381,002 and Durkin in U.S. Patent No. 4,457,303. A thermistor-type sensor responsive to directional gas flow may also find use in the devices of this invention. Also, a sensitive pressure-to-electric switch, such as the Microswitch, Series 160, may be employed. Following the operation of the device through one complete respiratory cycle, Figure 1 shows the source of respirating gas, typically oxygen, connected through valve 95 to the interior of cylinder 90 at the left end thereof. The other end of cylinder 90 is in open communication with the cannula 26 by way of line 22a, valve ports 96a to 96b, and line 26a for the delivery of a dose of oxygen to a patient through nares 27. Because the oxygen supplied through line 23 is at an elevated pressure, typically about 1.4 kg/cm² (20psig), it forces piston 92 to the right end of cylinder 90 pushing out the oxygen in that end of the cylinder through line 22a. When the piston reaches the right end of the cylinder 90, it stops and the free space, or cylinder volume, to the left of the piston is filled with oxygen at a pressure equal to the supply pressure. Upon detection by sensor 28 of the onset of the next inhalation, control circuit 31 causes each of the valves 95 and 96 to move to its other position whereat port 95a is now connected to port 95c and likewise with valve 96 wherein port 96a is now connected to port 96c. In this second position, oxygen at source pressure is routed to the right end of cylinder 90 by way of line 23a to valve port 96c, out of the valve at port 96a and through line 22a to the interior of cylinder 90. Also, the left end of cylinder 90 is now connected with cannula 26 by way of line 22, valve ports 95a and 95c and line 26 for delivery of an oxygen dose to the patient. Piston 92 is forced to the left end of cylinder 90 by pressure of oxygen from the supply line and the oxygen pressure within the cylinder 90 at the free space to the right of the piston thereafter reaches equilibrium with the oxygen supply. Upon detection by sensor 28 of the onset of the next inhalation, valves 95 and 96 are caused by control circuit 31 to return to their original position and the cycle begins anew. It has earlier been noted that the volume of a unit dose dispensed by the device of Figure 1 can be changed by replacing piston 92 with a similar piston of either greater or shorter length. Figure 1-A illustrates another approach to changing the unit dose in which there is provided an adjustable length piston 101. Piston 101 comprises two end members, 102 and 103, having sealing rings 104 and 105 respectively. A threaded connecting rod 106 is disposed between the two end members and is arranged so that the distance between end members 102 and 103 may be adjusted thus changing the overall length of piston 101. Turning now to Figure 2, there is shown a control circuit which has particular use with the embodiment of this invention illustrated in Figure 1. In the circuit shown, sensor 28 is arranged to produce a signal only upon the detection of the onset of an inhalation. That signal 30 is transmitted to a flip-flop relay 120 and is also transmitted to a time delay relay 121. The signal 30 triggers flip-flop relay 120 activating solenoid coil 123 of flow control valve 124 by way of the circuit comprising conductors 125 and 126, power supply 127 and conductor 128. Flow control valve 124 may be a pair of ganged three-way valves as shown in Figure 1. Trigger signal 30 also activates interval timer 121 which, upon receiving the trigger signal initiates a timed cycle of power from power supply 127 by way of conductors 129, 130 and 131 causing solenoid coil 132 to change the position of valve 133. Valve 133 is a simple two-way isolating valve which is inserted into line 29 connecting sensor 28 with cannula 26. Valve 133 is arranged to be in the closed position while solenoid coil 132 is activated by interval timer 121. The power pulse produced by interval timer 121 is long enough, typically about 1/2 second, to shield the sensor 28 from the rush of respirating gas released upon the onset of an inhalation by movement of flow control valve 124. At the end of timed interval, solenoid 132 is de-energized and valve 133 returns to the open position re-connecting sensor 28 with cannula 26. In each and all of the embodiments of this invention, the cannula, or other gas delivery means to the patient, is never in direct communication with the source of the respirating gas. Prior art devices can be generally characterized is providing direct communication, or an open flow path, between the source of the respirating gas and the patient while gas delivery is in progress. Pre-metering and temporarily storing each unit dose of respirating gas, as the devices of this invention do, inherently provides safety features not present in conventional gas delivery systems. As has been described in relation to the various embodiments, this invention provides both an improved and a simplified way to dispense gases to a patient by effecting a known displacement. The duration of delivery can still be relatively short so as to improve the patient's utilization of the dose but the duration of delivery does not need to be precisely controlled. In fact, by using the method and apparatus of this invention, the time of delivery will tend to be non-linear with variations in prescribed dosages.

Claims: A device for supplying doses of respirating gas to a patient in synchronization with the respiratory cycle of the patient, said device having a source of respirating gas (24, 25) at a pressure greater than atmospheric; a gas delivery system (21) for supplying doses of respirating gas to the patient; means connecting the gas delivery system to the respirating gas source; gas flow routing means for conveying doses of respirating gas from the gas delivery system to the patient; and sensing means (28) for sensing the onset of inhalations of the patient and for producing signals in response to said sensing; characterised in that said gas delivery system is a volumetrically metered gas dose delivery system comprising a cylinder (90) closed at both ends and having a piston member (92) disposed therein, said piston member being shorter than said cylinder and movable from a first end of said cylinder to the second end of said cylinder under the pressure of gas introduced at the cylinder ends, the displaced volume of said piston movement being that of a single dose quantity of respirating gas at source pressure to be supplied to the patient; a first gas supply line (22, 23) communicates between said source of respirating gas and both the first and second ends of said cylinder; a second gas supply line (22, 26) is arranged to convey doses of respirating gas from both the first an second ends of said cylinder to the patient; and multi-ported valve means (95, 96) are interposed in both said first conduit means and said second conduit means and arranged to move from a first position to a second position and from said second position back to said first position in response to signals representative of inhalations of the patient produced by said sensing means, said valve means in its first position connecting the source of respirating gas to the first end of said cylinder and connecting the second end of said cylinder to said second conduit means, said valve means in its second position connecting the source of respirating gas to the second end of said cylinder and connecting the first end of said cylinder to said second conduit means whereby respirating gas at source pressure drives said piston from the first end toward the second end of said cylinder when said valve means is in its first position, thereby forcing a single dose quantity of respirating gas from the second cylinder end for delivery to the patient while metering and storing another single dose quantity of respirating gas at the first cylinder end until a subsequent signal representative of another inhalation of the patient causes said valve means to move from its first position to its second position whereby respirating gas at source pressure drives said piston from the second toward the first end of said cylinder thereby forcing said stored single dose quantity of respirating gas from the first cylinder end for delivery to the patient while metering and temporarily storing yet another single dose quantity of respirating gas at the second cylinder end. A device according to claim 1, wherein said sensing means are adapted to respond to slight negative pressure changes indicative of the onsets of inhalations and to produce signals in response to said negative pressure changes. A device according to claim 2, wherein said signals are transmitted to a flip-flop relay (120) having a power supply (127) associated therewith; wherein said valve means are operated by a solenoid (123); and wherein successive transmitted signals cause said relay and said solenoid to move said valve means between its first position and its second position. A device according to claim 3, wherein a third gas supply line (29) connect said sensing means to said second conduit means, said third conduit means including closure means (133) adapted to isolate said sensing means from said second conduit means for a brief interval after a signal is transmitted to said relay thereby shielding the sensing means from the blast of respirating gas displaced from said cylinder upon movement of said valve means between its first position and its second position. A device according to claim 4, wherein said closure means comprise an on-off valve operated by a solenoid (132) and wherein each said signal transmitted to said relay is transmitted as well to an interval timer (121) which activates said on-off valve. A device according to an preceding claim, wherein said cylinder has at least one removable end cover (91) and wherein pistons of different length are adapted to fit therein, the volume displaced by a single stroke of the piston being that to hold a prescribed single dose quantity of respirating gas at source pressure.

Inventors: PERKINS, WARREN E.
Applicants: PERKINS, WARREN E.
Application year: 1987
Main classification: A61M16
IPC codes: A61M16