some oxygen delivery systems use a constant delivery of oxygen to a patient . the oxygen is supplied at an equal rate during the beginning and ending portions of a breath . when inhaling , the first portion of inspired oxygen goes to the lungs and the last portion of inspired oxygen remains in the patient &# 39 ; s airway to be expelled during exhalation . the last portion of oxygen delivered is therefore wasted . to achieve an efficient use of oxygen , a device is required for applying oxygen only during the first portion of a patient &# 39 ; s inspiratory cycle . breathing patterns in patients with lung disease have inspiratory times of approximately 0 . 5 to 1 . 7 seconds with an average of approximately 1 second . to be efficient , the pneumatic oxygen conserving device 30 should allow a specified volume of oxygen from oxygen tank 35 access to the patient 25 for about 0 . 5 seconds at the beginning of each breath , trailing off to a smaller volume thereafter for about another 0 . 5 seconds to avoid multiple pulse delivery . the pneumatic oxygen conserving device 30 comprises a breath sensor portion 60 for sensing when the patient 25 begins inhaling , a gas delivery timer portion 40 for providing a timed delivery of oxygen to the patient during the first portion of inhalation , a variable flow rate portion 70 for adjusting the volume of oxygen delivered to the patient and tail volume delivery portion 80 for storing and delivering a volume of oxygen to the cannula after the initial inhalation to keep the pressure therein up so that an inhalation is not detected too early thus preventing pulsing of oxygen delivery . see patent wo 99 / 22795 entitled oxygen therapy apparatus having a priority filing date of nov . 4 , 1997 , which is attached hereto and incorporated herein by reference for a device which uses pulsing for oxygen delivery to the patient . the wo 99 / 22795 oxygen therapy apparatus does not have a tail volume delivery portion 80 and therefore creates pulses of oxygen delivered to the patient as shown in fig5 and 6 of the wo 99 / 22795 patent . the pneumatic oxygen conserving device 30 is connected to an oxygen source such as a bottle of oxygen 35 having a regulator 17 thereon for dispensing oxygen at a relatively low pressure such as from about 20 to about 100 psi for use by a patient 25 . although approximately 20 psi is preferred the pneumatic oxygen conserving device can be scaled to operate at any pressure . the patient 25 has a cannula 19 for receiving oxygen from line 12 . when the patient 25 begins to inhale a decrease in pressure draws a vacuum in cannula 19 , line 12 and line 23 , which is connected to the sensing chamber 11 in the breath sensor portion 60 of the pneumatic oxygen conserving device 30 . the drop in pressure in the breath sensing chamber 11 draws the breath sensing diaphragm 10 away from breath sensing seat 16 . the breath sensing diaphragm 10 may be spring loaded by spring 13 to bias the breath sensing diaphragm 10 in the closed position against breath sensing seat 16 . with the breath sensing diaphragm 10 pulled back from the breath sensing seat 16 , oxygen can flow from timing chamber 18 , through connecting tube 8 , to venting chamber 24 , which is vented to the atmosphere by vent passage 9 . the resulting drop in pressure in timing chamber 18 allows gas delivery diaphragm 7 to move away from gas delivery seat 15 allowing oxygen in delivery passage 3 to pass through gas delivery chamber 29 supplying oxygen to gas delivery tube 45 for access to the patient 25 . the timing chamber 18 may have a delivery bias spring 14 for moving the gas delivery diaphragm 7 against gas delivery seat 15 to shut off the oxygen to the patient 25 . when gas delivery diaphragm 7 moves away from gas delivery seat 15 , oxygen flows to the patient 25 for a limited time through the gas delivery chamber 29 of gas delivery timing portion 40 . the gas pressure in delivery passage 3 and gas delivery chamber 29 tends to hold the gas delivery diaphragm 7 open , initially , due to the pressure applied to the diaphragm . once flow commences to patient 25 , from gas delivery chamber 29 , pressure builds in cannula 19 and sensing chamber 11 causing sensing diaphragm 10 block sensing seat 16 with the aid of sensing biasing spring 13 . this is countered by the gas delivery bias spring 14 and pressure building up from oxygen passing through tube 55 , adjustable timing orifice 5 and , tube 57 into the timing chamber 18 to adjustably time the gas delivery through gas delivery seat 15 . the timing orifice 5 has an adjustable opening such that the timing of oxygen flowing through the gas delivery timer portion 40 is variable . the size of timing chamber 18 combined with the orifice size of timing orifice 5 varies the time the timing chamber 18 takes to fill up with gas to a pressure high enough for pushing gas delivery diaphragm 7 up against gas delivery seat 15 thus cutting off the oxygen flow through gas delivery chamber 29 to the patient 25 . to be most efficient , gas should be delivered in the first half of the patients &# 39 ; inspiratory cycle . later delivery would not be effective , because late delivered gas never reaches the lungs . breathing patterns in patients with lung disease create inspiratory times of approximately 0 . 5 to 1 . 7 seconds , with an average of approximately 1 . 0 second . to be efficient , the device should deliver most of the oxygen in 0 . 5 seconds or less . if this timing is used , most patients will still be inhaling when the gas delivery timer portion 40 finishes delivering gas . the volume of gas and the shape of the pulse of gas delivered to the patient is controlled by the variable gas volume delivery portion 70 of the pneumatic oxygen conserving device 30 . typical oxygen delivery wave forms for the oxygen delivered through cannula 19 is shown in fig2 . the wave forms are adjustable for time and volume by use of timing orifice 5 and flow control valve 6 . fig2 shows volumes for different settings of flow control valve 6 . the initial pulse has a sharp rise in flow followed by a steady flow for an adjustable period of time , from about 0 . 4 seconds to about 0 . 5 seconds . the volume of oxygen delivered then drops quickly to a low flow , and tails off slowly to zero , getting to zero at about 0 . 8 to 1 . 3 seconds . by adjusting the flow control valve 6 the volume of oxygen passing into tube 22 can be controlled , thus the flow delivery waveform in fig2 can be adjusted . restricting the flow of oxygen through flow control valve 6 will decrease the volume of oxygen getting to the patient 25 through cannula 19 . in order to avoid a second , ‘ false ’ pulse of oxygen in the event that the patient &# 39 ; s breathing effort is longer in duration than the oxygen delivery pulse , a ‘ tail ’ of oxygen delivery is added after the main pulse . this tail of low flow oxygen shown in fig2 creates a back - pressure in the delivery cannula 19 , shown in fig3 keeping a positive pressure in sensing chamber 11 to avoid a false inhaling signal from being detected . back - pressure measured in two typical cannulas ( one with relatively high resistance to flow , and one with low resistance to flow ) is shown in the graph of fig3 . experience has shown that a typical patient , breathing normally through the nose will create about 1 cm h2o as a peak pressure ( vacuum ) in the cannula . this would imply that the presence of flows in the range of 0 . 2 to 0 . 3 lpm ( with these cannulas ) would create enough back pressure in the cannula that the sensing diaphragm could not be moved by the patient &# 39 ; s inspiratory effort . to accomplish this ‘ tail ’ flow , a reservoir 20 having a volume of about 2 - 5 ml is placed in between the gas delivery diaphragm 7 and the flow control orifice 6 . an orifice 21 of approximately 0 . 010 inch diameter is placed at the inlet to reservoir 20 . when the delivery diaphragm 7 is open , the inlet to reservoir 20 is pressurized to the regulator 17 pressure which is preferably approximately 20 psig . this causes the reservoir 20 volume to be ‘ filled ’ through the inlet orifice 21 . when the delivery diaphragm 7 closes , the inlet orifice 21 to reservoir 20 volume is depressurized , so the gas bleeds back out of the inlet orifice 21 , at a rate of approximately 1 - 2 lpm initially , decreasing as the gas pressure in reservoir 20 is depleted creating the “ tail ” flow in cannula 19 . this back pressure from the “ tail ” is only needed to prevent an new inhalation from being detected until the patient begins to exhale . by varying the inlet orifice 21 and the volume of the reservoir 20 , the profile of the tail can be tailored to optimize the effect . ideally , the total time of the pulse delivery and the tail should be approximately 1 . 5 seconds . in this way , a patient with a breathing rate of 13 per minute ( slow ), and an inspiratory / expiratory time ratio of 1 : 2 would not get a double pulse , because their inspiratory time is approx . 1 . 5 second . on the other end of the scale , a patient breathing at 40 breaths per minute ( quite fast ) would still get a pulse on every breath , because their total breathing cycle is 1 . 5 seconds . in reality , the total time can be less than 1 . 5 second , because a patient &# 39 ; s inspiratory flow decreases throughout their breath , so the time late in a long inspiratory time is not likely to create a double pulse , as there is less negative pressure generated in cannula 19 . although the invention has been described herein as an oxygen delivery system any therapeutic gas delivered to the patient can be used in conjunction with the invention . the sensing of the inhalation , the timing of the gas delivery and the control of the volume of gas can be detected and controlled by means other than those shown . the embodiment shown is for a pneumatic design . cannulas have been used to describe how oxygen is delivered to the patient however masks or other means for oxygen delivery to the patient may also be used with the invention . pistons or other movable barriers can replace the diaphragms in the embodiments shown . obviously , many modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that , within the scope of the appended claims , the invention may be practiced otherwise than as specifically described .
a pneumatic oxygen conserving device for efficiently dispensing oxygen or other gas used during respiratory therapy such that only the first part of the patient &# 39 ; s breath contains the oxygen or other therapeutic gas . a gas delivery device is used which is triggered when the patient begins to inhale . a tail of gas flow is delivered to the patient after the initial inhalation timed period to prevent pulsing of gas delivery to the patient . in this manner gas is only delivered to the patient during the first portion of inhalation preventing gas from being delivered which will only fill the air passageways to the patient &# 39 ; s lungs . by efficiently using the oxygen , cylinder bottles of oxygen used when a patient is mobile will last longer and be smaller and easier to transport . by pneumatically delivering the gas to the patient no batteries or electronics are used .