The valve may be used to supply a small dose of therapeutic gas, such as NO, or diagnostic gas, such as SF6, into the breathing circuit for the patient. The valve has a reduced internal volume to achieve accurate measurement of pulse volume. The present invention also relates to a special gas dose delivery unit and respiration equipment incorporating such a valve.

U. S. Patent application 08/841,466 filed April 22,1997 by the present applicant describes an apparatus and method for the pulsatile dosing of a specified, special gas into a patient airway. The dose volume is defined by the dose pulse length and the flow occurring during the pulse. The volumes to be delivered may range from 10 yl up to 20 ml. The pulse lengths may vary from 100 ms up to ls, and the flows from 0.05 ml/s to 20 ml/s.

Proportionally adjustable valves can accommodate this flow range.

A problem with these valves is, however, in their dynamic behavior. They may not be sufficiently rapid, particular- ly when considering the smallest flows, where the fastest response is needed. Thus the system may have difficulties in dosing gas pulses of the smallest volumes.

In current state of the art, the dynamic range problem has been dealt with by diluting the special gas to enlarge the actual dose volumes to be delivered. European patent document EP 659,445 discloses a nitric oxide (NO) delivery system where this dilution can be done on"on fly"when the"system is otherwise unable to reduce the concentration to the desired point."The technique employs an additional diluting gas (nitrogen) source and a diluted NO concentration sensor for controlling the dilution.

The disadvantages of this system are the increased complexity, size, weight, and cost caused by the diluting apparatus and instrumentation. Alternatively, the dilution may take place by selecting a tank of an appropriate concentration for the current need. A range of tank concentrations are presented, e. g. in U. S.

Patent 5,531,218 and European patent document EP 640,357. If the concentration in the tank is inappropriate for the treatment of the patient, it may be necessary to change tanks. Cumbersome

maneuvers may be required when a need to change the concentration arises during the treatment of the patient.

A technique for creating small pulses is presented in patent document WO 95/10315. The delivery system shown in the document has a constant 12 1/min flow source and an on/off switch valve to create pulses. This kind of construction is cost- effective and simple. The low limit for the doses is set by the valve control time resolution. The system can provide pulses with a minimum width of 5 ms, corresponding to 1 ml of volume.

However, even this volume is large compared to portions of the specified pulse volume range noted above. Furthermore, user control over the pulse amplitude and width are lost when pulse width is employed for dose control and the flow rate is fixed.

Pulse width control is needed when a need to spread out the dose over a definite period of inspiration exists. The flow control may be beneficial in adjusting the local effectiveness of the treatment.

For safety reasons, a special gas dose delivery system should have two redundant means to prevent unintentional dosing of the patient. The apparatus described in applicant's earlier application and in European patent document EP 659,445 use a proportionally adjustable solenoid valve for the flow regulation, whereas U. S. Patent 5,561,218 shows a control valve which could also be a proportional valve, but the disclosure of the patent does not have a detailed description. All of these systems do have the safety redundancy in the form of an on-off type solenoid valve in addition to the proportional valve. A fast response time is characteristic of an on-off solenoid valve.

The proportional adjustability of the proportional valve and the fast dynamic behavior of an on-off valve suggest the use of the proportional valve as a variable orifice and the on-off valve for delivery of the doses of gas.

However, a problem in such an arrangement comes from the volume existing between the proportional valve and the on-off valve. This volume comprises the internal volume of the valves and the intermediate channel volume between the valves. Due to the construction of such valves, the intermediate channel volume is not likely to be less than 20 yl. The internal volumes of the valves depend on the valve type, but for commercially available

miniature valves, it starts from about 40 gel. These volumes, which together comprise easily 100 pl, represent a pressure chamber for an uncontrollable dose of gas. The quantity of such a dose is dependent on the pressure chamber volume and the chamber pressure. As a result of the foregoing, the dose volume becomes uncontrollable when using the proportional valve as a variable orifice and the on-off valve for delivery of the doses.

The flow measurement of the dose has to be carried out upstream of the on-off valve to avoid the pumping effect on the flow measurement caused by the variable pressure conditions in the breathing circuit. The proportional valve acts as a flow restric- tor. The more it restricts the flow the less the volume of the pulse. Downstream of the proportional valve are the uncontrolla- ble dose volume and the on-off valve. Upon opening of the on-off valve, the pressure existing in the intermediate channel volume discharges and the pressure rapidly equilibrates with the pressure downstream of the on-off valve, which is practically near ambient pressure. After closing the on-off valve, the intermediate chamber will be reloaded with gas and re-subjected to the pressure of the gas. This re-application of the pressure takes place slowly through the orifice of the proportional valve. The reload volume can be detected and measured by the dose flow sensors, but only after the dosing has taken place.

At sea level ambient pressure, the upstream pressure of the delivery system is preferably 90 kPa overpressure or more, e. g. 150 kPa, to guarantee sonic flow in the discharge orifice when the valve opens for gas flow. The advantage of such a flow is the elimination of the effect of the variable pressure condition in the breathing circuit on the dose flow. With 100 kPa overpressure in the 100 yl pressure chamber formed in the valves and intermediate channel, the uncontrollable dose will become 100 y boy volume. This represents a volume tenfold greater than the minimum dose requirement noted, but could be even more depending on the valves used, and represents the minimum dose volume that can be delivered with such an arrangement.

Inverting the order of the proportional and on-off valves, to place the on-off valve upstream of the proportional valve would help in regulating the dose volume. However, the dose timing would be totally lost, the dose pulse"leaking"little by

little through the orifice of the proportional valve over a relatively long time period.

BRIEF SUMMARY OF THE INVENTION The object of the present invention is to overcome the problem heretofore caused by the intermediate chamber volume existing between the separate proportional and dosing valves by providing a unitary, variable orifice, pulse valve combining the different characteristics previously provided by the two separate valves. When operating the valve of the present invention, a variable orifice is used to adjust the flow through the valve.

The variable orifice is adjusted by a proportional solenoid to match the flow with the required dose volume to be delivered.

This orifice may be adjusted on a pulse to pulse basis or even within the pulses. Advantageously the valve is not closed between the pulses, thereby to avoid the need for large and, hence, slow changes. The pulse valve is used to enable and disable the flow through the variable orifice to match the needs of the pulsatile delivery.

In the valve of the present invention, the intermediate volume between the variable orifice and the pulse orifice can be easily reduced down to 2 yl and the internal volume of the valve minimized. Thus, with 100 kPa overpressure, the uncontrollable dose of gas will be 2 gl, complying with the minimum anticipated dose in a highly satisfactory manner.

Very small dose pulse volumes may be trapped in the internal volume of the outlet portions of the valve. To eliminate this, it is advantageous also to minimize the volume of these portions. Further, a carrier gas for the special gas doses may be conducted through the outlet portion of the valve and out the valve discharge to flush the special gas doses out of the valve.

The present invention is also directed to providing a special gas dose delivery unit and respiration equipment incorpo- rating such a valve.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING The invention will be further understood by reference to following detailed description taken in conjunction with the drawing in which: FIG. 1 is a cross sectional view of a variable orifice pulse valve of the present invention;

FIG. 2 is a cross sectional view of a modification of the variable orifice pulse valve of the invention; and FIG. 3 is a cross sectional view of a further modifica- tion of the variable orifice pulse valve of the invention; FIG. 4 is a schematic diagram showing a special gas dose delivery unit and patient respiration equipment incorporating a variable orifice pulse valve.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows the structural elements of the variable orifice pulse valve 1 of the present invention in cross section.

The special gas to be dosed is supplied in the inlet connector opening 2 of variable orifice pulse valve body 10. This opening leads to the variable orifice chamber 3 where a variable orifice member 4 and the orifice 5 are located. The variable orifice chamber 3 is defined by the variable orifice pulse valve body 10 and the variable orifice housing 11. Seal 12 is provided between body 10 and housing 11. The variable orifice member 4 is located at the end of a ferromagnetic stem member 7 located in variable orifice housing 11. Variable orifice member 4 may incorporate a resilient seal for coacting with orifice 5, if desired. Ferromag- netic stem member 7 will be located in the magnetic field produced by solenoid coil 8 when supply cables 9 are connected to a source of electrical current. Variable orifice pulse valve 1 also includes a spring 6, shown in annular plate form in FIG. 1, surrounding and secured to stem member 7, and retained between body 10 and housing 11. Spring 6 could as well be of another suitable type.

An electrical current in solenoid coil 8 creates, through the resulting magnetic field, an opening force on the stem member 7 and variable orifice member 4 tending to move stem member 7 to the left in FIG. 1. This opening force acts against the force of spring 6. The larger the current in solenoid coil 8, the larger the force, and the larger the opening between the member 4 and the orifice 5 so as to vary the size of the orifice.

While FIG. 1 shows use of solenoid coil 8 and spring 6 to control the movement of stem member 7, as shown in FIG. 2, it is also possible to use two, opposing solenoids 8,8A connected to supply cables 9,9A, if desired, with suitable modification of stem member 7.

The gas flows through the variable orifice 5 to the intermediate chamber 13 formed in valve body 10. The volume of intermediate chamber 13 is minimized in the invention to a level which is negligible or small with respect to the volumes involved in the application to which the valve is put. From the intermedi- ate chamber 13, the flow path continues through the pulse valve orifice 14 into outlet chamber 15. The opening and closure of the pulse valve orifice 15 is controlled by a pulse valve member 16 at the end of a ferromagnetic stem member 17. Pulse valve member preferably has a seal formed of resilient material for coacting with orifice 14. Ferromagnetic stem member 17 is moveable within pulse valve housing 21 under the effects of an opening force caused by the magnet field created by solenoid 18 when electrical current is applied to the solenoid through supply cables 19 and a closing force caused by pulse spring 20. Pulse spring 20 may be a coil spring acting on the end of stem member 17 opposite pulse valve member 16. The outlet chamber 15 is enclosed between valve body 10 and pulse valve housing 21 which is sealed with the body by seal 22. The outlet chamber 15 has an outlet connector opening 23. This opening is the end point of the variable orifice pulse valve flow path that commences with the inlet connector opening 2.

The movement of stem member 17 may be controlled by two solenoids in the manner shown in FIG. 2, if desired.

To optimize the construction of variable orifice pulse valve 1 for minimal volume of intermediate chamber space 13, it is advantageous to make the intermediate chamber in the form of a straight channel having the variable orifice 5 at one end and the pulse valve orifice 14 at the other end. This suggests the positioning of the stem members 7,17 and the solenoids 8,18 in the aligned manner presented in FIG. 1.

The valve 1 shown in figure 1 also has optionally another connector opening, flush flow inlet connector opening 24, leading to outlet chamber 15. As hereinafter described in detail, this inlet connector opening supplies a carrier gas for the pulse doses that enhances the washout of the pulse doses from the valve into the discharge from the valve. The volume of the outlet chamber 15 may be as much as 100/il. Thus very small pulse doses are easily trapped in this volume and the accuracy of dose measurement will be lost. A supply of carrier gas avoids this

problem. Alternatively, the flush flow inlet connector opening may be located at the end of pulse valve housing 21 as shown in FIG. 3 by the numeral 24a. This positioning will further enhance the washout when the carrier gas flow sweeps throughout outlet chamber 15.

FIG. 4 shows a special gas dose delivery unit 50 and respiration equipment incorporating the above described variable orifice pulse valve 1. The respiration equipment includes respirator 103 used to ventilate the lungs of a patient. Variable orifice pulse valve 1 may be used to supply, or"dose", a special gas into the breathing gases provided to the patient by the respirator 103. A typical special gas is nitric oxide (NO), used <BR> <BR> <BR> for improving lung perfusion and thus patient 02 uptake raising blood oxygen saturation. Other special gases that may be used are SF6 (sulphur hexa-fluoride) for measuring the lung functional residual volume (FRC) and nitrous oxide (N20) for measuring lung capillary blood flow.

Respirator 103 is connected to a breathing circuit 109 of the respiration equipment comprising an inspiratory limb 109a, a Y-piece connector 109b, a patient limb 109c, and an expiratory limb 109d. A flow measuring element 102 may be connected in patient limb 109c. The construction and operation of the respira- tor shown in FIG. 4 is more fully described in applicant's earlier patent application 08/841,466, noted above.

FIG. 4 shows the special gas dosing unit 50 separated from respirator 103, but the two elements could be integrated together, if desired. The special gas dosing unit 50 includes a high pressure special gas source 113 connected to pressure regulator 114. Pressure sensor 115 monitors the output pressure of pressure regulator 114 in conduit 116. Redundant flow sensors 104 and 105 measure the flow in special gas supply conduit 116.

Special gas supply conduit 116 is connected to inlet connector opening 2 of variable orifice pulse valve 1.

Control unit 100 of the special gas dosing unit 50 is connected with the breathing gas flow sensor 102 connected in patient limb 109c. Control unit 100 is also connected to control panel 101 which provides dose related parameters to control unit 100. The dose parameters may comprise, for example, dose volume, pulse length, dose flow, inhaled gas concentration, triggering

information, and the type of special gas to be dosed. Control unit 100 also receives inputs from pressure sensor 115, flow sensors 104 and 105, and a special gas source identification signal line from special gas source 113. Control unit 100 provides output signals to solenoid coils 8,18 of variable orifice pulse valve 1 in supply cables 9 and 19, respectively.

Outlet connector opening 23 of variable orifice pulse valve 1 is connected to special gas dosing line 112 which is connected in the patient limb 109c of breathing circuit 109.

In operation, control unit 100 provides a signal to start the dose which will activate the variable orifice elements 4,5,7, and 8 of valve 1 to a preferably precalibrated initial value and activate the pulse valve elements 14,16-18. The variable orifice 5 is made small, compared to the pulse valve orifice 14, so that gas in the intermediate chamber 13 will be discharged by the overpressure existing in the chamber. This discharge is not sensed by the dose monitoring means 104 and 105.

Thereafter during the dosing time, control unit 100 monitors the dosing to dosing line 112, as by comparing information from sensors 104,105 with reference dose information. The control unit stops the pulse at a time derived from the reference and monitored information by closing pulse valve 1 at pulse valve orifice 14. The pulses of gas will be supplied to special gas dosing line 112 for delivery to patient limb 109c.

It is preferable that variable orifice 5 is not completely closed so that the intermediate chamber 13 will reload slowly with gas through the variable orifice 5 to the supply pressure. The quantity of gas used to reload space 13 is sensed by sensors 104,105. Thus the initial volume of gas discharged from the intermediate chamber 13 can be taken into consideration when adjusting the variable orifice for the next dose of special gas. Therefore, uncontrollability in the dose can be totally eliminated, as long as the amount of the dose is larger than the discharge volume of intermediate chamber 13, of variable orifice pulse valve 1. In a typical embodiment, this would be a dose larger than 3. 1. Particularly when dosing tiny pulses of special gas, the variable orifice 5 is not closed but advanta- geously only modified for the next dose according to the reference and monitored information obtained from the previous dose. This

is because closing the variable orifice between the pulses does not achieve the benefit of the high speed dosing. With large pulses of special gas, closure of variable orifice 5 may take place e. g. for purposes of power consumption optimization. The limit between large and tiny pulses depends largely on the overall dimensioning and configuration of the variable orifice 5, but as an example it could be 10% of the maximum dynamic capacity of the variable orifice.

The advantageousness of positioning the variable orifice 5 upstream of pulse valve orifice 14 becomes apparent from FIG. 1.

If the order of the orifices in the flow stream was reversed, the variable orifice 5 would remain open between the doses. The intermediate chamber 13, which is reloaded with gas during the period of the gas pulse would discharge slowly between the pulses, so that the timing accuracy would be lost. However, it is possible to employ variable orifice pulse valve 1 in the reversed flow stream manner, if desired.

The use of the valve of the present invention provides the features noted above while at the same time providing redundant means for preventing unintentional dosing of the patient as a result of the presence of the two orifices in the valve.

FIG. 4 also shows source 106 for a carrier gas which receives the special gas dose and carries it through dosing line 112 to the patient. Source 106 withdraws respiratory gases from the inspiration limb 109a of the breathing circuit 109 through conduit 120. Carrier gas source 106 includes pump 107 controlled by pump actuator 121. Check valve 122 is provided in the output of pump 107.

Pump 107 pressurizes tank 108 with gas obtained from inspiratory limb 109a of breathing circuit 109. The tank pressure is monitored to an appropriate level by pressure sensor 111. Tank 108 is connected through flush valve 110 to inlet connector opening 24,24a of valve 1 by conduit 123.

To obtain carrier gas flow, control unit 100 actuates flush valve 110. The supply of carrier gas from carrier gas source 106 through conduit 123 to variable orifice pulse valve 1 and dosing line 112 flushes the special gas dose from outlet chamber 15 and provides a high speed flow that advances the dose in dosing line 112 rapidly to the dosing point in patient limb

109c of breathing circuit 109. The operation of flush valve 110 may be synchronized in a desired manner with the operation of variable orifice pulse valve 1.

Positioning pulse valve orifice 14 down stream of variable orifice 4 insures that the flush flow does not enter the intermediate chamber 13, which might cause, e. g. contamination problems, depending on the application to which the valve is put.