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`USO05558083A
`
`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,558,083
`
`Bathe et al.
`
`[45] Date of Patent:
`
`Sep. 24, 1996
`
`[54] NITRIC OXIDE DELIVERY SYSTEM
`
`FOREIGN PATENT DOCUMENTS
`
`[75]
`
`Inventors: Duncan P. L. Bathe, Madison; Thomas
`S. Kohlmann, McFarland; John R.
`Pinkert, Madison; Robert Q. Thain,
`Middleton, all of Wis.
`
`[73] Assignee: Ohmeda Inc., Liberty Corner, N.J.
`
`[21] Appl. No.: 156,175
`
`[22]
`
`Filed:
`
`Nov. 22, 1993
`
`Int. Cl.6 .................................................. .. A61M 15/00
`[51]
`[52] U.S. Cl.
`................................ 128/203.12; 128/203.14;
`128/203.25
`
`[58] Field of Search ......................... 128/202.22, 203.12,
`128/203.14, 203.25, 205.23
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,127,121
`4,191,952
`4,328,823
`4,336,798
`4,345,612
`4,442,856
`4,511,590
`4,770,168
`5,159,924
`5,197,462
`
`............. 128/203.14
`11/1978 Westenskow et al.
`.. 128/203.14
`3/1980 Schreiber et al.
`'128/203.14
`5/1982 Schreiber
`128/205.23
`6/1982 B
`..... ..
`__ 128/203.14
`8/1982 Kirnainet a1_
`128,2O2_22
`4/1984 Bea ___________._
`__ 123/20314
`9/1935 Ryschka at 31
`.. 128/203.14
`9/1988 Rusz et al.
`..... ..
`.. 128/203.25
`11/1992 Cegielski et al.
`3/1993 Falb et al.
`.......................... 128/203.14
`
`
`
`Canada .
`2121384 of 1994
`4325319
`of 1994
`Germany .
`W092/11052 of 1992 WIPO .
`W092/10228 of 1992 WIPO .
`
`OTHER PUBLICATIONS
`
`The Journal of Clinical Investigation, vol. 90, No. 2, Aug.
`1992, pp. 421-428.
`
`Primary Exami'ner—-Aaron J. Lewis
`Attorney, Agent, or Firm—Roger M. Rathbun; R. Hain
`Swope; Larry R. Cassett
`
`[57]
`
`ABSTRACT
`
`A nitric oxide delivery system that is useable with any of a
`variety of gas delivery systems that provide breathing gas to
`a patient. The system detects the flow of gas delivered from
`the gas delivery system at various times and calculates the
`flow of a stream of nitric oxide in a diluent gas from a gas
`control valve. The flow of gas from the gas delivery system
`and the flow established from the flow control valve create
`
`'
`
`a mixture having the desired concentration of nitric oxide for
`the patient
`
`.
`.
`The system does not have to interrogate the particular gas
`delivery system being used but is an independent system that
`can be used with various flows; flow profiles and the like
`from gas delivery systems.
`
`27 Claims, 2 Drawing Sheets
`
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`

`
`U.S. Patent
`
`Sep.24, 1996
`
`Sheet 1 of 2
`
`5,558,083
`
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`
`U.S. Patent
`
`Sep. 24, 1996
`
`Sheet 2 of 2
`
`5,558,083
`
`
`
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`

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`5,558,083
`
`2
`
`1
`NITRIC OXIDE DELIVERY SYSTEM
`
`BACKGROUND OF THE INVENTION
`
`to
`The administration of inhaled nitric oxide (NO)
`patients is currently being investigated for its therapeutic
`effect. The use of NO has a vasodilatory effect on such
`patients and is particularly of importance in the case of
`newborns having persistent pulmonary hypertension.
`In
`such cases,
`the administration of NO has significantly
`increased the oxygen saturation in such infants.
`\
`The function of the administration of NO has been fairly
`widely published and typical articles appeared in The Lan-
`cet, Vol. 340, October 1992 at pages 818-820 entitled
`“Inhaled Nitric Oxide in Persistent Pulmonary Hypertension
`of the Newborn” and “Low-dose Inhalational Nitric Oxide
`in Persistent Pulmonary Hypertension of the Newborn” and
`in Anesthesiology, Vol. 78, pgs. 413-416 (1993), entitled
`“Inhaled NO—the past, the present and the future”.
`The actual adnrinistration of NO is generally carried out
`by its introduction into the patient as a gas along with other
`normal inhalation gases given to breathe the patient. Such
`commercially available supplies are provided in cylinders
`under pressure and may be at pressures of about 2000 psi
`and consist of a nrixture of NO in nitrogen with a concen-
`tration of N0 of between about 800-2000 ppm. As such,
`therefore, some means must be used to reduce the pressure
`of the supply to acceptable levels for a patient and also to
`very precisely meter the amount of the NO and nitrogen
`mixture so that the desired concentration of NO is actually
`administered to the patient. Such administration must also
`be added in sympathy with the respiration pattern of the
`patient.
`The concentration administered to a patient will vary
`according to the patient and the need for the therapy but will
`generally include concentrations at or lower than 150 ppm.
`There is, of course, a need for that concentration to be
`precisely metered to the patient since an excess of NO can
`be harmful
`to the patient. In addition, the administration
`must be efficient in a timely manner in that NO is oxidized
`in the presence of oxygen to nitrogen dioxide and which is
`a toxic compound. Therefore, care in its administration is
`paramount.
`Current known methods of such administration, therefore
`have been limited somewhat to clinical situations where
`attending personnel are qualified from a technical sense to
`control the mixing and administration of the NO to a patient.
`Such methods have included the use of a forced ventilation
`device, such as a mechanical ventilator where a varying flow
`os breathing gas is delivered to the patient as well as gas
`blenders or proportioners that supply a continuous flow of
`the breathing gas to the patient to which NO has been added.
`In the former case, the use of a ventilator is constrained
`in that
`the user must know the precise flow from the
`ventilator and then the amount of NO to be added is
`determined on a case-to-ease and moment-to-moment basis.
`Furthermore, the flow profile in forced ventilation varies‘
`continuously thereby making it impossible to track the flow
`manually. In the use of the latter gas blenders, the introduc-
`tion of the NO containing nitrogen has been accomplished
`through the use of hand adjustment of the gas proportioner
`in accordance with a monitor that reads the concentration of
`NO being administered to the patient. Thus the actual
`concentration is continuously being adjusted by the user in
`accordance with the ongoing conditions of the apparatus
`providing the breathing mixture.
`
`5
`
`While such modes of providing a known concentration of
`NO to the patient may be acceptable from a closely con-
`trolled and monitored clinical setting, it is advantageous to
`have a system that could be used with various means of
`providing the breathing gas, whether by mechanical means
`such as a ventilator, or by the use of a gas proportioner and
`which could automatically adjust for that particular equip-
`ment and assure the user that the desired, proper concentra-
`tion of NO is being administered to the patient.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, there is pro-
`vided a nitric oxide delivery system that is useable with
`various means of administering the NO, including the use of
`any mechanically assisted ventilation and ventilatory pat-
`tern, such as a ventilator or with spontaneous ventilation
`where the NO is introduced by means of a gas proportioning
`device that provides a continuous fiow to the patient. The
`invention includes a flow transducer that senses the flow of
`gas from the gas delivery system and uses that information
`with a selective algorithm to provide an operator selectable
`concentration of NO to the patient. As used herein, the term
`gas delivery system is intended to include various types of
`gas proportioning devices, gas mixers and various types of
`mechanical ventilators used to provide breathing gas to a
`patient and may include an anesthesia machine, or manual
`bag, used with a patient undergoing an operation and which
`has a fresh gas supply.
`In the preferred embodiment, a CPU obtains information
`from the flow transducer and from an input device that
`allows the user to select the desired concentration of NO to
`be delivered to the patient and calculates the flow of NO/ni-
`trogen to obtain that selected concentration. It will be noted,
`however, that while a CPU is preferred, the signal process-
`ing needed by this system can readily be accomplished
`through the use of alternate technologies, such as analog or
`digital circuitry, lluidic circuits, optical means or mechanical
`components. The
`term “signal processing means” is
`intended to encompass the variety of ways that may be
`utilized to carry out the various signal processing functions
`toopcrate the subject NO delivery system.
`Accordingly, the present system can be used with preci-
`sion with various gas delivery systems, including ventilators
`of different manufacturers operating with diverse ventilatory
`patterns without
`the need to calculate output from the
`ventilator,
`to interrogate the gas delivery means, or to
`regulate the concentration manually. The user is thus free to
`concentrate on other procedures that will
`improve the
`patient.
`By use of the CPU, various algorithms may be stored and
`used as appropriate. For example, there may be one algo-
`rithm that is used to obtain a steady concentration of NO in
`a spontaneous or continuous flow situation such as when a
`gas proportioner of gas blender is used. A differing use of
`that same algorithm may be used to achieve an instantaneous
`change in the NO/nitrogen supply flow to maintain the
`desired flow to the patient or, that same algorithm may be
`used to calculate a breath-by-breath flow of NO/nitrogen
`such that the flow from the gas delivery system may be
`determined and used to adjust the NO/nitrogen flow to
`maintain the desired NO concentration to the patient in the
`next breath delivered to the patient. In any manner, the CPU
`takes over the manual setting of any valves and established
`the concentration of NO to the patient as set or selected by
`the user.
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`5,558,083
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`Another use of the preferred signal processor, the CPU, is
`to supervise the safe operation of the NO delivery system by
`providing alarm functions and other functions to protect the
`patient in the event of faults in the delivery of NO.
`As an alternate embodiment, a further means is included
`that adjusts the 02 concentration to the patient to compen-
`sate for the diminution of O2 to the patient as the patient
`inspiratory gas is loaded with NO/nitrogen to achieve a
`specified concentration of NO in the patients inspired gases.
`As a still further embodiment, a purge system is included
`that is activated to purge the various components and to fill
`the system with a gas having a known nitric oxide concen-
`tration from the supply.
`The system also includes various controls, alarms and
`safety devices to prevent excess concentrations of N02 in
`the administration of NO to the patient, including means to
`shut down the NO system or to reduce the NO concentration
`to the patient to a safer level. The NO delivery system may
`thus provide an alarm or other appropriate action in the event
`of an increase in the NO level beyond a predetermined level,
`a decrease in 02 below a predetermined level and/or an
`increase of N02 above a predetermined level. Depending on
`the severity of the alarm condition, an alarm may sound or
`the entire system may be controlled to alleviate the unsafe
`condition sensed.
`
`These and other objects, features and advantages of the
`present invention will be more apparent from the detailed
`description of the preferred embodiment set forth below,
`taken in conjunction with the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`10
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`15
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`20
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`25
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`
`FIG. 1 is a schematic view, partially in block diagram
`form, of apparatus in accordance with an embodiment of the
`present invention.
`
`35
`
`FIG. 2 is a schematic view, partially in block diagram
`from, of apparatus in accordance with another embodiment
`of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Turning first to FIG. 1, there is shown a schematic view,
`partially in block diagram form, showing an apparatus
`constructed in accordance with the present invention. In the
`FIG. 1, a supply of nitric oxide is provided in the form of a
`cylinder 10 of gas. That gas is preferably nitric oxide mixed
`with nitrogen and is a commercially available mixture.
`Although the preferred embodiment utilizes the present
`commercial NO/nitrogen mixture, it is obvious that the NO
`may be introduced to the patient via some other gas,
`preferably an inert gas. Generally, of course, the cylinder 10
`of nitric oxide is delivered pressurized and a typical pressure
`is on the order of about 2000 psi with a concentration of
`nitric oxide in the order of about 1000 ppm. Alternatively,
`the NO/nitrogen gas may be available in a central supply
`within a hospital and be available through the normal
`hospital piping system to various locations such as operating
`rooms. In such case, the pressure may already be reduced to
`a relatively lower amount that the cylinder pressures.
`A pressure regulator 12 is used, therefore, to reduce the
`pressure of the gas in cylinder 10 down to acceptable levels
`for operation of the system, and again, typically, the regu-
`lator 12 reduces the pressure to about 40 psi or lower. An
`on—off shutoff valve 14 receives the reduced pressure gas
`from regulator 12 through a suitable conduit and is prefer-
`ably solenoid operated. The use and purpose of the shutoff
`
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`valve 14 will later be explained in conjunction with the
`operation of the nitric oxide delivery system.
`A separate supply of pure nitrogen may be employed and,
`again, generally is provided by a cylinder 16 of nitrogen
`although pipeline nitrogen is available in numerous hospi-
`tals. The pressure of the nitrogen within cylinder 16 is
`reduced to the desired system level by means of regulator 17
`and the nitrogen thereafter supplied via a conduit
`to a
`proportional control valve 18 that is controlled in a manner
`to be described. Suffice at this point is to state that the
`proportional control valve 18 provides a predetermined flow
`of nitrogen through a suitable conduit into the conduit to be
`mixed with the NO/nitrogen gas from cylinder 10 and which
`then enters the shutoff valve 14.
`
`The purpose of the additional supply of nitrogen is to
`dilute, if necessary, the concentration of nitric oxide in the
`supply to the shutofl valve 14 to a desired amount. For
`example, the cylinder 10 may be supplying a concentration
`of nitric oxide that is too high for the particular flows in the
`system and therefore the concentration may be reduced to a
`more desirable level. If, of course, the supply of nitric oxide
`from cylinder 10 is suitable for the particular application, the
`addition of supplemental nitrogen is unnecessary.
`Further downstream in the conduit carrying the NO/ni-
`trogen stream is a purge valve 20 and which may be a
`solenoid operated valve that diverts the stream of NO/nitro-
`gen from shutoff valve 14 to a sidestream 22 where the
`mixture is removed from the environment by means of a
`hospital evacuation or other system to remove such gases.
`Such system may, of course, have various treatment means
`such as a NO2 and NO scrubber 23 if required in a particular
`hospital.
`Again, the control of the purge valve 20 and its use will
`be later explained in connection with the overall operation of
`the nitric oxide delivery system, and which is optional.
`A further proportional control valve 24 is positioned with
`suitable conduit to receive the NO/nitrogen gas from the
`purge valve 20. Typical of such proportional control valves
`for both the proportional control valve 18 in the nitrogen
`supply system and the proportional control valve 24 in the
`NO/nitrogen stream may be obtained commercially from
`various companies,
`including MKS Instruments,
`Inc. of
`Andover, Mass. and which provide electronic control of
`gases. As may be seen, alternately, the valve may be a digital
`controlled valve rather that analog and which is controlled
`by timing its on/off cycles to eflect the desired flow through
`the proportional control of flow thcrethrough. Combination
`of several valves used singly or in combination can be used
`to extend the delivery range.
`A flow sensor 26 is located in the downstream conduit
`from proportional control valve 24 and senses the flow from
`such valve. Typically, in view of the values of flow at this
`point in the nitric oxide delivery system, the flow transducer
`may be of a technology such as the thermal mass llowmetcr
`available from MKS Instruments, Inc. or may be of other
`technology of other suppliers.
`A delivery adaptor 28 receives the NO/nitrogen gas via a
`suitable conduit for introduction into a further gas stream
`from the gas delivery system (not shown).
`Delivery adaptor 28 is preferably a one piece reusable
`device and which has an inlet 30 which receives the gas
`delivered from the gas delivery system. As indicated, that
`gas delivery system may be a mechanical means providing
`a varying flow such as a ventilator, may be gas continuously
`supplied by a gas proportioning device for spontaneous
`ventilation or may be gases supplied to a bag for manual
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`ventilation. As can be seen, the actual gas delivery system
`itself is not critical since the present system independently
`ascertains the flow from that system and proceeds to calcu-
`late and then deliver the proper flow of nitric oxide to arrive
`at the concentration to the patient that is selected by the user.
`The delivery adaptor 28 has a main passage 32 there-
`through and which receives the gas from the gas delivery
`device through inlet 30 for delivery to a patient. The gas
`actually delivered to the patient is transmitted via a patient
`wye piece 34 having an inspiratory limb 36 and an expira-
`tory limb 38 of conventional design. The patient limb 40,
`obviously, leads to the patient indicated by the block 42.
`A further inlet 44 is formed in the delivery adaptor 28 and
`which receives the NO/nitrogen gas from the proportional
`control valve 24 through flow sensor 26-. As can be seen from
`FIG. 1, a flow transducer 46 is also included in the delivery
`adapter 28 and which detects the flow of gas from the gas
`delivery system. The inlet 44 is positioned downstream in
`the delivery adapter 28 from flow transducer 46. Flow
`transducer 46 may be of a variety of technologies, including
`pneumotach, hot wire anemometer,
`thermal flow sensor,
`variable orifice, thermal time—of—flight, rotating vane and the
`like. Included, obviously, are flow transducers that actually
`measure pressure, such as a pressure drop though an orifice,
`in order to determine flow.
`
`A sampling port 48 is formed in the delivery adapter 28
`and which communicates with the flow of gas passing
`through the main passage 32. It should be noted that the
`sampling port 48 thus samples the mixed gases, that is the
`gas downstream from the inlet 44 and thus downstream from
`a confluence 50 where the NO/nitrogen stream of gas is
`mixed with the inspiratory gas from the gas delivery system.
`Accordingly, the flow from the gas delivery means enters
`the inlet 30 at a flow rate Q, and at a certain concentration
`of oxygen yO2,. and is mixed in the main passage of delivery
`adapter 28 with the NO/nitrogen gas from proportional
`control valve 24 at confluence 50. Flow transducer 46 is
`upstream of the confluence 50 and thus senses the flow only
`of the gas from the gas delivery system while sampling port
`48 is downstream of the confluence S0 and thus provides
`access to samples of the gases that are mixed together at
`confluence 50. At confluence 50, there may be a diffuser
`such as a screen or sintered, porous block that enhances the
`' mixing of the NO/nitrogen with the gases from the gas
`delivery system.
`Therefore, the concentration of mixed gases at sampling
`port 48 contains the concentration of NO that actually enters
`the patient for therapeutic treatment and is the concentration
`set by the user, yNOS,_,,.
`Connected to the gas sampling port 48 is a gas sensing
`bench 52 and which analyzes the concentrations of certain
`components of the gas stream administered to the patient. In
`the preferred embodiment, the gas sensing bench 52 samples
`the gases through conduit 54 and senses and quantifies the
`concentration of NO as well as N02 and O2. Altemately, a
`sensor may be directly attached to the delivery adaptor 28
`and directly sense such gas passing through the main pas-
`sage 32.
`A signal processing means, such as a CPU 56 is provided
`to solve certain equations and algorithms to operate the
`nitric oxide delivery system. CPU 56 receives a signal from
`an input device 58 indicative of the concentration the user
`desires to be administered to the patient. CPU 56 also
`receives signals from the flow transducer 46 indicative of the
`flow of gas delivered by the gas delivery system, Q, through
`a signal line 60 and also receives signals indicative of the
`
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`concentration of NO, as well as N02 and 02 from gas sensor
`bench 52 via a signal line 62 and a signal from flow sensor
`26 indicative of the flow from proportional control valve 24,
`QM, respectively via a signal line 64.
`Another input to CPU 56 is provided by the NO sensor 65
`through signal line 67. The NO sensor 65 senses the con-
`centration of NO in the supply cylinder 10 so that the user
`can verify that
`the proper supply is being utilized or,
`alternatively, the CPU 56 may use that input to adjust the
`system to adapt for any concentrations of NO in the supply
`within certain limits. NO sensor 65 could, of course, be
`eliminated if the NO cylinder 10 is always constant or by
`keying into the NO sensor in the gas sensing bench 52. A
`switching mechanism (not shown) would be required to
`sample from the multiple sources of samples.
`Control signals are transmitted from CPU 56 to propor-
`tional control valve 18, shutoff valve 14, purge valve 20, and
`proportional valve 24 via signal lines 66, 68, 70, and 72
`respectively.
`In the operation of the present NO delivery system,
`therefore, the inlet 30 is connected to a gas delivery system,
`whether that gas delivery system is a mechanical ventilator
`or gas proportioning device or other means of supplying a
`breathing gas to a patient. As the gas is delivered from the
`gas delivery system, its flow is sensed by the flow transducer
`46 in delivery adapter 28 and a signal is transmitted indica-
`tive of that flow to the CPU 56.
`
`The user activates the input device 58 to select the desired
`concentration of NO that is to be administered to the patient.
`That input device 58 may be of a variety of devices, such as
`a keyboard, dial, encoder, touch screen, thumb wheel or the
`like. Alternatively, the input may be a signal that is built into
`the delivery system by the manufacturer and not be select-
`able by the actual end user. For example, the delivery system
`may be designed to operate to provide a fixed concentration
`of NO and the use of the system with any gas delivery
`system would result in that fixed, predetermined concentra-
`tion of NO to be administered to the patient.
`In the preferred embodiment, however, the desired NO
`concentration to be administered to the patient is set by the
`user by means of an input to CPU 56.
`As can be seen, the CPU 56 has sufficient information to
`carry out the proper calculations, that is, it knows the flow
`of breathing gas from the gas delivery device by means of
`flow transducer 46 (Q,,) and the concentration of NO in the
`NO/nitrogen supply by means of NO sensor 65 (YNOM).
`With that information, CPU 56 can calculate the desired flow
`(QM) from the proportional control valve 24 that needs to be
`provided to the confluence 50 to mix with the gas from the
`gas delivery system to produce the desired or set concen-
`tration (yN0M) established by the user through input device
`58.
`
`Basically, CPU 56 calculates the flow of NO/nitrogen to
`be added to the confluence 50 through the following equa-
`tion;
`
`Q.:.l(t)={Y~o.....(t)/(rm...-v~o..e.(t)1*Ql(t)
`
`By this equation, the concentration of NO to the patient
`can be changed at an instantaneous rate limited only by the
`speed and sensitivity of the components such as flow trans-
`ducer 46. The faster the response of flow transducer 46 is,
`the faster changes can be made in flow of the NO/nitrogen
`to confluence 50 by proportional control valve 24 such that
`the NO to the patient can instantaneously account for
`changes in the flow profile from the gas delivery system to
`
`006
`
`006
`
`

`
`7
`
`8
`
`5,558,083
`
`maintain that concentration set by the user. The flow deliv-
`ered (Q,,,,) from the proportional control valve 24 to the
`confluence 50 is determined from the concentration set by
`the user, (YNOM). The concentration NOW, is the concen-
`tration of NO in nitrogen from the supply cylinder 10 and the
`flow from the gas delivery system is Q,.. By this equation, the
`CPU 56 can make extremely rapid, such as 20 millisecond,
`changes to the flow delivered from proportional control
`valve 24 (QM) in order to maintain the concentration of the
`flow delivered to the patient at the desired level as deter-
`mined by the user (ym).
`As an alternate, the system may operate on a breath—by-
`breath basis, that is, the system can take a reading of the
`flow, or a portion thereof, from the gas delivery system at
`each breath and calculate the desired flow of NO/nitrogen
`for delivery at the next breath. Although such delivery is less
`rapid than the instantaneous equation, slower flow transduc-
`ers and control valves may by employed and thus less
`expensive components used in the system. Therefore mean
`values can be used for the values set by the user (yN0,.,_,,,,,,_,_,,,,,)
`and the flow delivered by the proportional control valve 24
`(QM) is expressed as a function of the inspired tidal volume
`of gas (V,_,.,,_,I,_) and the time of inspiration (t,,,W). In such
`system, the equation is basically the same:
`
`Qde!:lYNO:u1.m:un/(YNocm‘YNom,mean) l * V1,irl:p./‘imp.
`
`With the breath—by-breath analysis, however, the flow
`transducer 46 may detect the start and end of a breath, or
`selected portion thereof, integrate to determine the total or
`fixed selected volume of the breath, and adjust the propor-
`tional control valve 24 to provide the set or desired concen-
`tration of NO at the next breath.
`
`For constant or continuous flow ventilation from the gas
`delivery system as might be provided by a gas mixer or
`proportioning device, the same basic equation is used:
`
`QderzlYNom/(YNauu‘YN0.m) l *Q.'
`
`In this case, however, since the flow is continuous and the
`tidal volume assure to be constant, the flow from the gas
`delivery system, (Q,.) may be sampled at a relatively slow
`rate, for example, once per second, and the flow of NO/ni-
`trogen calculated and established from proportional control
`valve 24 on that particular timing cycle.
`In any of the foregoing cases, the principal of operation is
`the same and the operative equation is basically the same.
`By knowing the flow from the gas delivery system by means
`of flow transducer 46 and the concentration of NO in the
`main supply from N0 sensor 65, a derivation is made by the
`CPU 56 and the proportional control valve 24 is adjusted to
`provide then calculated How of NO/nitrogen to arrive at the
`desired concentration set by the user in the breathing gas
`actually administered to the patient.
`Confirmation of the flow from the proportional control
`valve 24 is made by the flow sensor 26 so that CPU 56 can
`check to see of the actual flow corresponds to the flow
`calculated and established by the CPU 56 through signal line
`72 to proportional control valve 24. Alternatively, the flow
`sensor 26 can control the proportional control valve 24 using
`a feedback system and which is available in the commmer-
`cial valves from, for example, MKS Instruments Inc.
`As is also be apparent from FIG. 1, CPU 56 also controls
`the proportional control valve 18 via signal line 66 and can
`operate that valve to further reduce the concentration of the
`NO in nitrogen from cylinder 10 in the event very low
`concentrations are set by the user and the system is other-
`wise unable to reduce the concentration to the desired point.
`
`10
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`SO
`
`55
`
`60
`
`65
`
`The gas sensing bench 52 provides a continuous monitor
`of the actual NO concentration administered to the patient
`and therefore is a further safety monitor. In the event the NO
`detected by the gas sensing bench 52 is a predetermined
`value away from the set point established by the user, an
`alarm may be triggered so the user can attend to the problem.
`In the event that the NO level rises to a dangerous level,
`CPU 56 will have that information and can take more drastic
`steps such as to discontinue use of the NO to the patient by
`shutting off the shutoff valve 14 or by automatically reduc-
`ing the NO level to a lower, safe level established in the
`system.
`As further alarms or triggers to actively change or termi-
`nate the NO system, the gas sensing bench 52 also monitors
`and provides the CPU 56 with a continuous reading of the
`concentrations of O2 and N02 being administered to the
`patient and, again, the CPU 56 can be programmed to take
`the appropriate action, be it trigger an alarm or reduce the
`NO concentration in the event the 02 level falls below a
`predetermined value or the N02 rises above a predetermined
`value.
`
`Finally, in the event of a loss of pressure in the supply at
`any time, CPU 56 can activate purge valve 20 to purge the
`system of any other gases that may be in the supply line and
`refill the supply lines from cylinder 10 to the purge valve 20
`with fresh NO/nitrogen. In this way, the system is recharged
`with the correct supply gas and no extraneous gases, such as
`ambient air, will be introduced into the system to cause error.
`Accordingly, through the use of the present NO delivery
`system, the concentration of NO delivered to the patient may
`be established, either by the selection by the user, or set by
`a predetermined value by the system itself, and that desired
`value will be transmitted to the patient without any interro-
`gation of the gas delivery device. The system is thus
`independent and may be readily used with any mechanical
`ventilator, gas proportioning device or other gas delivery
`system to deliver a known, desired concentration of NO to
`a patient.
`Turning briefly to FIG. 2, there is shown in schematic
`view, partially in block form, of another embodiment of the
`present NO delivery system. In FIG. 2, all of the corre-
`sponding components have been numbered with the same
`identification numbers as in FIG. 1.
`
`In this embodiment, however, an additional supplemental
`oxygen supply has been added by means of an oxygen
`cylinder 74 containing pressurized oxygen and which pres-
`sure is reduced by means of a regulator 76. Again it should
`be noted that the control of the oxygen supply is by means
`of a proportional control valve 78 which is controlled by the
`CPU 56 via a signal line 80.
`Thus the operation of the FIG. 2 embodiment is the same
`as previously explained with respect to the FIG. 1 embodi-
`ment however the supplemental oxygen system may be used
`to add oxygen to the system in the event the gas sensing
`bench 52 indicates to the CPU 56 that the concentration of
`oxygen has been reduced to an unacceptable level. Such
`reduction in oxygen could occur in the event the concen-
`tration of NO is set to a very high level and the flow of
`NO/nitrogen from proportional control valve 24 to conflu-
`ence 50 is very high and the combined flow to the patient
`thus is deprived of the needed amount of oxygen being
`supplied by the gas delivery system.
`In such event, the CPU 56 merely signals proportional
`control valve 78 to add or increase the flow of oxygen to the
`NO/nitrogen stream being admitted to confluence 50, that is,
`upstream of confluence 50 by means of a suitable conduit
`Numerou