Abstract:
Methods and related systems for individually sensing airflow in the breathing orifices of a patient, and preferentially delivering therapeutic gas to those breathing orifices based on the amount of airflow sensed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   None. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the invention are directed to preferentially delivering therapeutic gas to a patient. More particularly, the embodiments are directed to delivering therapeutic gas to one, a combination, or all of a patient&#39;s left naris, right naris and mouth selectively. 
   2. Background of the Invention 
   Patients with respiratory ailments may be required to breathe a therapeutic gas, such as oxygen. The therapeutic gas may be delivered to the patient from a therapeutic gas source by way of a nasal cannula. 
   Delivery of therapeutic gas to a patient may be continuous, or in a conserve mode. In continuous delivery, the therapeutic gas may be supplied at a constant flow throughout the patient&#39;s breathing cycle. A significant portion of the therapeutic gas provided in continuous delivery is wasted, i.e. the therapeutic gas delivered during exhalation of the patient is lost to atmosphere. In order to overcome the wastefulness of continuous delivery, related art devices may operate in conserve mode using a conserver system. 
   A conserver may be a device which senses a patient&#39;s inspiration, and delivers a bolus of therapeutic gas only during inspiration. By delivering therapeutic gas only during inspiration, the amount of therapeutic gas lost to atmosphere may be reduced. Conserver systems of the related art may sense a patient&#39;s inspiration at one naris and delivery the bolus of therapeutic gas to the other naris, such as through a bifurcated nasal cannula. Alternatively, conserver devices of the related art may sense a patient&#39;s inspiration at the nares generally, and delivery a bolus of therapeutic gas to the nares generally, such as through a non-bifurcated (single lumen) nasal cannula. 
   Sensing at one naris and delivering to a second naris may not work properly in all situations. If the patient has a blocked naris, e.g. because of congestion or some physical abnormality, either the sensing may not operate properly or the delivery of therapeutic gas may be to the blocked naris. Sensing and/or delivery may also fail to operate properly if the nasal cannula becomes dislodged, such as during sleep. Even if a nasal cannula stays properly on the patient and neither naris is blocked, delivering the patient&#39;s entire prescription of therapeutic gas through a single naris may cause nasal irritation. 
   When sensing inspiration by monitoring both nares simultaneously, congestion and/or abnormalities in the nares may cause the system to not sense properly. Moreover, when delivering therapeutic gas to the nares generally, such as through a single lumen cannula, congestion and/or physical abnormalities of the nares may affect the volume inhaled in each naris, wasting therapeutic gas in some cases and not providing sufficient therapeutic gas in other cases. 
   SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS 
   The problems noted above may be solved in large part by a method and system of individually sensing airflow of the breathing orifices of a patient, and preferentially delivering therapeutic gas to those breathing orifices. One exemplary embodiment may be a method comprising sensing airflow of a first and second breathing orifice of a patient, delivering therapeutic gas to the first breathing orifice in proportion to the airflow of the first breathing orifice, and delivering therapeutic gas to the second breathing orifice in proportion to the airflow of the second breathing orifice. 
   The disclosed devices and methods comprise a combination of features and advantages which enable it to overcome the deficiencies of the prior art devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
       FIG. 1  illustrates a preferential delivery system in accordance with embodiments of the invention; 
       FIG. 2A  illustrates, in shorthand notation, the system of  FIG. 1 ; 
       FIG. 2B  illustrates an alternative embodiment of the system of  FIG. 1 ; 
       FIG. 2C  illustrates yet another alternative embodiment of the system of  FIG. 1 ; 
       FIG. 3  illustrates a preferential delivery system in accordance with alternative embodiments of the invention; 
       FIG. 4A  illustrates, in shorthand notation, the system of  FIG. 3 ; 
       FIG. 4B  illustrates an alternative embodiment of the system of  FIG. 3 ; 
       FIG. 4C  illustrates yet another alternative embodiment of the system of  FIG. 3 ; and 
       FIG. 5  illustrates an alternative embodiment of the system of  FIG. 3  using fewer three-port valves. 
   

   NOTATION AND NOMENCLATURE 
   Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. 
   In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical or mechanical connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices and connections. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a preferential delivery system  100  in accordance with at least some embodiments of the invention. The preferential delivery system  100  may be coupled to a therapeutic gas source  10  by way of a gas port  11 . The therapeutic gas source  10  may be any suitable source of therapeutic gas, such as a portable cylinder, an oxygen concentration system or a permanent supply system as in a hospital. The selective delivery system also couples to a patient (not shown) by any of a variety of devices and systems by way of a variety of ports, such as narial ports  23 ,  25  and an oral port  27 . For example, the preferential delivery system  100  may couple to a patient&#39;s nares by way of a nasal cannula. In accordance with embodiments of the invention, the preferential delivery system  100  monitors patient breathing and selectively delivers therapeutic gas to a left naris (LN), right naris (RN) and/or to the mouth (M) of the patient. 
   In accordance with at least some embodiments, the preferential delivery system  100  comprises both electrical components and mechanical components. In order to differentiate between electrical connections and mechanical connections,  FIG. 1  (and the remaining figures) illustrate electrical connections between components with dashed lines, and fluid connections, e.g. tubing connections between devices, with solid lines. The preferential delivery system  100  in accordance with at least some embodiments of the invention comprises a processor  12 . The processor  12  may be a microcontroller, and therefore the microcontroller may be integral with read-only memory (ROM)  14 , random access memory (RAM)  16 , a digital-to-analog converter (D/A)  18 , and an analog-to-digital converter (A/D)  20 . The processor  12  may further comprise communication logic  17 , which allows the system  100  to communicate with external devices, e.g., to transfer stored data about a patient&#39;s breathing patterns. Although a microcontroller may be preferred because of the integrated components, in alternative embodiments the processor  12  may be implemented by a stand-alone central processing unit in combination with individual RAM, ROM, communication D/A and A/D devices. 
   The ROM  14  may store instructions executable by the processor  12 . In particular, the ROM  14  may comprise a software program that implements the various embodiments of the invention discussed herein. The RAM  16  may be the working memory for the processor  12 , where data may be temporarily stored and from which instructions may be executed. Processor  12  may couple to other devices within the preferential delivery system by way of A/D converter  20  and D/A converter  18 . 
   Preferential delivery system  100  also comprises three-port valve  22 , three-port valve  24 , and three-port valve  26 . In accordance with embodiments of the invention, each of these three-port valves may be a five-volt solenoid operated valve that selectively fluidly couples one of two ports to a common port (labeled as C in the drawings). Three-port valves  22 ,  24  and  26  may be Humprey Mini-Mizers having part No. D3061, such as may be available from the John Henry Foster Co., or equivalents. By selectively applying voltage on a digital output signal line coupled to the three-port valve  22 , the processor  12  may be able to: couple gas from the gas source  10  to the common port and therefore to the exemplary left naris; and couple the pressure sensor  28  to the common port and therefore the exemplary left naris. Likewise, the three-port valve  24 , under command of the processor  12 , may: couple gas from the gas source  10  to the narial port  23  and therefore the exemplary right naris; and couple the pressure sensor  30  to the narial port  23  and therefore the exemplary right naris. Further still, three-port valve  26  under command of the processor  12 , may: couple gas from the gas source  10  to the narial port  25  and therefore the patient&#39;s mouth; and couple the pressure sensor  32  to the narial port  25  and therefore the mouth. When the pressure sensors  28 ,  30  and  32  are coupled to the respective ports, the processor  12  may read (through corresponding A/D converter  20  input signal lines) pressures indicative of airflow by the patient through the respective breathing orifice. Thus, the processor  12  may be able to determine when the patient is inhaling, and how much of the air drawn by the patient flows through each of the monitored breathing orifices. 
   Consider a situation where the preferential delivery system  100  couples to the nares of the patient by way of a bifurcated nasal cannula. As the patient inhales, outlet ports in the nasal cannula proximate to the openings of each naris experience a drop in pressure. The drop in pressure may be sensed through the nasal cannula and associated hosing by each of the pressure sensors  28  and  30 . Likewise, a sensing and delivery tube may be placed proximate to the patient&#39;s mouth, and thus pressure sensor  32  may detect an oral inspiration by the patient. In accordance with embodiments of the invention, the preferential delivery system  100  senses whether a patient has airflow through a monitored breathing orifice, and delivers therapeutic gas to the location or locations where the therapeutic gas may be inhaled by the patient. 
   Still considering the situation where the patient couples to the preferential delivery system  100  by way of a bifurcated nasal cannula and a separate sensing and delivery tube for the mouth, if there is no obstruction to inhalation in either of the nares or the mouth, therapeutic gas may be provided to any one or a combination of the nares and the mouth. Here, the preferential delivery system  100  may beneficially alternate the delivery site periodically so as to reduce discomfort associated with the therapeutic gas. Should the nasal cannula become partially dislodged, therapeutic gas may be provided only to the naris where the outlet port of the nasal cannula is still in operational relationship to the naris. Should the patient&#39;s nares become congested or blocked, therapeutic gas may be provided to the naris that is open. 
   The embodiments of the invention described above may work equally well in systems delivering a continuous flow of therapeutic gas, as well as systems operating in a conserve mode. In the continuous mode of operation, each of the three-port valves  22 ,  24  and  26  may couple therapeutic gas to their respective breathing orifice for extended periods of time, e.g. several respiratory cycles. Periodically, therapeutic gas delivery may cease and the preferential delivery system  100  may monitor the breathing pattern of the patient. That is, one or more of the three-port valves  22 ,  24  and  26  may change valve position, thus coupling pressure sensors to their respective breathing orifices and stopping therapeutic gas flow. If a monitored breath or breaths show that none of the possible breathing orifices are blocked, then the system  100  may simply switch back to the continuous mode of operation. If the preferential delivery system cannot detect an inhalation for any one of the breathing orifices, continuous flow mode may be resumed without providing therapeutic gas to the breathing orifice experiencing a problem. 
   In alternative embodiments, the preferential delivery system  100  may operate in a conserve mode, delivering a bolus of gas during each inhalation of the patient. Consider for purposes of explanation the left naris illustrated in  FIG. 1 , as well as its associated three-port valve  22  and pressure sensor  28 . Prior to an inspiration, the three-port valve  22  may couple the pressure sensor to the common port of three-port valve  22  and therefore the left naris. As the patient starts an inhalation, as sensed by the pressure sensor  28  and read by processor  12 , the three-port valve  22  changes valve position (as commanded by processors  12 ) and couples the therapeutic gas source  10  to the common port (and effectively blocking the pressure sensor from the common port). For a period of time, e.g. 100 mili-seconds, therapeutic gas may flow to the exemplary left naris. When the desired bolus volume has been delivered, possibly as a function of flow rate of the therapeutic gas and time, the processor  12  may command the three-port valve  22  to its original state, again fluidly coupling the pressure sensor  28  to the left naris. During exhalation, again sensed by pressure sensor  28 , the three-port valve  22  remains in the valve position coupling the pressure sensor to the common port, and therefore no therapeutic gas is delivered. This exemplary process is equally applicable to three-port valve  24  and pressure sensor  30  in operational relationship to the right naris, as well as three-port valve  26  and pressure sensor  32  in operational relationship to the patient&#39;s mouth. Thus, in conserve mode, the preferential delivery system  100  may detect whether the nares and/or mouth are open to therapeutic gas flow with each inspiration. In the event an inspiration on any particular delivery path is not detected, indicating a blockage or other gas delivery problem (such as a dislodged cannula), the preferential delivery system  100  may refrain from providing therapeutic gas to that breathing orifice. 
     FIG. 2A  illustrates the preferential delivery system  100  of  FIG. 1  in a shorthand notation, showing only pressure sensors  28 ,  30  and  32  coupled to the respective breathing orifices.  FIG. 2B  illustrates alternative embodiments of the invention monitoring and delivering therapeutic gas only to the nares of a patient. In the embodiments of  FIG. 2B , if both the left naris and right naris are open to flow the preferential delivery system  100  may deliver therapeutic gas to either naris, to both nares, or in an alternating fashion. In the event that either the left or right naris become clogged or blocked, or if the sensing and delivery tubing (such as a nasal cannula) become dislodged, the preferential delivery system may provide therapeutic gas to the naris where airflow is sensed.  FIG. 2C  illustrates alternative embodiments of the invention where two pressure sensors are used, but in this case only one pressure sensor is associated with the nares, and the second pressure sensor is associated with the mouth. In the embodiments of  FIG. 2C , a patient may utilize a single lumen cannula and a second sensing and delivery tube associated with the mouth. The preferential delivery system  100  may thus selectively provide therapeutic gas to the nares and/or to the mouth. In the event that either of the nares as a group or the mouth become blocked or otherwise unavailable for inspiration, the preferential delivery system  100  preferably provides therapeutic gas to the breathing orifice through which inhalation takes place. 
     FIG. 3  illustrates a preferential delivery system  102  constructed in accordance with alternative embodiments of the invention. Like the system of  FIG. 1 , the preferential delivery system  102  comprises a processor  12 , possibly in the form of a microcontroller, comprising ROM  14 , RAM  16 , a D/A converter  18  and an A/D converter  20 . Rather than pressure sensors, the preferential delivery system  102  may use flow sensors  40 ,  42  and  44 . Thus, the preferential delivery system  102  may sense a portion of the flow associated with each breathing orifice. Consider for purposes of explanation the flow sensor  40  and three-port valves  46 ,  48  coupled to the left naris. Three-port valve  46 , under command of the processor  12 , may: couple the gas source  10  to the common port and therefore the exemplary left naris; and couple the flow sensor  40  to the common port and therefore the exemplary left naris. Thus, during a period of time when the preferential delivery system  102  provides therapeutic gas to the left naris (whether continuous or in a bolus form), the three-port valve  46  provides the therapeutic gas to the left naris and blocks the flow sensor. In a second valve position, the three-port valve  46  fluidly couples the flow sensor to the common port and therefore the exemplary left naris. However, and in accordance with embodiments of the invention, the flow sensor  40  may not be operational until gas can flow through the sensor. Three-port valve  48 , in a first valve position, couples the flow sensor  40  to an atmospheric vent (marked ATM in the drawing), thus allow gas to flow through the flow sensor for measurement purposes. The three-port valve  48 , in a second valve position, couples to a blocked port  49 . Consider for purposes of explanation a preferential delivery system  102  operating in a conserve mode, where a bolus of gas is provided to one or more breathing orifices during inspiration. After a bolus has been delivered, the three-port valve  46  (and possibly the three-port valves  50  and  54 ) may change valve positions, thus fluidly coupling the flow sensor  40  to the common port and the exemplary left naris. If the flow sensor  40  outlet is not blocked, a portion of the therapeutic gas may reverse flow through the flow sensor  40  and out the atmospheric vent. Three-port valve  48  (as well as corresponding three-port valves  52  and  56 ) may be used to temporarily block reverse flow and loss of therapeutic gas, i.e. the valves may remain in a position that blocks flow for about 300 milliseconds after therapeutic gas delivery has stopped by a change of valve position by upstream three-port valves  46 ,  50  and  54 . After the expiration of the period of time of possible reverse flow has ended, one or more of the three-port valves  48 ,  52  and  56  may change valve positions, thus allowing the flow sensors to sense airflow. The description with respect to the three-port valves  46 ,  48  and flow sensor  40  for the left naris is equally applicable for the corresponding structures for the right naris and mouth. 
     FIG. 4A  illustrates the preferential delivery system  102  of  FIG. 3  in a shorthand notation, showing only flow sensors  40 ,  42  and  44  coupled to their respective breathing orifice.  FIG. 4B  illustrates alternative embodiments of the invention where only a patient&#39;s nares are used for sensing and delivery. In the embodiments of  FIG. 4B , if both the left naris and the right naris are open to flow, the preferential delivery system  102  may deliver therapeutic gas to either naris, to both nares, or in an alternating fashion. In the event that either the left or right naris become clogged or blocked, or if the sensing and delivery tubing become dislodged, the preferential delivery system may provide therapeutic gas only to the unblocked naris.  FIG. 4C  illustrates further alternative embodiments where two flow sensors are used, but in this case only one flow sensor is associated with the nares, and the second flow sensor associated with the mouth. In the embodiments of  FIG. 4C , a patient may utilize a single lumen cannula, and a second sensing and delivery tube associated with the mouth. The preferential delivery system  100  may thus selectively provide therapeutic gas to the nares and/or the mouth. In the event that either of the nares as a group or the mouth become blocked or otherwise unavailable for inspiration, the preferential delivery system  102  preferably provides therapeutic gas to the open breathing orifice. 
     FIG. 5  illustrates alternative embodiments of the invention utilizing flow sensors, but reducing the number of three-port valves used. The electrical components have been omitted from  FIG. 5  for purposes of clarity. In particular,  FIG. 5  illustrates that the three three-port valves  48 ,  52  and  56  of  FIG. 3  may be replaced by a single three-port valve  58 . Blocking reverse flow through the flow sensors in the embodiments of  FIG. 5  may be accomplished by single three-port valve  58 . Relatedly, opening the second port of each of the flow sensors to the atmosphere vent so that flow may be detected may likewise be accomplished with a single three-port valve  58 . 
   The embodiments discussed to this point control therapeutic gas flow in a boolean fashion. That is, therapeutic gas is either delivered to a breathing orifice, or the preferential delivery systems  100 ,  102  refrain from delivering therapeutic gas to a breathing orifice. However, alternative embodiments of the invention, which may be implemented using any of the exemplary embodiments described above, may control flow to each breathing orifice in proportion (either direct or inverse) to the amount of airflow drawn by that breathing orifice. Consider, for purposes of explanation, the pressure and flow sensor embodiments illustrated by  FIGS. 2B and 4B . For a variety of reasons, such as congestion, physical abnormalities, periodic swelling of the nasal tissue, and the like, the amount of air flow drawn by a patient during inhalation through the nares may not be equal. By detecting a pressure and/or detecting a portion of the air flow through each naris, the preferential delivery systems  100 ,  102  may quantify the relationship between the air flow as between the nares. For example, the left naris of an exemplary patient may carry 20% of the airflow, and the right naris of a patient may carry the remaining 80% of the air flow. In the embodiments discussed above, therapeutic gas may only be delivered to the right naris, carrying the bulk of the airflow. In the alternative embodiments, the selective delivery systems  100 ,  102  may proportion delivery of therapeutic gas. In the example of an 20–80 split between the left naris and the right naris respectively, the preferential delivery system  100 ,  102  may correspondingly proportion therapeutic gas flow 20% to the left naris and 80% to the right naris, or vice-versa. As the patient&#39;s left naris becomes less congested (or the patient changes head position that affects air flow or swelling, the preferential delivery system may likewise change the proportion of therapeutic gas flow. Referring again to  FIG. 3 , proportioning therapeutic gas flow may be accomplished by pulse width modulating each of the three-port valves  46 ,  50  and  54  by the processor  12 . In an exemplary situation where a patient&#39;s left naris carries only 20% of the total airflow and control is a direct proportion, the electrical signal from the processor  12  to the three-port valve  46  may be pulse width modulating at a duty cycle where only 20% of the therapeutic gas is delivered to the left naris. Although the discussion with respect to the alternative embodiments where therapeutic gas may be proportioned between breathing orifices focused only on proportioning the nares, the proportioning may likewise be done between the nares in general and the mouth, or all three breathing orifices. 
   In all of the embodiments, in the event an inhalation is not detected through any breathing orifice, an alarm may be sounded. Relatedly, if the preferential delivery systems sense an apnea event, an alarm may be sounded. Moreover, the patient&#39;s breathing patterns may be stored, such as in RAM  16 , and communicated to external devices through communication port  17 . 
   The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, while the use of a cannula, at least with respect to coupling the preferential delivery system to the nares, has been discussed, this is only exemplary and any system and method by which the therapeutic gas is fluidly coupled from the preferential delivery system to the breathing orifices of the patient may be equivalently used. A single lumen cannula may be operable in some situations with respect to the nares. Likewise, a bifurcated nasal cannula may be used with respect to the nares. Alternatively, a cannula may be used where the sensing lines couple to the flow sensors are separate and distinct from the lines in which therapeutic gas is delivered proximate to the breathing orifices. Further, while the various embodiments described use electrical components as the control system, other pneumatic/mechanical systems may be equivalently used. It is intended that the following claims be interpreted to embrace all such variations and modifications.