fig1 illustrates a first embodiment of tonometric catheter 20 . the tonometric catheter comprises a length of suitable tubing 22 , one end 32 of which is closed , and the opposite end of which has a connector such as a luer - lock 24 . luer - lock 24 is adapted to receive a complementary fitting 26 , which in turn couples through a second length of tubing 28 to a three - way stopcock 30 . three - way stopcock 30 may be used to selectively connect tubing 28 to various sources of irrigation or aspiration . adjacent the closed end 32 , tubing 22 is perforated as at 34 . a balloon - like tonometric catheter membrane 36 is fitted over the closed end so that the perforations 34 are enclosed , as illustrated . the tonometric catheter membrane 36 has an internal sleeve diameter at 38 which forms a tight fit with tubing 22 . the preferred form of tonometric catheter membrane is polydimethylsiloxane elastomer . the membrane may be sealed to the tubing 22 with appropriate adhesive so that the tonometric catheter membrane is sealed in a closed relationship to the outer wall of tubing 22 , thereby forming a sampling chamber 40 adjacent closed end 32 . the tonometric catheter membrane has a certain elasticity to allow the membrane to expand when filled with an aspirating liquid in order to contact the wall of the organ under examination , as will be explained below . the membrane 36 is preferably constructed such that at least a portion of it is selectively permeable to the gas or fluid property of interest . in a preferred embodiment , it is selectively permeable to hydrogen , oxygen , or h + , so that ph , pco 2 and / or po 2 can be measured . it is also preferably impermeable to other materials that would interfere with the desired measurements , such as other gases , proteins , and the like . in a highly preferred embodiment , an ion - selective membrane is employed . bonded to either the inner wall or the outer wall of tubing 22 are one or more sensors 42 for detecting a property indicative of ph and / or temperature . two such sensors are illustrated in fig1 bonded to the outside wall of tubing 22 with suitable adhesive . fig2 a and 2b illustrate two alternate means of sensor attachment , fig2 a illustrating the sensor attached to the inner wall of tubing 22 and fig2 b illustrating the sensor attached to the outer wall of tubing 22 . in a preferred embodiment , at least a portion of the tubing , but not all of it , is made of a co 2 impermeable material , such as polyester elastomers derived from the reaction of dimethylterephtalate 1 , 4 - butanediol and α - hydro - ω - hydroxypoly ( oxytetramethylene ). in a highly preferred embodiment , this is a material such as hytril , sold by dupont . for purposes of sensing temperature , thermistor devices are presently preferred . for sensing properties indicative of ph chemically responsive field effect transistors or &# 34 ; chemfets &# 34 ; may be employed . in this regard , chemfet sensors 44 have been illustrated in fig2 a and 2b . chemfet sensor 44 comprises a field effect semiconductor device 46 , which is encapsulated in a solution impervious material 48 , such as a polymerized epoxy resin . the encapsulation material 48 in turn may be encapsulated in a housing 50 ( fig2 a ). semiconductor device 46 is electrically coupled by bonding wires 52 to a terminal 54 . suitable electrical conductors such as conductor 56 are attached to terminal 54 for electrically communicating between the chemfet device 44 and the electronic circuitry described below in connection with fig9 . conductor 56 is preferably routed through tubing 22 and exits through a sealed aperture at or near the luer - lock end of tubing 22 , as at 58 . a more detailed description of a suitable electronic sensor may be found in u . s . pat . no . 4 , 020 , 830 to johnson , entitled &# 34 ; selective chemical sensitive fet transducers ,&# 34 ; incorporated herein by reference . in order to allow a solution to contact the chemically sensitive surface of semiconductor device 46 , tubing 22 may be provided with an aperture 60 when implementing the embodiment of fig2 a . such an aperture is not needed in the embodiment of fig2 b , since the semiconductor device 46 is exposed to sampling chamber 40 by virtue of the external mounting configuration . the sampling chamber 40 can be filled with an aspiration or sampling medium that is used to absorb or otherwise provide a means for incorporating and delivering or measuring the the fluids or gases of interest . such a medium is selected depending upon many factors , including the properties of the fluids or gases of interest , the type of sensor 42 employed , and the type of calibration that is necessary . such mediums include bicarbonate solutions and saline solution . it might be noted that gases often behave as fluids and are therefore frequently considered to be fluids . as noted above , when the sensor employed does not require frequent recalibration , the need for the sampling chamber 40 to be in communication with the proximate end of the tonometric catheter ( that remains outside the patient ) may be eliminated since no aspiration is needed . however , in many instances such communication may still be desirable as aspiration may be required to calibrate the sensor or sensors , to replace the aspirating or sampling medium with a fresh medium , and to incorporate the gas or gases of interest . another embodiment of the tonometric catheter is illustrated in fig4 a and 4b . as illustrated , the tonometric catheter is appropriately configured to also serve as a nasogastric sump , either with or without gastric suction . with reference to fig4 the tonometric catheter 20a comprises a multipassage tubing 62 which defines three individual noncommunicating ( between each other ) passageways or lumens , an air lumen 64 , an optional suction lumen 66 and a tonometric catheter lumen 68 . a tonometric catheter membrane , similar to that previously described , is attached at an intermediate location on tubing 62 , allowing a portion of the tubing to extend beyond the end of membrane 36 to define the nasogastric sump 70 . tubing 62 is provided with a plurality of perforations 72 which communicate between tonometric catheter lumen 68 and the sampling chamber 40 defined by membrane 36 , if desired , one or more sensors 42 can be included in accordance with the above teachings , in which case a suitable conductor 56 may be routed through tonometric catheter lumen 68 to exit at sealed aperture 58 . the nasogastric sump portion 70 is suitably provided with a plurality of openings 74 through which the stomach may be aspirated . at the opposite end of tubing 62 the tubing splits to form three separate connections . air lumen 64 communicates with air lumen passageway 76 , suction lumen connects with suction lumen passageway 78 and tonometric catheter lumen 68 communicates with tonometric catheter lumen passageway 80 . the tonometric catheter lumen passageway is fitted with three - way stopcock 30 , similar in function and purpose to the three - way stopcock 30 described in connection with fig1 . if desired , a quick connect fitting 82 may be used to couple the suction lumen passageway 78 with an aspiration source . as illustrated , the quick connect fitting preferably has angularly cut ends and a slightly enlarged midsection , making it easy to insert into the end of passageway 78 and also into the aspiration hose coupling ( not shown ). the enlarged midsection helps form a seal with the adjoining passageways . preferably the quick connect fitting is fabricated of disposable plastic . yet another embodiment of the tonometric catheter is illustrated in fig5 and 5a . this embodiment is a multiple tonometric catheter embodiment employing a tubing 84 having a plurality of passageways or lumen as shown in the cross - sectional view of fig5 a . specifically , tubing 84 includes an air lumen 86a which communicates with the endmost tonometric catheter 36a and three additional tonometric catheter lumens 86b , 86c and 86d , which communicate respectively with tonometric catheters 36b , 36c and 36d . as with the other embodiments , each tonometric catheter may be provided with one or more sensors such as sensors 42 . a radiopaque tungsten plug 88 is positioned within each of the three tonometric catheter lumen 86b , 86c and 86d adjacent the distal end of each tonometric catheter , serving to block the remainder of the tonometric catheter lumen passageway and thereby ensuring that fluid pressure introduced into each tonometric catheter lumen will cause the associated tonometric catheter to balloon outwardly as required during use . similarly , a radiopaque tungsten rod 90 is fitted as a plug in the end of air lumen 86a , serving to terminate the end of the air lumen passageway . being radiopaque , the tungsten plugs and tungsten rod aid in properly positioning the tonometric catheters by being visible under fluoroscope or x - ray . in addition , if desired , tubing 84 can be provided with a radiopaque stripe along all or part of its length . at the proximal end of tubing 84 the lumen 86a - 86d diverge to define four separate tubes 92a - 92d . each tube is fitted with a three - way stopcock similar to those described above . each sampling connector may optionally be coded numerically by color , etc . while four approximately equally spaced tonometric catheters have been illustrated in fig5 it will be understood that the invention can be modified to include a greater or fewer number of tonometric catheters at different spacing as required for a particular application . it will also be understood that some or all of the tonometric catheters can include one or more sensors coupled to conductors 56 , each preferably routed through the corresponding lumen passageway . referring now to fig9 a suitable electronic monitoring circuit will now be described . in fig9 chemfet semiconductor device 46 has been shown schematically by the equivalent circuit model enclosed in dotted lines . the device 46 thus comprises drain electrode 150 , source electrode 152 and reference electrode 154 . the chemically selective system , such as a membrane system is depicted diagrammatically at 156 . the substrate is grounded as at 158 . source electrode 154 is coupled to an input lead of operational amplifier 160 which includes feedback network diagrammatically depicted at 162 . operational amplifier 160 senses the drain source current flowing through device 46 and converts this signal into a voltage signal which is output on lead 164 . the drain source current changes in accordance with changes in the chemical system under test . more specifically , as the pco 2 level changes in the fluid exposed to device 46 , the drain source current changes accordingly . hence the output voltage signal on lead 164 is likewise an indication of the pco 2 level of the organ under test . this voltage signal on lead 164 is coupled to an input of comparator 166 which also receives a reference voltage v ref , which may be supplied using a voltage divider network ( not shown ) or which may alternatively be provided by a digitally controlled voltage source 168 . the output of comparator 166 is fed to reference electrode 154 to provide a stable reference bias voltage . if a digitally controlled voltage source is used , this reference voltage can be adjusted and calibrated by a computer circuit yet to be discussed . the voltage signal on lead 164 is also fed to an analog to digital convertor 170 , which is in turn coupled to a microprocessor - based microcomputer 172 . in order to automatically determine the ph of the wall of the hollow viscous organ under test , a separate gas analyzer sensor 174 is used to determine the bicarbonate concentration in the arterial blood of the patient . the output of sensor 174 is coupled through analog to digital convertor 176 to microcomputer 172 . microcomputer 172 is preprogrammed to calculate the ph of the organ wall using the values provided by analog to digital convertors 170 and 176 . conversion of pco 2 measurements can be converted into ph measurements automatically by microcomputer 172 using various equations and references well - known in the art . although many different types of output devices may be employed , strip chart recorder 178 and crt monitor 180 have been illustrated . strip chart recorder 178 and monitor 180 are coupled as output devices to microcomputer 172 . strip chart recorder 178 offers the advantage of developing an easily readable , permanent record of the fluctuations in organ wall ph . monitor 180 offers the advantage of providing digital readout of the ph value as well as displaying the upper and lower excursions of ph fluctuation . if desired , microcomputer 172 can be preprogrammed using keyboard 182 to compare the instantaneous ph value with doctor - selected upper and lower alarm limits . if the measured instantaneous ph fluctuates outside those limits , microcomputer 172 can sound an alarm to alert hospital staff . while a single semiconductor device 46 has been illustrated in conjunction with the electronic circuit of fig9 the circuit may be readily adapted for use with a plurality of semiconductor devices in order to measure the ph at different locations substantially simultaneously . in such an embodiment , the data coming from each sensor can be fed to a separate i / 0 port of microcomputer 172 . in the alternative , a single i / 0 port can be used with the individual input signals being time multiplexed . as an alternative to electronic ph sensors , the invention may also be practiced using optical sensor technology . referring to fig1 , the presently preferred optical sensor embodiment uses a first fiber optic cable 94 which is optically coupled through a series of lenses 96 , selectable color filters 98 and heat absorber 100 to an illumination source 102 , such as a 100 watt tungsten - halogen lamp . fiber optic cable 94 is routed through the tonometric catheter lumen in a fashion similar to the conductor 56 of the above - described embodiments , with the end thereof protruding through the tubing and into the sampling chamber 40 . a second fiber optic cable 104 is routed parallel to the first fiber optic cable 94 , with one end protruding through the tubing and held in place adjacent the end of first cable 94 with a collar 106 . collar 106 may be adhesively bonded to the outside wall of the tubing . the opposite end of second fiber optic cable 104 is positioned for optically coupling with a phototransistor 108 which is electrically connected to an operational amplifier circuit 110 . the operational amplifier circuit can be coupled to an analog to digital converter , such as a / d converter 170 of fig7 . in use , fiber optic cable 94 illuminates a region within the sampling chamber 40 which is filled with a sampling fluid containing a colorimetric ph indicator , the illumination from fiber optic cable 94 reflects from the molecules suspended in the ph indicator solution , with some of the reflected illumination passing back through second fiber optic cable 104 to the phototransistor . by selecting the appropriate filter 98 , a monochromatic illumination or illumination of otherwise known spectral content is employed to illuminate the colorimetric ph indicator solution . when the color of the filtered illumination matches that of the indicator , the illumination is absorbed and a low illumination signal is received at the phototransistor . when a ph change causes a color change in the indicator away from the color of the filtered illumination , more illumination is reflected back to the phototransistor , with an attendant increase in detected signal output . in this fashion , the proper selection of indicator dye and illumination filtration can be used to detect ph ranges . for a further description of fiber optic ph sensor technology , refer to g . g . vurek &# 34 ; a fiber optic pco 2 sensor ,&# 34 ; annals of biomedical engineering , vol . 11 , pp . 499 - 510 , 1983 , which is available from pergamon press , ltd ., and is expressly incorporated herein by reference . while the preferred embodiments have been disclosed in connection with monitoring of the gastrointestinal tract and the urinary and ureteric tracts it will be appreciated that its principles are applicable to other hollow internal organs to monitor ph and hence perfusion of those organs . also while several presently preferred detailed constructions for tonometric catheters have been disclosed , it will be appreciated that other constructions may be developed which are equally suitable . the disclosed constructions are presently preferred for the reason that they are readily fabricated using existing available materials . other embodiments may include other , but equivalent materials for the tonometric catheter membrane and / or connective tubing . they may also differ in the specific fabrication details . as an example , the sampling chamber may be eccentric rather than symmetric about the connective tubing . in still another embodiment , conventional gas analyzers may be employed externally . a device such as that shown in fig1 may be used in combination with a pump or aspiration means ( not shown ) for continuous or regular intermittent aspiration of a sample of the aspirating liquid or medium that is used to fill the sampling chamber 40 . the sample removed by pump or aspiration means via attachment to the luer - lock 24 can be optionally designed so that the sample aspirated at each sampling interval can be brought in contact with an exterior , separate gas analyzing means or sensor ( not shown ) to determine the ph , po 2 , pco 2 and / or the like , of the sample . such automatic sampling can be conducted employing a system as shown in fig1 . in the assembly a sampling system employs a personal computer to conduct evaluations and analysis of the samples withdrawn from the tonometric catheter 299 . pump 203 is loaded with the sampling or aspirating medium such as saline . next , valve 201 is activated to withdraw a desired amount of the sampling fluid . the valve 201 is deactivated and pump 203 is used to enforce the sampling chamber of the tonometric catheter 299 using a calibrated amount or optionally a pressure transducer 215 . the sampling fluid or medium is allowed to come to equilibrium with the wall of the organ or area of interest . next the &# 34 ; dead space ,&# 34 ; i . e ., the area of the lumen filled with the sampling fluid that is not in equilibrium , is removed by activating valve 205 , activating pump 207 , activating valve 209 and infusing pump 207 ; the waste 219 is discarded . a sample for analysis is then withdrawn by deactivating valve 209 , activating pump 207 to then deliver the sampling to a gas analyzer ( not shown ) that provides data from the sample to the pc 217 , and the evaluation is conducted as described herein . the sample gas analyzer or a separate gas analyzer may be employed to determine the bicarbonate concentration in the arterial blood of the patient , as described above . another embodiment of the tonometric catheter is illustrated in fig1 and 11a . as illustrated , the tonometric catheter is appropriately configured to also serve as a urinary or ureteric catheter , either with or without suction , which optionally employs sensors . with reference to fig1 and 11a , the tonometric catheter 220 comprises a multipassage tubing 262 which defines three individual noncommunicating ( between each other ) passageways or lumens , an optional air or irrigation lumen 264 , a drainage or suction lumen 266 and a tonometric catheter lumen 268 . a tonometric catheter membrane , similar to that previously described , is attached at a distal location on tubing 262 , allowing an intermediate portion of the tubing not extending beyond the end of membrane 236 to define the uretary or uretary catheter 270 . tubing 262 is provided with a plurality of perforations 272 which communicate between tonometric catheter lumen 268 and the sampling chamber 240 defined by membrane 236 . if desired , one or more sensors 242 can be included in accordance with the above teachings , in which case a suitable conductor 256 may be routed through tonometric catheter lumen 268 to exit at sealed aperture 258 . the urinary catheter or ureteric catheter portion 270 is suitably provided with a plurality of openings 274 through which the bladder or ureters may be aspirated or irrigated . at the opposite end of tubing 262 the tubing splits to form three separate connections . air or irrigation lumen 264 optionally communicates with air lumen passageway 276 , urinary lumen connects with suction or drainage lumen passageway 278 and tonometric catheter lumen 268 communicates with tonometric catheter lumen passageway 280 . the tonometric catheter lumen passageway is fitted with three - way stopcock 230 , similar in function and purpose to the three - way stopcock 30 described in connection with fig1 . if desired , a quick connect fitting 82 as seen in fig4 may be used to couple the suction urinary passageway 278 with an aspiration source . as illustrated , the quick connect fitting preferably has angularly cut ends and a slightly enlarged midsection , making it easy to insert into the end of passageway 278 and also into the aspiration hose coupling ( not shown ). the enlarged midsection helps form a seal with the adjoining passageways . preferably the quick connect fitting is fabricated of disposable plastic . yet another embodiment of the urinary catheter / tonometric catheter combination illustrated in fig1 and 11a may employ a multiple tonometric catheter embodiment employing a tubing having a plurality of passageways or lumen as shown in the cross - sectional view of fig5 a . in another embodiment * of the present invention , a tonometric catheter may be adopted to deliver a pharmaceutically - active agent , either for systemic , local or topical activity , or a combination thereof . for example , an additional lumen may be added such as that and for irrigation or aspiration , to deliver the active . for example , the irrigation / aspiration lumen 264 shown in fig1 and 11a , may be used to deliver an active agent . in another embodiment , a portion of the device may be modified so as to provide sustained release of the active agent of interest . thus , for example , the problems of nosacomial infection associated with catheter insertion can be overcome by incorporating an antimicrobial into at least a portion of the polymeric material used to manufacture the tonometric catheter , or by coating at least a portion of the device with a sustained release composition , or by delivering the antimicrobial via the tonometric catheter . such modifications are well known to those skilled in the art . see u . s . pat . no . 4 , 677 , 143 , incorporated herein by reference . classes of useful agents include antimicrobial agents , nonsteroidal anti - inflammatory agents , topical anesthetics , topical vasodialators , metabolic suppressants , and other agents that could be delivered for absorption at the sites of the tonometric catheter . accordingly , while several preferred embodiments of the invention have been disclosed , it will be appreciated that principle of the invention , a set forth in the following claims , are applicable to other embodiments .
a tonometric device for use in hollow viscus tonometry and remote sensing of patient fluid parameters is disclosed . the device is capable of monitoring certain critical fluid properties of interest , such as oxygen gases and carbon dioxide gases in the wall tissue itself of the patient &# 39 ; s organ , rather than monitoring such properties in a lumen of the organ . a walled sampling chamber , which is preferably an inflated balloon member , is provided on an elongated tube , with provisions for positioning the sampling chamber in direct contact with a wall portion of the patient &# 39 ; s internal organ .