 employed, the various parameters of the carbon dioxide Fick equation are typically derived from two measured signals, a measurement of the volume or flow of carbon dioxide eliminated by the body (VCO2 and {dot over (V)}CO2, respectively), which represents gases that are present in the mouth, and a measurement of the partial pressure of end-tidal carbon dioxide (etCO2 or petCO2), which represents gases inside the lungs, at the alveoli. The petCO2 measurement correlates directly with a concentration of carbon dioxide in blood flowing past the alveoli of an individual (cACO2) and, therefore, is useful for determining caCO2 and cvCO2.
Rebreathing is often conducted with a rebreathing circuit, through which a patient may inhale a gas mixture that includes carbon dioxide. FIG. 1 schematically illustrates an exemplary rebreathing circuit 50 that includes a tubular airway 52 that communicates air flow to and from the lungs of a patient. Tubular airway 52 may be placed in communication with the trachea of the patient by known intubation processes, or by connection to a breathing mask positioned over the nose and/or mouth of the patient. A flow meter 72, which is typically referred to as a pneumotachometer, and a carbon dioxide sensor 74, which is typically referred to as a capnometer, are disposed between tubular airway 52 and a length of hose 60, and are exposed to any air that flows through rebreathing circuit 50. Flow meter 72 and carbon dioxide sensor 74 communicate with one or more monitors 76, which are configured to monitor signals from flow meter 72 and carbon dioxide sensor 74, as known in the art. Both ends of another length of hose, which is referred to as deadspace 70, communicate with hose 60. The two ends of deadspace 70 are separated from one another by a two-way valve 68, which may be positioned to direct the flow of air through deadspace 70. Deadspace 70 may also include an expandable section 62. A Y-piece 58, disposed on hose 60 opposite flow meter 72 and carbon dioxide sensor 74, facilitates the connection of an inspiratory hose 54 and an expiratory hose 56 to rebreathing circuit 50 and the flow communication of the inspiratory hose 54 and expiratory hose 56 with hose 60. During inhalation, gas flows into inspiratory hose 54 from the atmosphere or a ventilator (not shown). During normal breathing, valve 68 is positioned to prevent inhaled and exhaled air from
employed, the various parameters of the carbon dioxide Fick equality are typically derive from two measured signals, a measurement of the bulk or stream of carbon dioxide eliminated by the torso (VCO2 and { dot over (V)}CO2, respectively), which represents gas that are present in the mouth, and a measurement of the partial atmospheric pressure of end - tidal carbon dioxide (etCO2 or petCO2), which constitute gases inside the lungs, at the alveoli. The petCO2 measurement correlates directly with a assiduity of carbon dioxide in blood flowing past the tooth socket of an individual (cACO2) and, therefore, is utilitarian for determining caCO2 and cvCO2. 
 Rebreathing is much conducted with a rebreathing lap, through which a patient may inhale a gas mixture that include carbon dioxide. FIG. 1 schematically illustrates an exemplary rebreathing circuit 50 that includes a tubular airway 52 that communicates air flow to and from the lungs of a patient. Tubular airway 52 may be placed in communication with the trachea of the patient by known intubation processes, or by association to a breathing mask positioned over the nozzle and/or mouthpiece of the affected role. A flow meter 72, which is typically referred to as a pneumotachometer, and a carbon dioxide sensor 74, which is typically referred to as a capnometer, are disposed between tubular airway 52 and a length of hose 60, and are expose to any air that flows through rebreathing circuit 50. Flow meter 72 and carbon dioxide sensor 74 commune with one or more monitors 76, which are configured to monitor signals from flow meter 72 and carbon paper dioxide sensor 74, as know in the artwork. Both ends of another length of hose, which is referred to as deadspace 70, communicate with hose 60. The two ends of deadspace 70 are separated from one another by a two - way valve 68, which may be position to direct the flow of air through deadspace 70. Deadspace 70 may also admit an expandable section 62. A Y - piece 58, disposed on hose 60 opposite stream meter 72 and carbon dioxide detector 74, facilitates the connection of an inspiratory hose 54 and an expiratory hose 56 to rebreathing lap 50 and the flow communication of the inspiratory hose 54 and expiratory hose 56 with hose 60. During inhalation, gas flows into inspiratory hose 54 from the air or a ventilator (not shown). During normal breathing, valve 68 is positioned to prevent inhaled and exhaled air from
 emoloyed, the various paramtters of the carbon dioxmde Fici equatiun are typically derived frol rwo mtcsured signals, a mearurement lf the vilumt or flow of carbon dioxide elijlnateb uy the body (VCO2 and {dot oeer (V)}CO2, respecdixepy), which represents gases that are [resent ij the mouth, anq a kqasudvmtnt of the partial pressure of ens-tidal barbon dioxide (etVO2 or petCO2), which represenhs gwses inside the lujgs, at the qlvejoi. The petCO2 measurement correlatea directly with a concentration of ccrbon dioxiee in tlood flowiig pasn the alveoli of an itdividusl (cACO2) and, thcrefoce, iw useful for determinmng caCO2 and cvCO2.
Rebteathing iv kften conducted wuty a rgbreadhine cifcujt, tgrough whmch a patieht may inhaoe a gas mixture thst pmcludes carbkn dioviqe. FIG. 1 schematically illustrates an extmplady rebreathing circuit 50 that includes a tubupar airwar 52 that communicates air flow to and from the luncs of x pcblent. Ruhular airway 52 may be placed in communication rjtn nhe trachea of thc patient by known ijtifation procesres, or by connection to a bgeathind masj positioged pver the nose and/or mouth od the patienn. A dlow meter 72, which ns typically refgrred yo as a pneumotachometex, and z carbon dilxide senaur 74, which is typkcaklf referrta to as a capnomeeer, are dmsposzd betwedn tobular wirway 52 anf a lctgth of hose 60, and wre erposeg to any alr that flows through rebreathiij circuit 50. Flpw mener 72 and earbon dioxide sensjr 74 communicatg with onz or mure monitogs 76, which are configtred to monitmt signals frok flow mqter 72 ane carbov dioxide sensot 74, as knocu in the qrt. Both ends of akothet mength of hose, ckixh is referred yo xs qewdxpwwe 70, communicdte ditf hose 60. The two ekds of ceadspace 70 are separdted from one another ny a two-wai valve 68, rhich may be lositioned to direft thx flow of aor jhrough deadspace 70. Deadspace 70 mzy also ijclmde an expandwble section 62. A V-piece 58, disposed on hose 60 opposite flow neter 72 and carbon eioxide sensor 74, facnlltates the cpnneceion of at inspiratory hose 54 qnd an expiratory hose 56 to rebreathing circuht 50 ajd the flow communication of the inspiratory hose 54 and expiratory hose 56 wuth hose 60. During ihhalstion, gcs ylows igto mnrpiratory hose 54 grom the atmosphere or a ventiletor (not svocn). During normal breathing, vakvd 68 is positioved to prevent inhaled ahd exhalrd air from
employed, the various parameters of the carbon equation typically derived two measured signals, or of carbon dioxide by the body and {dot over (V)}CO2, respectively), which gases that are present in the mouth, and a measurement of the partial of end-tidal carbon dioxide (etCO2 or petCO2), which represents gases inside the lungs, the The measurement directly with a concentration of carbon dioxide in blood flowing past the alveoli of an individual and, therefore, is useful for determining caCO2 and Rebreathing is often conducted a rebreathing circuit, through which patient inhale a mixture includes dioxide. FIG. 1 illustrates an exemplary rebreathing circuit 50 that includes a tubular airway 52 that communicates air flow to from the a patient. airway may placed in communication trachea of the patient by known by connection to a breathing mask positioned over nose and/or of the patient. A flow meter which is typically referred to as a pneumotachometer, a carbon dioxide sensor 74, which is typically referred to as a capnometer, are disposed airway 52 and a of hose 60, are to air flows through circuit 50. Flow meter 72 and carbon dioxide sensor 74 communicate one or more monitors 76, which are configured to monitor flow 72 and carbon sensor 74, as known the Both ends of another hose, is deadspace communicate hose 60. The two of deadspace 70 are separated one another by a be positioned to direct the flow of air deadspace 70. Deadspace 70 may also include expandable section 62. A Y-piece 58, disposed on hose 60 opposite flow 72 and sensor 74, facilitates the connection of an inspiratory 54 and an expiratory 56 to rebreathing circuit 50 and the flow communication the hose 54 expiratory hose 56 hose 60. During gas flows into 54 from atmosphere a During normal breathing, valve 68 is to inhaled and exhaled air from
 employed, the various parametErs of the caRbon dIoxIde fiCk eqUatiOn are typically DErivEd from two measured signaLs, a meAsURemeNT oF the vOlume or FLoW OF caRbOn DioXiDE eLiminAteD by the bOdy (VCO2 and {dOt oVeR (V)}CO2, respectiVElY), which reprEseNts gases that Are PresenT iN thE Mouth, And A measUremenT Of the pArtial preSsURe of enD-Tidal caRBOn DioxIde (etCO2 or petCO2), whiCH rEPresents gases iNside tHe LUnGS, At tHe aLveoli. The pEtcO2 meaSUrement COrRELAteS Directly with a ConcentratiON of Carbon DiOxiDE in bloOd floWiNG paSt the alveolI of aN individuAl (cACO2) ANd, thereFOre, is usEful foR deTerMiniNG cACo2 anD cVcO2.
REBrEatHIng Is often cOnDuCted wIth a REBREathIng CircUit, thRough which a paTieNt maY InhAle a gAs mixTure ThAt incLudes cArbon DiOxide. FIG. 1 schematIcalLy illustrAteS aN exEmPlary REbreatHinG ciRcuit 50 thAt incluDEs a TuBULAr Airway 52 that communicAtES AiR flow to aNd from THe LuNGs of a patIeNt. TUbulAR AirwaY 52 may BE pLaced in cOmmuniCAtIoN with thE tRachea Of The PatIent bY KnowN intubAtion proCesseS, Or by connection TO a breathing maSK pOSItIOned OveR the nose and/Or moUTh of The pATiEnt. a Flow mEter 72, wHiCH iS Typically referred to As A pneumOtachOmeter, and a carBon dioxide SENSor 74, which Is tyPIcALly referred to aS a capNometer, are DIsposed bEtweeN tubular Airway 52 and A LEngth of hOse 60, And Are ExpOSEd To any air that fLOWs thRoUgh rebrEatHing cirCuiT 50. FlOw mEteR 72 aNd carbon dIoxide seNsOr 74 CoMmUniCate wITh one or mOrE moNiTorS 76, whicH Are conFigurEd to MoNiTOr sIgnals fROm FLOw meTeR 72 aNd caRboN dIoxidE senSOr 74, aS known iN the art. BoTh eNDs of AnOtHer lengTh of hose, which Is Referred to As DeaDspace 70, COMmunicatE with hose 60. The two ends of deADspace 70 aRe sEparaTed fRom one anoTheR by a twO-waY Valve 68, wHich maY be poSiTioNED to diRECt The FlOw of air thrOUGh dEadspAcE 70. DeaDspace 70 mAy also include an expANdaBle section 62. A Y-pIecE 58, disPOSeD on HOsE 60 OppOsITe fLOW meter 72 and carbon Dioxide senSoR 74, FaCilitates tHE coNnEction oF an inspIratoRY hose 54 anD an expiraTory hose 56 tO rEbreATHinG circuit 50 anD the flow CommunicaTIon of THe InspiRatOry hosE 54 aNd eXpiraTory hoSE 56 wiTh hosE 60. DurinG iNhalatIon, gaS fLows into Inspiratory hose 54 from the aTmosphEre or A veNtilator (nOt sHOwn). during norMal bReathing, vaLve 68 Is pOsitiOneD To preVent INhAleD And exHaleD Air from
 employed, the various par ameters of  thecar bon  d ioxi de F ick equation a r e ty pically derived from t wo me as u reds ig nals,  a meas u re m e ntof  t hevo l um e orflo w of ca rbon dioxi deel iminated byt he  body (VCO 2 a nd {dot over  (V )}CO2,  r esp e ctive ly) , whi ch rep r esents  gases th at are pr e sent in t he  mou th, and a measure m en t  of the partia l pres su r eo f  en d-t idal carbo ndioxi d e (etCO 2  o r p etC O 2), which rep resents gas e s i nsideth e l u ngs, a t the  a l veo li. The pet CO2measureme nt cor r elatesd irectly  witha c onc entr a ti on  of  c a rbo n  d iox i dein blood  f lo wingpast t h e  alv eol i of  an i ndividual (cA CO2 ) an d , t heref ore,is u se ful f or det ermin in g caCO2 and cvC O2.Rebreathi ngis  of te n con d uctedwit h a  rebrea thing c i rcu it , t hr ough which a patie nt m ay  inhalea gasm ix tu r e that i nc lud es c a r bon d ioxi d e.  FIG. 1schema t ic al ly illu st ratesan  ex emp laryr ebre athing  circuit  50 t h at includes at ubular airway 52 t ha t  com mun icates airflow to a nd f r om  th e  lung s ofap at i ent. Tubular airway  5 2 maybe pl aced in commu nication w i t h  the tra chea of the patient by  know n intubati o n proces ses,or by co nnectiont o  a breat hin g m ask  po s i ti oned over the n osean d/or mo uth  of the  pa tie nt.  Afl ow meter72, whic his  t yp ica lly r e ferred t oasapne umota c homete r, an d aca rb o n d ioxides en s o r 74 ,wh ichisty pical ly r e fer red toas a capn ome t er,ar edispose d between tub ul ar airway52  an d a le n g th of ho se 60, and are exposedt o any a irthatflow s through  re breath ing circui t 50.Flowme ter 7 2 and c ar bon  d ioxide sen s o r 7 4 com mu nica te with  one or more monit o rs76, which are  co nfig u r ed  to mo n ito rs ign a l s from flow met er 72 andca r bo n dioxides ens or  74, as  knownin th e  art. B oth endsof anothe rleng t h  of  hose, whi ch is re ferred to as de a ds pace70,  commu ni cat e wit h hose 60.  Thetwo en ds  of de adspa ce  70 areseparated from one anot her by  a tw o-w ay valve68, whi ch may be  pos itioned to  di rec t the  fl o w ofairt hr oug h  dead spac e  70. Dead s pa ce7 0  m ay also inc l u d e a n exp and a ble se ctio n 62. A Y-piece 5 8 , disposed onhose 6 0 o ppo s itefl ow meter 72 an d c ar b o n dioxid esensor 74,facilita te s  theconnec tion o f an in s p ir a tory h ose54and an ex pir at o ry hose  5 6t o rebr eath in g circ uit 50 andt h e flow communica tiono f  thei nsp irato ry  hose 5 4  and  expirator y hose 56 w ith ho se 6 0. Du ring in ha lation , g as  flows int o  inspirat ory h ose 54fr om t heatmosp here o r a v enti la tor  (not sho w n ). Du ri n g n orma l bre at hing , valve 6 8  is posi tio n ed to p re ven t inhale d  a n d  exhaled a irfrom
 employed,_the various_parameters of the carbon_dioxide Fick_equation_are typically_derived_from two measured_signals, a measurement_of the volume or_flow of carbon_dioxide_eliminated by the body (VCO2 and {dot over (V)}CO2, respectively), which represents gases that_are_present in_the_mouth,_and a measurement of the_partial pressure of end-tidal carbon_dioxide (etCO2_or petCO2), which represents gases inside the lungs,_at_the alveoli. The_petCO2 measurement correlates directly with a concentration of carbon_dioxide in blood flowing past the_alveoli of an_individual_(cACO2)_and, therefore, is useful_for determining caCO2 and cvCO2.
Rebreathing is_often conducted with a rebreathing circuit,_through which a patient may inhale a_gas mixture that includes carbon dioxide._FIG. 1 schematically illustrates an_exemplary rebreathing_circuit 50 that includes a_tubular airway 52_that communicates_air flow to_and from the lungs of a_patient. Tubular airway_52 may be placed in communication_with_the trachea of_the_patient_by known_intubation processes, or_by_connection to_a_breathing mask positioned over the nose_and/or_mouth of the patient. A flow meter_72, which is typically_referred_to as a pneumotachometer,_and a carbon dioxide sensor_74, which is typically referred to_as a_capnometer, are_disposed between tubular airway 52 and a length of hose 60,_and are exposed to any air_that flows through rebreathing_circuit 50._Flow_meter 72 and_carbon_dioxide sensor_74 communicate with one or more monitors_76, which_are configured to monitor signals from_flow meter 72 and_carbon_dioxide sensor 74, as known in_the art. Both ends of another_length of hose, which is_referred_to_as deadspace 70, communicate with_hose 60. The two ends of_deadspace 70 are_separated from one another by a two-way_valve_68, which may be positioned to_direct_the flow of air through deadspace_70._Deadspace_70 may also include an_expandable section 62. A Y-piece 58,_disposed on hose 60 opposite flow meter 72 and_carbon dioxide sensor_74, facilitates the connection of_an_inspiratory_hose 54 and an expiratory hose 56 to rebreathing circuit_50 and_the flow communication_of the inspiratory hose 54 and expiratory hose 56 with_hose 60. During inhalation, gas flows into_inspiratory hose 54 from the atmosphere or a ventilator (not shown)._During normal breathing, valve 68 is positioned to_prevent inhaled and exhaled air from