Ventilation, Transport of gases and oxygen delivery

Dr. Megha Jain

University College of Medical Sciences & GTB Hospital, Delhi

Contents

Lung volumesLung volumes Mechanics of ventilationMechanics of ventilation Work of breathingWork of breathing Diffusion of gasesDiffusion of gases Transport of gases and oxygen deliveryTransport of gases and oxygen delivery

Lung volumesLung volumes

Tidal volume-Tidal volume- Volume of air breathed in or out of the Volume of air breathed in or out of the lungs, during quiet respiration. Average: lungs, during quiet respiration. Average: 500ml 500ml in adult.in adult.

Inspiratory reserve volume-Inspiratory reserve volume- Maximal volume of air Maximal volume of air which can be inspired after normal tidal inspiration. which can be inspired after normal tidal inspiration.

Average: Average: 3000 ml.3000 ml.

Expiratory reserve volume-Expiratory reserve volume- Maximal volume that can be Maximal volume that can be expired below normal tidal expiration. Average: expired below normal tidal expiration. Average: 1100ml.1100ml.

Residual volume-Residual volume- Volume of air remaining in lungs after Volume of air remaining in lungs after maximal expiration. Average: maximal expiration. Average: 1200ml.1200ml.

Total lung capacity-Total lung capacity- Volume of air contained in lungs Volume of air contained in lungs after maximal inspiration. Averageafter maximal inspiration. Average: 5800ml.: 5800ml.

Lung volumesLung volumes

Vital capacity-Vital capacity- Maximal volume of air that can Maximal volume of air that can be exhaled following maximal inspiration. be exhaled following maximal inspiration. Average: Average: 60-70 ml/kg.60-70 ml/kg.

Functional residual capacity-Functional residual capacity- Lung volume at Lung volume at the end of normal exhalation. Average: the end of normal exhalation. Average: 2300ml.2300ml.

Closing capacity-Closing capacity- Volume at which the small Volume at which the small airways begins to close in the dependent parts of airways begins to close in the dependent parts of the lung. Normally – well below FRC, but the lung. Normally – well below FRC, but ↑ with age.↑ with age.

It equals FRC in supine position( at around 44 yrs)It equals FRC in supine position( at around 44 yrs) in upright position( at around 66 yrs)in upright position( at around 66 yrs) Unlike FRC unaffected by posture.Unlike FRC unaffected by posture.

Lung volumesLung volumes

Spirometry

VentilationVentilation

Defined asDefined as mechanical movement of air into and mechanical movement of air into and out of the lungs.out of the lungs.

Primary mechanism for excretion of Carbon dioxidePrimary mechanism for excretion of Carbon dioxide Cyclic activity-Cyclic activity- 2 components 2 components Inward flow of air- Inhalation- Inward flow of air- Inhalation- active processactive process Outward flow of air- Exhalation- Outward flow of air- Exhalation- passive processpassive process Minute ventilation-Minute ventilation- sum of all exhaled gas sum of all exhaled gas

volumes in one minute.volumes in one minute.

MV= RR MV= RR X TV.X TV.

Normal range= Normal range= 5 to 10 lts/min in resting state.5 to 10 lts/min in resting state.MV= RR X TV

Ventilation

Dead space ventilation-Dead space ventilation- some of the minute volume some of the minute volume occupies space in conducting zones, does not participate in occupies space in conducting zones, does not participate in gas exchange and forms gas exchange and forms anatomic dead spaceanatomic dead space

Average in upright position – Average in upright position – 150 ml or 2 ml/kg150 ml or 2 ml/kg

Alveolar dead space-Alveolar dead space- adequately ventilated alveoli not adequately ventilated alveoli not participating in gas exchange as perfusion is absent.participating in gas exchange as perfusion is absent.

Physiologic dead space-Physiologic dead space- sum of anatomic and alveolar sum of anatomic and alveolar dead space.dead space.

Alveolar ventilation-Alveolar ventilation- volume of inspired gas actually volume of inspired gas actually taking part in gas exchange in one minute.taking part in gas exchange in one minute.

AV= RR X (TV – DV) = 12 X (500-150) = AV= RR X (TV – DV) = 12 X (500-150) = 4200 ml/min4200 ml/min

Ventilation

Dead space to tidal volume ratio:Dead space to tidal volume ratio: a numeric index of a numeric index of the total amount of wasted ventilation the total amount of wasted ventilation

Vd/Vt = PAco2 – PEco2/PAco2 (N value=0.2 - 0.4)Vd/Vt = PAco2 – PEco2/PAco2 (N value=0.2 - 0.4)

It represents the primary clinical measure of It represents the primary clinical measure of efficiency of efficiency of ventilationventilation

Clinical significance:Clinical significance: Alveolar ventilation depends on relationship b/w RR and Alveolar ventilation depends on relationship b/w RR and

TV.TV. * High RR and low TV result in higher prop. of wasted * High RR and low TV result in higher prop. of wasted

ventilation per min.ventilation per min.

* * Most efficient breathing pattern is slow and deep breathing.Most efficient breathing pattern is slow and deep breathing.

Ventilation

RRRR

TVTV MVMV Physio.Physio.

Dead Dead spacespace

AlveolarAlveolar

ventilatioventilationn

NormalNormal 1212 500500 60006000 150150 42004200

High High rate,low rate,low volumevolume

2424 250250 60006000 150150 24002400

Low Low rate,high rate,high volumevolume

0606 10001000

60006000 150150 51005100

↑↑ed dead ed dead spacespace

1212 500 500 60006000 300300 24002400

CompensatiCompensation for on for ↑ed ↑ed dead spacedead space

1212 650650 78007800 300300 42004200

Effectiveness of ventilation

Ventilation is effective when the body’s need for removal of Ventilation is effective when the body’s need for removal of CO2 is adeqately met.CO2 is adeqately met.

Under resting metabolic conditions the body produces Under resting metabolic conditions the body produces about 200 ml CO2 per min.about 200 ml CO2 per min.

The relative balanceThe relative balance b/w CO2 production and alveolar b/w CO2 production and alveolar ventilation determines the level of CO2 in lungs and in the ventilation determines the level of CO2 in lungs and in the blood.blood.

PAco2 = V CO2/V A or total CO2 production/CO2 PAco2 = V CO2/V A or total CO2 production/CO2 eliminationelimination

Normal- alveolar and arterial partial pressures of CO2 are in Normal- alveolar and arterial partial pressures of CO2 are in close equilibrium at approx 40 mmhg. close equilibrium at approx 40 mmhg.

Effectiveness of ventilation

In cases where alveolar ventilation is In cases where alveolar ventilation is ↓ed:↓ed: rate of CO2 production > rate of excretionrate of CO2 production > rate of excretion thus PA CO2 will rise above its normal value.thus PA CO2 will rise above its normal value.

Thus, ventilation that is insufficient to meet metabolic needs – Thus, ventilation that is insufficient to meet metabolic needs – hypoventilationhypoventilation

Very high arterial PaCO2 – depress ventilatory responseVery high arterial PaCO2 – depress ventilatory response(CO2 narcosis)(CO2 narcosis)

Alveolar hypoventilation: by definition it exists when arterial PaCO2 Alveolar hypoventilation: by definition it exists when arterial PaCO2 ↑ses above normal range of 37 to 43 mmhg(hypercarbia)↑ses above normal range of 37 to 43 mmhg(hypercarbia)

Mechanics of ventilation

Forces opposing lung inflation

ELASTICLung, thorax, surface tension

FRICTIONALAirflow

Tissue movement

In intact thorax,

Lungs & thorax recoil in opposite directions

Point at which these forces balance = resting vol of lung

AT THIS POINT Ppulm =Patm No air flows Vol. retained in lungs = FRC = 40% of TLC

ElastancePhysical tendency to return to original state after deformation

Lung vol at any given P is

slightly more during deflation

than it is during inflation.

↓HYSTERESIS

↓(Due to surface

tension)

GRAVITY DEPENDENT ventilation exploited to direct ventilation towards healthy lung by changing position of patient

Frictional forces opposing inflation

Tissue viscous resistance(20%)

Due to tissue displacement during ventilation (lungs, thorax, diaphragm)

↑ by obesity, fibrosis, ascites

Airway resistance(80%)

Raw = ∆P(driving P)/ ∆V(flow rate)

= transrespiratory P/flow rate

= 0.5-2.5 cmH2O/L/sec

Flow measured by PNEUMOTACHOMETER

P measured by PLETHYSMOGRAPH Affected by pattern of flow

Distribution of airway resistance

80% Nose, mouth, large

airways TURBULENT FLOW

20%Airways < 2 mm diameterLAMINAR FLOW

Branching of airway ↑ totalcross sectional area with each generation ↑ area → ↓ velocity→ + laminar flow

Deflation - ↑ airway diameter → ↑ resistanceWheezing heard during EXPIRATION

Types of airflow

LAMINAR TRANSITIONAL TURBULENT

Governed by Poiseulle’s Hagon equation

LAMINAR ∆P = 8ηL X flow π r4

↑ Reynold’s number

Re = ρ D V η

TURBULENT∆P = flow2 X ρ r5

η – viscosity L – length of tube r – radius ∆P – driving P

ρ -density

1. Helium is less dense but more viscous than airAdvantageous in turbulent flow but not laminar flow

Inferences from poiseulle’s hagen equation

∆P = 8ηL X flow

π r4

∆P α flow

r4

Flow α ∆P X r4

Reducing tube diameter by half requires 16 fold ↑in P to maintain same flow

Small changes in bronchial caliber can markedly change flow rates.

Basis for - 1. bronchodilator therapy 2. using largest practical size of artificial airway

Flow – volume loops

To diagnose lung pathologies as

Extra / intrathoracic Variable / fixedObstructive / restrictive

AIRWAY OBSTRUCTION

FIXED VARIABLECircumferential narrowingNot affected by thoracic P

INTRATHORACICBelow 6th tracheal ringExpiratory curve plateaus

EXTRATHORACICAbove suprasternal notch Inspiratory curve plateaus

Fixed

Variableextrathoracic

Variableintrathoracic

Done by respiratory msls to overcome elastic & frictional forces opposing inflation.

Work of breathing

W = F X S ( force X distance) = ∆P X ∆V = area under P-V curve Normal breathing – active inhalation - passive exhalation ( work of

exhalation recovered from potential energy stored in expanded lungs & thorax during inspiration)

Area 1 = work done against elastic forces ( compliance) = 2/3Area 2 = work done against frictional forces ( resistance work) = 1/3

Area 1+2 = total work done = 2/3 + 1/3 = 1

↑TV → ↑ elastic component of work↑ RR ( flow) → ↑ frictional work

People with diseased lungs assume a ventilatory pattern optimum for minimum work of breathing.

FIBROSISRestrictive disease

Rapid shallow breathing(↓elastic work)

COADObstructive disease

Slow breathing with pursed lips (↓ frictional work)

Transport of gases

Diffusion:Diffusion: gas movement b/w the lungs and gas movement b/w the lungs and tissue occurs via simple diffusion.tissue occurs via simple diffusion.

For OFor O2 there is a stepwise downward cascade of “partial” pressure.

PP of oxygenAtmospheric = 147

Alveolar = 100Arterial = 97Venous = 40Tissue = 5

Mechanism of diffusion

Physical process whereby gas molecules move Physical process whereby gas molecules move from area of high partial pressure to low one.from area of high partial pressure to low one.

Five barriersFive barriers

* RBC* RBC* Capillary membrane* Capillary membrane* Interstitial fluid* Interstitial fluid* Alveolar membrane* Alveolar membrane* Surfactant* Surfactant

Fick’s law of diffusion

Describes bulk movement of gases through Describes bulk movement of gases through biological membranes biological membranes

Vgas = A X D X (P1 – P2)/T A = Cross sectional area A = Cross sectional area

D = Diffusion coefficient of gases D = Diffusion coefficient of gases T = Thickness of memb. T = Thickness of memb. P P11 – P – P22 = Diff. in = Diff. in

partial pressurepartial pressure

Pulmonary end capillary OPulmonary end capillary O22 tension (Pc’O tension (Pc’O22) ) depends on:depends on: # rate of O# rate of O22 diffusion diffusion

# pulmonary capillary blood # pulmonary capillary blood volumevolume # transit time# transit time

Capillary transit time = pulm cap bld vol/COCapillary transit time = pulm cap bld vol/CO = 70 ml/5000 ml per = 70 ml/5000 ml per

minmin = = 0.8 seconds.

High fever, septic shock often cause High fever, septic shock often cause ↑ed CO, limit ↑ed CO, limit diffusion time due to ↑ed blood flowdiffusion time due to ↑ed blood flow

Maximum Pc’OMaximum Pc’O22 attained after only 0.3 sec ,providing a attained after only 0.3 sec ,providing a large safety margin (like exercise where transit time ↓ large safety margin (like exercise where transit time ↓ due to ↑ blood flow)due to ↑ blood flow)

For practical purposes, Pc’OFor practical purposes, Pc’O22 is considered identical to is considered identical to PAOPAO2.2.

Diffusion of gases

Diffusion capacity

Defined as no. of ml of a specific gas that diffuses Defined as no. of ml of a specific gas that diffuses across the ACM into the bloodstream each min for across the ACM into the bloodstream each min for each mmhg diff in pressure gradienteach mmhg diff in pressure gradient DLODLO22 = O = O2 2

uptake/ uptake/ PAOPAO2 2 - Pc’O- Pc’O22

Carbon monoxide is preferred over OCarbon monoxide is preferred over O22 as test gas as test gas since its higher affinity for Hb keeps its cap pp very since its higher affinity for Hb keeps its cap pp very low, so low, so Pc’OPc’O22 can be considered as zero can be considered as zero DL CO = CO DL CO = CO uptake/PA COuptake/PA CO

Reduction in DL CO implies impaired gas transfer Reduction in DL CO implies impaired gas transfer seen in seen in * abnormal V/Q ratio* abnormal V/Q ratio * *

destruction of membdestruction of memb * very * very short capillary transit timeshort capillary transit time

Determinants of alveolar gas tensions

Alveolar OAlveolar O2 2 tension:tension: * pp of O* pp of O22 in air (Pi O in air (Pi O22 = P = PBB x Fi O x Fi O22) = 760x0.21 = ) = 760x0.21 = 159.6 mmhg159.6 mmhg

* * accounting foraccounting for humidification humidification for inspired gases Pi for inspired gases Pi OO22 = P = PBB – P – PH2O H2O x Fi Ox Fi O2 2 = 760 - 47X0.21 = 149 mmhg= 760 - 47X0.21 = 149 mmhg

* accounting for * accounting for residual COresidual CO22 from previous from previous breaths final alveolar Obreaths final alveolar O2 2 tension is defined by:tension is defined by:alveolar air equaalveolar air equann: :

PAOPAO22 = Fi O = Fi O22 x (P x (PB B – 47) – (PA CO– 47) – (PA CO22/0.8)/0.8) = 0.21 x (760 – 47) – (40/0.8) = 0.21 x (760 – 47) – (40/0.8)= 99 mmhg.= 99 mmhg.

Arterial OArterial O2 2 tension:tension: approximated by approximated by PaPaOO22 = 102 – age/3, n range = 60 – 100 mmhg = 102 – age/3, n range = 60 – 100 mmhg

Determinants of alveolar gas tensions

Alveolar CO2 tension: PA COPA CO2 2 = V CO= V CO2 2 x 0.863/V A = 40 mmhg x 0.863/V A = 40 mmhg

Arterial CO2 tension: readily measured, n = 38+/-4 mmhgreadily measured, n = 38+/-4 mmhg

End tidal CO2 tension: used clinically as an estimate of PaCOused clinically as an estimate of PaCO22..

PA COPA CO22 – P – PETCO2ETCO2 gradient is normally gradient is normally < < 5 mmhg.5 mmhg.

Compliance

Compliance = Distensibility of lung Elastance = resisting deformation

Compliance = 1/ elastance = ∆V/ ∆P = 0.2L/cm H2O (lung) = 0.2L/cm H2O (Thorax) = 0.1L/cm H2O (lung+

thorax)Affected by

ObesityKyphoscoliosis

Ankylosing spondylitisFibrosis

Emphysema

Steep curve + Lt shift = ↑compliance (loss of elastic tissue)

Flat curve + Rt shift = ↓compliance(↑ connective tissue)

Compliance

Static compliance:Static compliance: measured when air flow is measured when air flow is absent,absent, reflects elastic resistance of lung & reflects elastic resistance of lung & chest wall.chest wall. =Corrected tidal vol./(plateau =Corrected tidal vol./(plateau pressure – PEEP)pressure – PEEP) n value: 40 to 60 ml/cm n value: 40 to 60 ml/cm H2O.H2O.

Dynamic compliance:Dynamic compliance: measured when air flow is measured when air flow is present,present, reflects airway + elastic resistance,reflects airway + elastic resistance,

= Corrected tidal vol./(peak airway = Corrected tidal vol./(peak airway pressure – PEEP)pressure – PEEP) n value: 30 to 40 ml/cm H2O.n value: 30 to 40 ml/cm H2O.

LOW Compliace: Lung expansion difficult.LOW Compliace: Lung expansion difficult.HIGH Compliance: Incomplete CO2 elimination.HIGH Compliance: Incomplete CO2 elimination.

Compliance is reduced in

AtelectasisARDS

Tension PneumothoraxObesity

Retained secretions

BronchospasmKinking of ET tubeAirway obstruction

STATIC DYNAMIC

Transport of oxygen

2 forms: 2 forms: 1. Small amount dissolved in 1. Small amount dissolved in

plasmaplasma 2. Chemically combined with 2. Chemically combined with Hb in RBCHb in RBC

Dissolved oxygen: Dissolved oxygen: henry’s lawhenry’s lawGas conc = S x PP in solnGas conc = S x PP in soln

* S - gas solubility * S - gas solubility coefficient for given soln at a given coefficient for given soln at a given temptemp Dissolved ODissolved O22 = = 0.003 x 100 = 0.3ml/dl0.003 x 100 = 0.3ml/dl

Transport of oxygen

Chemically Chemically combined with Hb:: accounts for accounts for max blood oxygen blood oxygen

Hemoglobin - conjugated protein:Hemoglobin - conjugated protein: four polypeptide four polypeptide (globin) chain, chain, each combined with a porphyrineach combined with a porphyrin complex called complex called heme.

each heme complex has a centraleach heme complex has a central ferrous ion to which Oferrous ion to which O22 binds binds converting Hb into oxygenated state.converting Hb into oxygenated state.

1 gram of normal Hb carries 1.34 ml of O1 gram of normal Hb carries 1.34 ml of O2,2, if Hb is 15 g/dl , if Hb is 15 g/dl ,

O2 carrying capacity of blood = 1.34 ml x 15 g/dl = 20.1 ml/dl

Transport of oxygen

OO2 content: dissolved + combined with Hb OO2 content = (0.003 x PO2) + (Hb x 1.34 x SaO2)

= (0.003 x 100) + (15 x 1.34 x 0.975)= 19.5 ml/dl (arterial)

OO2 content = (0.003 x 40) + (15 x 1.31 x 0.75)= 14.8 ml/dl (venous)

O2

content Arterial Venous

Combined 19.5 14.7

Dissolved 0.3 0.1

Total 19.8 14.8

Transport of oxygen

Total oxygen delivery to tissues: = oxygen content x CO= oxygen content x CO

= 20 ml/dl x 50 dl blood/min= 20 ml/dl x 50 dl blood/min = 1000 ml/min.= 1000 ml/min.

O2 Flux: amount of O amount of O2 2 leaving the left ventricle leaving the left ventricle per min in the arterial blood.per min in the arterial blood.

Fick equation describes O2 consumption (VO2)= CO x diff b/w arterial and venous oxygen = CO x diff b/w arterial and venous oxygen contentcontent = 250 ml/min.= 250 ml/min.

Extraction ratio for O2 = (Ca O= (Ca O2 2 - Cv O- Cv O22)/ Ca O)/ Ca O2 2

= 5/20 = 25% = 5/20 = 25%

Oxygen stores

Normally in adults = Normally in adults = 1500 ml * O* O2 2 remaining in lungs remaining in lungs * bound to Hb* bound to Hb* dissolved in body fluids* dissolved in body fluids

OO2 2 contained within lungs at FRC – most imp contained within lungs at FRC – most imp source of oxygen.source of oxygen.

Apnea in pt breathing Apnea in pt breathing room air = FiO = FiO22 x FRCx FRC= 0.21 x 2300= 0.21 x 2300

= = 480 ml depleted in 90 sec

Preoxygenation with 100% oxygen for 4-5 min with 100% oxygen for 4-5 min leaves leaves 2300 ml of oxygen – delays hypoxemia of oxygen – delays hypoxemia following apnea following apnea

HbO2 Dissociation Curve

Relates SpO2 to the PO2

Sigmoid shaped (comb of 1st heme Hb

molecule with O2↑ affinity of other heme

molecules)

SHIFTING AFFINITY

Measure of Hb affinity for O2

quantified by Pquantified by P5050.. PP5050 - PO - PO22 at which Hb is 50% saturted. at which Hb is 50% saturted. PP5050 = 26 mmhg at PCO = 26 mmhg at PCO22 40 mmhg, pH 7.4, 40 mmhg, pH 7.4,

temp. 37temp. 37°C.°C.

↓ Hb affinity, Rt shift of ODC

↑ P50

(facilitates O2 release)

Factors affecting O2 loading and unloading

Blood pH Blood pH Body tempBody temp Organic phosphates in RBCOrganic phosphates in RBC Variations in structure of Hb Variations in structure of Hb

Shift of curve to right

Fall in blood pH due toa. ↑ CO2

b. Presence of any acid in blood ↑ temp Inhalational anesthetics: Isoflurane shifts P50 to right

by 2.6 mmhg. ↑ conc of 2,3- DPG

By product of glycolysis (accumulates in anaerobic met.)Competes with O2 for binding sites on Hb

↓ in: acidosis, blood stored in acid citrate dextrose sol in blood bank↑ in: high altitude, chronic anemia, exercise

Bohr effect

Double Bohr Effect -

* 2 – 8% of the trans placental transfer of oxygen

* concomitant fetal to maternal transfer of CO2 makes maternal blood more acidic & fetal blood more alkalotic

↑ in blood H+ ionreduces oxygen binding to Hb

Rt shift of ODCO2 release

right shift in maternal ODC

left shift in fetalODC

Shift of curve to left

Carbon monoxide – inhibits synthesis of 2,3 DPG. – inhibits synthesis of 2,3 DPG. Affinity of CO for Hb is 200 times than Affinity of CO for Hb is 200 times than

that of Othat of O2 2

Fetal Hb - has greater affinity for O - has greater affinity for O22

Alkalosis Alkalosis HypothermiaHypothermia ↓ ↓ 2,3 DPG2,3 DPG Abnormal Hb:Abnormal Hb: * Hbs in * Hbs in sickle cell anemia has has

less affinity for oxygen than HbA, deoxygenated blood is less affinity for oxygen than HbA, deoxygenated blood is less soluble, crystallization & sickling occursless soluble, crystallization & sickling occurs

* In * In methHb Fe2+→ Fe3+, cannot bind cannot bind with with OO22

Transport of CO2

CO2 is carried in blood in 3 forms:* Ionized as bicarbonate* Ionized as bicarbonate

* Chemically combined with * Chemically combined with proteinsproteins * Dissolved in physical * Dissolved in physical solnsoln

Transport of CO2

Ionized as bicarbonates(80%)a. a. In plasma – partly in soln, – partly in soln,

- remaining combines - remaining combines with water forming carbonic acid.with water forming carbonic acid.

COCO22 + H + H22O O → → HH22COCO33 (slow reaction) b. b. In RBC – this reaction is – this reaction is rapid due to presence of enzyme carbonic due to presence of enzyme carbonic anhydrase.anhydrase.

Transport of CO2

As carbamino compds COCO22 can react with amino can react with amino group on proteinsgroup on proteins a. a. In plasma – with plasma – with plasma proteins (slow rxn)proteins (slow rxn) b. b. In RBC – with Hb – – with Hb – carbaminoHb (fast rxn) carbaminoHb (fast rxn)

* Deoxygenated Hb has a higher affinity(3.5 * Deoxygenated Hb has a higher affinity(3.5 times) for COtimes) for CO22, thus venous blood carries more CO, thus venous blood carries more CO22

As dissolved CO2 (8%) CO CO2 2 is more soluble in blood is more soluble in blood than oxygen with a solubility coefficient of 0.067 than oxygen with a solubility coefficient of 0.067 ml/dl/mmhg at 37ml/dl/mmhg at 37°C °C

Transport of CO2

Hb acts as a buffer at physiologic pH Hb acts as a buffer at physiologic pH * * In tissue capillaries deoxygenated deoxygenated

Hb behaves like a base, takes up HHb behaves like a base, takes up H+ + ions, ions, ↑ bicarb ↑ bicarb formn.formn.

CO2 + H2O + HbO2 → HbH+ + HCO3 + O2

Thus, deoxyHb ↑ amount of COThus, deoxyHb ↑ amount of CO22 that is carried in venous that is carried in venous blood as bicarbonate.blood as bicarbonate.

Transport of CO2

Chloride shift or hamburger phenomenon

To maintain To maintain electrical electrical neutrality Clneutrality Cl¯̄ ions shift from ions shift from plasma to plasma to RBCs in RBCs in exchange of exchange of HCO3 ions.HCO3 ions.

Transport of CO2

In lungs oxyHb oxyHb behaves as acid, behaves as acid, release release HH+ + ions, ions, favour favour COCO22 production production

HbH+ + HCO3 + O2→ CO2 + H2O + HbO2

Thus COThus CO22 is is eliminated from lungs.eliminated from lungs.

CO2 dissociation curve

•Depicts relationship b/w PCO2 & CO2 content

•Haldane effect- when oxygen combines

with Hb it ↓ affinity of Hb for CO2

Haldane and Bohr effect

Transport of CO2

COCO22 content of blood(mmol/lt) content of blood(mmol/lt)

ArterialArterial VenousVenous

Dissolved Dissolved 1.21.2 1.41.4

BicarbonatBicarbonatee

24.424.4 26.226.2

CarbaminoCarbamino negligiblenegligible negligiblenegligible

TotalTotal 25.625.6 27.627.6

References

1. Respiratory physiology, the essentials. John 1. Respiratory physiology, the essentials. John B.West.2003, 3B.West.2003, 3rdrd ed. ed.

2. Egan’s fundamentals of respiratory care 92. Egan’s fundamentals of respiratory care 9th th ed.ed.

3. A practice of anaesthesiology. Wylie 53. A practice of anaesthesiology. Wylie 5thth, 7, 7thth ed. ed.

4. Lee’s synopsis of anaesthesia 134. Lee’s synopsis of anaesthesia 13thth ed. ed.

5. Miller’s Anaesthesia 65. Miller’s Anaesthesia 6thth ed. ed.

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