TRANSPORT OF OXYGEN

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TRANSPORT OF OXYGEN CARBON DIOXIDE

• Scott Stevens D.O.
• Gannon University
• College of Health Sciences
• Graduate Program Department of Nursing

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Respiratory Gas Transportation
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Gas Exchange in Lungs Tissues
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Tissue Oxygenation

• Process of moving O2 CO2 in and out of body
  tissues
• Diffusion too slow for distances gt 100 µm
• Respiratory circulatory systems provide
  transportation to peripheral organs and tissues

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Failure To Oxygenate

• Four Types Of Hypoxia
• Hypoxic hypoxia
• Inadequate O2 uptake into blood in lungs
• Chronic obstructive pulmonary disease
• Stagnant (ischemic) hypoxia
• Inadequate blood flow to an organ
• Arteriosclerosis peripheral vascular disease
• Anemic hypoxia
• Inadequate blood oxygen carrying capacity
• Inactivated hemoglobin
• Histotoxic hypoxia
• Interference with mitochondrial respiration
• Cyanide poisoning

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Oxygen Transport

• O2 carried by red blood cells (erythrocytes)
• Hemoglobin (Hb)
• Normal hemoglobin concentration is 150 g/L or
  15g/dL
• Carries 65 times more O2 than plasma
• Dissolved O2 in plasma
• Low capacity to carry or transport O2
• Small amount of O2 dissolved in solution (plasma)

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Hemoglobin

• Oxygen carrier protein
• 4 subunits 2 alpha 2 beta
• Normal adult HbA a2b2
• Four heme groups - iron-porphyrin compound at O2
  binding site
• Iron containing porphyrin rings, only Fe2 can
  bind O2
• Each heme combines with one globin protein chain
• Molecular weight of hemoglobin is 64,000
• Each gm of Hb can carry up to 1.31ml of O2,
  theoretically up to 1.39 ml/gm

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Chemical Binding of Hemoglobin Oxygen

• Hemoglobin combines reversibly with O2
• Hemoglobin is the unoxygenated form
• Oxyhemoglobin is when O2 combined
• Association and dissociation of Hb O2 occurs
  within milliseconds
• Critically fast reaction important for O2
  exchange
• Very loose coordination bonds between Fe2 and
  O2, easily reversible
• Oxygen carried in molecular state (O2) not ionic
  O2-
• Sigmoid shaped HbO2 equilibrium curve
• Molecular reaction between the four heme groups
• Heme groups O2 binding capacity enhancement

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Oxygen Saturation Capacity

• Up to four oxygen molecules can bind to one
  hemoglobin (Hb)
• Ratio of oxygen bound to Hb compared to total
  amount that can be bound is Oxygen Saturation
• Maximal amount of O2 bound to Hb is defined as
  the Oxygen Capacity

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Saturation (Hb) and PaO2

• Saturation PaO2 100 100 95 75
  90 60 75 40 (mixed venous blood in
  pulm. artery) 60 30 50 27 (Hb P50 point)
• Very rough rule PaO2 40,50,60 for Sat.
  70,80,90

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50
27
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Pathological Ligands of Hemoglobin

• Ligands form covalent bonds to the ferrous iron
  in Hb
• These bonds have more affinity to iron than
  oxygen which binds weakly to Hb
• Carbon Monoxide
• 250 times the affinity than oxygen
• Does not dissociate readily
• Requires hours to rid body of CO
• Nitric Oxide
• Binds to Hb 200,000 times more strongly
• Hemoglobin binds irreversibly to NO
• Used to treat pulmonary hypertension

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Hemoglobin-Oxygen Equilibrium Curve

• Relationship between hemoglobin O2 concentration
  oxygen partial pressure
• Percentage oxygen saturation as function of Po2
• Dependant on hemoglobin concentration oxygen
  partial pressures
• Sigmoidal shape
• P50 is the Po2 when hemoglobin is 50 saturated
• P50 of Hb Po2 of 27mmHg

LUNG
CAPILLARY
50
TISSUE
27
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Altered Hemoglobin Affinity for Oxygen

• HbO2 equilibrium curve modified by a number of
  physiological or pathological factors
• Curve affected in two ways
• Shift in position
• Change in shape
• A change in shape indicates a greater
  interference with O2 transport than curve shift

SHIFT
50
Less affinity ? ? More affinity
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27
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---
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50
27
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Venous Hb Affinity Shift

• Shift to the right reducing the affinity for O2
  below Po2 of 70 mmHg
• Shift occurs because of rising Pco2 H ions
  Bohr effect an increase in H decreases Hbs
  affinity for O2
• Enhances the quantity of O2 released in systemic
  capillaries
• Increases delivery of O2 to tissues

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Hb-O2 dissociation curve

• Right shift Hb has less affinity for O2,
  releases O2, saturation will be less for a given
  PO2
• Left shift Hb has higher affinity for O2, binds
  O2, saturation will be higher for a given PO2
• Causes of right shift (less affinity for
  O2) increased CO2 cellular metabolism
  increased temp. increased metabolism,
  muscle increase H acidosis, lactic acid
  production, Bohr effect increased 2,3
  DPG 2,3 diphosphoglycerate, generated by
  glycolysis during anaerobic metabolism, binds
  to Hb and decreases affinity for O2

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Stored blood

• Packed red blood cells (PRBC) used for virtually
  all blood transfusions are stored cold and have
  significantly diminished levels of 2,3 DPG
• Hb in stored blood would initially show a left
  shift in the Hb-O2 disassociation curve

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Hemoglobin Myoglobin

• Myoglobin is single chained heme pigment found in
  skeletal muscle
• Myoglobin has an increased affinity for O2 (binds
  O2 at lower Po2)
• Mb stores O2 temporarily in muscle

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(27)
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O2 Content in blood (CaO2)

• The sum of O2 carried on Hb and dissolved in
  plasma
• CaO2 (SO2 Hb 1.31) (PO2 0.003)
• CaO2 O2 content in blood (ml/dL)
• SO2 Hb saturation (SpO2-pulse ox. or
  SaO2-saturation from blood gas (ABG), as a
• Hb Hb concentration in gm/dL
• 1.31 O2 binding to Hb (ml/gm)
• PO2 arterial bloods partial pressure of O2
• Example Pt with sat. of 97, Hb 15, and PO2
  200 CaO2 (0.97 15 1.31) (200
  0.003) CaO2 (19) (0.6) ml/dL
• DO2 (oxygen delivery) CaO2 CO (cardiac
  output)

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Effects of Blood Oxygen Capacity

• Factors which reduce Hbs ability to transport O2
  alter the equilibrium curve
• CO reduces the available Hb able to transport O2
• Anemia
• Decrease in Hb/L
• Decrease in O2 content in blood

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Carbon Dioxide

• Volatile waste product of cellular metabolism
• Tissue Ptco2 is 50 mmHg
• Diffuses into systemic capillaries with lower
  Pco2 levels
• Carbonic Acid converted to CO2 to be exhaled in
  the lungs
• Total amount of CO2 transported in blood
• CO2 production averages 200 ml/min in resting
  adult
• During exercise this amount may increase six-fold
• Large amount of CO2 remains in blood and is
  required in maintenance of the hydrogen ion
  concentration

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Mechanisms of CO2 Transport

• Complex mechanism of CO2 transport
• Carbon dioxide transported by blood in three
  forms
• Dissolved directly in blood
• Bicarbonate ion (HCO3-) Carbonic acid (H2CO3)
• Bound to hemoglobin plasma proteins

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CO2 Equilibrium Curve

• HbCO2
• Different than HbO2 curve
• Relationship is linear
• Venous blood transports more CO2 than arterial
  blood
• CO2 equilibrium is affected by O2 saturation of
  Hb
• Ability to bind with CO2 increased in
  deoxygenated Hb
• deoxygenated Hb is weaker acid than oxygenated Hb
• Haldane effect upon binding O2 Hb releases CO2
  and H which in turn is converted to CO2
• A-a Pco2 levels not as effected by V/Q mismatch
• Diffusing capacity 20x greater with CO2 than O2

PO2 40mmHg
PO2 100mmHg
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Carbon Dioxide Exchange
PLASMA
(fast)
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MOST CO2 TRANSPORTED AS BICARBONATE (HCO3-)
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H HCO3- CO2 and H2O
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• THATS ALL