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Dry Atmospheric Gas at Standard Barometric Pressure
Po torr Pco torr PN torr
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Inspired Gas at Standard Barometric Pressure
PIo torr PIco torr PIN torr PIH2O torr
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Alveolar Gas at Standard Barometric Pressure
PAo torr PAco torr PAN torr PAH2O torr
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ALVEOLAR AIR EQUATION 2 PACO2 PAO2 = PIO2 - + F R PAO2 = FIO2
( PB - PH O) -
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Mixed Expired Air at Standard Barometric Pressure
PEo torr PEco torr PEN torr PEH2O torr
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Solubility of O2 in Plasma
At 37°C 1 ml of plasma contains ml O2 / torr PO2
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O2 Carrying Capacity of Hemoglobin
1 gram of hemoglobin can combine with 1.34ml of oxygen when fully saturated
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O2 bound to Hb % Hb saturation = x 100% O2 capacity of Hb
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Hemoglobin saturation, %
100 80 Pco2 , pH temp, BPG Pco2 , pH temp, BPG 60 Hemoglobin saturation, % 50% 40 20 Figure Maximal expiratory flow-volume curves representative of obstructive and restrictive diseases 20 40 60 80 100 120 140 160 P50 Partial pressure of oxygen, torr
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CYANOSIS Occurs when more than 5 grams of hemoglobin/100 ml of arterial blood are in the “deoxy” state Absence of cyanosis does not rule out hypoxemia (anemia) Presence of cyanosis does not always indicate hypoxemia (polycythemia)
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At 37°C 1 ml of plasma contains 0.03 mmol of CO2 / torr Pco2
Solubility of CO2 in Plasma At 37°C 1 ml of plasma contains mmol of CO2 / torr Pco2 Or ml of CO2 / torr Pco2
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Carbamino Compound R - N + CO2 R - N + H+ H COO- Terminal amine group
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Transport of CO2 by the Blood
(Gas phase) Carbonic Anhydrase _ CO2 + H2O H2CO3 H+ + HCO3 (Dissolved in the aqueous phase)
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TISSUE PLASMA ERYTHROCYTE CO2 CO2 dissolved CO2 H2O H2O + CO2 CO2 Carbonic anhydrase dissolved H2CO3 Cl- Cl- CAPILLARY WALL HCO3- HCO3- + H+ H+ + HbO2 O2 O2 O2 O2 + HHb HHb+CO2 Carbamino compounds
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ALVEOLUS PLASMA ERYTHROCYTE CO2 CO2 dissolved CO2 H2O H2O + CO2 CO2 Carbonic anhydrase dissolved H2CO3 Cl- Cl- CAPILLARY WALL HCO3- HCO3- + H+ H+ + HbO2 O2 O2 O2 O2 + HHb HHb+CO2 Carbamino compounds
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A Classification of the Causes of Hypoxia
Increased FIo2 helpful? PAo2 Pao2 Cao2 Pvo2 Cvo2 Classification Hypoxic hypoxia Low alveolar Po2 Diffusion impairment Right to left shunts V/Q mismatch Anemic hypoxia CO poisoning Hypoperfusion hypoxia Histotoxic hypoxia Low Norm Low Norm Low Norm Low High Low High Yes No Possibly
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