Lectures on respiratory physiology Blood gas transport

DRY AIR: 21% IS OXYGEN [O2] = 21 ml/dl FO2 = 0.21 CONCENTRATION AND PARTIAL PRESSURE O2 MOLECULES IN AIR DRY AIR: 21% IS OXYGEN [O2] = 21 ml/dl FO2 = 0.21 As PB = 760 mm Hg PO2 = 0.21 x 760 mm Hg = 160 mm Hg

37oC PO2 = 0.21 x 713 mm Hg EFFECT OF WATER VAPOR PB = 760 mm Hg PH2O = 47 mm Hg PDRY = 713 mm Hg PO2 = 0.21 x 713 mm Hg = 150 mm Hg

O2 IN PHYSICAL SOLUTION 37oC AFTER EQUILIBRATION, AIR: PO2 = 150 mm Hg WATER AFTER EQUILIBRATION, AIR: PO2 = 150 mm Hg AIR WATER: PO2 = 150 mm Hg AIR: [O2] = 21 ml/dl WATER: [O2] = 0.45 ml/dl 37oC SOLUBILITY = 0.45 / 150 = 0.003 ml/(dl.mmHg)

SOLUTION DURING EXERCISE TRANSPORT OF O2 IN SOLUTION DURING EXERCISE Solubility = 0.003 ml/(dl.mmHg) PO2 in arterial blood = 100 mm Hg [O2] = 0.3 ml/dl = 3 ml/liter Cardiac output = 30 liters/min Maximum O2 available = 90 ml/min But O2 requirement is 3000 ml/min

Structure of hemoglobin

Normal cells Sickle cells

Oxygen dissociation curve

ARTERIAL BLOOD VENOUS BLOOD P50 27

TOTAL O2 IN BLOOD IS THE SUM OF Hb-BOUND AND DISSOLVED O2 TOTAL [O2] = 1.39 x [Hb] x % SATURATION/100 + 0.003 x PO2

TOTAL O2 IN ARTERIAL BLOOD (1.39 x 15 x 0.97) + (0.003 x 100) = 20.5 ml/dl

Effects of changing hemoglobin concentration

Shifting the O2 dissociation curve

CO-Hb DISSOCIATION CURVE SATURATION, % O2 PARTIAL PRESSURE, mm Hg

Effects of CO on the O2 dissociation curve

Carbon dioxide is carried in the blood in three forms Dissolved As bicarbonate 3. As carbamino compounds

Solubility of Oxygen 0.003 ml/(dl.mmHg) Solubility of Carbon Dioxide 0.067 ml/(dl.mmHg)

Carriage of CO2 in the blood

Formation of bicarbonate CO2 + H2O H2CO3 H2CO3 H+ + HCO3-

Formation of carbamino compounds Hb.NH2 + CO2 Hb.NH.COOH

Uptake of CO2 in systemic capillaries

Carriage of CO2 in the blood

CO2 dissociation curves

Comparison of O2 and CO2 dissociation curves