BIOL 2P93 Lecture Notes - Weighted Arithmetic Mean, Fraction Of Inspired Oxygen, Homeostasis

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Gas Exchange I & II
I. O2 & CO2 transport in blood
a. Carried mainly in chemical combination
i. Blood can carry more than in a physical solution
ii. Content isn’t linearly related to partial pressure
b. Oxygen
i. Bohr Effect—chem. interactions that facilitate unloading of O2 in tissue;
when CO2 is added (at tissues), pH↓ => ↑ dissociated O2 (right shift)
1. ↑Temperature, ↑PCO2, & pH↓ => rightward shift
ii. O2 content in blood = bound O2 + dissolved O2
O2 Content = CO2 = SO2*Cmax + 0.003*PO2 ml/dl
Cmax = max amount of O2 that can combine with Hgb
c. Carbon Dioxide
i. Haldane effect—chem. interactions facilitating CO2 unloading at lungs;
↑HbO2 at lungs => ↓ pH => rightward shift of CO2 dissociation curve =>
facilitates unloading at lungs
ii. CO2 principally transported as bicarbonate
d. Bohr & Haldane effects make CO2 & O2 transport mutually dependent!
II. CO2 & O2 Exchange
a. CO2—very simple!
i. Amount removed = amount produced
22 *ACOaCO FVV =
ii. Alveolar PCO2 determined by balance between alveolar ventilation &
CO2 production
iii. Arterial PCO2 is indicator of adequacy of alveolar ventilation—direct
relationship! (Eg: doubling Ventilation => ½ CO2)
b. O2 Exchange
i. Respiratory QuotientRQ = VCO2/VO2 represents CO2 production & O2
consumption in tissues
1. APPLIES STRICTLY TO TISSUE METABOLISM
ii. Respiratory Exchange Ratio R = VCO2/VO2 represents CO2 excretion
& O2 uptake at lungs; at rest ~0.8 (↑ during exercise)
1. APPLIES STRICTLY TO VENTILATION
iii. For homeostasis, R = RQ
c. Alveolar Air Equation
i. PAO2 = PIO2 – PACO2 if R = 1
ii. PAO2 = PIO2 – PACO2 [FIO2 + (1-FIO2) / R] exact equation
iii. PAO2 = PIO2 – PACO2 / R approximate eqn
III. Gas Stores
a. CO2 stores in body are much larger than O2 stores
b. Can store enough O2 in body for ~2 min
c. Can store ~16L CO2 in body; gives several hours => takes a long time to
equilibrate
IV. Shunt Flow
1
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