Glossary of 18 Pulmonary Gases and Equations

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Oxygen pathway
1) ventilation
- active
- variables = rate V
2) Diffusion
- passive diffusion
- variables = SA, distance
3) Circulation
- active
- rate V
4) Diffusion
- passive diffusion
- SA, distance

-in series, any one can be rate limiting for O2 uptake
- each has variables that ↑ O2 transfer
O2 uptake
- mitochondria 80% resting O2 uptake (high affinity)
- non MT pathways (synthesis of NE, Dopamine, Serotonin) hepatic cell function --> other 20% more sensitive to hypoxia
- basal metabolic rate or resting O2 consumption
- 250 ml O2 per minute in 70 kg adult
Critical PO2
- diffusion from blood to tissues last step
- PO2 in cap. ↓, rate of diffusion limits and tissue will infarct (die)
- brain and heart have highest critical PO2
CO2 production
- same as O2 consumption (pure carbo diet)
- ratio of CO2 production to O2 consumption --> respiratory quotient in tissues, respiratory exchange ration (R) in lungs
- R = V(flow)CO2/ V(flow)O2
Steady state
- R = RQ
- gas exchange is matched in tissues and lungs
-non steady state: crying, breath holding
Fats metabolized: RQ=.7 (fasting metabolism)
Proteins RQ= .8
Respiratory gases
- alveolar ventilation and fraction of ispired O2 --> amt of O2 delivered to alveoli
- PAO2 + PAN2 + PACO2 + PAH2O= PB
- inspired oxygen pressure, dependent on O2 inaled in air and PB
- PIO2 = (PB-PH2O)(FIO2)
-PH2O water vapor pressure (temp) 47 mm hg at 37c
FIO2 - .21
PB = 760
Alveolar gas equation PO2
- calculate efficiency of gas exchange by comparing arterial and alveolar values
- need PaO2
- water vapor added to inspired air reduced PIO2
- CO2 from pulmonary cap into alveoli reduces PIO2
- PIO@ = (Pb-Ph20) x FO2
- PaO2 = PIO2 - PACO2
if R<1
PaO2= PIO2 - (PACO2/R)
R = tissue< 1 (CO2 being removed is greater than O2 being added)
(RQ lungs)
Alveolar-arterial PO2 difference
- PaO2 5-20 mmHg > PAO2
- increases with incraseing fraction of PIO2 (upper flat portion of oxyHg dissociation flat)
-PAO2 falls with age, Pa02 constant
- PACO2 doesn't change with age, meduallary brain stem control
Alveolar CO2
- only source is from tissues
- increased alveolar ventilation dilutes PCO2
- PACO2 = V(flow)CO2/VA(flow) x 863
863 = gas constant
- excess of what's needed to maintain normal PACO2

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