Flashcards in Gas transport in airways Deck (19):
Transport of O2 through airways into alveoli depends on what?
What are PIO2 and PAO2
PIO2: partial pressure of O2 in inspired air at the point at which it has just entered the airways. PAO2: partial pressure of O2 in alveoli. These limit the amount of O2 that can enter the blood
Calculate the partial pressure of oxygen in inspired air PIO2.
PIO2 = (PB – 47 Torr) × 0.21. 47 Torr represents the partial pressure of water vapor, PB is barometric pressure(760Torr at sea level, or 630 at denver), and 0.21 is the percentage of O2 in the air.
Why is alveolar oxygen pressure lower than inspired air oxygen pressure?
Inspired air only has O2 and N2, whereas alveolar air has O2, N2 AND CO2. The overall barometric pressure can not change, so the pressure of oxygen decreases in alveolus as the pressure of CO2 increases
Calculat alveolar oxygen PAO2 when there is 1:1 exchange of CO2 for O2
PAO2 = PIO2 - PACO2. Where PIO2 is inspiratory oxygen pressure, PACO2 is alveolar CO2 pressure
Define the respiratory exchange ratio and describe why values can vary.
ratio of amount of CO2 generated (VCO2) per amount of O2 consumed (VO2). R varies for different metabolites (carbs vs fats)
Calculate alveolar PAO2 given known values of PACO2, barometric pressure, and respiratory exchange ratio.
PAO2= PIO2 - (PACO2/R) + k. Where R (respiratory exchange ratio)= VCO2/ VO2 and k is negligible
Which alveolar gas equation is used when patient is breathing 100% O2?
The equation for R=1 (PAO2 = PIO2 - PACO2) b/c th only gas present to make up for CO2 deficit is oxygen
What is rate-limiting for CO2 removal.
CO2 transport from alveoli to outside air depends on alveolar ventilation. If ventilation decreases, alveolar CO2 pressure goes up followed by arterial CO2 goes up.
compare arterial to alveolar CO2 pressure
PACO2 (alveolar) = PaCO2 (arterial). Diffusion is very fast, so CO2 is at near perfect equilibrium in alveoli and pulmonary capillaries.
Calculate arterial PaCO2 and alveolar PACO2 given known values of alveolar ventilation and CO2 production.
PACO2 = (VCO2/ VA) x k. Where VCO2 is volume of CO2 produced in one minute, VA is alveolar ventilation, k is constant. This also calculates PaCO2 which is nearly equivalent to PACO2.
Define hypoventilation, hyperventilation
Hypoventilation: Alveolar ventilation is low in relation to CO2 production and elimination rate. PaCO2 increases and Va decreases. Hyperventilation: alveolar ventilation is high in relation to CO2 production and elimination rate. PaCO2 is low and Va is high.
What is normal PaCO2 at sea level and at Denver
sea level: 35-45Torr. Denver: 30-40Torr.
What is normal PaO2
90-100 Torr (sea level), 80-85 Torr (Denver)
What is hyperpnea
Increased ventilation during moderate exercise
What causes hyperventilation
acute hypoxemia (low arterial oxygen), metabolic acidosis, or CNS stimulation
What causes hypoventilation
obstructive/restrictive disease, metabolic alkalosis, or CNS
Blood CO2 is directly or indirectly regulated by alveolar ventilation?