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Flashcards in Gas Transport in Airways Deck (16):
1

Calculate the partial pressure of oxygen in inspired air P-IO2.

PIO2 is the partial pressure of O2 in inspired air at the point at which it has just entered the airways.

PIO2 = (PB – 47 Torr) × 0.21

PB is barometric pressure (sum of partial pressure of gases in air). At body temp, the partial pressure of water vapor is 47 Torr). O2 is approximately 21% of air.

2

Define the respiratory exchange ratio and describe why values can vary.

The exact relationship between O2 consumed and CO2 produced

R=Vco2/Vo2

For many important metabolic reactions such as oxidative phosphorylation, there is less carbon dioxide produced as compared to oxygen consumed. Therefore, R varies for different metabolites. It is near one for carbohydrates but drops to 0.7 for fats. The typical diet yields R ~.8

3

Calculate alveolar P-AO2 given known values of P-ACO2, barometric pressure, and respiratory exchange ratio.

Pao2 = Pio2 - (Paco2/R) + k
Can typically ignore k

For R

4

Describe whether diffusion or ventilation is rate-limiting for CO2 removal.

Ventilation -- SLOW and Rate-limiting for removal of CO2 from blood

Diffusion is FAST

5

Calculate arterial P-aCO2 and alveolar P-ACO2 given known values of alveolar ventilation and CO2
production.

Paco2 = (Vco2/Va)( k )

where Vco2 is the CO2 production in
one minute and Va is Alveolar ventilation in one minute

Meaning, partial pressures of CO2 in alveoli is inversely proportional to Alveolar ventilation

6

Define hypOventilation and the causes

alveolar ventilation is abnormally low in relation to CO2 production and elimination rate

In a subject breathing atmospheric air, an increase in PaCO2 (a decrease in V ˙A ) means hypoventilation.

Causes: obstructive/restrictive disease, metabolic alkalosis, or CNS depression

7

Define hypERventilation and the causes

alveolar ventilation is abnormally high in relation to CO2 production and elimination rate

In a subject breathing atmospheric air, a decrease in PaCO2 (and an associated increase in V ˙A ) means
hyperventilation

Causes: acute hypoxemia (low arterial oxygen), metabolic acidosis, or CNS stimulation

8

Define hyperpnia

The increase in ventilation during moderate exercise

9

Calculate alveolar P-AO2 given known values of P-ACO2, barometric pressure, and respiratory exchange ratio.

x

10

Describe whether diffusion or ventilation is rate-limiting for CO2 removal.

x

11

Define hypOventilation and the causes

x

12

Define hypERventilation and the causes

x

13

Calculate arterial P-aCO2 and alveolar P-ACO2 given known values of alveolar ventilation and CO2
production.

x

14

Define hypoventilation and the causes

x

15

Define hyperventilation and the causes

x

16

Define hyperpnia and the causes

x