Gas Exchange and Transport questions 1-20 94- 106
What are the three barriers to diffusion in the lung?
-Alveolar epithelium -Interstitial space -Capillary endothelium
Describe the relationship between PACO2 and VCO2.
-PACO2 varies directly with CO2 production (VCO2) and
1. What is the formula used to calculate expected PaO2 based on age?
100 - (0.323 x age in years)
What is the normal range of PACO2?
35-45 mmHg
What is the value for the partial pressure of water vapor at 37 degrees C?
47mm Hg
What is the normal DA-aO2 (A-a gradient) for a person breathing room air?
5 - 10 mm Hg
1. Define dysoxia.
Abnormal cellular function prevents proper uptake of O2
1. Define hypoxemia.
Arterial blood content is decreased
1. What is the reaction formula for hydrolysis of CO2?
CO2 + H2O
1. What is the movement of chloride ions into the RBC in exchange for the movement of bicarbonate ions out to the plasma called (both names)?
Hamburger phenomenon
1. What are causes of hypoxia?
Hypoxmia CO or diffusion decreased dysoxia
1. When can a decrease in alveolar ventilation occur?
Minute ventilation is inadequate Deadspace VE is increased V/Q imbalance exists
1. Define hypoxia.
O2 delivery falls short of cellular needs
Moderate ARDS
P/F 100-200 mmHg
-Mild ARDS =
P/F 201-300 mmHg
Severe ARDS
P/F < 100 mmHg
Based on the alveolar air equation, what is the relationship between PAO2 and PACO2 if the FiO2 is constant?
PAO2 will vary inversely with PACO2
List the partial pressures of O2 from the atmosphere to the cell.
PIO2 159 trachea +/- 140mmHg alveoli +/- high 90s tissues +/- 40's cells +/- 5
1. What is the most common cause of hypoxemia in patients with respiratory diseases? (See Rule of Thumb on page 265)
Perfusion imbalance or V/Q mismatch and shunting
What is the rule of thumb on page 250?
When breathing normal air PAO2 and PACO2 is about 140 mmHg
1. What enzyme is responsible for accelerating the reaction between CO2 and H2O?
carbonic anhydrases
List the partial pressures of CO2 from the cells to the atmosphere.
cells +/- 60 mmHg tissues +/- 40's mmHg alveoli +/- 30's mmHg trachea +/- 20's mmHg air 1mmHg
Define diffusion.
from areas of high partial pressure to low partial pressure
How does increased dead space affect PACO2?
increase in PACO2 is an increase in dead space:
1. What is the Haldane effect?
influence of HbO2 on CO2 dissociation
Define dead space.
is the portion of inspired air that is exhaled without being exposed to perfused alveoli
1. What can cause dysoxia?
there is abnormal tissue oxygen metabolism,
State what causes gas to move between and tissues
•CO2 builds up in the tissues due to metabolism and diffuses into capillary blood •Then it is transported to the lungs for exchange with gas from the alveoli
State what causes gas to move between the lungs
•O2 is moved into the lungs where it diffuses into the pulmonary circulation •Then it is transported in the blood to the tissues
List the alveolar air equation.
•PAO2 = FiO2 x (Pb - 47) - PACO2 0.8
How do you calculate DA-aO2?
•difference between the alveolar (A) and arterial (a) PO2
What is the barrier to diffusion in the RBC?
•the erythrocyte membrane
