Pulmonary Physiology Flashcards
What are the stages of respiration for oxygen?
- ventilation 2. pulmonary gas exchange 3. gas transports 4. peripheral gas exchange
Contrast the gas exchange system and the conductive system.
Conductive: continues until terminal bronchioles, anatomical dead space, roughly 150 mL Gas exchange: repiratory bronchioles starts, alveolar exchange, roughly 2.5-3 L
Describe Fick’s Law of Diffusion.
D = (A/T)*D*(P1-P2) Diffusion constant = solubility/sqrt(MW)
What is the air fraction of oxygen in room air?
21%
How much of the pressure in the trachea is due to water vapor that needs to be subtracted out?
47 mmHg
Contrast elasticity and compliance.
Elasticity is the ability to return to original shape and compliance is the ability to change shape. (Think of a rubber band!) They are inverses of each other. Compliance = 1/elasticity = change in V/change in P
What equation is used to calculate alveolar O2?
Palv O2 = (760-47) X FiO2 – PalvCO2/0.8 You have to subtract out the partial pressure of carbon dioxide that is present at this level of the exchange. The 0.8 is the gas exchange ratio between CO2 and O2.
What are the four lung volumes?
Tidal volume, residual volume, inspiratory reserve volume, expiratory reserve volume
What are the four lung capacities?
Total lung capacity, functional reserve capacity, vital capacity, inspiratory capcity
If you breathed in 500 mL of air, how much air is in the gas exchange system? How much is in the conductive system?
150 ml in conductive 350 ml in gas exchange
Which lung volumes and capacities cannot be measured by spirometry?
residual volume, FRC, and TLC
What is the equation for minute ventilation?
VE = RR x TV Normally 7500/min
Describe the relationships between alveolar minute ventilation and blood flow?
They are usually a 1:1 ratio
Contrast anatomic dead space and physiologic dead space.
Anatomic dead space is the conducting zone. In physiologic dead space, there are alveoli but they are not functioning properly and therefore functionally is considered dead space.
What is the relationship between PaCO2 and minute ventilation? How is this related to adjusting ventilators?
VeCO2 x 0.862/ (1-Vd/VT) = Ve x PaCO2 = constant (in a steady state) If you adjust the respiratory rate, then the PaCO2 and Ve have an inverse relationship. If you adjust the tidal volume, this is a more difficult relationship to govern.
Fowler method
Used to measure anatomical dead space. Patient inhales 100% O2, when nitrogen or carbon dioxide starts to appear on expiration, then they know that have reached the physiologic area.
Bohr method
Collect patient breathe and measure expired CO2 to infer the physiologic dead space.
What does it mean for a gas to be perfusion limited?
This means that the gas diffuses readily accross the membrane, but what limits it is how much blood and how quickly it can perfuse that area. For example, N20.
What does it mean for a gas to be diffusion limited?
The gas does not easily cross diffuse accross the barrier and so it is limited by how quickly it can perfuse rather than by perfusion. For example, CO. Because CO gets bound up by hemoglobin, there is always a gradient (P1-P2), so what determines the amount of gets through is how fast it can diffuse, not perfusion.
Explain oxygen in terms of perfusion limited and diffusion limited.
Oxygen is considered both perfusion and diffusion limited. Intiially, oxygen is more limited by perfusion, but later on it is limitted by diffusion. (0 to 0.25 then 0.25 to 0.75)

How would oxygen limitation change with fibrosis?
This would shift oxygen to be more limited in terms of diffusion because of the increased of thickness in the alveolar membrane per Fick’s Law of Diffusion.

How do we measure a patient’s diffusion capability?
We use CO because it is a gas that is diffusion dependent and Fick’s Law of diffusion. We dervie that DL (transfer factor) = Vgas/PACO.
What are the five physiologic causes of hypoxemia?
Low PaO2
- Low inspired O2
- Hypoventilation
- Diffusion limitations
- Shunt
- V/Q imbalance
Describe hypoxemia caused by low PiO2.
This results in lower oxygenation and can be corrected by putting the patient on 100% oxygen.

