Lecture 2: Alveolar Gas Exchange Flashcards
What is the function of anatomic dead space?
To direct air flow to alveoli
What is airway resistance and how does the body is overcome it?
Resistance to airflow
factors in the resistance equation, but mostly by changing bronchiole diameter (via smooth muscle in airway walls)
What does the body do to minimize blood going to dead space?
Restrict blood flow to alveoli that cannot gas exchange (stop wasting blood on incompetent alveoli!)
How do you calculate the diffusion rate of a gas?
Diffusion Rate = [(surface area) x (diffusion constant) x (P1 - P2)] / distance
P1 = P in alveoli P2 = P in capillary
How much oxygen is exchanged every minute?
How much carbon dioxide is exchanged every minute?
250 mL of O2
200 mL of CO2
(not even! diffusion of O2 is not dependent on diffusion of CO2»_space;> not actual gas “exchange”)
What does surface area correspond to?
How does it affect diffusion rate?
Number of number of alveoli in the lungs and number of open pulmonary capillaries
Directly proportional (usually large, decreased in diseased states)
What does distance mean?
How does it affect diffusion rate?
Thickness of the alveolar barrier (normally thin, thickened in diseased states)
Inversely proportional
What is more soluble - carbon dioxide or oxygen?
Why?
Carbon Dioxide
-more soluble and weighs more than O2, DCO2 is 20x greater than DO2
What does it mean to be “perfusion limited?”
How does this relate to exercise?
- Amount of blood passing by alveoli is limiting factor for how much oxygen is diffused.
- During exercise, perfusion of blood is faster so it spends less time diffusing stuff to alveoli
What does it mean to be “diffusion limited?”
How does this relate to exercise?
- Ability of gas to cross is limiting factor for how much oxygen is diffused
- If gas already has trouble crossing, exercise worsens it by increasing the perfusion rate, not giving the blood and alveoli to trade things»_space;> why people with lung problems usually have trouble breathing during exertion
What does diffusion capacity of the lung mean and what is the amount for oxygen at rest?
How much O2 can diffuse over the course of the entire lung
21 mL O2/min/mm Hg
How is the diffusion capacity of oxygen calculated?
Why do we use the diffusion capacity of CO to measure this?
1.23 x Diffusion capacity of carbon monoxide
O2 also dissolves in blood, so not accurate since some got dissolved. CO doesn’t so you don’t lose diffused CO to the blood
Describe the diffusion capacity for carbon dioxide?
Since carbon dioxide has such a high diffusion capacity, compared to O2, people have problems with O2 before they have problem with CO2 diffusion
What is LaPlace’s Law?
Pressure in alveolus = (2 x surface tension) / radius
- More surface tension = more pressure
- Smaller radius = more pressure
What happens when some alveoli have greater pressure than others?
Air moves from alveoli A with high pressure to alveoli B with low pressure, causing the alveoli A to collapse.
Alveoli A is collapsed and cannot inflate, Alveoli B is too expanded»_space;> surface area is screwed
