Gas Exchange

Question 1

What factor in the Resistance equation has the biggest impact on airflow?

Answer 1

radius

Question 2

How is the radius changed to affect airflow?

Answer 2

-by contracting or relaxing smooth muscle of the airway

Question 3

What is the significance of being able to contract or relax airway smooth muscle?

Answer 3

-air can be directed to alveoli w/ lots of blood

Question 4

What is alveolar ventilation?

Answer 4

• volume of air reaching the alveoli

- tidal volume minus dead space

Question 5

What is minute alveolar ventilation?

Answer 5

amt of air reaching the alveoli per minute

• (tidal volume minus dead space) times RR
• average approx. 4L/min

Question 6

What is the quantity of blood flow from the R ventricle into the lungs?

Answer 6

5L/min

same as cardiac output

Question 7

What is the equation for gas diffusion rate?

Answer 7

J =
[SA x diffusion coefficient x (P1-P2)]
divided by distance

Question 8

How does the diffusion coefficient of carbon dioxide compare to that of oxygen?

Answer 8

D of carbon dioxide is 20x greater than D of oxygen

Question 9

What comprises the “distance” in the diffusion rate equation?

Answer 9

• thickness of the alveolar barrier (approx. 6 microns)

- fluid layer, alveolar epithelium, interstitial space, and blood vessel wall

Question 10

How does interstitial lung disease impair gas diffusion?

Answer 10

• deposition of collagen in the interstitial space increases the diffusion distance of gas across the alveolar barrier
• increased diffusion distance means a slower diffusion rate

Question 11

How does the diffusion capacity of the lung for carbon dioxide compare with the diffusion capacity of the lung for oxygen?

Answer 11

-diffusion capacity of the lung for carbon dioxide is much greater than for oxygen

• 400 mL/min of carbon dioxide per mm Hg
• 21 mL/min of oxygen per mm Hg

Question 12

How long is a RBC in the pulmonary capillary before carbon dioxide has reached equilibrium?

Answer 12

-carbon dioxide reaches equilibrium almost immediately

Question 13

How long is a RBC in the pulmonary capillary before oxygen has reached equilibrium?

Answer 13

0.25 seconds

Question 14

How long is a RBC in the pulmonary capillary during rest?

Answer 14

0.75 seconds

Question 15

How long does a RBC spend in the pulmonary capillary during heavy exercise?

Answer 15

0.25 seconds

Question 16

What does it mean if something is “perfusion-limited”?

Answer 16

it has reached equilibrium and no more gas exchange is happening

Question 17

What does it mean if something is “diffusion-limited”?

Answer 17

it doesn’t spend enough time in the capillary bed to completely reach equilibrium

Question 18

How is the diffusion capacity of the lung for oxygen measured?

Answer 18

pt inhales a small amt of carbon monoxide

-diffusion capacity of the lung for oxygen is 1.23 times that of diffusion capacity for carbon monoxide

Question 19

What is surface tension?

Answer 19

tension created when air molecules come into contact w/ water molecules

-“like molecules” want to be together

Question 20

What is the equation for pressure and surface tension?

Answer 20

P=2T/r

Question 21

Based on the equation for pressure and surface tension, how does the pressure in small alveoli relate to pressure in larger alveoli?

Answer 21

pressure in the small alveoli (smaller radius) is larger

Question 22

Without surfactant, what would happen to small alveoli?

Answer 22

• airflow would move from area of high pressure (small alveoli) to lower pressure (large alveoli)
• small alveoli would collapse and the SA available for diffusion would decrease

Question 23

How does surfactant act on alveoli?

Answer 23

-decreases the surface tension in the small alveoli moreso than the large alveoli