respiratory - topic 5

Question 1

what is pulmonary gas exchange?

Answer 1

diffusion of O2 from alveolar air to pulmonary blood (and CO2 in reverse)

Question 2

what is systemic gas exchange?

Answer 2

exchange of O2 and CO2 between systemic capillaries and tissue cells

Question 3

what is Dalton’s gas law?

Answer 3

partial pressure are independent
partial pressure = total pressure x percent of mixture

Question 4

how do you calculate partial pressure of O2?

Answer 4

without humidity = Pb x 21%
with humidity = (Pb - PH2O) x 21%

Question 5

give an example of O2 partial pressure calculations?

Answer 5

dry inspired air = 760 mmHg x 0.21 = 160 mmHg
moist alveolar air = (760 mmHg - 47 mmHg) x 0.21 = 150 mmHg

Question 6

What are the normal pressures of O2?

Answer 6

40 venous, 100 arterial, 105 alveolar, 160 atm

Question 7

what are the normal pressures of CO2?

Answer 7

46 venous, 40 arterial, 40 alveolar, 0.3 atm

Question 8

what is Henry’s gas law?

Answer 8

how much gas dissolves in liquid = Px of gas

Question 9

what is Fick’s gas law?

Answer 9

Vx (volume of gas) = (AD▲P) / T
A = surface area
D = diffusion coefficient
▲P = pressure gradient
T = membrane thickness

Question 10

what is the relationship between diffusion coefficients of O2 and CO2

Answer 10

Co2 is 20x higher than O2, so hypoxia usually happens before hypercapnia

Question 11

what is lung diffusing capacity?

Answer 11

measures diffusion barrier of alveoli-capillary membrane

Question 12

how is DL measured?

Answer 12

using a breath of CO (good at diffusing)

Question 13

how does emphysema affect DL?

Answer 13

decreases surface area - decreases DL

Question 14

how does fibrosis affect DL?

Answer 14

thickens the membrane - decreases DL

Question 15

how does anemia affect DL?

Answer 15

reduces Hb, messes up Px gradient - decreases DL

Question 16

how does exercise affect DL?

Answer 16

recruits capillaries, increases SA - increases DL