Ventilation and Diffusion

Question 1

Partial pressure equation

Answer 1

Pi Gas = Fgas (Patm - P H2O)

take into consideration dry air when doing calculation

FO2 - usually 0.21

Question 2

tidal volume

Answer 2

normal breathing

Question 3

vital capacity

Answer 3

maximum inspiration and expiration

Question 4

residual volume

Answer 4

after maximum expiration some volume leftover

Question 5

functional residual capacity

Answer 5

volume after a normal expiration

Question 6

what cannot be measured spirometry?

Answer 6

residual or FRC

Question 7

helium dilution method

Answer 7

use known [helium]
after some breaths, concentration eqilibriate

C1 x V1 = C2 x (V1 + V2) = C2 x (V1 + FRC)

Question 8

body plethysmography

Answer 8

P1 x V1 = P2 x (V1 - deltaV)

with inspiratory effort against closed airway:

• increases volume of lung
• decreases airway pressure
• box pressure increases
• box volume decreases

Question 9

anatomic dead space

Answer 9

volume of conducting airways

Question 10

alveolar dead space

Answer 10

alveoli containing air but not participating in gas exchange

Question 11

physiologic dead space

Answer 11

total dead space for system

space that does not eliminate CO2

Question 12

alveolar ventilation

Answer 12

room air delivered to respiratory zone per minute

Va = (Vt - Vd) x f

Va  = alveolar ventilation
Vt = tidal volume
Vd = dead space
f = respiratory rate

Question 13

Bohr’s method for alveolar ventilation

Answer 13

Vd / Vt = PaCO2 - PeCO2 / PaCO2

based around all expired CO2 derived from alveolar space and none from dead space

Question 14

regional differences in ventilation?

Answer 14

lower lung - more ventilation (gravity)

lower zones - more compliant
upper zones - less compliant

changes in supine or laying on side

Question 15

Fick’s Law of Diffusion

Answer 15

Vgas ~ A x D x (P1-P2) / T
A = area
D = sol / sqrt(MW) **diffusion constant**
P1-P2 = pressure difference
T = thickness

Question 16

what diffuses faster?

Answer 16

CO2

because of greater solubility

Question 17

what makes up respiratory membrane?

Answer 17

alveolar space
surfactant
water layer
alveolar epithelial cells
alveolar basement membrane
alveolar interstitium
capillary basement membrane
capillary endothelium
capillary lumen filled with fluid
red blood cell

Question 18

diffusion limited

Answer 18

molecule getting into blood dependent on diffusion properties of blood-gas barrier and not amount of blood available

ex/ carbon monoxide

Question 19

perfusion limited

Answer 19

molecule getting into blood dependent on amount of blood available
-as it diffuses, sharp increase in partial pressure

ex/ nitrous oxide

Question 20

O2 gas diffusion?

Answer 20

resting - perfusion limited

some conditions - diffusion limited
-exercise, thick blood-gass barrier, reduced PiO2

Question 21

uptake of O2 in capillary?

Answer 21

normal conditions - PaO2 equals PAO2 when RBC 1/3 through capillary bed

decreasing PiO2 - increased time to equilbriate

Question 22

CO2 transfer

Answer 22

diffusion of CO2 is 20x higher than O2
-however, concentration gradient is lower

hypercapnia is rare
-there is potential for elevated levels of CO2 due to thickening of blood-gas barrier

Question 23

diffusing capacity

Answer 23

D-L
distance gas travels across membrane into blood and time it takes to react with hemoglobin

measured by uptake of CO in lung
-units mL / min x mmHg

normal ~ 25 mL / min x mmHg

Question 24

pathology and D-L

Answer 24

pulmonary fibrosis - destruction of capillaries
COPD - loss of lung elastic and capillaries and Hb
loss functional lung tissue - decreased SA and Hb
anemia - fall in Hb