Introduction to gas exchange

Question 1

Alveolar ventilation

Answer 1

vol of air per minute that enters/exists alveoli and participate in gas exhange
minute ventilation - dead space ventilation

Question 2

Physiologic dead space

Answer 2

anatomic (~150 ml) + alveolar (20-30 ml)

Question 3

Pulmonary arterial O2 and CO2 pressures

Answer 3

O2 = 40 mmHg
CO2 = 46 mmHg

Question 4

Alveolar O2 and CO2 pressures (normal)

Answer 4

O2 = 100 mmHg
CO2 = 40 mmHg

Question 5

Alveolar ventilation equation

Answer 5

PACO2 = (VCO2/VAdot) x 0.863

Question 6

Hyperventilation

Answer 6

hypocapnia

Question 7

Hypoventilation

Answer 7

hypercapnia
not enough total ventilation
too much of total ventilation in dead space

Question 8

Fick’s Law of Diffusion

Answer 8

Vgas = (A x D x (P1-P2) ) / T
A = surface area
D = diffusion coefficient
T = thickness of membrane

Question 9

Blood time spent in pulmonary capillary

Answer 9

normal = 0.75 s

diffusion complete in ~1/3 of time (normal)

Question 10

Diffusion capacity

Answer 10

DLCO = VCO / PACO

Question 11

Single-breath test

Answer 11

Patient breathes in He + CO after max. expiration
hold breath for 10 sec
breathe out
measure vol. CO before and after, and lung volume (He)

Question 12

Conditions that decrease SA for diffusion

Answer 12

Emphysema
Lung/lobe resection
PE
Bronchial obstruction
Anemia

Question 13

Conditions that increase wall/membrane thickness

Answer 13

Pulmonary fibrosis
Asbestosis
Sarcoidosis, involving parenchyma
Collagen vascular disease - scleroderma, systemic lupus erythematosus

Question 14

Alveolar air equation

Answer 14

PAO2 = FIO2 (Patm - PH2O) - PaCO2/R
FIO2 = 0.81 (sea level)
Patm = 760 mmHg (sea level)
PH2O = 47 mmHg (room temp)
R = 0.8