Alveolar-Blood Gas Exchange

Question 1

Atmospheric Dry O2
vs
Humidified O2

Answer 1

Dry ~160mmHg / 21%

Humidified 150mmHg / 20%

Question 2

pressures of O2 and CO2 in the alveolar air

Answer 2

PO2 = 100
PCO2 = 40

Question 3

pressures of O2 and CO2 in systemic arterial blood

Answer 3

PO2 = 100
PCO2 = 40

Question 4

pressures of O2 and CO2 in mixed venous blood

Answer 4

PO2 = 40
PCO2 = 46

Question 5

Alveolar Ventilation

Answer 5

VCO2 = VA x PACO2 x K

*** if AV is double, CO2 is half

PaCO2= 1/VA

Question 6

hypercapnia

Answer 6

Hypoventilation
(inadequate ventilation)
↑ arterial PCO2
≥ 45 mm Hg

Question 7

hypocapnia

Answer 7

Hyperventilation
(excessive ventilation)
↓ arterial PCO2
≤ 35 mm Hg

Question 8

Alveolar Gas Equation for dry air

Answer 8

PAO2 = PIO2 - (PACO2/R)

Normally, R= 0.8

Question 9

Alveolar Gas Equation to humidified air

Answer 9

PAO2=(Patm – 47) * FO2 – PACO2 / R

Question 10

*** An individual’s inspired pO2 was 150 mm Hg and his alveolar PCO2 was 40 mm Hg. If this person’s alveolar ventilation then doubled, his alveolar pO2 would be expected to change by: (assume a new steady state and an R value of 1.0

Answer 10

20 mm Hg

Question 11

*** A group of third year medical students accompanied a medical mission team to Peru. After arriving at the airport in Bolivia, they hiked to a remote mountain village in the Andes. At this elevation of 18,000 ft, the barometric pressure was 380 mmHg, resulting in a PO2 of the dry inspired air of what?

Answer 11

= (barometric pressure * PO2)/normal atmospheric pressure

= (380*160)/760

= 80 mmHg

Question 12

Rate of diffusion

Answer 12

Rate of diffusion = (Surface area * Partial pressure difference * Solubility) / Distance

Question 13

*** What gas diffuses fastest?

Answer 13

CO2

Question 14

Factors Affecting Diffusing Capacity:

Answer 14

1. Molecular weight of the gas
2. Thickness of respiratory membrane
3. Pressure Gradient
4. Solubility of gas in fluid medium

Question 15

1 gm of Hb can bind to how much O2

Answer 15

1.34ml O2

Question 16

Shift to right (↑)

Answer 16

Hb gives out O2

• ↓ PO2
• ↑P CO2
• ↑[H+] (acidosis)
• ↑temperature
• ↑2,3-DPG

Question 17

Shift to left (↓)

Answer 17

Hb accepts O2

• ↓P CO2
• ↓[H+] (alkalosis)
• ↓ temperature
• ↓ DPG

Question 18

Carbon monoxide (CO)

Answer 18

causing shift of the curve to left

*** cherry-red skin

Question 19

*** A series of gas mixtures is inhaled by a healthy subject. Which one of the following gases would diffuse most slowly from the lungs into the blood?

Answer 19

A. CO2 at PC02 of 60 mm Hg

***B. CO at a PCO of 0.5 mm Hg

C. O2 at a P02 of 130mm Hg

D. O2 at a P02 of 150 mm Hg

Question 20

*** A 56-year-old man presents to the Emergency Department with severe abdominal pain and a temperature of 103°F. The patient is in severe respiratory distress. Moderate amounts of pulmonary edema fluid are aspirated during suctioning. The patient is placed on a ventilator with an FIO2 of 0.5 and an arterial blood gas sample reveals a PO2 of 160 mmHg and a PCO2 of 40 mmHg. His alveolar oxygen tension, at a barometric pressure of 747 mmHg (P H2O = 47mmHg) and a respiratory exchange ratio (R) of 0.8, is approximately what?

Answer 20

300 mmHg

Question 21

*** A 23-year-old man with no medical problems is brought to the emergency center by family members who found him to be confused, nauseated, short of breath, and complaining of a headache. The patient was found in the basement of their home next to a furnace, where he was trying to stay warm on a cold winter day. On examination, the patient is lethargic and confused. His lips appear a bright pink. A urine drug screen is obtained and is negative. His serum carboxyhemoglobin level is elevated. Which of the following is the most probable diagnosis?

Answer 21

Carbon monoxide poisoning