Alveolar-Blood Gas Exchange Flashcards
Atmospheric Dry O2
vs
Humidified O2
Dry ~160mmHg / 21%
Humidified 150mmHg / 20%
pressures of O2 and CO2 in the alveolar air
PO2 = 100 PCO2 = 40
pressures of O2 and CO2 in systemic arterial blood
PO2 = 100 PCO2 = 40
pressures of O2 and CO2 in mixed venous blood
PO2 = 40 PCO2 = 46
Alveolar Ventilation
VCO2 = VA x PACO2 x K
*** if AV is double, CO2 is half
PaCO2= 1/VA
hypercapnia
Hypoventilation
(inadequate ventilation)
↑ arterial PCO2
≥ 45 mm Hg
hypocapnia
Hyperventilation
(excessive ventilation)
↓ arterial PCO2
≤ 35 mm Hg
Alveolar Gas Equation for dry air
PAO2 = PIO2 - (PACO2/R)
Normally, R= 0.8
Alveolar Gas Equation to humidified air
PAO2=(Patm – 47) * FO2 – PACO2 / R
*** 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
20 mm Hg
*** 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?
= (barometric pressure * PO2)/normal atmospheric pressure
= (380*160)/760
= 80 mmHg
Rate of diffusion
Rate of diffusion = (Surface area * Partial pressure difference * Solubility) / Distance
*** What gas diffuses fastest?
CO2
Factors Affecting Diffusing Capacity:
- Molecular weight of the gas
- Thickness of respiratory membrane
- Pressure Gradient
- Solubility of gas in fluid medium
1 gm of Hb can bind to how much O2
1.34ml O2
Shift to right (↑)
Hb gives out O2
- ↓ PO2
- ↑P CO2
- ↑[H+] (acidosis)
- ↑temperature
- ↑2,3-DPG
Shift to left (↓)
Hb accepts O2
- ↓P CO2
- ↓[H+] (alkalosis)
- ↓ temperature
- ↓ DPG
Carbon monoxide (CO)
causing shift of the curve to left
*** cherry-red skin
*** 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?
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
*** 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?
300 mmHg
*** 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?
Carbon monoxide poisoning
