Atmosphere
What is the composition of gases in the atmosphere?
What is atmospheric pressure at sea level?
760mmHg
What is the normal pH range for arterial blood?
7.35-7.45
What law governs the partial pressure of gases in the atmosphere (and what is it)?
Dalton's law (the total pressure of a gas mixture is equal to the sum of the partial pressure of its individual gases)
How does the fraction of inspired Oxygen change at altitude compared to sea level?
Unchanged - still ~21%
What two factors do you need to know the partial pressure of O₂ in the atmosphere at any altitude?
- total atmospheric pressure
- % of Oxygen in atmosphere
At what altitude is atmospheric pressure ~1/2 of sea level?
5895m (Kilimanjaro summit)
What range does the body aim to keep PaCO₂ at?
35-45mmHg
How does Henry's Law change the solubility of gases into water/capillaries at high altitude?
As the amount of gas that dissolves is determined by its solubility in water and partial pressure in the air, as partial pressure of the gas decreases, solubility will degrease, meaning at altitude O₂ is less soluble in the blood plasma
What does the alveolar gas equation tell us?
The partial pressure of oxygen in the alveoli available for diffusion - this is critical to understand how efficiently oxygen is diffusing into the blood.
Bonus: what is the alveolar gas equation?
At sea level, what is the partial pressure of O₂ in the alveolus?
~100mmHg =(0.21*[760mmHg-47mmHg])-(40/0.8)
What change occurs in the respiratory tract that changes the partial pressure of inspired air between the atmosphere and the alveoli?
Humidification - dilution by H₂O vapour
BONUS Question: What is the pressure of water vapour at 37degrees & how much would this temperature affect the partial pressure of O₂ between the atmosphere and alveoli?
In ABG, what does low bicarbonate (HCO₃-) indicate about respiratory compensation?
kidneys compensation for respiratory alkalosis by excreting bicarbonate to balance the pH, often seen after hyperventilation at high altitudes
What is the typical diffusion gradient for oxygen between the alveoli and capillary in a healthy human lung at sea level?
<5mmHg
How does respiratory alkalosis affect the alveolar gas equation at altitude?
Respiratory alkalosis (due to hyperventilation) lowers PaCO₂, thus reducing the second term of the alveolar gas equation (PaCO2/RQ) and increasing oxygen partial pressure at the alveoli (PAO₂)
Bonus: What is PaCO₂/RQ telling us in the alveolar gas equation?