1. You make it to the top of Mt. Everest (30,000 feet; P ATM =228 mmHG). A. Calc

Question

1. You make it to the top of Mt. Everest (30,000 feet; PATM=228 mmHG).

A. Calculate the partial pressure of N2, O2, and CO2 in the air at this altitude (assume the same mixture percentages as sea level).

B. Caclulate the alveolar O2 pressure (PAO2) at this altitude. Assume PH2O=47 mmHg and Alveolar CO2 (PACO2)=13 mmHg.

C. Assume you ascend to altitude with no existing health issues. Based on your answers to A & B, would you experience hypoxia? Why or why not?

D. Bae has been waiting for you at the summit for a few days. Unlike you, Bae has asthma. As you run to hug them, they start to have an asthma attack.

Before the asthma attack, would you expect Bae's respiratory rate to be at altitude (less, same, more) compared to sea level?

If you were to measure P02 levels in the alveoli after teh asthma attack would they be elevated, normal, or depressed compared to before the asthma attack?

What would happen to the PO2 in Bae's blood? Would you expect there to be a difference between the alveolar PAO2 and the arterial P02? Why or why not?

Explanation / Answer

Answer A:-

Air contains

78.09% Nitrogen

21.0% Oxygen

0.04% Carbon dioxide

Now,

Partial pressure of gas (Pgas) = (percentage of gas in air*pressure of air)/100 ---equation 1

Given :- Pressure of air = 228 mmHg

Considering same percentage composition of oxygen nitrogen and carbon dioxide, partial pressure for the three gases would be(from equation 1) as follows:-

PO2 = (21*228)/100 = 47.88 mmHg

PN2= (78*228)/100 = 177.84 mmHg

PCO2 = (0.04*228)/100 = 9.12 mmHg.

Answer B:-

Given:- PACO2 (partial pressure of alvelolar CO2= 13mmHg, Partial pressure of water vapour in alveoli (PAH2O)= 47 mmHg, Pressure of air (P) = 228 mmHg, Fractional concentration of oxygen (FO2) = 21%/100 = 0.21.

Now,

PAO2 = [FO2*(P-PAH2O)] – [PACO2*(FO2 + 1)

{Note:- 1 value is of [(1-FO2)/respiratory exchange ratio]. As 1-0.21 is approximately 0.8 and normal respiratory exchange ratio = 0.8}

Therefore,

PAO2 = [0.21 * (228-47)] – [13*(0.21+1)]

PAO2 = 38.01 -15.73

PAO2 = 22.28 mmHg

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