In a person breathing room air (and with all else being normal), ...

[james0929]

In a person breathing room air (and with all else being normal), if the alveolar PCO2 rises from 40 to 70 mm Hg, what would you expect?
 
  a. PAO2 to fall by approximately 30 mm Hg
  b. PAO2 to fall by approximately 40 mm Hg
  c. PAO2 to rise by approximately30 mm Hg
  d. PAO2 to rise by approximately 40 mm Hg

Question 2

A healthy person breathing 100 O2 at sea level would have PAO2 of approximately what level?
 
  a. 149 mm Hg
  b. 670 mm Hg
  c. 713 mm Hg
  d. 760 mm Hg

Question 3

Which of the following best represents the partial pressures of all gases in the normally ventilated and perfused alveolus when breathing room air at sea level?
 
  a. PO2 = 40 mm Hg; PCO2 = 100 mm Hg; PN2 = 573 mm Hg; PH2O = 47 mm Hg
  b. PO2 = 100 mm Hg; PCO2 = 40 mm Hg; PN2 = 573 mm Hg; PH2O = 47 mm Hg
  c. PO2 = 100 mm Hg; PCO2 = 40 mm Hg; PN2 = 713 mm Hg; PH2O = 47 mm Hg
  d. PO2 = 149 mm Hg; PCO2 = 40 mm Hg; PN2 = 573 mm Hg; PH2O = 47 mm Hg

[aidanmbrowne]

Answer to Question 1

ANS: A
Based on the alveolar air equation, if the FiO2 remains constant, then the PAO2 must vary in-versely with the PACO2.

Answer to Question 2

ANS: B
If the FiO2 is 1.0, the PB is 760 mm Hg, and the PACO2 is 40 mm Hg, the alveolar partial pres-sure of O2 can be estimated as follows:
PAO2 = 1  (760 mm Hg  47)  (40 mm Hg  0. = 663 mm Hg

Answer to Question 3

ANS: B
Nitrogen is inert and plays no role in gas exchange. However, nitrogen does occupy space and exert pressure. According to Dalton's law, the partial pressure of alveolar nitrogen must equal the pressure it would exert if it alone were present. Thus, to compute the partial pressure of alveolar nitrogen, subtract the pressures exerted by all the other alveolar gases, as follows:
PAN2 = PB  (PAO2 + PACO2 + PH2O)
PAN2 = 760 mm Hg  (100 mm Hg + 40 mm Hg + 47 mm Hg)
PAN2 = 760 mm Hg  187 mm Hg
PAN2 = 573 mm Hg

[james0929]

Excellent

[matt95]

Thanks for the timely response, appreciate it