1a. The top of Long’s Peak, Colorado, is 14,259 feet above sea level and the total atmospheric pressure is 440 mm Hg. Assuming that the fractional content of oxygen in air is 0.21 (or 21%), what is the PO2 in dry air at the top of Long’s Peak?
1b. If normal ventilation of alveoli results in oxygen partial pressure in the alveolus that is 65% of atmospheric PO2, then what would be the predicted alveolar PO2 of someone at the top of Long’s Peak?
1c. If blood passing through the capillaries of the lung comes into equilibrium with alveolar PO2, what would be the PO2 of arterial blood?
1d. Draw a “typical” oxygen dissociation curve for hemoglobin (P50 = 30 mm Hg), label both axes, and indicate the point on this curve at the value of arterial PO2 determined above (1c). Is hemoglobin fully saturated at this PO2?
1e. What would be the response of peripheral chemoreceptors and lung ventilation at arterial PO2 determined above (1c)?
1f. If the response in 1e caused arterial PCO2 to decrease to 25 mm Hg (from a normal value of 40 mm Hg), what would be the resulting arterial pH? Assume [HCO3-] = 24.0 mM, pK1 for carbonic acid = 6.10, and CO2 solubility coefficient = 0.0300 mmol/(L mm Hg).
1g. Compared to a “normal pH”, hemoglobin’s oxygen affinity at the pH determined in 1f is:
a. increased.
b. decreased.
c. unchanged.
1h. Compared to a “normal pH”, hemoglobin’s P50 at the pH determined in 1f is:
a. increased.
b. decreased.
c. unchanged.
1i. Compared to a “normal pH”, the percent saturation of hemoglobin in lung capillaries at the pH determined in 1f is:
a. increased.
b. decreased.
c. unchanged.
1j. Compared to normal conditions, the acid-base conditions in 1f are best described as:
a. respiratory acidosis
b. respiratory alkalosis
c. metabolic acidosis
d. metabolic alkalosis
At rest, a female subject has a tidal volume (VT) of 480 ml and a respiratory rate (RR) of 15 breaths per minute. Assume a dead space volume of 120 ml. Calculate this individual’s minute ventilation (VE) and alveolar ventilation (VA).
During moderate exercise, the subject from 2a increases both VT and RR by exactly 2 times (with no change in dead space). Calculate this individual’s VE and VA during exercise.What is the ratio of this person’s exercise VE to rest VE? What is the ratio of this person’s exercise VA to rest VA? Are these ratios the same? Why or why not?
Sample Solution
