Which of the following statement(s) is/are true concerning the pathophysiology of gas exchange?

a. Hypoventilation in relation to perfusion can result in an oxygen saturation of less than 100%

b. Diffusion block and / mismatch can almost completely be overcome by breathing 100% oxygen

Under normal conditions, red blood cells in the pulmonary capillaries become fully saturated and oxygen dissolves in plasma resulting in blood PO2 of 100 and O2 saturation of 100%. This equilibration may be disturbed by hypoventilation in relationship to the perfusion (/ mismatch), diffusion block caused by interstitial fibrosis, or perfusion of nonventilated alveoli. Diffusion block and / mismatch can almost be completely overcome by breathing 100% oxygen, hence hypoxemia during exposure to high alveolar PO2 is caused by total / mismatch, so-called transpulmonary shunting or venous ad mixture. Under normal circumstances, about 5% of the blood entering the left atrium has been shunted away from the pulmonary capillaries, either as the result of bronchial nutritive blood flow or through thebesian veins opening directly into the left side of the heart. This phenomenon, combined with a normal minor / mismatch associated with breathing at rest and positional changes in pulmonary blood flow, result in the fact that normal arterial PO2 is 90–100 mm Hg and the normal O2 saturation is 98%.