Which of the following is not typically altered during pregnancy regarding pulmonary function testing?

Vital capacity typically remains relatively unchanged during pregnancy, despite other pulmonary function parameters being affected. During pregnancy, hormonal changes, particularly increased progesterone, lead to an increase in tidal volume and consequently minute ventilation, as the body works to meet the increased oxygen demands of both the mother and the developing fetus.

As pregnancy progresses, women also experience a compensatory increase in the respiratory rate and tidal volume which contributes to elevated minute ventilation. However, vital capacity, which is the maximum amount of air that can be exhaled after taking the deepest breath, may not see significant changes, as the mechanical constraints of the enlarging uterus can affect the ability to take deep breaths but do not usually result in a change of this specific measurement.

PaO2 levels typically rise as well due to increased ventilation, reflecting improved oxygenation, while the overall lung volume and mechanics shift due to the physical changes from pregnancy. Therefore, among the options presented, vital capacity stands out as the parameter that is not typically altered during pregnancy.