The main idea is that arterial oxygen tension (PaO2) increases when the inspired oxygen fraction (FiO2) is raised. In the alveolar gas equation, PAO2 depends on FiO2; increasing FiO2 raises the oxygen available to diffuse into the blood, so PaO2 tends to rise as well. This is why giving supplemental oxygen improves arterial oxygen tension, especially in those with hypoxemia. While the exact increase can be influenced by lung diffusion capacity and V/Q matching, the overall relationship is direct: higher FiO2 leads to higher PaO2.

Pulmonary capillary wedge pressure reflects the pressure in the left atrium and serves as a surrogate for left-sided filling pressures. When a balloon-tipped catheter is wedged in a small pulmonary artery, the pressure read is equilibrated with the left atrial pressure, giving a measure of LV preload. The normal range is 6–12 mmHg. This window indicates normal left atrial pressures at rest. Values below this suggest low preload, while values above 12 mmHg point to elevated left-sided pressures, such as in left heart failure, significant mitral valve disease, or volume overload. The other ranges fall outside the normal window, either being too low or too high for typical resting left atrial pressure.

Understanding normal ranges for cardiovascular pressures helps identify the correct choice. The mean pulmonary artery pressure in a healthy person is about 12 to 16 mm Hg, so a mean value of 13–14 mm Hg fits this range. The other pressures have different typical means: mean arterial pressure is usually much higher (roughly 70–105 mm Hg), right atrial pressure is quite low (around 2–6 mm Hg), and pulmonary capillary wedge pressure is also low (about 6–12 mm Hg). Therefore, the pressure with a mean value of 13–14 mm Hg is the mean pulmonary artery pressure.

TLC percent predicted compares your measured total lung capacity to a normal value expected for someone of the same age, height, and sex. The range considered normal is 80-120% of that predicted value. Staying within this band means the lungs can hold a typical amount of air for the person’s body size. If TLC falls below 80% of predicted, it suggests a restrictive issue where the lungs or chest wall can’t hold as much air. If TLC rises above 120% of predicted, it indicates hyperinflation or air trapping, which is common with obstructive conditions like emphysema or chronic asthma. So, the statement that 80-120% of predicted is the normal TLC range aligns with standard reference values.