Final answer:
The fraction of inspired oxygen (FIO₂) increases primarily with the use of supplemental oxygen, as this raises the oxygen concentration in the inspired air.
Step-by-step explanation:
The fraction of inspired oxygen (FIO₂) will increase primarily with supplemental oxygen. When you breathe in air that has a higher concentration of oxygen than the standard atmospheric level, the FIO₂ in the air becomes higher. Essentially, supplemental oxygen therapy can increase this concentration, thereby raising the amount of oxygen available to the lungs for gas exchange.
While increasing the tidal volume (amount of air inhaled or exhaled during a normal breath), performing a forceful inhalation, or increasing the respiratory rate can affect the amount of air moving into and out of the lungs, these actions do not directly change the composition of the air, which determines the FIO₂.