What physiological change occurs due to excessive hyperventilation before diving?

Excessive hyperventilation before diving leads to a decrease in carbon dioxide (CO2) levels in the blood. When a diver hyperventilates, they breathe rapidly and deeply, which increases the amount of oxygen drawn into the lungs while simultaneously expelling a larger quantity of carbon dioxide. This reduction in CO2 can cause respiratory alkalosis, resulting in physiological changes such as a heightened sense of euphoria and potentially impaired decision-making, as well as diminishing the urge to breathe due to lower CO2 levels.

The critical point about hyperventilation is that it's not merely about managing oxygen intake; it's primarily about how CO2 levels are affected. A decrease in CO2 can mask the body's natural respiratory drive, which is dangerous for divers. This underscores the importance of maintaining balanced respiratory patterns before and during dives to ensure safe diving practices.