Name a physiological effect of using EANx at depth.

Using Enriched Air Nitrox (EANx), which contains a higher percentage of oxygen than regular air, can lead to enhanced oxygen uptake at depth. This physiological effect is significant because deeper dives increase the partial pressure of gases, including oxygen, which can lead to greater oxygen availability in the lungs and thus more efficient oxygen uptake into the bloodstream.

However, this increased oxygen exposure at depths also poses a risk of hyperoxia, a condition that results from having too much oxygen in the body, which can be detrimental to divers. The risk of hyperoxia rises as the diver descends deeper and the partial pressure of oxygen increases, potentially leading to symptoms ranging from visual disturbances to seizures.

While decreased nitrogen absorption is a benefit of using EANx compared to regular air, the direct physiological effect at depth pertains more to oxygen and the risk of hyperoxia. Reduced breathing rates and increased carbon dioxide buildup are also physiological effects, but they are not directly linked to the specific impact of using EANx at depth in the same way that increased oxygen uptake is. Therefore, the correct choice focuses on the critical relationship between oxygen exposure and depth in EANx diving.