Why Would a Terrestrial, Air-Breathing Mammal Choose to Go Underwater?

Humans underwater face unique physiological challenges due to a non-respirable, thermally demanding, and high-pressure environment. Breathing dense gases through underwater apparatus can disrupt normal breathing control, leading to carbon dioxide retention. Increased pressure makes nitrogen and oxygen more narcotic and toxic, necessitating synthetic gases at greater depths. Respiration can become a significant source of heat loss, and high pressure can trigger neurological issues known as high pressure neurological syndrome. Upon resurfacing, dissolved breathing gases form bubbles, potentially causing decompression sickness (DCS). While DCS symptoms are often linked to bubbles in tissues, those in venous blood are significant because they can be detected easily and have a complex relationship with DCS risk. Diving physiology aims to understand and alleviate these stresses to enhance underwater activities.