Diving: Breathing, Respiration, and the Circulatory System

We may imagine dolphins as continuous breath-holding divers or marathon swimmers that continuously exercise. However, just by admitting this simple comparison, we immediately come out with a number of questions that has been difficult to answer: What about the energy required to move uninterruptedly in and out of the water surface? What about the oxygen stores required to perform prolonged breath-hold dives? What about heartbeat or breathing frequency, diaphragm movements, and the effects of external pressure? Some of these complex aspects of diving physiology are still partially unsolved in dolphins, and are outside the scope of the present book.