Diving Feats and Behavior

Types of Dives and the Importance of Method

Physiology: The Big Picture

The Oxygen Stores of Divers

• The blood O₂ store tends to be large in diving mammals
• Diving mammals have high myoglobin concentrations and large myoglobin-bound O₂ stores
• Diving mammals vary in their use of the lungs as an O₂ store
• Total O₂ stores never permit dives of maximum duration to be fully aerobic

Circulatory Adjustments during Dives

• Regional vasoconstriction: Much of a diving mammal’s body is cut off from blood flow during forced or protracted dives
• Diving bradycardia matches cardiac output to the circulatory task
• Cardiovascular responses are graded in freely diving animals
• Red blood cells are removed from the blood between dive sequences in some seals
• BOX 26.1 The Evolution of Vertebrate Cardiac and Vascular Responses to Asphyxia

Metabolism during Dives

• The body becomes metabolically subdivided during forced or protracted dives
• Metabolic limits on dive duration are determined by O₂ supplies, by rates of metabolic O₂ use and lactic acid production, and by tissue tolerances

The Aerobic Dive Limit: One of Physiology’s Key Benchmarks for Understanding Diving Behavior

• Marine mammals exploit multiple means of reducing their metabolic costs while underwater

Decompression Sickness

• Human decompression sickness is usually caused by N₂ absorption from a compressed-air source
• Breath-hold dives must be repeated many times to cause decompression sickness in humans
• Marine mammals have been thought—perhaps erroneously—to avoid decompression sickness during deep dives by alveolar collapse
• Decompression sickness is an unresolved phenomenon

A Possible Advantage for Pulmonary O₂ Sequestration in Deep Dives

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