29
chapter two
Oxygen stores and diving
Paul J. Ponganis and Cassondra L. Williams
2.1 The big picture challenge and summary
Marine mammals are able to dive for incredibly long durations. One of the central questions in marine mammal physiology is how these air-breathing vertebrates are able to
remain underwater so long on a single breath (Butler and Jones 1997; Ponganis 2015).
Elephant seals and beaked whales can dive for as long as 2 hours. And many species
make routine, frequent dives to depth with only very short surface periods and little rest
between dives. The key to such dive patterns and long dive durations is found both in the
amount of oxygen (O 2 ) marine mammals take down with them and in the rate of consumption of that O 2 during diving. In general, marine mammals store much greater amounts of
O 2 than terrestrial mammals. But enhanced O 2 storage is not enough to explain the routine, let alone, the longest dive durations of these animals. Regulation of the depletion rate
Contents
2.1 The big picture challenge and summary ......................................................................... 29
2.2 What is known .....................................................................................................................30
2.2.1 Magnitude and distribution of total body O 2 stores ...........................................30
2.2.1.1 Respiratory O 2 stores ................................................................................ 31
2.2.1.2 Blood O 2 stores .......................................................................................... 32
2.2.1.3 Muscle O 2 stores ........................................................................................ 32
2.2.2 The dive response .................................................................................................... 33
2.2.3 Aerobic dive limits ...................................................................................................34
2.3 Toolbox: How these parameters are measured ............................................................... 36
2.3.1 Measuring the respiratory O 2 store ....................................................................... 36
2.3.2 Measuring the blood O 2 store ................................................................................ 37
2.3.2.1 Blood volume ............................................................................................. 38
2.3.2.2 Hb concentration ....................................................................................... 38
2.3.2.3 Hb saturation (SaO 2 and SvO 2 ) ................................................................ 38
2.3.3 Measuring the muscle O 2 store .............................................................................. 39
2.3.3.1 Muscle mass ............................................................................................... 39
2.3.3.2 Mb concentration analysis and potential problems ............................. 39
2.3.4 Measuring heart rate ............................................................................................... 40
2.3.5 Measuring blood lactate to determine the ADL .................................................. 40
2.3.6 Summary ................................................................................................................... 41
2.4 Unanswered questions ........................................................................................................42
Glossary ..........................................................................................................................................42
References .......................................................................................................................................43
chapter two
Oxygen stores and diving
Paul J. Ponganis and Cassondra L. Williams
2.1 The big picture challenge and summary
Marine mammals are able to dive for incredibly long durations. One of the central questions in marine mammal physiology is how these air-breathing vertebrates are able to
remain underwater so long on a single breath (Butler and Jones 1997; Ponganis 2015).
Elephant seals and beaked whales can dive for as long as 2 hours. And many species
make routine, frequent dives to depth with only very short surface periods and little rest
between dives. The key to such dive patterns and long dive durations is found both in the
amount of oxygen (O 2 ) marine mammals take down with them and in the rate of consumption of that O 2 during diving. In general, marine mammals store much greater amounts of
O 2 than terrestrial mammals. But enhanced O 2 storage is not enough to explain the routine, let alone, the longest dive durations of these animals. Regulation of the depletion rate
Contents
2.1 The big picture challenge and summary ......................................................................... 29
2.2 What is known .....................................................................................................................30
2.2.1 Magnitude and distribution of total body O 2 stores ...........................................30
2.2.1.1 Respiratory O 2 stores ................................................................................ 31
2.2.1.2 Blood O 2 stores .......................................................................................... 32
2.2.1.3 Muscle O 2 stores ........................................................................................ 32
2.2.2 The dive response .................................................................................................... 33
2.2.3 Aerobic dive limits ...................................................................................................34
2.3 Toolbox: How these parameters are measured ............................................................... 36
2.3.1 Measuring the respiratory O 2 store ....................................................................... 36
2.3.2 Measuring the blood O 2 store ................................................................................ 37
2.3.2.1 Blood volume ............................................................................................. 38
2.3.2.2 Hb concentration ....................................................................................... 38
2.3.2.3 Hb saturation (SaO 2 and SvO 2 ) ................................................................ 38
2.3.3 Measuring the muscle O 2 store .............................................................................. 39
2.3.3.1 Muscle mass ............................................................................................... 39
2.3.3.2 Mb concentration analysis and potential problems ............................. 39
2.3.4 Measuring heart rate ............................................................................................... 40
2.3.5 Measuring blood lactate to determine the ADL .................................................. 40
2.3.6 Summary ................................................................................................................... 41
2.4 Unanswered questions ........................................................................................................42
Glossary ..........................................................................................................................................42
References .......................................................................................................................................43