Diving and Asphyxia

A harbor seal (Phoca vitulina) exhales and submerges. As water contacts its nostrils, there is a rapid increase in firing of the cardiac vagus nerve and the heart rate drops from 100 to 10 beats per minute. Simultaneously, an alpha-adrenergic peripheral vasoconstriction results in a central shift in oxygen-rich blood volume. The inferior vena cava enlarges to the size of a football. Though cardiac output is reduced in proportion to heart rate, central blood pressure is maintained and the brain, retina, adrenal glands, and placenta are perfused. Coronary blood flow drops to levels which would infarct a dog's heart but metabolic wastes are washed from the coronary vessels by intermittent vasodilatations. The seal continues to swim and search for food for 10-15 minutes during which time blood oxygen and carbon dioxide have reached levels which would render a man unconscious. Shortly after surfacing, the seal's heart rate returns to normal and the peripheral blood vessels selectively vasodilate, releasing high concentrations of lactic acid into the central circulation. After a minute of hyperventilation, the seal exhales and dives again. Diving and Asphyxia is the first book to review the world literature on the physiological adaptations to underwater excursion, characteristic of seals and ducks but also manifest in many other aquatic and terrestrial animals and, to a variable extent, in man. Elsner of Fairbanks, Alaska, and Gooden of Adelaide, Australia, are more than qualified to assimilate such a review with more than 35 years of research in the field between them. The easily readable book adds considerably to previous reviews of Herald Andersen [1] and Michael Strauss [2] but doesn't mention another recent review by Y. Chong Lin [3]. The first three chapters relate the general metabolic, cardiovascular, pulmonary, and cellular changes involved in the diving response. A discussion of some of the diving response studies on humans and an attempt to integrate a control mechanism for the diving response follow. Diving and Asphyxia concludes with some medical implications of the diving response research with respect to treatment of paroxysmal supraventricular tachycardia, increased tolerance of coronary insufficiency, and the revivability of some victims of coldwater drowning. Thirty pages of references follow and, as a book, this is the first diving response review with an index. Diving and Asphyxia uses an adequate but minumum amount of illustration. The diving response is a remarkable adaptation. Even as such, the students of this aspect of physiology are finite in number and therefore Diving and Asphyxia will be considered a must in only a relatively small number of libraries of physiologists, comparative biologists, or physicians. Unfortunately, the cost of this rather small monograph will be prohibitive to many for whom the diving response is of only passing interest.