Hyperlink to full size Cover Illustration.


Questions and Answers on
Physiology and Medical Aspects of Scuba Diving


Lawrence Martin, M.D. Copyright 1997


Buy the book
Scuba quiz
Myths & Misconceptions
Disclaimer & Invitation

Brief History of Diving
Recreational  Diving
The Respiratory System
Explanation of Pressure

Water & Physical Laws
Unequal Air Pressures
Decompression Sickness
Oxygen Therapy
Gas Pressure at Depth

Dive Tables & Computers
Stress & Diving
Non-air Gas Mixtures
Women & Diving
Medical Fitness for Diving
Asthma & Diving
The Great Debate

All About DAN
Scuba Training Agencies
Magazines & Newsletters
Books & Videos

Diving Odds N' Ends

Internet Links


Unless you score 80% or better on the short scuba quiz, you can probably benefit from reading this book. Knowledge of basic underwater physiology is critical to diving safety, of course, and the subject is taught in every certification class. For example, the first rule of diving -- don't hold your breath -- is based on Boyle's law of gas pressures, which predicts that a scuba diver's lungs will expand if breath is held on ascent. The consequence can be a serious and even fatal over-expansion injury.

Although all certification manuals and general scuba books review underwater physiology, the coverage is necessarily limited. Typically, one chapter is devoted to the subject. Important effects of altered physiology, such as decompression sickness and arterial gas embolism, are covered only briefly.

As a recreational diver and pulmonary physician, I believe there is need for a book that more fully explains this material. Not a textbook for the doctor, engineer or scientist, but a book any recreational diver can understand. A book that answers questions frequently pondered by the recreational diver. After searching and finding no such book, I decided to write one! Scuba Diving Explained is intended for all sport divers because the material is important for all of us, from beginner to people with years of experience.

Subjects include: the concept of pressure, the four major gas laws as they apply to diving, composition of air, changes in gas pressures with depth, ear and sinus squeeze, lung barotrauma, air embolism, decompression sickness, nitrogen narcosis, oxygen toxicity, carbon monoxide and carbon dioxide toxicity, stress, hypothermia, hyperventilation, and oxygen therapy.

I also answer some questions on "deep diving" (below 130 feet), and diving with non-air mixtures such as Nitrox. Both activities are outside the realm of recreational diving (as defined by the scuba training agencies), but their physiology is fascinating and germane to all diving. If you understand, for example, what Nitrox is and why it does not allow one to dive deeper than with ordinary air, you can better appreciate the effects of water pressure on nitrogen and oxygen in any gas mixture, including ordinary air.

A separate section answers some commonly-asked questions about women and diving, e.g., "Do women have an increased risk of the bends?" and, "Is diving safe during pregnancy?" A section on medical fitness for diving explains the rationale of some published guidelines, most of which are based on theory rather than hard data. Another section reviews perhaps the most controversial of all conditions for scuba diving, asthma.

Scuba Diving Explained is designed to increase your understanding and enjoyment of the sport. However, the book is not an instruction manual; it contains relatively little information about scuba equipment (better taught with hands-on instruction in a scuba course), diving skills or marine life. Instead, emphasis is on the physiology vital to all sport divers. I go to great length to explain changes in gas pressures with depth because, quite simply, that singular feature most affects the diver's safety.

In sections B through L are brief questions to 'test your understanding' of the material. Placement of some questions within the text is preferable to putting all of them at the end of a section or in an appendix. Each question is germane to the proceeding paragraphs; answers are at the end of the section. For diversion, you will find paragraphs of 'Diving Odds N' Ends' at the end of each section, in gray boxes. Some of this information is gleaned from various popular periodicals and non-technical books. Because scuba magazines are a prime source of information for the sport diver, I have prepared a list of nationally-circulated periodicals published in the U.S., along with addresses, circulation figures and phone/fax numbers (Section T). For U.S. distributors of scuba books and dive videos, as well as a list of some comprehensive internet scuba sites, go to Section U. Also included for most sections is an extensive bibliography, covering both quoted sources and other books and articles that may be of interest to recreational divers.

Although you will probably get more out of Scuba Diving Explained if you have some scuba experience, it should also be useful to anyone interested in diving who has yet to don scuba gear. There seem to be as many "wannabe" divers as there are the certified kind. If you don't dive but plan to learn, it is not too soon to begin your exposure to underwater physiology. There is no substitute for basic training from one of the national scuba certification agencies. These agencies, listed in Section S, teach the basic scuba skills and provide a general introduction to underwater physiology. Scuba Diving Explained should help you better understand this physiology and the effects of breathing compressed air underwater.

Happy and safe diving!

Lawrence Martin, M.D.
June 1997


Several scuba divers reviewed the draft of this manuscript. They made many useful suggestions, most of which I readily incorporated, and caught some errors, for which I am grateful. For their efforts I thank (in alphabetical order): Pam Alderman, Anne Cath, M.D., Jolie Bookspan, Ph.D., John Comley, Bernard Martin, Robert Martin, M.D., Ruth S. Martin, M.D., and Lorain Rimko. I would also like to thank Debra Shirley for her many excellent line drawings; and Diver's Alert Network and the Diving Historical Society for permission to use some of their photos.

To Ruth, my wife and dive buddy.

Pulmonary Medicine Home Page
e-mail: martin@lightstream.net
HTML Optimization by Richard F. Laporte

Last updated: 28/10/97