Pumping, ROVing and Whistling Dixie
By E.R. Cross
There are a number of things in diving for which we have only an incomplete or vague explanation. One of these is a reason for the reduction in the heart rate of divers when submerged. It has been observed that the pulse rate is 12 to 15 beats per minute less in water than when on land. This can be expected to some extent in swimmers as well as in divers for comparable in-water exercise.
A Cross Talk reader wrote asking, Is this reduced heart rate due to less energy being exerted to exist and work in the water? Or, are there other reasons? Will we get the same aerobic benefits for our exercise in spite of the reduced heart rate?
Being weightless in water may contribute to the physiological response of reduced heart rate. However, I suspect the principal reason is the surrounding water acts as a better cooling agent. Body heat is dissipated into surrounding water more rapidly than in air. Therefore, the heart slows to compensate for this more efficient cooling medium. The heart does not have to pump quite so fast to get the blood to the surface to keep the body cool. Based only on limited experience, I believe we do achieve nearly the same aerobic benefits, even at the reduced heart rate. Aerobic benefits are derived from several factors, not all of which are related to exercise and increased heart rate.
Deep Submersibles and ROVs
Recently, Cross Talk received correspondence asking for information on classification, uses and availability of modern submersible operations. In the strictest sense, almost everything operated or dragged underwater by surface power can be classified as a submersible. ROVs (remotely operated vehicles), AUVs (autonomous underwater vehicles) and manned units can all be classified as submersibles.
The History of American Deep Submersible Operations offers information of interest to most divers, including recreational groups. The publication covers manned submersibles known to have existed from 1775 to the present. Most are no longer available, but were historically important. Written by Will Forman, this book is available from Best Publishing Company, (520) 527-1055. Some 50 deep submersibles are briefly discussed.
The latest issue of Jane's Ocean Technology contains information on current submersibles and related support vessels. First published in a 1974-75 edition, it illustrates and discusses the principle submersibles of each country that has developed underwater manned vehicles. The information provided is more detailed than in the above publication. Also discussed are underwater habitats, unmanned underwater vehicles, sea bed vehicles, research vehicles, major diving facilities, offshore drill rigs, survival systems, tugs and supply systems and oil spill control vessels. A chapter also deals with the safe operation of manned submersibles. It was published by Jane's Yearbooks, Franklin Watts Inc., (212) 951-2650.
Whistling Up A Storm
A reader wrote, Fellow students attending a commercial diving school are having an argument over why we cannot whistle while wearing helmet gear. [There is also an inability to whistle while under pressure in a decompression chamber.] Can you provide a reason?
There are probably several factors involved in a diver's inability to whistle while working under pressure. The sound producing mechanism utilized to produce a whistling sound is adjusted to certain pressure limits. Also, a certain velocity of air is necessary to produce a tone. One group in the class felt that in helmet gear the diver's expired air is too slow to produce a sound. Another group felt that it was due to the changed density of expired air on the sounding column.
In either case, whistling under pressure is not impossible. They were not whistling Dixie, but I have known a few divers who were able to produce whistling sounds while diving in helmet gear.