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AD 2016 Q3

Alert Diver is the dive industry’s leading publication. Featuring DAN’s core content of dive safety, research, education and medical information, each issue is a must-read reference, archived and shared by passionate scuba enthusiasts. In addition, Alert Diver showcases fascinating dive destinations and marine environmental topics through images from the world’s greatest underwater photographers and stories from the most experienced and eloquent dive journalists in the business.

RESEARCH, EDUCATION &

RESEARCH, EDUCATION & MEDICINE FROM THE MEDICAL LINE The Boutique Liveaboard Pristine coral reefs √ Pelagics from mantas to mola √ Macro from pygmies to blue-rings √ Raja Ampat √ Ambon, Maluku √ Komodo & Alor √ Luxury cabins √ Massage & Spa √ 5 star service √ WWW . THEARENUI . COM facility available at the time of the call, if necessary. Access to a hyperbaric facility is always through an emergency department, especially after normal working hours. Even 24/7/365 chamber facilities are not staffed after hours until they’re notified of an emergency. A common misconception is that all diving emergencies require hyperbaric treatment. For lung-expansion injuries — including pulmonary barotrauma, pneumothorax (collapsed lung), and mediastinal emphysema (air under the skin) — hyperbaric treatment is contraindicated. The DAN Emergency Hotline is available 24 hours a day, 365 days a year, to both DAN members and nonmembers. Call us at +1-919-684-9111 at the time of the emergency, and we will provide you with the most current information for the most appropriate chamber near you. — Frances Smith, MS, EMT-P, DMT STEPHEN FRINK Q: What is the current thinking regarding scuba diving and freediving on the same day? A: Shallow, low-intensity freediving before scuba diving creates only mild concern. The stress of repeated middle-ear equalization can make subsequent efforts more difficult. Increasingly deep or aggressive freediving requires progressively longer surface intervals before scuba diving. For example, the decompression implications of a few relaxed breath-hold dives in the 40- to 50-foot depth range prior to scuba diving are probably very small with a 15- to 30-minute surface interval before commencing the scuba dive. Deeper or more numerous breath-hold dives should be followed by a longer surface interval that increases along with intensity, but we do not have the data available to make specific recommendations. Freediving after scuba diving is more of a concern; it requires consideration of the existing inert gas load, the intensity of the exercise during the freediving and the depth of the freediving. The goal is to reduce bubble formation and the potential for migration of bubbles into the systemic circulation. Even shallow freediving after scuba diving is a problem because of the diver’s inert gas load. The primary concern is not the additional gas loads the freediving can produce but the pulmonary shunting that will occur with exercise. Any bubbles present following a scuba dive can be driven across the lung at a much higher rate because of physical activity. (Physical activity may also increase the bubble load.) It is reasonable to recommend that divers not mix meaningful freediving and compressed-gas diving on the same day. I realize that the word “meaningful” is vague, but it’s probably necessary given the wide range of ability and activity possible. I would not worry about casual freediving after a 30-minute scuba dive to a maximum depth of 40 feet because the 58 | SUMMER 2016

STEPHEN FRINK risk of substantial bubble formation would be low. But maintaining a low level of physical effort during the freediving would still be advisable. The deeper the freediving and the more intense the exercise, the greater the recommended delay after scuba diving. The primary issue is that bubble formation is more likely after significant decompression stress. As a rough rule of thumb, when a scuba dive approaches half of the U.S. Navy no-decompression limit, the stress of postdive freediving becomes an increasing concern. If the breath-hold activity is in the “snorkel” zone (that is, with vertical excursions of not much more than two body lengths) and relaxed, I would not be concerned at all. The “relaxed” part is subjective though, so thoughtfulness is needed. The risk for depths beyond 50 feet increases before or after scuba diving — before, because of potential exertion and middle-ear stress issues, and after, because of exertion, shunting and, increasing as a function of depth, direct gas loading from the freediving. Increasingly deeper depths warrant increasingly longer predive surface intervals. Ultimately there is theoretical risk that should be controlled by conservative surface intervals and the lowest exertion levels possible. There is very little outcome data, but that should not discourage smart practice. Shallow, truly relaxed freediving before scuba diving probably has negligible consequences, given a modest surface interval and provided that equalizing during the subsequent dive is not compromised. But even shallow, relaxed freediving after scuba diving should be delayed if only for an abundance of caution. More aggressive freediving is best left for the next day. The potential negative outcome is simply not worth the risk. AD — Neal W. Pollock, Ph.D. ALERTDIVER.COM | 59

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