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ULTRASONIC DOPPLER MEASUREMENT OF SPORT DIVERS AT ALTITUDE. C.J. Wachholz, R. Dunford, P.B. Bennett, Divers Alert Network (DAN), Box 3823, Duke University Medical Center, Durham, NC
The Divers Alert Network (DAN) has since 1985 used ultrasonic Doppler to measure sport divers making unsupervised dives in open water. Most of these measurements have taken place in warm tropical ocean waters at sea level. In 1990, two groups of sport divers were measured at altitude following sport diving. The first group of 15 divers were measured while diving off the Caribbean Island of Saba Netherlands Antilles. Measurements fo 12 subjects were conducted both at sea level and at an elevation of 1200 feet, the altitude of the divers' hotel. Excursions to 1200 feet occurred each day following the last dive of the day, between 40-80 minutes after exiting the water from the last dive. Divers made three dives per day on most days. One Doppler measurement was taken between 30-40 minutes following each repetitive dive. Divers were measured immediately prior and immediately following the excursion to 1200 feet. Of the 15 divers, 10 (75%) had positive bubble scores, all grade one or two (Kisman Masurel Scale). There was no increase in bubble scores following the excursions to altitude for any of the subjects. Because of Saba's close proximity to St. Maarten, tourists regularly fly over to dive for the day. For over ten years, following scuba dives, return flights to St. Maarten have occurred at altitudes of 1500-4000 feet. No cases of DCS as a result of these flights have been reported to Divers Alert Network. This information is important in light of the recently issued minimum 12-hour Flying-After-Diving recommendations (Sheffield, et al., UHMS, Publ. no. 77, 12/89). Dive resort operations in the Caribbean that relied on one to three day dive package business have complained that the 12-hour guideline is too conservative. Another group that has taken issue with the necessity of a 12-hour delay to altitude are the freshwater divers of the Rocky Mountain region. A second group of 12 Doppler subjects from Grand Junction, Colorado, elevation 4,843 ft, were measured following single day diving at Lake Powell, UT, elevation 3736 feet. In this group, 7 of the divers (58%) had bubbles, all grade one or two, except one individual who had a grade three bubble score. Both the Saba and Utah dives were repetitive, with the deepest dive first in all cases. In both groups, the effect of depth (dive #1) produced more bubbles than subsequent repetitive dives or from any altitude effect. As the '89 Flying-After-Diving workshop guidelines were only concerned with excursions on commercial aircraft assuming an 8000 foot cabin altitude, alternate recommendations for altitude excursions following sport dives to lower altitudes should be considered
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