DAN Medical Research
Flying After Diving Calibration Study : Project Overview

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The three specific goals of the Flying After Diving project are:

1. Test air dive-flight profiles included in the USN flying after diving tables that would benefit from additional validation.
2. Use existing data and data generated from Aim 1 to develop a decompression model capable of computing risk of DCS for altitude exposures following air dives.
3. Use the resultant decompression model to (a) compute a comprehensive set of flying after diving guidelines for air diving; (b) make predictions for dive-altitude exposures for nitrogen oxygen mixtures other than air; and (c) make preliminary predictions for diving at altitude procedures.

The results of all our related studies are pooled to form a decompression model calibration data set.

Methods

The FAD Calibration study will be limited to tests of only a few specific dive-altitude combinations because of time and cost considerations. A comprehensive medical screening questionnaire and medical examination by a physician will ensure that subjects meet the physical requirements for participation. The studies are conducted in the hypo-/hyperbaric chambers at Duke University. Subjects will perform light exercise continuously throughout the simulated dive, randomly either while dry or immersed as randomly assigned. Dive depths between 60 and 100 fsw (feet of sea water; 18 and 30 msw, or meters of sea water) will be used with bottom times selected from the U.S. Navy dive tables. Following a planned surface interval, subjects will complete a resting exposure of four hours at a pressure equivalent to an 8,000 ft (2,438 m) altitude. This is the maximum altitude (minimum pressure) allowed in commercial, pressurized aircraft. The outcome of each experimental dive-surface interval-flight profile will be evaluated statistically to determine the next profile to be tested. Three alternatives are possible: (1) accept the surface interval without additional testing and begin testing a shorter surface interval; (2) reject the surface interval from further testing and begin testing a longer surface interval; or 3) test a different dive-surface interval-flight profile.

Two experiments, with up to 4 subjects per experiment, are conducted monthly. Exercise will be administered using a specially designed leg cycle ergometers for both dry and immersed exercise. Subjects are certified scuba divers or experienced in hypo-/hyperbaric exposures who are qualified upon completion of: 1) a medical history review and physical examination by a Hyperbaric Center physician; 2) body composition assessment; and 3) baseline ultrasonic measures. Subjects will be monitored for bubbles throughout the study with precordial Doppler (sound only) and transthoracic echocardiographic (two-dimensional picture) ultrasound for the presence of bubbles in the circulation.

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