DAN Medical Research
U.S. Navy Flying After Diving : Project Overview

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The four specific goals of the U.S. Navy (USN) 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.

This study will not repeat exposures tested in previous Duke studies. However, all previous Duke exposure data as well as germane exposures from other sources will be included with those from the present study to form a decompression model calibration data set.

Methods

This 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 diving. Air dives in a dry hypo- / hyperbaric chamber with resting subjects will be followed by a interval at ground level up to 29 hours in duration, and then an 8,000-feet / 2,438-meter altitude exposure for four hours. The 8,000-foot altitude is the allowable lower limit of cabin pressures in commercial airliners. 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.

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 10 subjects per experiment, are conducted monthly. Subjects are dry and at rest throughout the dives and dry and at rest during the flight. 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 measure. 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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