Flying After Diving

Overview

U.S. Navy divers undertake both training and missions which may require flying soon after diving. To reduce the risk of decompression sickness (DCS) as a result of flying-after-diving (FAD), guidelines were published in the USN Diving Manual that specify how long a diver should remain at sea level pressure before further decompression to altitude for a flight. The Navy guidelines were loosely based on FAD studies for recreational divers done at Duke (Vann et al., in prep). Certain of the Navy guidelines are untested and require validation. In addition, as some dives may require preflight surface intervals as long as 24 hrs, studies will be conducted to investigate the possibility of decreasing the long preflight surface intervals by breathing oxygen before flight.

The four specific study aims are:

1. Test current U.S. Navy (USN) flying after diving procedures on air dives that are currently untested.
2. Find the minimum safe surface intervals for flying after diving while breathing 100 percent O₂ at ground level during the preflight surface interval.
3. Use existing data and data generated from Aims 1 and 2 to develop a decompression model capable of computing risk of DCS for altitude exposures following air dives.
4. 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 done in previous Duke studies but will concentrate on areas not covered in those studies. However, all previous exposures done at Duke 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 or with subjects performing moderate exercise will be followed by a 2-29 hour interval at ground level followed by an 8,000 ft altitude exposure for four hours. The 8,000 ft altitude is the allowable upper limit of cabin pressures in commercial airliners. Dive depths of 60 and 100 fsw will be used with bottom times selected according to U.S. Navy dive tables. The initial surface interval will be the one currently prescribed by the U.S. Navy Diving manual.

At the end of each experiment, a preflight surface interval will be evaluated for further testing based upon all its previous trials and the classification of any incidents that occurred. 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 a different dive-surface interval profile; or (3) continue testing the same surface interval.

Two experiments, with up to 8 subjects per experiment, are conducted monthly. Subjects are dry and at rest or exercising moderately, throughout the dives and dry and at rest during the flight. Subjects are certified SCUBA divers or experienced in hyper-hypobaric exposures who undergo a medical history review and physical examination by a physician. Subjects will be monitored for bubbles using a precordial Doppler ultrasound post-dive and during the flight phase of the study (and following flight if bubbles are present). Bubbles will be graded in accordance with a standard 0-4 scale. Any subject with Grade 2 or higher scores will be monitored with transthoracic echocardiography for the presence of bubbles in the left ventricle that might enter the aterial circulation. Experiments can take one or two days plus follow-up.

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• Overview
• Methods
• Typical Trial Schedule
• How to Participate

Typical Trial Schedule

Note: When short surface intervals are tested, 3 hrs, the activities of the first 2 days are combined into a single day.

One Week prior to study date
Submit Medical History Form for review by study physician

Day 1
8:00 Subjects assemble at the Center for Hyperbaric Medicine and Environmental Physiology
8:00 - 8:30 Complete paperwork, dress in scrubs
8:30 - 9:00 Study Brief
9:00 - 10:00 Physicals and Baseline Doppler exams
10:00 - Chamber briefing and commence dive
13:00 - End dive - Start medical watch
13:30 - 14:00 Doppler
14:00 - Lunch
16:00 - Interview with physician and release

Day 2
12:00 - Subjects assemble at the Center for Hyperbaric Medicine and Environmental Physiology
12:00 - 13:00 Interview with physician
13:00 - Start flight
17:00 - End flight
17:30 - 19:30 - Dinner
20:00 - Interview with physician and release

Day 3
AM interview with physician at the Center for Hyperbaric Medicine and Environmental Physiology

Day 4
Phone interview