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Flying After Diving (FAD) Calibration Study

Divers 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 U.S. Navy Diving Manual that specify how long a diver should wait between dive and flight. The Navy guidelines were developed in part with data from previous FAD studies for recreational divers done at Duke (Vann et al., 2007*). Additional testing is required to evaluate profiles not previously tested. These include some very long dives and decompression dives. In addition, studies will be conducted to investigate the possibility of decreasing preflight surface intervals by breathing oxygen before flight.

*Vann RD, Pollock NW, Freiberger JJ, Natoli MJ, Denoble PJ, Pieper CF. Influence of bottom time on preflight surface intervals before flying after diving. Undersea Hyperb Med 2007; 34(3): 211-20.

Overview

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

  • Test air dive-flight profiles included in the U.S. Navy flying-after-diving tables that would benefit from additional validation.
  • 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.
  • 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 feet of seawater (fsw) or between 18 and 30 meters of seawater (msw) 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-foot (2,438-meter) 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 four 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.

    Participation

    Participants must be:
  • between 18 and 60 years of age
  • certified scuba divers, or have experience with hyperbaric exposure (They may be a student diver if accompanied by their instructor.)
  • in good physical condition (Subjects must be within 3 percent of the age-indexed "recommended" range for body fat based on national standards. Body composition will be assessed with a skinfold caliper.)
  • healthy, without any disqualifying conditions, such as:
  • pregnancy (Females of child-bearing age must allow a small blood sample to be drawn for pregnancy testing.)
  • pneumothorax
  • asthma that is active and requires medication (Check with study physician.)
  • chronic seizure disorder
  • certain chronic diseases (Check with study physician.)
  • recent joint surgery (within six months of study date)

  • Subjects are eligible for more than one study as the profiles change, but a subject may participate only once in a given dive-surface interval-flight profile.

    Restrictions prior to the study:
  • One week — no prescription or over-the-counter medication, including aspirin other than those approved by the study physician
  • 48 hours — no diving, flying or other altitude exposure
  • 24 hours — no organized sports or other intense exercise

  • Restrictions following the study:
  • 24 hours — no organized sports or other intense exercise
  • 48 hours — no diving, flying or other altitude exposure

  • Compensation
    Participants will receive prorated compensation for a total of $120 per trial. Completion of the study is required for full payment. This includes brief follow-up interviews on each of the first two mornings after the study flight. The medical outcome is just as important as the dive. Prorated compensation is $45 for the dive day, $45 for the flight day, $15 for the first morning-after health check, and $15 for the second morning-after health check. (Note: Volunteers disqualified after completing the baseline evaluations but before beginning the dive will receive a total compensation of $20.)

    DAN membership and Preferred Plan insurance will be provided for participants who complete the dive phase of the study if they are not currently covered. (Current DAN Members with lesser insurance coverage will have their level increased to Preferred for the remainder of their annual membership cycle.)

    Meals will be provided at the chamber during the study, and some meals may be compensated up to $7 for lunch and $13 for dinner. Individuals living outside a 60-minute driving radius from Duke University are asked to stay overnight following the dive and flight (room cost is covered by the study on a shared basis).

    Please refer to the Study Cancellation Policy.

    Current Schedule
    The FAD Calibration Study is currently scheduled for the following dates:
    Oct. 27-28, 2011
    Nov. 10-11, 2011
    Dec. 1-2, 2011
    Dec. 8-9, 2011

    Sign Up or Ask Questions
    If you would like to participate in this study, complete a Medical History Form and return it by email to research@dan.org, by fax to +1-919-493-3040, or mail to DAN Research, 6 West Colony Place, Durham, NC 27705.

    For additional information, contact DAN Research at +1-919-684-2948 ext. 260 or send a message.

    Download directions to the Duke hyperbaric center.

    Frequently Asked Questions

    What is the study about?
  • The Flying After Diving Study is designed to evaluate the effect of altitude exposure following diving on the production of circulating bubble production and/or the development of decompression sickness.

  • How do we receive our compensation?
  • Participants are paid by check sent to the address supplied on the Compensation Form (DUMC Research Subject Registration Form). Checks usually arrive within four to five weeks.

  • Where do we go diving?
  • This study involves a chamber dive followed by a surface interval and then a chamber flight at a pressure equivalent to that a commercial aircraft cabin. All trials are conducted at the Center for Hyperbaric Medicine and Environmental Physiology at the Duke University Medical Center in Durham, N.C.

  • Do I bring any gear? What should I wear?
  • Subjects are randomly assigned to dry or wet exercise during the dive. Dry exercise requires comfortable shorts, shirt and shoes for cycling. Wet exercise requires bathing suits and the option of personal mask and wet boots. We ask that females wear a two-piece bathing suit, shorts and halter top or aerobic-type top and bottoms. The abdomen, front and back and the chest and legs need to be exposed for the physical examination. The abdomen and as much of the rib cage as possible need to be accessible to facilitate the ultrasound monitoring.

  • What is a typical study like?
  • Participants arrive at the hyperbaric center and receive a detailed briefing on the study before providing written consent to participate. Then follows a physical examination, body composition estimation and ultrasound assessments. The dive follows, usually two hours from arrival. The flight follows after the scheduled surface interval. There is a four-hour medical watch after the flight, largely filled by a leisurely meal. Post-flight interviews are completed on each of the two mornings following the flight.