Decompression Tables for Diving at Altitude

Not Applicable

Completed

• Conditions: Acute Mountain Sickness; Decompression Sickness
• Interventions: Other: Pressure; Other: Breathing Gas

• Registration Number: NCT03390335
• Lead Sponsor: Duke University

Brief Summary

The aims of this proposal are to test current USN procedures for adjusting decompression procedures during air diving at 8,000 and 10,000 ft altitude and to provide a decompression algorithm for no-stop dives to 100 feet of sea water (fsw) at 10,000 and 12,000 ft altitude using enriched O2 (PO2=1.3 ATM). Additionally, the experiments will determine whether a period of hyperbaric hyperoxia, such as would be experienced during a dive at altitude, reverses altitude acclimatization, resulting in a return of acute mountain sickness (AMS) symptoms.

Detailed Description

Three different types of experiments will be performed:

(A). Testing of Cross corrections breathing air at 8,000 (0.743 ATA) and 10,000 ft (0.688 ATA). Subjects will be decompressed in a hypobaric chamber to one of the altitudes above. A no-stop dive to 60 fsw will be tested at each altitude (2.82 ATA at sea level, 2.56 ATA at 8,000 ft, 2.51 ATA at 10,000 ft). Using the Cross corrections, the virtual depth for both altitudes is 90 fsw, for which the no-stop time is 30 minutes. During the dive the subject will be immersed/submersed at rest/mild exercise in 28°C water. Ascent rate will be 30 fsw/min. Upon surfacing the diver will be monitored for 12 hours for symptoms of decompression sickness and transthoracic echocardiography (rest and leg/arm motion) to examine for venous gas embolism (VGE) at 5, 15, 30, 60 and 120 minutes after surfacing. After that, measurements will be continued until no bubbles are detected.

(B). Testing of a no-stop dive to 100 fsw at 10,000 ft and 12,000 ft breathing 35% O2. For this series of experiments all subjects will remain at altitude for 48 hours before diving, in order to allow for resolution of AMS symptoms. Appropriate depth-time profiles have been assessed by calculating the equivalent sea level air depth for each of these dives (PN2 values 2.42 and 2.36 ATM, respectively). These yield equivalent air depths of 68 and 66 fsw, respectively. Cross corrected virtual depths would therefore be 99 and 104 fsw, yielding no-stop times of 25 and 20 minutes, respectively. The Cross correction method will be used in this instance because, although largely untested, it is presently in use by the Navy. As with the air dives described above, the more provocative dives (12,000 ft) will be completed before the ones at 10,000 ft, which will increase the confidence for the bottom time used at the lower altitude.

(C). Testing to determine whether a high PO2 dive would reverse altitude acclimatization and re-establish susceptibility to AMS. Subjects will ascend in the chamber to 15,000 ft in a graded fashion over 12 hours (15,000 ft has been chosen due to extensive Duke experience with this altitude). Then, after 48 hours they will simulate a hyperoxic dive by breathing 100% O2 for 120 minutes at 1.3 ATA. This will simulate, for example, a 2 hour dive at 12,000 ft to 65 fsw breathing 50% O2. The diver will then return to 15,000 ft and remain at that altitude for 24 hours to allow for AMS symptoms to recur (if indeed they do). Lake Louise AMS scores will be collected every 8 hours. AMS symptoms will be treated with acetaminophen, NSAIDs and anti-emetics as needed. Subjects will be assessed clinically every 12 hours for high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). Occurrence of either HAPE or HACE will require that the subject be returned immediately to 1 ATA and treated appropriately.

Study Timeline

• Study First Submitted: 2017-12-28
• Study First Submitted QC: 2017-12-28
• Study First Posted: 2018-01-04
• Study Start: 2018-02-13
• Primary Completion: 2021-10-29
• Study Completion: 2021-10-29
• Status Verified: 2021-11
• Last Update Submitted: 2021-11-30
• Last Update Posted: 2021-12-14

Recruitment & Eligibility

• Status: COMPLETED
• Sex: All
• Target Recruitment: 103

Inclusion Criteria

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Exclusion Criteria

• smoking, cardiorespiratory disease (including hypertension, airways obstruction), seizure disorder, pregnancy, history of middle ear or sinus disease or high altitude cerebral or pulmonary edema (HACE, HAPE), inability to perform middle ear autoinflation, anemia, sickle cell disease and sickle cell trait. Individuals with VO2peak <35 mL.kg-1.min-1 (males) and <30 mL.kg-1.min-1 (females)

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Study & Design

• Study Type: INTERVENTIONAL
• Study Design: SEQUENTIAL

Arm && Interventions

Group	Intervention	Description
Altitude Dive Altitude profile	Pressure	Subjects are exposed to Pressure profiles (Altitude followed by a Dive with a return to Altitude) and Breathing Gases during dive exposures.
Altitude Dive Altitude profile	Breathing Gas	Subjects are exposed to Pressure profiles (Altitude followed by a Dive with a return to Altitude) and Breathing Gases during dive exposures.

Primary Outcome Measures

Name	Time	Method
Maximum Acute Mountain Sickness (AMS) Score Change	48 hour, 72 hours	Lake Louise Scoring System for Acute Mountain Sickness. Subjects will fill out a six-question questionnaire (0 - 3, higher scores are worse symptoms) and a three-question clinical assessment (0-4, 0-4, 0-2, higher score is worse a assessment). The total score of all questions and assessments (0 - 28, higher is worse AMS), is determined every eight hours for 48 hours at altitude pre-dive and 24 hours at altitude post-dive.
Decompression Sickness	12 hours	Subjects will be evaluated for symptoms of decompression sickness when returning to the initial altitude following a dive exposure.

Secondary Outcome Measures

Name	Time	Method
Venous Gas Emboli	12 hours	2D ultrasound will be used to assess right ventricular bubble score at 5, 15, 30, 60 and 120 minutes and hourly until no bubbles are detected using the following scale: Modified Eftedal-Brubakk Scale for Venous Gas Embolism (VGE); Grade Definition 0 No observable bubbles; 1. Occasional bubbles; 2. At least 1 bubble every 4 heart cycles; 3. At least 1 bubble every heart cycle; 4. A Continuous bubbling, 1-2 bubbles per cm2 in every image; 4B Continuous bubbling, at least 3 bubbles per cm2 in every image 4C Almost complete whiteout in the right heart, individual bubbles can still be discerned 5 "White out", single bubbles cannot be discriminated

Trial Locations

Locations (1)

Duke University Hospital; 🇺🇸 Durham, North Carolina, United States