The plane after the dive: finally the facts

by Stefano Ruia

The data collected during the first research campaign of DAN Europe's Diving Safety Laboratory (DSL), entitled "Flying bubbles", has been completed. The results are quite surprising, to the point of deserving a publication in the renowned scientific journal Aviation Space and Environmental Medicine.

Different theories

We've seen what came before, what happened during, and now… we're going to see what happens after. When it comes to getting on a plane after diving, DAN's “Flying bubbles” project bridges the gap between theory and fact.

Prior to this project, there were several recommendations regarding the time interval between diving and taking the plane to avoid the risk of decompression problems caused by cabin depressurization. All these recommendations, however, rested on theory only. At DAN, the recommended wait times were based on the analysis of actual cases of decompression sickness, while in others they are based on the assumption that "there was no problem so far, so let's continue like this. "

Divers who have used the old US Navy tables may have vague memories of having been classified as "Group D" before flying. In some cases, it was even allowed to fly immediately! Subsequently, fixed intervals were introduced (24 or 48 hours), depending on whether the last dive was a single or repetitive dive, and whether it had been performed in the safety curve or not. Even among professional and military divers, waiting times before boarding a commercial aircraft range from 2 to 24 hours.

The first Flying After Diving (Flying After Diving) seminar was organized in 1989 by the Undersea and Hyperbaric Medical Society (UHMS). According to DAN, the recommendations provided on this occasion were not very restrictive, but had been implemented to increase the safety of diving. Many dive center leaders complained, however, that the implementation of such recommendations would be detrimental to their business on the islands.

From 1992 to 1999, DAN conducted research at the Environmental Lab at the Duke University Medical Center in North Carolina, USA. The "flying flights" were actually simulations, since they took place in a hyperbaric chamber. DAN then investigated the link between the risk of decompression sickness and the surface interval before aircraft landing in a retrospective study of "accident" and "other" situations. without ".

Nevertheless, in many fields of medicine, laboratory studies provide results that differ from those obtained "in the field". Moreover, certain phenomena can not be reproduced in the laboratory. Further details of such discrepancies are provided in an article published in the Alert Diver (European edition, 3 / 2006) by Dr. R. Vann. "The taking of the airplane or reaching high altitudes after multiple dives performed over several consecutive days can not be the subject of a laboratory study (in a hyperbaric chamber)."

In 2011, back from a research stay in the Maldives, Dr. Danilo Cialoni and Massimo Pieri, both members of our Diving Safety Laboratory, had a fascinating idea that should involve the DAN department. Europe Research (especially Prof. Alessandro Marroni and Costantino Balestra). Their idea for a research project resonated like a challenge: it was to perform echocardiograms in full flight by plane following a diving trip.

Echocardiography in full flight

Meeting such a challenge has been difficult, almost impossible, especially from a bureaucratic point of view. In this aspect, two DAN partners, Albatros Top Boat and Neos Air, were of fundamental help. In order to obtain EMC (electromagnetic compatibility) certification, necessary for the use of the echocardiograph during the flight, DAN Europe technicians and researchers were forced to spend several nights at Malpensa Airport in Milan. After many hours of work, their efforts paid off: for the first time, we were able to see what was really going on in a diver's body during a flight.

The first week of research in the Maldives had already allowed us to log 4 000 files, which of course have been the subject of lengthy and detailed analysis.

The methodology used for echocardiography includes four control phases. The first takes place during the outward flight, when the diver has not plunged for at least 48 hours. These first tests are useful for capturing data that has not yet been influenced by hyperbaric exposure and for determining what, in medical jargon, is called the "echocardiographic window". The iDive Pro dive computer from Dive System, a partner of DAN Europe and the DSL laboratory, recorded an accurate measurement of cabin pressure every 15 minutes.

The second phase consists of administering echocardiography and other tests after each dive for one week of cruising-diving. Weeks dedicated to specific research are slowly becoming part of the routine of the elegant "Duke of York" cruise ship. These weeks are very similar to the usual cruises made in the Maldives, except that they are of scientific importance. Indeed, every time a diver comes to the surface, he must go through the spa which, for the occasion, was transformed into "research room" and medical center, to perform various tests.

The dive profiles are checked by the computer and downloaded for subsequent tests. All dives are done in the safety curve, lifts are performed at the appropriate speed, and divers are required to respect a safety stop of 3 minutes to 5 meters. None of the divers have so far suffered from decompression sickness.

The third phase of control takes place at the airport, where divers undergo echocardiography just before boarding the plane, after observing a surface interval of 24 hours.

Finally, the last phase is during the return flight and consists of an echocardiogram and a Doppler examination at exactly 30, 60 and 90 minutes after reaching the cruising altitude.

Data analysis

During its presentation in 2013 at the conference held by the European Underwater and Baromedical Society (EUBS), the research project received the Zetterström prize for the best scientific project presentation poster.

Some of the data collected is easy to understand. For example, during examinations carried out on the outgoing flight, no bubbles were observed among the divers participating in the study. Even if the result of this test seems obvious, it is necessary to prove that the possible bubbles found in the divers during the return flight were not caused by the flight, but by the combined effect of diving. and subsequent depressurization in the aircraft.

Other data revealed by the study were unexpected. For example, it has always been thought that a long-duration flight poses a greater risk than a medium-duration flight, whereas it is quite the opposite. This phenomenon is probably due to the maximum altitude reached, about 1 500 to 1 800 m for the trip to the Maldives, and about 2 400 m (the maximum allowed) for journeys less distant.

Examination of the divers at the airport prior to the return trip, during which no bubbles were observed, allowed us to estimate that a waiting interval of 24 hours after the last dive was sufficient if the divers stay at sea level, so that no bubbles can form in their bodies.

Remember that some divers develop more bubbles than others, even for similar dive profiles. The cruising week examinations divided the topics into three categories: those who do not develop bubbles, those who develop bubbles occasionally, and so-called "bubble-subject" divers who develop bubbles after each dive. . For a consistent comparison, the dive profiles must have a minimal influence on this classification (it is obvious that a heavier profile will have more bubbles than a lighter profile).

The analyzes carried out in full flight revealed that the majority of the divers had not developed bubbles during the return flight following a wait of 24 hours after the last dive. The only ones to escape this rule were "bubble-subject" divers. It is therefore advisable for divers in this category to extend the waiting time before taking the plane. During the week, two of the divers proved to be "very bubble-prone", and were asked to refrain from their last dive, to extend the waiting time before taking the plane to 36 hours. It is important to note that neither of these divers developed any bubbles during the flight. For divers inclined to bubbles, it is therefore appropriate to observe a waiting interval greater than 24 hours. Alternatively, researchers at the DAN Research Department suggest taking a preventive measure of breathing normobaric oxygen before taking the plane.

The highest levels of bubbles detected were observed 30 minutes after reaching cruising altitude. Bubble levels then dropped in the period from 60 to 90 minutes, similar to the rise to the surface at the end of the dive. As for the depressurization, it has the same effects as the exit of the water. As time passes at this altitude, the body "desaturates" and the amount of bubbles decreases. Another possible explanation is that tiny bubbles are already present in the blood, but are so small that they do not appear on a normal echocardiogram. Depressurization could increase their size and make them visible.

What could be the future consequences of this study for divers? As the teacher says. Alessandro Marroni, "we are heading straight for a future where the individual component is likely to influence the mathematical model, with particular emphasis on the practical application of research in the field of diving safety. Previously, when we studied the functioning of the body, we juggled with applied mathematics and specific algorithms. Today, we are embarking on a fascinating new path that will allow us to incorporate simple physiological parameters into mathematics so that these algorithms fit better into the body. We still have some way to go, and to get there, DAN Europe is committed to making every effort, with the precious help of the divers, to keep them informed of current and future developments.