Increased Risk of Decompression Sickness When Diving With a Right-to-Left Shunt: Results of a Prospective Single-Blinded Observational Study (The "Carotid Doppler" Study).

Peter Germonpré,Costantino Balestra,Pierre Lafère,William Portier,Faye-Lisa Germonpré,Alessandro Marroni

doi:10.3389/fphys.2021.763408

Abstract

Introduction: Divers with a patent Foramen Ovale (PFO) have an increased risk for decompression sickness (DCS) when diving with compressed breathing gas. The relative risk increase, however, is difficult to establish as the PFO status of divers is usually only determined after a DCS occurrence.Methods: This prospective, single-blinded, observational study was designed to collect DCS data from volunteer divers after screening for right-to-left shunt (RLS) using a Carotid Doppler test. Divers were blinded to the result of the test, but all received a standardized briefing on current scientific knowledge of diving physiology and “low-bubble” diving techniques; they were then allowed to dive without restrictions. After a mean interval of 8 years, a questionnaire was sent collecting data on their dives and cases of DCS (if any occurred).Results: Data was collected on 148 divers totaling 66,859 dives. There was no significant difference in diving data between divers with or without RLS. Divers with RLS had a 3.02 times higher incidence of (confirmed) DCS than divers without RLS (p = 0.04). When all cases of (confirmed or possible DCS) were considered, the Relative Risk was 1.42 (p = 0.46). DCS occurred mainly in divers who did not dive according to “low-bubble” diving techniques, in both groups.Conclusion: This prospective study confirms that DCS is more frequent in divers with RLS (such as a PFO), with a Relative Risk of 1.42 (all DCS) to 3.02 (confirmed DCS). It appears this risk is linked to diving behavior, more specifically diving to the limits of the adopted decompression procedures.

Highlights

Divers with a patent Foramen Ovale (PFO) have an increased risk for decompression sickness (DCS) when diving with compressed breathing gas
For confirmed DCS, the incidence was 7.6% vs. 27.3%, yielding an incidence of 1.8 and 5.46 DCS per 10,000 dives, respectively
For “all DCS, confirmed and possible,” the incidence was 16.2% vs. 27.3%, which amounts to 3.83 and 5.46 DCS per 10,000 dives (Relative Risk 1.42; CI 0.5616 to 3.6110, p = 0.46) (Table 3B)

Summary

Introduction

Divers with a patent Foramen Ovale (PFO) have an increased risk for decompression sickness (DCS) when diving with compressed breathing gas. Several attempts have been made to quantify the increased risk of diving for divers with a PFO based on retrospective diving accident data (Bove, 1998; Torti et al, 2004) In these “risk-comparison” papers, a 2.9 (Bove, 1998) to 5.7 times higher risk (Torti et al, 2004) for DCS has been reported, the latter figure has been criticized based on the subjective definition criteria used for DCS (Germonpre and Balestra, 2004). Unless all these factors can be accounted for, estimates of increased DCS risk remain highly speculative (Vann et al, 2008; Wilmshurst, 2019)

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