Vascular Function Recovery Following Saturation Diving

Abstract

Background and Objectives: Saturation diving is a technique used in commercial diving. Decompression sickness (DCS) was the main concern of saturation safety, but procedures have evolved over the last 50 years and DCS has become a rare event. New needs have evolved to evaluate the diving and decompression stress to improve the flexibility of the operations (minimum interval between dives, optimal oxygen levels, etc.). We monitored this stress in saturation divers during actual operations. Materials and Methods: The monitoring included the detection of vascular gas emboli (VGE) and the changes in the vascular function measured by flow mediated dilatation (FMD) after final decompression to surface. Monitoring was performed onboard a diving support vessel operating in the North Sea at typical storage depths of 120 and 136 msw. A total of 49 divers signed an informed consent form and participated to the study. Data were collected on divers at surface, before the saturation and during the 9 h following the end of the final decompression. Results: VGE were detected in three divers at very low levels (insignificant), confirming the improvements achieved on saturation decompression procedures. As expected, the FMD showed an impairment of vascular function immediately at the end of the saturation in all divers but the divers fully recovered from these vascular changes in the next 9 following hours, regardless of the initial decompression starting depth. Conclusion: These changes suggest an oxidative/inflammatory dimension to the diving/decompression stress during saturation that will require further monitoring investigations even if the vascular impairement is found to recover fast.

Keywords: FMD; arterial stiffness; commercial diver; decompression; endothelial dysfunction; flow-mediated dilation; human; hyperbaric; off-shore energy operation; underwater.

Figure 1

A typical saturation worksite. The divers are deployed from the diving support vessel inside a diving bell. Once on site, the bell’s door opens, and the divers lock out in the water using an umbilical attached to the bell to breathe and being supplied with hot water in their suit for thermal comfort. The working depth corresponds to the maximum depth reached by the divers. The working depth defines the chamber storage depth from excursion tables prepared in the company diving manual. The bell depth is usually set at 5 msw deeper than the storage depth to clear from subsea structures when opened. The “storage” and the “bell” are almost at the same pressure allowing for getting back to storage after work without decompression needed. The excursion of the diver out of the diving bell is limited to some meters not to add additional decompression time. The breathing gas is Heliox (Helium-Oxygen) to limit the density of the breathed gas (significant at such pressures) to reduce the work of breathing as well as Oxygen toxicity and Nitrogen narcosis.

Figure 2

Description of the saturation in the UK sector: depth profile (compression, storage depth, bell dives, decompression) and associated PO₂ profile.

Figure 3

Experimental flowchart.

Figure 4

Bar graph illustrating FMD changes during the first 2 h (First 120 min.) (n = 23) and last 2 h (n = 29) (7–9 h) after saturation decompression (**** = p < 0.0001) (One sample t-test). (FMD Changes are presented compared to predive values represented by the dotted line at 100%).

Figure 5

FMD evolution after exiting saturation the linear solution has been selected as the best fit approach, and the dotted lateral bands represent the 95% prediction bands.