Selected scientific publications on diving medicine and physiology.
2014 Dec 1
Preconditioning as a tool to improve diving safety
Balestra C, Blatteau J, Gempp E & Rozloznik M
Vascular gas bubbles are considered the principal element in decompression sickness (DCS) development. Traditionally these bubbles were called VGE (venous gas emboli), however scientific knowledge indicates that similar bubbles may also be present in the arterial circulation, therefore we propose to use “VGE” for “Vascular Gas Emboli”, and we will do so throughout the text. Reduction of VGE production represents an interesting endpoint to decrease decompression stress and DCS risk. Here we will discuss state of the art pre-dive techniques and approaches, commonly known as preconditioning, used to reduce post-dive VGE load and decompression stress. Evidence based approaches clearly show that some types of preconditioning are more potent in VGE reduction, some indecompression stress reduction and there are some with a positive impact on both. Nevertheless, further research is required to investigate the mechanisms underlying these positive effects.
Decompression illnesses (DCI), or as they are called more scientifically: dysbaric disorders, represent a complex spectrum of pathophysiological conditions with a wide variety of signs and symptoms related to dissolved gas and its subsequent phase change.1,2 Any significant organic or functional dysfunction in individuals who have recently been exposed to a reduction in environmental pressure (i.e., decompression) must be considered as possibly being caused by DCI until proven otherwise.
Diving above sea level has different motivations for recreational, military, commercial and scientific activities. Despite the apparently wide practice of inland diving, there are three major discrepancies about diving at altitude: threshold elevation that requires changes in sea level procedures; upper altitude limit of the applicability of these modifications; and independent validation of altitude adaptation methods of decompression algorithms. The first problem is solved by converting the normal fluctuation in barometric pressure to an altitude equivalent.
Flying after diving: in-flight echocardiography after a scuba diving week
Cialoni D, Pieri M, Balestra C, Marroni A.
INTRODUCTION: Flying after diving may increase decompression sickness risk (DCS), but strong evidence indicating minimum preflight surface intervals (PFSI) is missing.
METHODS: On return flights after a diving week on a live-aboard, 32 divers were examined by in-flight echocardiography with the following protocol: 1) outgoing flight, no previous dive; 2) during the diving week; 3) before the return flight after a 24-h PFSI; and 4) during the return flight.
RESULTS: All divers completed similar multiple repetitive dives during the diving week. All dives were equivalent as to inert gas load and gradient factor upon surfacing. No bubbles in the right heart were found in any diver during the outgoing flight or at the preflight control after a 24-h PFSI following the diving week. A significant increase in the number and grade of bubbles was observed during the return flight. However, bubbles were only observed in 6 of the 32 divers. These six divers were the same ones who developed bubbles after every dive.
CONCLUSIONS: Having observed a 24-h preflight interval, the majority of divers did not develop bubbles during altitude exposure; however, it is intriguing to note that the same subjects who developed significant amounts of bubbles after every dive showed equally significant bubble grades during in-flight echocardiography notwithstanding a correct PFSI. This indicates a possible higher susceptibility to bubble formation in certain individuals, who may need longer PFSI before altitude exposure after scuba diving.
Just say NO to decompression bubbles: is there a real link between nitric oxide and bubble production or reduction in humans?
Vascular gas emboli (VGE) start forming during the degassing of tissues in the decompression (ascent) phase of the dive when bubble precursors (micronuclei) are triggered to growth. The precise formation mechanism of micronuclei is still debated, with formation sites in facilitating regions with surfactants, hydrophobic surfaces or crevices. Ho wever, significant inter-subject variability to VGE exists for the same diving exposure and VGE may even be reduced with a single pre-dive intervention. The precise link between VGE and endothelial dysfunction observed post dive remains unclear and a nitric oxide (NO) mechanism has been hypothesized.
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