Decompression Illness in Repetitive Breath-Hold Diving: Why Ischemic Lesions Involve the Brain?

Nitrogen (N2) accumulation in the blood and tissues can occur due to breath-hold (BH) diving. Post-dive venous gas emboli have been documented in commercial BH divers (Ama) after repetitive dives with short surface intervals. Hence, BH diving can theoretically cause decompression illness (DCI). “Taravana,” the diving syndrome described in Polynesian pearl divers by Cross in the 1960s, is likely DCI. It manifests mainly with cerebral involvements, especially stroke-like brain attacks with the spinal cord spared. Neuroradiological studies on Ama divers showed symptomatic and asymptomatic ischemic lesions in the cerebral cortex, subcortex, basal ganglia, brainstem, and cerebellum. These lesions localized in the external watershed areas and deep perforating arteries are compatible with cerebral arterial gas embolism. The underlying mechanisms remain to be elucidated. We consider that the most plausible mechanisms are arterialized venous gas bubbles passing through the lungs, bubbles mixed with thrombi occlude cerebral arteries and then expand from N2 influx from the occluded arteries and the brain. The first aid normobaric oxygen appears beneficial. DCI prevention strategy includes avoiding long-lasting repetitive dives for more than several hours, prolonging the surface intervals. This article provides an overview of clinical manifestations of DCI following repetitive BH dives and discusses possible mechanisms based on clinical and neuroimaging studies.

Diving-related disorders in commercial breath-hold divers (Ama) of Japan

Decompression illness (DCI) is well known in compressed-air diving but has been considered anecdotal in breath-hold divers. Nonetheless, reported cases and field studies of the Japanese Ama, commercial or professional breath-hold divers, support DCI as a clinical entity. Clinical characteristics of DCI in Ama divers mainly suggest neurological involvement, especially stroke-like cerebral events with sparing of the spinal cord. Female Ama divers achieving deep depths have rarely experienced a panic-like neurosis from anxiety disorders. Neuroradiological studies of Ama divers have shown symptomatic and/or asymptomatic ischaemic lesions situated in the basal ganglia, brainstem, and deep and superficial cerebral white matter, suggesting arterial insufficiency. The underlying mechanism(s) of brain damage in breath-hold diving remain to be elucidated; one of the plausible mechanisms is arterialization of venous nitrogen bubbles passing through right to left shunts in the heart or lungs. Although the treatment for DCI in Ama divers has not been specifically established, oxygen breathing should be given as soon as possible for injured divers. The strategy for prevention of diving-related disorders includes reducing extreme diving schedules, prolonging surface intervals and avoiding long periods of repetitive diving. This review discusses the clinical manifestations of diving-related disorders in Ama divers and the controversial mechanisms.

Executive Function among Chilean Shellfish Divers: A Cross-Sectional Study Considering Working and Health Conditions in Artisanal Fishing

Knowledge about professional diving-related risk factors for reduced executive function is limited. We therefore evaluated the association between decompression illness and executive functioning among artisanal divers in southern Chile. The cross-sectional study included 104 male divers and 58 male non-diving fishermen from two fishing communities. Divers self-reported frequency and severity of symptoms of decompression illness. Executive function was evaluated by perseverative responses and perseverative errors in the Wisconsin Card Sorting Test. Age, alcohol consumption, and symptoms of depression were a-priori defined as potential confounders and included in linear regression models. Comparing divers and non-divers, no differences in the executive function were found. Among divers, 75% reported a history of at least mild decompression sickness. Higher frequency and severity of symptoms of decompression illness were associated with reduced executive function. Therefore, intervention strategies for artisanal divers should focus on prevention of decompression illness.

Decompression Illness Incidence and Hypoxia Symptoms After Prebreathing in Hypobaric Hypoxia Training

INTRODUCTION: Hypobaric hypoxia training utilizing the environmental chamber is often preceded by prebreathing of 100% oxygen with the goal of reducing decompression illness (DCI). We aimed to study the impact of prebreathing 100% oxygen for 30 min prior to hypobaria exposure to 7600 m (25,000 ft) on the incidence rate of DCI, as well as the impact of prebreathing on hypoxia symptoms felt during training.METHODS: Records of participants who underwent hypobaric hypoxia training in the Republic of Singapore Air Force (RSAF) from 2011 to 2014 (before introduction of prebreathing) were compared to those who underwent similar training from 2014 to 2017 (after introduction of prebreathing) to determine the incidences of DCI for both groups. Participants who underwent hypobaric hypoxia training from January 2017 to July 2017 completed a survey to assess the impact of prebreathing on the presentation and severity of hypoxia symptoms.RESULTS: Two DCI events were recorded in 1530 hypobaric chamber exposures without prebreathing while two DCI events were recorded in 1729 exposures with prebreathing. There was no significant difference in the incidence of DCI between the two groups. The survey findings showed no significant difference in the presentation and severity of hypoxia symptoms with 30 min of prebreathing.DISCUSSION: Incidence of DCI remains low during hypobaric chamber training, with no statistical difference with or without prebreathing. Possible reasons were the short duration of hypobaric exposure of 10 min during hypoxia training, and that 30 min of prebreathing was insufficient to further decrease or eliminate the risk of DCI in short duration hypobaric exposures.Cheok LJ, Goh BLY, Soh FW, Chuan BTB. Decompression illness incidence and hypoxia symptoms after prebreathing in hypobaric hypoxia training. Aerosp Med Hum Perform. 2021; 92(5):289293.

Cutis marmorata as a manifestation of decompression illness

We present imagines of skin lesions due to a decompression illness (known as cutis marmorata). These alterations are usually transient, but they could be a warning sign of a more severe manifestation of decompression illness.

First impressions: Use of the Azoth Systems O’Dive subclavian bubble monitor on a liveaboard dive vessel

Germonpré P, Van der Eecken P, Van Renterghem E, Germonpré F-L, Balestra C. First impressions: Use of the Azoth Systems O’Dive subclavian bubble monitor on a liveaboard dive vessel. Diving and Hyperbaric Medicine. 2020 December 20;50(4):405–412. doi: 10.28920/dhm50.4.405-412. PMID: 33325023.) Introduction: The Azoth Systems O’Dive bubble monitor is marketed at recreational and professional divers as a tool to improve personal diving decompression safety. We report the use of this tool during a 12-day dive trip aboard a liveaboard vessel. Methods: Six divers were consistently monitored according to the user manual of the O’Dive system. Data were synchronised with the Azoth server whenever possible (depending on cell phone data signal). Information regarding ease of use, diver acceptance and influence on dive behaviour were recorded. Results: In total, 157 dives were completely monitored over 11 diving days. Formal evaluations were only available after six days because of internet connection problems. Sixty-one dives resulted in the detection of bubbles, mostly in one diver, none of which produced any symptoms of decompression illness. Conclusions: The O’Dive system may contribute to increasing dive safety by making divers immediately aware of the potential consequences of certain types of diving behaviour. It was noted that bubble monitoring either reinforced divers in their safe diving habits or incited them to modify their dive planning. Whether this is a lasting effect is not known.