Relation between cervical and thoracic spinal canal stenosis and the development of spinal cord decompression sickness in recreational scuba divers.

STUDY DESIGN: Retrospective case-control study. OBJECTIVES: The intent of this study was to investigate the relationships between vertebral degenerative changes resulting in spinal canal stenosis, spinal cord lesions and the development of spinal cord decompression sickness (DCS) in scuba divers. SETTING: Referral hyperbaric facility, Toulon, France. METHODS: We examined 33 injured divers less than 50 years old by cervical and thoracic MRI and compared them with 34 matched control divers. The number of intervertebral disk abnormalities and the degree of canal compression were analyzed on T2-weighted sagittal images using a validated grading system developed recently. The presence and the distribution of hyperintense cord lesions in relation with the accident and the recovery status at 6 months were also assessed. RESULTS: Canal spinal narrowing was more common in injured divers than in controls (79% vs. 50%, OR=3.7 [95% CI, 1.3-10.8], P=0.021). We found a significant linear association between the extent of canal stenosis, multisegmental findings and the development of spinal cord decompression sickness. MRI intramedullary lesions were significantly more frequent in divers with incomplete recovery (OR=16 [95% CI, 2.6-99], P=0.0014), but statistical analysis failed to demonstrate a significant relationship between canal compression, signal cord abnormalities and a negative clinical outcome. CONCLUSIONS: These results suggest that divers with cervical and thoracic spinal canal stenosis, mainly due to disk degeneration, are at increased risk for the occurrence of spinal cord decompression sickness.

Risks factors for recurrent neurological decompression sickness in recreational divers: a case-control study.

AIM: Individual or environmental factors that predispose to the recurrence of neurological decompression sickness (DCS) in scuba divers are not known and preventive measures designed to mitigate the risk of a subsequent episode remain empirical. The aim of this controlled study was to examine some potential risk factors predictive of recurrent DCS event that may lead to practical recommendations for divers who wish to continue diving after an initial episode. METHODS: Age, gender, diving experience, presence of a large right-to-left shunt (RLS) and diving practice following post-DCS resumption were evaluated as potential predictors of a further DCS in recreational divers admitted in our hyperbaric facility over a period of 12 years. RESULTS: Twenty-four recurrent cases and 50 divers treated for a single DCS episode which continued diving were recruited after review of medical forms and follow-up interview by telephone. After controlling for potential confounding variables between groups, multivariate analysis revealed that experienced divers (OR, 3.8; 95%CI, 1.1-14; P=0.03), the presence of large RLS (OR, 5.4; 95%CI, 1.5-19.7; P=0.006) and the lack of changes in the way of diving after prior DCS (OR, 8.4; 95%CI, 2.3-31.1; P=0.001) were independently associated with a repeated episode. CONCLUSION: The findings highlight the importance for divers to adopt conservative dives profiles or to use preferentially oxygen-enriched breathing mixtures after an initial DCS. Closure of a documented RLS through a large patent foramen ovale as a secondary preventive procedure for individuals that cannot adapt their diving practice remains debatable.

Specific diving training-induced arterial circulation changes.

OBJECTIVE: Several stressors such as cold water immersion, hyperoxic exposure and decompression-induced circulating bubbles can alter arterial circulation after a dive. The aim of this study was to investigate the arterial modifications induced by a specific diving training including repeated hyperbaric exposures and physical training. METHOD: Arterial pressure measurement and pulse wave velocity (PWV) recordings were performed in 12 student military divers before and after 15 weeks' training. The results were compared with the same investigations performed in 12 non-diver healthy subjects. RESULTS: A decrease in systolic blood pressure and pulse pressure was observed at both upper and lower limbs in student military divers after the training. Non-significant decreases in both carotido-femoral PWV and carotido-pedal PWV were found after the training. When the pulse time transit was divided by the cardiac cycle length between two R peaks ((RR) interval), a significant increase was observed between the carotid and femoral sensors. On the other hand, some differences were noticed between military divers and controls. Controls and divers were matched appropriately according to age and height, although the divers had a higher aerobic capacity as well as lower resting heart rate and lower pulse wave velocity. CONCLUSION: In trained military subjects, a training which includes repeated diving exposures and endurance exercises leads to vascular modifications suggesting an increase in central arterial compliance. There was no sign of arterial alteration induced by repeated diving exposures.

Preventive effect of pre-dive hydration on bubble formation in divers.

OBJECTIVE: To investigate whether prehydration 90 min before a dive could decrease bubble formation, and to evaluate the consequent adjustments in plasma volume (PV), water balance and plasma surface tension (ST). METHODS: Eight military divers participated in a crossover trial of pre-dive hydration using saline-glucose beverage (protocol 1) and a control dive with no prehydration (protocol 2). Drink volume was 1300 ml (osmolality 324 mOsm/l) and drinking time was 50-60 min. The diving protocol consisted of an open sea field air dive at 30 msw depth for 30 min followed by a 9 min stop at 3 msw. Haemodynamic parameters, body weight measurements, urine volume and blood samples were taken before/after fluid intake and after the dive. Decompression bubbles were examined by a precordial pulsed Doppler. RESULTS: Bubble activity was significantly lower for protocol 1 than for protocol 2. PV increased after fluid ingestion by 3.5% and returned toward baseline after diving for protocol 1, whereas it decreased by 2.2% after diving for protocol 2. Differences in post-dive PV between the two conditions were highly significant. Body weight loss before/after diving and post-dive urine volume after diving were significant in both protocols, but the relative decline in weight remained lower for protocol 1 than for protocol 2, with reduction of negative water balance due to higher fluid retention. There were no differences in ST after fluid intake and after diving for the two protocols. CONCLUSION: Pre-dive oral hydration decreases circulatory bubbles, thus offering a relatively easy means of reducing decompression sickness risk. The prehydration condition allowed attenuation of dehydration and prevention of hypovolaemia induced by the diving session. Hydration and diving did not change plasma surface tension in this study.

Military diving training improved arterial compliance.

This study was aimed at investigating whether repeated SCUBA diving might induce long term cardiovascular and autonomic modifications. In 11 military mine clearance diving students, arterial compliance (ultrasound scan study of brachial artery and ratio of stroke volume to pulse pressure: SV/PP), resting spectral analyses of heart rate and blood pressure variability, and a cold pressor test were performed before and after a 15-week military diving training course. After the diving training, arterial compliance was improved, as indicated by the significant increase in brachial arterial compliance (from 24+/-10 to 37+/-14 ml.mmHg (-1)) and SV/PP (from 1.7+/-0.2 to 1.9+/-0.2 ml.mmHg (-1)), and by the significant decrease in systolic, diastolic and pulse pressures (from 130+/-8 to 120+/-7; from 71+/-4 to 67+/-4; and from 58+/-8 to 53+/-5 mmHg, respectively). The peak oxygen uptake increased significantly from 54.3+/-2.0 to 56.8+/-4.0 mL.kg (-1).min (-1). Finally, the vasoconstrictive response during the cold pressor test increased (p<0.05). These findings point to a positive effect of a 15-week military diving training course on vascular function, and for a concomitant development of some peripheral vascular acclimatization to cold.

Influence of repetitive open sea dives and physical exercises on right-to-left shunting in healthy divers.

OBJECTIVE: Paradoxical gas embolism through right-to-left (R/L) shunts is considered as a potential cause of certain types of decompression sickness. AIM: To assess whether 4 months of repetitive diving and strenuous exercises would lead to an increased prevalence of R/L shunting in a group of military divers. METHODS: Using a standardised contrast-enhanced transcranial Doppler technique, 17 divers were re-examined for the presence of a R/L shunt 4 months after their initial examinations. R/L shunts were classified as type I if observed only after a straining manoeuvre, and type II if present at rest. RESULTS: Initial prevalence of R/L shunt was 41%: six type I shunts and one type II. At the second examination, prevalence was 47%, with the appearance of one type I shunt that was not previously present. We found no significant increase in the prevalence and size of R/L shunts. CONCLUSION: It is speculated that diving-related phenomena, such as variations in right atrial pressures during the end stages of or events immediately after a dive could generate an R/L shunt. However, extreme conditions of repetitive diving and strenuous exercises do not cause permanent modification in R/L permeability over a period of 4 months.

[Acute coronary syndrome with impaired left ventricular function in a carbon monoxide poisoning]. / Syndrome coronaire aigu avec dysfonction ventriculaire gauche lors d'une intoxication au monoxyde de carbone.

Carbon monoxide poisoning is the leading cause of death by poisoning in France. Neuropsychological symptoms are most common. We report on a patient with acute coronary syndrome and transient left ventricular dysfunction in carbon monoxide poisoning. Patient improved under hyperbaric oxygen therapy. Coronary angiography shows no significant lesion leading to myocardial stunning diagnose. Patients exposed to carbon monoxide must have systematic cardiac evaluation with electrocardiogram and dosage of biomarkers.

[Early detection of asymptomatic dysbaric osteonecrosis of the shoulder after type 1 decompression sickness: a case report]. / Découverte précoce d'une ostéonécrose dysbarique asymptomatique de l'épaule après un accident de décompression ostéomyoarticulaire: à propos d'une observation.

INTRODUCTION: Dysbaric osteonecrosis is a rare illness in professional divers and compressed-air workers. The correlation between dysbaric osteonecrosis and previous decompression sickness with osteoarthromuscular pain (type 1 decompression sickness) remains a controversial subject. The probability for ischemic lesions detected with MRI to turn into osteonecrosis after decompression sickness is still not established. EXEGESIS: The authors report the case of a military diver declared definitely medically unfit to dive after the occurrence of advanced dysbaric osteonecrosis of the shoulder, eight months after decompression sickness treated with hyperbaric oxygen, in the same area. A close link between those two events and the requirement for monitoring the follow-up of acute type 1 decompression sickness are discussed. CONCLUSION: Every decompression sickness with osteoarthromuscular pain should be early examined with MRI in order to screen osteomedullar damages liable to worse with diving and change subsequently in bone necrosis.

[Acute respiratory distress syndrome after prolonged hyperbaric oxygen therapy: a case of pulmonary oxygen toxicity?]. / Syndrome de détresse respiratoire aiguë après oxygénothérapie hyperbare prolongée: un cas d'intoxication pulmonaire à l'oxygène?

A 42-year-old patient was admitted to our ICU for severe decompression illness with tetraplegia. He presented an acute respiratory distress syndrome (ARDS), following a very long hyperbaric oxygen therapy (using a US. Navy Treatment Table 7). The ARDS resulted in pulmonary fibrosis, and the patient died despite maximal support in ICU. The risk of pulmonary toxicity of oxygen must be considered when using a prolonged recompression treatment table.

Cerebellar infarction presenting as inner ear decompression sickness following scuba diving: a case report.

INTRODUCTION: Inner ear decompression sickness following scuba diving is not uncommon and the characteristic features of this disorder are acute peripheral vestibular syndrome, sometimes associated with cochlear signs, requiring urgent hyperbaric oxygen therapy. Cerebellar infarction can also mimic isolated peripheral vestibulopathy. CASE REPORT: The authors report the case of a 47-year-old man in good general health admitted with acute left vestibular dysfunction suggestive of inner ear decompression sickness 6 hours after scuba diving. Normal videonystagmography and delayed onset of occipital headache finally led to brain MRI that confirmed the presence of recent ischaemic infarction in the territory of the medial branch of the posterior inferior cerebellar artery. Complementary investigations revealed the presence of a patent foramen ovale with atrial septal aneurysm. No underlying atherosclerotic disease or clotting abnormalities were observed. DISCUSSION/CONCLUSION: Cerebellar infarction can present clinically with features of inner ear decompression sickness following scuba diving. An underlying air embolism mechanism cannot be excluded, particularly in patients with a large right-to-left circulatory shunt and no other cardiovascular risk factors.

Relation between right-to-left shunts and spinal cord decompression sickness in divers.

The role of right-to-left shunting (RLS) in spinal cord decompression sickness (DCS) remains uncertain and could differ according to the distribution of lesion in spinal cord with a higher risk of upper spinal cord involvement in divers presenting a large patent foramen ovale. The aims of this study were to assess the prevalence of RLS with transcranial doppler ultrasonography in 49 divers referred for spinal cord DCS and compare it with the prevalence of RLS in 49 diving controls, and to determine a potential relation between RLS and lesion site of spinal cord. The proportion of large RLS was greater in DCS divers than in healthy control divers (odds ratio, 3.6 [95 % CI, 1.3 to 9.5]; p = 0.017). Shunting was not associated with the increased incidence of cervical spinal cord DCS (OR, 1.1 [95 % CI, 0.3 to 3.9]; p = 0.9) while a significant relationship between large RLS and spinal cord DCS with thoracolumbar involvement was demonstrated (OR, 6.9 [95 % CI, 2.3 to 20.4]; p < 0.001). From the above results, we conclude that the risk of spinal cord DCS in divers with hemodynamically relevant RLS is higher than in divers without RLS, particularly in their lower localization.