In recent years there has been much debate about whether repeated diving over years exerts chronic adverse effects on the CNS. Previous studies have shown neurologic and neuropsychological long-term effects on divers, suggesting spinal and cerebral dysfunction.1 Most of these studies were performed on divers with a history of neurologic decompression illness (DCI).2 Furthermore, an increased prevalence of hyperintense cerebral lesions in divers without neurologic DCI has been reported, suggesting a higher risk for accumulating these abnormalities during repeated diving.3 However, the question of long-term effects on divers without neurologic DCI remains controversial as controlled data regarding neuropsychometric test results, clinical, and MRI findings in this diving population are lacking. We investigated the neurologic, neuropsychological, and neuroradiologic status of divers without a history of DCI to detect possible deficits and abnormalities that may be attributed to repeated diving. We compared professional military divers with a long-term exposure to compressed-air diving with age-matched nondiving controls. METHODSStudy groups. Professional German Navy divers (n = 24) and 24 nondiving Navy employees were matched with respect to age and smoking habits. Subjects had no history of neurologic DCI, head trauma, cerebrovascular or cardiovascular disease, diabetes, or regular drug consumption. Diving History Mean diving experience was 1407 ± 675.7 hours ([mean ±SD]; range 500 to 2777 hours) with a mean of 1652 ± 694 dives (range 591 to 3170 dives) and 17.3 ± 5.5 diving years (range 8 to 29 years). The majority (84%) of all dives were performed in the diving depth range of 0 to 20 m. Neuropsychometric Evaluation The test battery for the assessment of attention included the following subtasks: phasic/tonic alertness, divided attention, go/no-go test, incompatibility, and change of reaction. Memory performance was evaluated with the Wechsler Adult Intelligence Scale?Revised (WAIS-R) (Digit Span), the Corsi Block-Tapping Test, and the Wechsler Memory Scale?Revised (WMS-R) (Verbal Paired Associates). General intellectual functions were tested using the WAIS-R (Information, Similarities, Picture Completion, Block Design). Premorbid level of intellectual abilities was assessed using the German Multiple Choice Vocabulary Test (MWT-B), which is the functional equivalent of the National Adult Reading Test (NART). Verbal fluency (letter/category) of spontaneous speech was evaluated with the Word Fluency Test in the Neurosensory Center Comprehensive Examination for Aphasia (NCCEA). The state of mood was assessed with the Beck Depression Inventory and with a self-rating mood scale. Fine motor skills were assessed by using the Halstedt-Reitan Test Battery (Finger Tapping Test). All subjects had a standard neurologic examination Neuroradiologic Study Cerebral MRI were performed on a 1.5-T unit. Images were acquired in the transversal (T2-weighted; fluid-attenuated inversion recovery [FLAIR]) and in the sagittal plain (T2-weighted) and were reviewed by two radiologists who were blinded to whether the subject was a diver. Focal hyperintensities were considered as a lesion in a consensus agreement if they were detectable in both T2 and FLAIR images. Signal hyperintensities were classified with respect to topography, absolute number, and size, as well as according to a semiquantitative rating scale. Statistical Analysis The following tests were applied: Wilcoxon signed rank test or t-test for paired samples (group variables), Pearson or Spearman correlation coefficient (correlation analysis), and the 2 test (MRI study). RESULTSThe groups did not differ with respect to subject characteristics (table 1). Neurologic examination findings were unremarkable. MRI Study Six divers (25%) showed a total of 10 hyperintense lesions, whereas 24 lesions were revealed in 10 controls (42%). Most signal hyperintensities were found in the subcortical parietal white matter (divers 5 lesions; controls 13 lesions). Otherwise, the distribution was as follows: subcortical frontal white matter (divers 2 lesions; controls 6 lesions); putamen (controls 3 lesions); thalamus (divers 2 lesions); internal capsule (controls 1 lesion); pons (divers and controls 1 lesion each). There was no difference in the absolute number and size of cerebral lesions between the groups or in a rating scale.4 | | Also, there was no correlation to the diving indices, neuropsychometric test results, or alcohol and nicotine consumption. A megacisterna magna was described in one diver and a mild frontal lobe atrophy in another. DISCUSSIONA longer reaction time in a visual reaction time test has been shown in compressed-air divers without a history of neurologic DCI.5 However, an examination of divided attention by the Trail Making Test (TMT-B) did not reveal any differences between groups.5 Compared to our group these divers had almost twice as many dives, although their total diving years and the mean age were comparable. In elderly compressed-air divers with a much longer diving experience an impairment in visual tracking and scanning and recall of nonverbal material compared to controls has been reported.6 Similar to our study, divided attention was significantly decreased in these elderly divers as analyzed by the TMT-B. Because impairment of divided attention may be the earliest indicator of cortical dysfunction7 these findings in middle-aged and elderly divers may point to a certain effect of repeated diving. However, when comparing our results with other diving populations, this putative impairment in divers seems not to increase with longer diving experience. Considering this, and that all results in our detailed neuropsychometric testing are subclinical and within the range of the applied tests, we did not find evidence for a clear impairment of neuropsychological performance due to long-term diving in our military population exposed to carefully controlled diving. Thus, our psychometric results are in line with studies in which no overt neuropsychological impairment was found that would suggest that an accumulation of subclinical decompression incidents results in distinct neuropsychological deficits.8 The long-term effect of compressed-air diving without neurologic DCI on the number of cerebral focal hyperintensities is controversial as a higher number of lesions in self-recruited amateur divers has been reported.3 This discrepancy may partly be explained by the recruitment protocol of the study,3 which has been criticized elsewhere.9 A correlation between the number and size of MRI abnormalities and the time spent in the deep air-diving range of 40 to 60 m was found in elderly divers.6 However, the total number of lesions did not differ significantly from the controls.6 This population6 consisted of older divers with a mean age of 50 years, which may partly account for a higher number of abnormalities, which increase with age.10 Our MRI findings are in line with other MRI studies in which no increased prevalence in cerebral hyperintense lesions was found and the range of signal hyperintensities corresponded to those reported for asymptomatic individuals.10 We conclude that neither neuropsychological nor MRI abnormalities can be detected in professional divers without decompression illness if diving is performed under controlled conditions. ACKNOWLEDGEMENTS The authors thank Dr. S. Sievers for recruiting the study participants. FOOTNOTES Dr. Cordes is currently affiliated with the Department of Neurology, Braunschweig City Hospital, Germany. REFERENCES 1. Calder I. Does diving damage your brain? Occup Med (Lond) 1992; 42: 213-214.
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