Magnetic resonance signal abnormalities and neuropsychological deficits in elderly compressed-air divers

Pulmonary Physiology and Medicine of Diving

Pulmonary physiology is significantly altered during underwater exposure, as immersion of the body and increased ambient pressure elicit profound effects on both the cardiovascular and respiratory systems. Thoracic blood pooling, increased breathing gas pressures, and variations in gas volumes alongside ambient pressure changes put the heart and lungs under stress. Normal physiologic function and fitness of the cardiovascular and respiratory systems are prerequisites to safely cope with the challenges of the underwater environment when freediving, or diving with underwater breathing apparatus. Few physicians are trained to understand the physiology and medicine of diving and how to recognize or manage diving injuries. This article provides an overview of the physiologic challenges to the respiratory system during diving, with or without breathing apparatus, and outlines possible health risks and hazards unique to the underwater environment. The underlying pathologic mechanisms of dive-related injuries are reviewed, with an emphasis on pulmonary physiology and pathophysiology.

Protein tau concentration in blood increases after SCUBA diving: an observational study

Purpose

It is speculated that diving might be harmful to the nervous system. The aim of this study was to determine if established markers of neuronal injury were increased in the blood after diving.

Methods

Thirty-two divers performed two identical dives, 48 h apart, in a water-filled hyperbaric chamber pressurized to an equivalent of 42 m of sea water for 10 min. After one of the two dives, normobaric oxygen was breathed for 30 min, with air breathed after the other. Blood samples were obtained before and at 30–45 and 120 min after diving. Concentrations of glial fibrillary acidic, neurofilament light, and tau proteins were measured using single molecule array technology. Doppler ultrasound was used to detect venous gas emboli.

Results

Tau was significantly increased at 30–45 min after the second dive (p < 0.0098) and at 120 min after both dives (p < 0.0008/p < 0.0041). Comparison of matching samples showed that oxygen breathing after diving did not influence tau results. There was no correlation between tau concentrations and the presence of venous gas emboli. Glial fibrillary acidic protein was decreased 30–45 min after the first dive but at no other point. Neurofilament light concentrations did not change.

Conclusions

Tau seems to be a promising marker of dive-related neuronal stress, which is independent of the presence of venous gas emboli. Future studies could validate these results and determine if there is a quantitative relationship between dive exposure and change in tau blood concentration.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-04892-9.

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.

Evaluation of cognitive performance in professional divers by means of event-related potentials and neuropsychology

OBJECTIVE

We investigated whether professional air diving with no decompression illness causes any long-term changes in cognitive functions.

METHODS

The all-male participants consisted of 18 healthy control (HC) volunteers and 32 divers. Divers were divided into two subgroups as moderate exposure group, Divers-I (DI) and extensive exposure group, Divers-II (DII). Participants were administered a comprehensive neuropsychological battery and event-related potentials (ERPs) were recorded while they performed auditory oddball task and visual continuous performance test (CPT).

RESULTS

P3 waves in oddball and CPT were significantly attenuated and peak latencies were prolonged in both diver groups compared with HC. Amplitude decrements in CPT P3 were graded with respect to level of diving exposure. Neuropsychologically, DII group displayed significantly poorer performance than HC and DI groups in measures of visuo-constructional and visual long-term memory tests. DI group performed better than HC group in some measures of planning ability.

CONCLUSIONS

Most of the changes in neurophysiological measures and poorer neuropsychological performance were found in DII group, and this might be interpreted as a red flag for the reflection of the slowly progressing deleterious effects of silent bubbles in brain function.

SIGNIFICANCE

This study reports impairments in certain neuropsychological measures and apparent neurophysiological markers pointing to slow cognitive decline referring to long-term effects of diving.

The Effect of 20 Minutes Scuba Diving on Cognitive Function of Professional Scuba Divers

BACKGROUND

Physical activity increases the performance of the nervous system by stimulating the body's metabolism and improving the efficiency of the ATP production system.

OBJECTIVES

In the present study, the effect of twenty minutes scuba diving in high depth (10m) on cognitive function and stress system activity was investigated.

METHODS

Twelve professional scuba divers with a mean age of 23 ± 1 year, weight of 80 ± 2.5 kg and height of 1.79 ± 3.5 cm resident in the city of Mashhad participated in the test. Their cognitive functions were measured 60 min before and 20 min after diving and the data were evaluated using the PASAT software. In the present study, parameters such as general mental health, sustained attention, average response speed, and mental fatigue were measured. Moreover, in order to determine the activity of the stress system, their salivary cortisol was collected before and after diving.

RESULTS

Results revealed that, the general mental health of these scuba divers was normal and it did not undergo a remarkable change after diving. Their average response speed and sustained attention had a significant decrease after scuba diving. Mental fatigue after diving increased. Also, salivary cortisol level significantly increased after diving.

CONCLUSIONS

According to our data, it seems that scuba diving as stress stimulant increases cortisol level and therefore reduces cognitive performance after diving.

Correlation between Patent Foramen Ovale, Cerebral "Lesions" and Neuropsychometric Testing in Experienced Sports Divers: Does Diving Damage the Brain?

SCUBA diving exposes divers to decompression sickness (DCS). There has been considerable debate whether divers with a Patent Foramen Ovale of the heart have a higher risk of DCS because of the possible right-to-left shunt of venous decompression bubbles into the arterial circulation. Symptomatic neurological DCS has been shown to cause permanent damage to brain and spinal cord tissue; it has been suggested that divers with PFO may be at higher risk of developing subclinical brain lesions because of repeated asymptomatic embolization of decompression-induced nitrogen bubbles. These studies however suffer from several methodological flaws, including self-selection bias. We recruited 200 volunteer divers from a recreational diving population who had never suffered from DCS; we then randomly selected 50 of those for further investigation. The selected divers underwent brain Magnetic Resonance Imaging to detect asymptomatic brain lesions, contrast trans-oesophageal echocardiography for PFO, and extensive neuro-psychometric testing. Neuro-psychometry results were compared with a control group of normal subjects and a separate control group for subjects exposed to neurotoxic solvents. Forty two divers underwent all the tests and are included in this report. Grade 2 Patent Foramen Ovale was found in 16 (38%) of the divers; brain Unidentified Bright Objects (UBO's) were found in 5 (11.9%). There was no association between PFO and the presence of UBO's (P = 0.693) or their size (p = 0.5) in divers. Neuropsychometric testing in divers was significantly worse from controls in two tests, Digit Span Backwards (DSB; p < 0.05) and Symbol-Digit-Substitution (SDS; p < 0.01). Compared to subjects exposed to neurotoxic solvents, divers scored similar on DSB and SDS tests, but significantly better on the Simple Reaction Time (REA) and Hand-Eye Coordination (EYE) tests. There was no correlation between PFO, number of UBO's and any of the neuro-psychometric tests. We conclude that for uneventful recreational diving, PFO does not appear to influence the presence of UBO's. Diving by itself seems to cause some decrease of short-term memory and higher cognitive function, including visual-motor skills; this resembles some of the effects of nitrogen narcosis and we suggest that this may be a prolonged effect of diving.

Patent foramen ovale (PFO): is there life before death in the presence of PFO?

Patent foramen ovale (PFO) is an embryologic remnant with incomplete postnatal adhesion of the cardiac atrial septum primum and secundum. After birth, the prevalence of PFO decreases from about 35% at young to approximately 20% at old age. PFO has been associated with numerous conditions such as decompression illness in divers, migraine, high-altitude pulmonary oedema, cerebrovascular and coronary ischaemia, and obstructive sleep apnoea syndrome. PFO is the cause of intermittent atrial right-to-left shunt, and it can be the source of cardiac paradoxical embolism. So far, randomized controlled trials have not documented a reduced rate of cerebrovascular recurrent events in patients receiving PFO device closure as compared to those on medical treatment. The purpose of this article was to critically evaluate evidence on the pathophysiologic, clinical as well as prognostic relevance of PFO.

A twelve-year longitudinal study of neuropsychological function in non-saturation professional divers

OBJECTIVES

Our main aim was to study the long-term neuropsychological effects of non-saturation diving. Further, we aimed to investigate whether neuropsychological performance was predictive of subsequent diving accidents and diving status.

METHODS

In this prospective longitudinal study, we enrolled 50 male diving students (mean age 25.3 years) at a diving school and followed them up six and 12 years later (43 and 37 divers, respectively). At each wave of the study, divers completed a comprehensive neuropsychological test battery and answered questionnaires on cumulative number of dives, incidents of decompression illness (DCI) and professional diver status.

RESULTS

At the 12-year follow-up, the divers reported a median number of 455 (range 40-5,604) cumulative dives. Cumulative number of dives was not associated with any adverse neuropsychological effects. However, divers with an incident of DCI performed worse in a memory test (Benton Visual Retention Test) and reported slightly more neuropsychiatric symptoms (Q 16). Diver students who performed well on a blindfolded memory test (tactual performance test) had an increased likelihood of becoming a professional diver 12 years later.

CONCLUSIONS

The main findings in the present study support the view that asymptomatic non-saturation divers who have dived under controlled conditions do not have an increased risk of impaired nervous system function, at least not to an extent that can be detected with neuropsychological tests while they still are relatively young. The observed associations between a history of DCI and impaired results in a memory test and reporting of neuropsychiatric symptoms may be due to a nervous system effect caused by DCI. The diver students' ability of problem-solving while they were blindfolded was predictive of their likelihood of becoming a professional diver 12 years later.

Neurological effects of deep diving

Deep diving is defined as diving to depths more than 50 m of seawater (msw), and is mainly used for occupational and military purposes. A deep dive is characterized by the compression phase, the bottom time and the decompression phase. Neurological and neurophysiologic effects are demonstrated in divers during the compression phase and the bottom time. Immediate and transient neurological effects after deep dives have been shown in some divers. However, the results from the epidemiological studies regarding long term neurological effects from deep diving are conflicting and still not conclusive. Prospective clinical studies with sufficient power and sensitivity are needed to solve this very important issue.

High incidence of venous and arterial gas emboli at rest after trimix diving without protocol violations

SCUBA diving is associated with generation of gas emboli due to gas release from the supersaturated tissues during decompression. Gas emboli arise mostly on the venous side of circulation, and they are usually eliminated as they pass through the lung vessels. Arterialization of venous gas emboli (VGE) is seldom reported, and it is potentially related to neurological damage and development of decompression sickness. The goal of the present study was to evaluate the generation of VGE in a group of divers using a mixture of compressed oxygen, helium, and nitrogen (trimix) and to probe for their potential appearance in arterial circulation. Seven experienced male divers performed three dives in consecutive days according to trimix diving and decompression protocols generated by V-planner, a software program based on the Varying Permeability Model. The occurrence of VGE was monitored ultrasonographically for up to 90 min after surfacing, and the images were graded on a scale from 0 to 5. The performed diving activities resulted in a substantial amount of VGE detected in the right cardiac chambers and their frequent passage to the arterial side, in 9 of 21 total dives (42%) and in 5 of 7 divers (71%). Concomitant measurement of mean pulmonary artery pressure revealed a nearly twofold augmentation, from 13.6 ± 2.8, 19.2 ± 9.2, and 14.7 ± 3.3 mmHg assessed before the first, second, and the third dive, respectively, to 26.1 ± 5.4, 27.5 ± 7.3, and 27.4 ± 5.9 mmHg detected after surfacing. No acute decompression-related disorders were identified. The observed high gas bubble loads and repeated microemboli in systemic circulation raise questions about the possibility of long-term adverse effects and warrant further investigation.

Risk of neurological decompression sickness in the diver with a right-to-left shunt: literature review and meta-analysis

OBJECTIVE

Literature review and meta-analysis to review the evidence of relationship between the presence of right-to-left shunts (RLSs) and the occurrence of neurological decompression sickness (DCS) in divers.

DATA SOURCES

MEDLINE, Google Scholar, and Health Technology Assessment databases.

STUDY SELECTION

Five case-control studies in which the prevalence of a RLS in a group of divers with neurological DCS was compared with that of a group of divers with no history of DCS, 3 cross-transversal studies in which the prevalence of RLS was measured in divers with neurological DCS, and 4 cross-transversal studies in which the prevalence of RLS was measured in divers with no history of DCS were reviewed.

DATA EXTRACTION

Only case-control studies were retained for meta-analysis.

DATA SYNTHESIS

This meta-analysis gathers 5 studies and 654 divers. The combined odds ratio of neurological DCS in divers with RLS was 4.23 (3.05-5.87). The meta-analysis including only large RLS found a combined odds ratio of 6.49 (4.34-9.71).

CONCLUSIONS

Because of a low incidence of neurological DCS, increase in absolute risk of neurological DCS due to RLS is probably small. Thus, in recreational diving, the systematic screening of RLS seems unnecessary. In professional divers, because of a chronic exposition and unknown consequences of cerebral asymptomatic lesions, these results raise again the benefit of the transcranial Doppler in the screening and quantification of the RLS, independently of their location.

Incidence of ischemic brain lesions in hyperbaric chamber inside attendants

Concern is growing about the negative long-term effects of hyperbaric exposure on the central nervous system of divers. This study was conducted with magnetic resonance imaging (MRI) to evaluate attendants that work inside hyperbaric chambers (known as inside attendants) for hyperintense brain lesions. Ten inside attendants and 10 healthy nondiving subjects were included in the study. A questionnaire was used to obtain information about subjects' medical history, hyperbaric exposure history, alcohol intake, and smoking habits. T1-weighted, T2-weighted, and fluid-attenuated inversion recovery images were acquired with a 1.5-T MRI device. A lesion was included in the count if it was hyperintense on both T2-weighted and fluid-attenuated inversion recovery images. Although MRI revealed 3 hyperintense brain lesions in 2 of 10 inside attendants and in none of the controls, the differences between groups were not statistically significant (P=.147). The number of brain lesions counted did not correlate with the age of the inside attendants (r=0.007; P=.978), the number of hyperbaric exposures (r=-0.203; P=.574), or the duration of work as an inside attendant (r=0.051; P=.890). Investigators found a correlation, however, between the number of cigarettes smoked in a day and the number of brain lesions identified (r=0.779; P<.01). An increased incidence of hyperintense brain lesions was not observed in inside attendants who had never experienced decompression sickness compared with nondiving controls. Additional multicenter epidemiologic studies are needed if the occupational safety of inside attendants is to be enhanced.

Microbubbles

Gas embolism is a known complication of various invasive procedures, and its management is well established. The consequence of gas microemboli, microbubbles, is underrecognized and usually overlooked in daily practice. We present the current data regarding the pathophysiology of microemboli and their clinical consequences. Microbubbles originate mainly in extracorporeal lines and devices, such as cardiopulmonary bypass and dialysis machines, but may be endogenous in cases of decompression sickness or mechanical heart valves. Circulating in the blood stream, microbubbles lodge in the capillary bed of various organs, mainly the lungs. The microbubble obstructs blood flow in the capillary, thus causing tissue ischemia, followed by inflammatory response and complement activation. Aggregation of platelets and clot formation occurs as well, leading to further obstruction of microcirculation and tissue damage. In this review, we present evidence of the biological and clinical detrimental effects of microbubbles as demonstrated by studies in animal models and humans, and discuss management of the microbubble problem with regard to detection, prevention, and treatment.

Psychobiology of altered states of consciousness

The article reviews the current knowledge regarding altered states of consciousness (ASC) (a) occurring spontaneously, (b) evoked by physical and physiological stimulation, (c) induced by psychological means, and (d) caused by diseases. The emphasis is laid on psychological and neurobiological approaches. The phenomenological analysis of the multiple ASC resulted in 4 dimensions by which they can be characterized: activation, awareness span, self-awareness, and sensory dynamics. The neurophysiological approach revealed that the different states of consciousness are mainly brought about by a compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Besides these severe alterations, environmental stimuli, mental practices, and techniques of self-control can also temporarily alter brain functioning and conscious experience.

Patent foramen ovale and diving

Patency of the foramen ovale is a risk factor for DCS in SCUBA divers, even if they adhere to the currently accepted and used decompression tables. The primary cause of DCS, however, is the nitrogen bubble, not the PFO. There are a number of techniques any diver can use to minimize the occurrence of nitrogen bubbles after a dive. The authors current practice is to inform civilian sports divers of the increased risk and to advise them to adopt conservative dive profiles. This can be achieved by selecting a more conservative dive computer, performing only dives that do not require obligatory decompression stops, or using oxygen-enriched breathing gas mixtures("nitrox") while still diving on "air profiles" [56].Dive-safety organizations are currently under-taking studies aimed at proposing changes in the decompression algorithms to produce low-bubble dive tables [12]. In the meantime, PFO remains a reason for caution. Whether all divers should be screened for PFOis an ongoing discussion [50] in view of methodologic and practical issues outlined in this article. Any definitive recommendations can be made only after a careful, prospective evaluation of the real relative risk for DCS and long-term cerebral damage.

Negative neurofunctional effects of frequency, depth and environment in recreational scuba diving: the Geneva "memory dive" study

OBJECTIVES

To explore relationships between scuba diving activity, brain, and behaviour, and more specifically between global cerebral blood flow (CBF) or cognitive performance and total, annual, or last 6 months' frequencies, for standard dives or dives performed below 40 m, in cold water or warm sea geographical environments.

METHODS

A prospective cohort study was used to examine divers from diving clubs around Lac Léman and Geneva University Hospital. The subjects were 215 healthy recreational divers (diving with self-contained underwater breathing apparatus). Main outcome measures were: measurement of global CBF by (133)Xe SPECT (single photon emission computed tomography); psychometric and neuropsychological tests to assess perceptual-motor abilities, spatial discrimination, attentional resources, executive functioning, and memory; evaluation of scuba diving activity by questionnaire focusing on number and maximum depth of dives and geographical site of the diving activity (cold water v warm water); and body composition analyses (BMI).

RESULTS

(1) A negative influence of depth of dives on CBF and its combined effect with BMI and age was found. (2) A specific diving environment (more than 80% of dives in lakes) had a negative effect on CBF. (3) Depth and number of dives had a negative influence on cognitive performance (speed, flexibility and inhibition processing in attentional tasks). (4) A negative effect of a specific diving environment on cognitive performance (flexibility and inhibition components) was found.

CONCLUSIONS

Scuba diving may have long-term negative neurofunctional effects when performed in extreme conditions, namely cold water, with more than 100 dives per year, and maximal depth below 40 m.

Effects of underwater sound exposure on neurological function and brain histology

To evaluate the safety of sonar exposure from a neurological perspective, the vulnerability of the central nervous system to underwater exposure with high-intensity, low-frequency sound (HI-LFS) was experimentally examined. Physiological, behavioral and histological parameters were measured in anesthetized, ventilated rats exposed to brief (5 min), underwater HI-LFS. Exposure to 180 dB sound pressure level (SPL) re 1 microPa at 150 Hz (n = 9) did not alter acute cardiovascular physiology (arterial blood pH, pO(2), pCO(2), heart rate, or mean arterial blood pressure) from that found in controls (n = 11). Rats exposed to either 180 dB SPL re 1 microPa at 150 Hz (n = 12) or 194 dB SPL re 1 microPa at 250 Hz (n = 12) exhibited normal cognitive function at 8 and 9 days after sound exposure. Evaluation of neurological motor function revealed a minor deficit 7 days after 180 dB SPL/150 Hz exposure that resolved by 14 days, and no deficits after 194 dB SPL/250 Hz exposure. No overt histological damage was detected in any group. These data suggest that underwater HI-LFS exposure may cause transient, mild motor dysfunction.

Decompression illness in divers: a review of the literature

BACKGROUND

Neurologists may be consulted to diagnose and treat the severe neurologic injuries that can occur in divers with decompression illness (DCI).

REVIEW SUMMARY

Subclinical bubbles form during normal diving activity. DCI, a diffuse and multifocal process, results when bubbles cause symptoms by exerting mass effect in tissues, or obstructing venous or arterial flow. The lower thoracic spinal cord is a commonly affected area of the central nervous system. The most commonly described form of brain DCI is cerebral arterial gas embolism with middle cerebral artery or vertebrobasilar distribution involvement. Bubbles exert secondary damage to the vascular endothelium, causing activation of numerous biochemical cascades.

CONCLUSIONS

Divers can develop DCI on very short dives or in shallow water, even when adhering to protocols. DCI should be strongly considered when divers experience pain after diving. Any neurologic symptoms after a dive are abnormal and should be attributed to DCI. Even doubtful cases should be treated immediately with hyperbaric oxygen (HBO), after a chest x-ray to rule out pneumothorax. The Divers Alert Network should be contacted for emergency consultation. Delay to treatment can worsen outcome; however, the overwhelming majority of divers respond to HBO even days to weeks after injury. Although DCI is a clinical diagnosis, magnetic resonance imaging, somatosensory evoked potentials, single-photon emission tomography, and neuropsychologic testing help to document disease and monitor response to therapy. Divers should be treated with HBO until they reach a clinical plateau. Complete relief of symptoms occurs in 50% to 70% of divers; 30% have partial relief.