Anxiety and panic in recreational scuba divers

Drowning incidents precipitated by unusual causes (DIPUCs): A narrative review of their diagnoses, evaluation and management

Drowning is a cause of significant morbidity and mortality worldwide. In most circumstances, the proximate cause is attributable to human factors, such as inexperience, fatigue, intoxication, or hazardous water conditions. The phenomenon of drowning incidents precipitated by unusual circumstances (DIPUCs) - either fatal or nonfatal - involving otherwise healthy individuals under generally safe conditions has not been comprehensively addressed in the medical and drowning literature to date. In this review, we discuss etiologies of DIPUCs, diagnostic clues, suggested workup, suggested postmortem testing, and implications for surviving patients and families. Identifying the cause of a drowning incident can be extremely challenging for the initially treating physician, relying perforce on historical context, environmental clues, physical exam, medical history, eyewitness accounts or video recordings. If no clear explanation for a drowning incident emerges despite a thorough investigation, clinicians should consider some of the less common diagnoses we describe in this paper, and, when appropriate, refer for an autopsy with postmortem molecular genetic testing. While time-consuming, these efforts can prove life-saving for some non-fatal drowning victims and the families of all victims of DIPUCs.

Anxiety and its relationship to demographic and personality traits data among special operations divers: a cross-sectional study

INTRODUCTION

Special operation diving is becoming increasingly prevalent but has received less attention. The anxiety profile in special operation divers and its influencing factors remain unclear, posing great challenges to medical and psychological security of this unique population. The current study aimed to investigate the anxiety profile and to analyse the correlations between anxiety with demographic and personality traits data among special operation divers.

METHODS

From July to October 2023, 650 special operation divers participated this analytical cross-sectional study. The Spielberg's State-Trait Anxiety Inventory and the Neuroticism Extraversion Openness Five-Factor Inventory were used to evaluate anxiety and personality traits of special operation divers.

RESULTS

27.2% and 30.3% special operation divers showed high scores on state anxiety and trait anxiety, respectively. Special operation divers who are 30 years or older and who have dived for 15 years or more are prone to higher level of trait anxiety and state anxiety (all p<0.001). Neuroticism showed a significantly positive correlation with both trait anxiety (r=0.675, p<0.001) and state anxiety (r=0.674, p<0.001). Extraversion, openness, agreeableness and conscientiousness are all negatively correlated with both trait anxiety and state anxiety (r=-0.670 to -0.400, all p<0.001). Additionally, significant differences in neuroticism, extraversion, openness, agreeableness and conscientiousness were observed between the high anxiety group and the low anxiety group (all p<0.001).

CONCLUSION

The prevalence of trait anxiety and state anxiety are both relatively high among special operation divers. Individuals with older age and longer diving years are more prone to be anxious. Higher neuroticism, lower extraversion, lower openness, lower agreeableness and lower conscientiousness may be predictors of higher trait anxiety and higher state anxiety.

Effects of Oxygen Prebreathing on Bubble Formation, Flow-Mediated Dilatation, and Psychomotor Performance during Trimix Dives

Introduction: This research was performed to examine the effects of air and oxygen prebreathing on bubble formation, flow-mediated dilatation, and psychomotor performance after scuba dives. Methods: Twelve scuba divers performed two dives using a gas mixture of oxygen, nitrogen, and helium (trimix). In a randomized protocol, they breathed air or oxygen 30 min before the trimix dives. Venous bubble formation, flow-mediated dilatation, and psychomotor performance were evaluated. The participants solved three psychomotor tests: determining the position of a light signal, coordination of complex psychomotor activity, and simple arithmetic operations. The total test solving time, minimum single-task solving time, and median solving time were analyzed. Results: The bubble grade was decreased in the oxygen prebreathing protocol in comparison to the air prebreathing protocol (1.5 vs. 2, p < 0.001). The total test solving times after the dives, in tests of complex psychomotor coordination and simple arithmetic operations, were shorter in the oxygen prebreathing protocol (25 (21-28) vs. 31 (26-35) and 87 (82-108) vs. 106 (90-122) s, p = 0.028). Conclusions: In the oxygen prebreathing protocol, the bubble grade was significantly reduced with no change in flow-mediated dilatation after the dives, indicating a beneficial role for endothelial function. The post-dive psychomotor speed was faster in the oxygen prebreathing protocol.

Psychophysiological stress response in SCUBA divers: The contribution of negative automatic thoughts and negative emotions

The research questions in this study were to examine the contribution of negative automatic thoughts and negative emotions, measured by two newly-constructed questionnaires, to psychophysiological stress responses among more experienced military and less experienced recreational divers. Further, we examined whether daily variations in cortisol levels could be attributed to the impact of negative thoughts/emotions rather than diving experience. Altogether 15 recreational and 14 military male divers participated in the dive wherein stress responses were measured by anxiety measures (DASS-21 and STAI) and cortisol salivary concentrations. The results of factor analysis and principal component analysis demonstrated acceptable construct validity and internal consistency of both questionanires. Recreational and military divers did not differ significantly in the proportion of negative thoughts and emotions, while recreational divers had significantly higher levels of cortisol release after awakening and immediately before/after diving, indicating their more intense stress responses. A significant interaction between daily variations in cortisol secretion and negative emotions indicated a greater importance of emotions in response to diving stress rather than diving experience. Accordingly, using a multiple regression analysis showed that more pre-diving negative emotions predicted higher levels of pre-diving anxiety and depression as well as more cortisol release. More negative thoughts predicted higher levels of depressive symptoms, while belonging to a group of recreational divers was a significant predictor of higher pre-diving anxiety. This study points to the importance of considering cognitive and emotional experiences, particularly in recreational divers, for the purpose of prevention of negative psychophysiological stress responses prior to diving.

Firefighters during training as divers: physiologic and psychomental stresses

Objectives. Fire departments train divers for search, rescue and recovery in and under water. Their tasks likely exert major physical and psychological stress. This study hypothesizes that training is well balanced, following a learning spiral. Methods. Seven firefighters participated, performing 272 dives in different waters. Measurements included pulmonary function (body plethysmography); heart rate (HR) and air consumption during dives; personality variables with the state-trait anxiety inventory (STAI) and psychological stress with the task load index (NASA-TLX). Results. Pulmonary function was maintained at the end of training dives. During the dives, mean HR was 108 ± 23 bpm and mean air consumption 37 ± 15 L/min. Both values remained unchanged during training. The three highest STAI stanines (severe trait anxiety) were not considered, but median stanines and very low values were over-represented. Demands within the seven NASA-TLX areas were perceived differently. Sum of the scales 'very low', 'low' and 'mean' was ≥60%. In turn, the scale 'very high' was in none of the demands >10%. Conclusion. Physiological values remained unaltered throughout training, i.e. workload and increase in competence properly matched. The moderate manifestation of psychomental stress speaks for a group of highly selected individuals. Both candidate selection and design of the learning spiral was successful.

Anxiety impact on scuba performance and underwater cognitive processing ability

INTRODUCTION

Anxiety is a substantial consideration in scuba diving and may influence a diver's performance and cognitive activities. This study aimed to simultaneously observe the effect of anxiety trait on actual diving performance and underwater cognitive processing ability.

METHODS

Twenty-seven scuba divers completed the STAI-T component of the State-Trait Anxiety Inventory, and were subdivided into two groups on the basis of trait anxiety scores ≥ 39 and < 39. Scuba diving performance was measured in a pool. The completion time of four standardised scuba skills was recorded by a diving instructor. The correct completion rate and response time for a cognitive function assessment (number-Stroop test) were measured both on land ('dry') and underwater at 5 metres' fresh water.

RESULTS

Anxiety trait was associated with prolonged mask clearing: mean completion time 7.1 (SD 3.2) s vs. 10.8 (5.4) s in low and high anxiety trait divers respectively (P = 0.04). Low (vs high) anxiety trait divers had reduced response times for the number-Stroop test: 49.8 (3.0) s vs. 53.3 (5.4) s (P = 0.04) dry, and 64.4 (5.0) s vs. 72.5 (5.5) s (P < 0.01) underwater. Performance of other skills was not significantly affected by trait anxiety nor correlated with the number-Stroop test results.

CONCLUSIONS

Personal anxiety trait prolongs mask clearing and underwater cognitive processing ability but the latter did not affect execution of other underwater scuba diving skills.

Diving and mental health: the potential benefits and risks from a survey of recreational scuba divers

INTRODUCTION

Scuba diving is physically and cognitively demanding. Medical guidance regarding physical and mental health (MH) issues and related prescribed medication is often based on limited evidence. There is a paucity of data concerning diving with MH issues. This survey aimed to investigate the prevalence of MH issues and use of prescription medications among United Kingdom (UK) sport divers, and the rate of non-compliance with current guidance among divers suffering depression and anxiety. The positive effects of scuba diving on MH were also considered.

METHODS

An anonymous online survey was publicised through diving exhibitions and social media. Measures included diver and diving demographics; GAD-7 Anxiety and PHQ-9 depression questionnaires; diagnosed current and/or past MH conditions; medication usage; comorbid medical conditions/treatments; disclosure of past/current MH issues; and perceived MH benefits of diving.

RESULTS

Data from 729 respondents revealed MH issues at rates comparable with the general population. Current and/or past MH issues were reported by 111/729, with 60 having active diagnoses, and 45/60 taking prescribed psychotropic medications; 21/45 did not declare their medication on diver self-certification medical forms. The activity of diving was thought to be beneficial to MH by 119/729 respondents.

CONCLUSIONS

Divers experienced expected levels of MH issues, but did not comply with current medical guidelines on modifying or abstaining from diving activity or reporting their MH condition. Changes may be needed to diver training to encourage more accurate reporting and aid development of evidence-based protocols. Guidelines could be reconsidered in light of current diver behaviour, risks and potential MH benefits.

The problem of experiencing anxiety among divers. Experiment in hyperbaric exposure conditions

The aim of the article is a review of psychological literature relating to the problem of anxiety in divers, where an emphasis is placed on the degree of mental adaptation of the individual to the underwater environment, primarily highlighting the trait of anxiety and the neuroticism of a person involved in a specific type of diving. The article presents selected reports from all over the world regarding research on anxiety in divers. Treating a high level of the indicator of anxiety as a predictor of panic anxiety reveals the importance of this trait in predicting the risk of an occurrence of diving accidents during the operation under water. In the own research presented in the article, the results on the levels of anxiety as a trait and a state in divers taking part in hyperbaric exposures indicate the fact that the majority of the examined divers have low levels of anxiety both as a trait and a state, which most probably indicates the good psychological condition of the examined divers.

Psychological Aspects of Diving in Selected Theoretical and Research Perspectives

The aim of the article is to conduct a literature review in relation to the psychological aspects of diving. The acquired knowledge can currently be qualified as belonging to various branches of applied psychology, as well as underwater medicine, sports medicine, psychiatry and psychotherapy. The literature on this subject matter raises two main issues of the psychological perspective: the degree of psychological adaptation of an individual to the underwater environment, and the psychophysical condition of a man involved in a specific type of diving and the resulting skills/competences to perform underwater tasks. The article presents selected reports from around the world related to diving psychology resulting from the applied structure/classification of psychological theories, explaining various mechanisms of psychological functioning underwater. The paper presents studies from the perspective of psychodynamics, psychology of health/stress, psychology of individual differences and personality. The main conclusions indicate that in addition to the main problem of an optimal/lack of adaptation of humans to the underwater environment, there is insufficient psychological knowledge (including Polish reports) in the area of personality differences between various types of divers, their social functioning, mental health and psychoeducation with regard to underwater exposures.

Personality and behavioural outcomes in diving: current status and recommendations for future research

This paper provides a brief overview of the shift from studies describing the personality profiles of divers to studies exploring associations between personality variables and diving performance in terms of behavioural outcomes. The personality associations that were investigated include performance during training, panic proneness, diving injuries, susceptibility to inert gas narcosis, and the behaviour of tourist divers. The paper concludes with a number of suggested directions for further research on personality and diving that may provide tangible benefits in terms of both enhanced safety and improved performance underwater.

Physiology Of Drowning: A Review

Drowning physiology relates to two different events: immersion (upper airway above water) and submersion (upper airway under water). Immersion involves integrated cardiorespiratory responses to skin and deep body temperature, including cold shock, physical incapacitation, and hypovolemia, as precursors of collapse and submersion. The physiology of submersion includes fear of drowning, diving response, autonomic conflict, upper airway reflexes, water aspiration and swallowing, emesis, and electrolyte disorders. Submersion outcome is determined by cardiac, pulmonary, and neurological injury. Knowledge of drowning physiology is scarce. Better understanding may identify methods to improve survival, particularly related to hot-water immersion, cold shock, cold-induced physical incapacitation, and fear of drowning.

Field Assessment of Cognitive Performance under Stress

Performance decrements have frequently been reported in combat but it has been difficult to demonstrate the specific causal source of cognitive degradation sufficient to disrupt performance during military operations. In the present study, seventeen infantrymen were assessed during both a one-week simulated combat exercise and a pre-dawn assault. Significant change did not occur during the one week exercise, however simple reaction time did increase following the assault. One planned field assessment occurred at the moment following a potentially serious medical event. A soldier perceived that he was experiencing heatstroke but medical evaluation indicated that he was still “fit for duty”. Cognitive evaluation of his failing state was characterized by slow Simple Response Time and rapid and inaccurate responding on more complex response tasks. Fortunately, the soldier could return to duty but his scores slowly recovered, such that he returned to baseline levels two days later. The present infantry operational environment did not produce significant-information processing change in infantrymen. However, significant performance cognitive decrements followed the specific acute event of assault that was perceived as life-threatening. As we demonstrate, increased reaction time after the assault is consistent with increased fatigue following an extended period in the infantry operating environment.

Cognitive Change in Special Forces Personnel following Stressful Survival Training

Understanding the deterioration in cognitive functioning produced by stress continues to gain in importance due to the increasing demands imposed by technologically sophisticated systems. Although the general deleterious effects of stress are well established, the relative sensitivity of different cognitive functions to stress and the pattern of cognitive recovery with rest have not been fully distinguished. In this paper, we examined the cognitive performance of Special Forces soldiers immediately prior to and immediately following one week of Survival, Evasion, Resistance and Escape (SERE) School training at Ft. Bragg, NC. Post-stress cognitive performance was characterized by significantly increased response time with minimal change in response accuracy. While response time increased for all tasks, memory appears to be most sensitive to stress. Performance returned to pre-stress levels the next morning following one night of sleep. The tasks affected most in the current study differed from changes which follow primarily upon physical stress, implying that the effects of combined psychological and physical stress on cognitive performance differ substantively from the effects of physical demand alone.

Injury survey in scuba divers of British Sub-Aqua Club: A retrospective study

Scuba diving itself is generally known as a safe sports. However, various injury accidents can happen, and the incidences vary depending on divers’ education grade levels about the risks. Therefore, the study set out to identify and analyze the causes and patterns of injuries depending on the divers’ safety education grade levels through a questionnaire survey targeting ocean divers (n=12), sports divers (n=16), and dive leaders (n=15), all of whom belong to the British Sub-Aqua Club. After conducting a frequency analysis on the collected questionnaires, the conclusions are made as follows. First, in terms of diving depth, the most frequent diving depth was 15–20 m among ocean divers, 20–25 m among sports divers, and 15–20 m in case of dive leaders. Second, with regard to the causes of injuries, the most frequently answered causes are ‘overtension’ and ‘low skill’ among ocean divers; ‘low skill’ among sports divers; ‘overaction’ among dive leaders. Third, in terms of injury patterns, the most frequently answered injury patterns are ‘ear’ injuries among ocean divers; ‘ankle’ injuries among sports divers; ‘ankle’ and ‘calf’ injuries among dive leaders. Fourth, with regard to who performed first-aid when an injury accident happened, the most frequent answers are ‘instructor’ among ocean divers; ‘instructor’ and ‘self’ among sports divers; ‘self’ among dive leaders. We might suggest that more efforts need to be made to improve divers’ low dependence on specialists for treatment and consultation so that we can prevent an injury from leading to the second injury accident.

A Brief Note on the Relationship between Anxiety and Performance in Scuba Diving in Adolescents: A Field Study

This study explored the relationship between anxiety and scuba diving performance of young individuals ( N = 44; 16.9yr., SD = 1.2) participating in an introductory scuba diving activity. The question was whether the well-known negative correlation between anxiety and scuba diving performance found for experienced and middle-aged scuba divers will be observed in young participants in their first dive experience. Diving instructors rated standardized scuba diving skills that were correlated with individual state and trait anxiety. There was no relationship between anxiety and scuba diving performance, neither for state nor for trait anxiety. This non-significant correlation between anxiety and performance was in contrast to recent findings observed for experienced divers or those who participated at a scuba diving training program. Considering the differences in methodological design between this study and recent investigations, further research is needed to reveal possible relations between anxiety, scuba diving performance, and panic behavior in beginner-level youth or adults.

The use of Spielberger's State-Trait Personality Inventory (trait anxiety subscale) with naval subaquatic specialists

OBJECTIVES

Panic behavior poses a particular threat to the health and safety of subaquatic occupational specialists. Trait anxiety has previously been identified as a marker of panic behavior under water, and Spielberger's State-Trait Personality Inventory (trait anxiety subscale) has been previously used to measure trait anxiety among subaquatic specialists. Using archived data, the trait anxiety scores of subaquatic specialists were analyzed to meet 3 objectives: 1stly - to develop a trait anxiety profile of subaquatic specialists; 2ndly - to investigate the predictive value of trait anxiety measures upon entering an occupational field; and 3rdly - to establish the reliability of these scores over time.

MATERIAL AND METHODS

Archival trait-anxiety data from 322 subjects were analyzed statistically.

RESULTS

Analysis of the available scores revealed a highly homogenous as well as a very low trait anxiety profile for the investigated occupational group. Additionally, low trait anxiety was somewhat associated with success during specialist training: fewer candidates with high trait anxiety scores completed their qualification. Moreover, measurement of trait anxiety was stable over time, which suggests that when scores for this occupational group are screened, deviations from previous scores could signify a potential need for referral to an intervention from health professionals.

CONCLUSIONS

Using the trait anxiety subscale as part of occupational health surveillance of subaquatic specialists could support prevention of accidents by identifying high-risk candidates during their annual health assessments, and referral for timeous intervention.

Clinical hypnosis with a Little League baseball population: performance enhancement and resolving traumatic experiences

A model for the use of clinical hypnosis with a Little League population was proposed and outlined with dual emphasis: performance enhancement and resolving traumatic experiences. The Performance Enhancement Training Model was developed to enhance performance with this non-patient population. It employed clinical hypnosis to bring to fruition recommendations made by coaches to enhance players' batting proficiency. The second emphasis of the proposed model focused on the resolution of involuntary maladaptive habits secondary to a traumatic experience that impede or compromise optimum performance. Included in this category were detrimental defensive habits "at the plate" after a beaming by a pitch and detrimental defensive habits "on the field" after being hit by a batted ball.

The psychological impact of accidents on recreational divers: a prospective study

OBJECTIVE

The present study aimed to examine the medium and long term psychological impact of diving accidents on the victims (n=52), compared with the impact on two control groups: the victim's diving "buddy" (n=40) who simply witnessed the accident, and a second control from the same boat who did not dive with the victim (n=38).

METHODS

This was a prospective cohort study of the impact of an accident on the victims who attended the Hyperbaric Unit, in comparison with the two control groups. Pre-accident psychological morbidity was assessed using the General Health Questionnaire. Trauma symptoms were assessed using the Revised Impact of Events Scale at 3, 6 and 12 months post accident.

RESULTS

The accident victims endorsed more trauma symptoms and experienced them more intensely and for longer, compared with the two control groups.

CONCLUSION

A significant minority of diving accident victims (between 25% and 50%) continued to suffer from the psychological impact of the accident, some for over a year. This has important implications for their future health care, for their safety on subsequent dives, and for dive training.

Comparison of pulmonary autopsy findings of the rats drowned at surface and 50ft depth

INTRODUCTION

When a body is recovered from the water after a fatal SCUBA diving accident, it is useful to know if the diver was under pressure or not when he/she took his/her last breath, in order to determine the cause and manner of the death. If the victim was under pressure, the air remained in the lungs of the diver will be equal to the environmental pressure. If the body comes to the surface, the air in the lung will expand according to the Boyle's Gas Law and give mechanical damage to the surrounding tissues, due to decreases in environmental pressure. We designed an experimental study to see the difference in pulmonary autopsy findings of the rats that drowned under normobaric and hyperbaric conditions.

METHOD

Forty five male, 250-300 g, Sprague Downey adult rats were divided into three groups. Two groups of rats were drowned under normobaric conditions (Groups DS Group DSS) and the third group at 50 ft pressure (Group DD). The pulmonary autopsy findings of the groups were compared. In the light microscopy, the number of the microscopic fields (x10) containing at least one emphysematous area with longitudinal dimension greater than 300 micro m were compared among the groups.

RESULTS

The gross examination revealed a prominent swelling of the lungs in all rats in the Group DD, in comparison to that of the Groups DS and DSS. The number of the microscopic fields, which included at least one emphysematous area with longitudinal dimension greater than 300 micro m out of 150 fields from each of the groups DS, DSS and DD, were 88, 101 and 115 respectively. The difference between the group DS and DD was found to be statistically significant.

CONCLUSION

We conclude that in investigating the fatal diving accidents, pulmonary autopsy findings give valuable information whether the death occurred at the surface or at the depth.

SCUBA diving for individuals with disabilities

Self-contained underwater breathing apparatus (SCUBA) diving has become an increasingly popular recreational activity, enjoyed by millions of individuals. There has also been a growing interest in SCUBA diving in the disabled population for rehabilitation and recreation. This review discusses medical issues relevant to individuals with disabilities who wish to participate in SCUBA diving. In addition, specialized equipment, adaptations in techniques, and additional precautions will be presented. SCUBA diving can be an enriching experience, potentially helping to improve self-image and quality of life. Knowledgeable healthcare professionals can help to guide their patients who are interested in SCUBA diving.

Epidemiology of non-submersion injuries in aquatic sporting and recreational activities

Although the issues of drowning and near-drowning in aquatic sporting and recreational activities receive considerable attention in the epidemiological literature, there is not a recognised literature on non-submersion injuries occurring in these activities. This review draws together the epidemiological literature on non-submersion injuries and describes the incidence, nature and causes of these injuries, common risk factors, and strategies for prevention. Activities covered by the review include swimming, diving, boating, surf sports, fishing, water polo and water sliding. For most activities there is a dearth of good quality descriptive studies, with most involving cases-series designs and few providing estimates of incidence. Inconsistencies in inclusion criteria and the reporting of incidence rates makes comparisons within and between activities difficult. Incidence rates were identified for most activities and in general the incidence of injury was low, especially for more serious injury. However, some activities were associated with severely disabling injury, such as spinal cord injury (diving) and amputation (from propeller strikes in water skiing and swimming). Only three studies reporting the significance of postulated risk factors were identified. Lack of knowledge about the water being entered and alcohol consumption are significant risk factors in recreational diving; increased blood alcohol concentrations were reported to increase the risk of death in boating; and obesity and tandem riding were reported to increase the risk of injury on public water slides. Few evaluations of preventive measures were identified. Two studies reported reductions in the incidence of water slide injuries following the introduction of design changes and supervision, but neither had a non-intervention comparison group. Improvements in swimming and diving skills were reported in three studies, but these were not designed to measure changes in the risk of injury.This review demonstrates that there is a need for well-designed epidemiological research on non-submersion injury in aquatic sporting and recreational activities. The first priority should be for studies designed to describe accurately the incidence, nature, severity and circumstances of these injuries, followed by research on the significance of postulated risk factors. Once this research has been undertaken, interventions targeted at reducing the incidence of injury in aquatic sporting and recreational activities can be designed and evaluated.

High altitudes, anxiety, and panic attacks: is there a relationship?

People exposed to high altitudes often experience somatic symptoms triggered by hypoxia, such as breathlessness, palpitations, dizziness, headache, and insomnia. Most of the symptoms are identical to those reported in panic attacks or severe anxiety. Potential causal links between adaptation to altitude and anxiety are apparent in all three leading models of panic, namely, hyperventilation (hypoxia leads to hypocapnia), suffocation false alarms (hypoxia counteracted to some extent by hypocapnia), and cognitive misinterpretations (symptoms from hypoxia and hypocapnia interpreted as dangerous). Furthermore, exposure to high altitudes produces respiratory disturbances during sleep in normals similar to those in panic disorder at low altitudes. In spite of these connections and their clinical importance, evidence for precipitation of panic attacks or more gradual increases in anxiety during altitude exposure is meager. We suggest some improvements that could be made in the design of future studies, possible tests of some of the theoretical causal links, and possible treatment applications, such as systematic exposure of panic patients to high altitude.

Diving and marine medicine review part II: diving diseases

Diving is a high-risk sport. There are approximately between 1 to 3 million recreational scuba divers in the USA (with over a quarter-million learning scuba annually); there are about 1 million in Europe and over 50,000 in the United Kingdom. In this population 3-9 deaths/100,000 occur annually in the US alone, and those surviving diving injuries far exceeds this. Diving morbidity can be from near-drowning, from gas bubbles, from barotrauma or from environmental hazards. In reality, the most common cause of death in divers is drowning (60%), followed by pulmonary-related illnesses. The mean number of annual diving fatalities in the USA from 1970 to 1993 was 103.5 (sd 24.0) and the median was 106. This article will focus primarily upon pressure effects on the health of a diver. There are two principle ways pressure can affect us: by direct mechanical effects and by changing the partial pressures of inspired gases. Dysbarism is a general term used to describe pathology from altered environmental pressure, and has two main forms: barotrauma from the uncontrolled expansion of gas within gas-filled body compartments and decompression sickness from too rapid a return to atmospheric pressure after breathing air under increased pressures. Greater than 90% of the human body is either water or bone, which is incompressible; the areas directly affected by pressure changes thus are those that are filled with air or gas. These sites include the middle ear, the eustachian tube, the sinuses, the thorax, and the gastrointestinal tract. Air in these cavities is compressed when the ambient pressure rises because the pressure of inhaled air must equilibrate with the ambient pressure.