Monoplace hyperbaric chamber use of U.S. Navy Table 6: a 20-year experience.

We report a 20-year experience at LDS Hospital, Salt Lake City, UT using the U.S. Navy Treatment Table 6 (TT6) in an oxygen-filled monoplace hyperbaric chamber (1985-2004). Air breathing was provided via a demand regulator fitted with a SCUBA mouthpiece while the patient wore a nose clip. Intubated patients were mechanically ventilated with a Sechrist 500A ventilator, with a modified circuit providing air, when specified. We treated 90 patients: 72 divers (decompression sickness [DCS] = 67, arterial gas embolism [AGE] = 5), 10 hospital-associated AGE, and 8 miscellaneous conditions. They received a total of 118 TT6 (9 TT6 in intubated patients). Ninety-four percent of the TT6 schedules were tolerated and completed. The intolerance rate from two surveyed multiplace chambers was zero and 3% of 100 TT6 schedules each. Failure to complete the TT6 was due to oxygen toxicity (4) and claustrophobia (3). The U.S. Navy TT6 was well tolerated by patients with DCS or AGE treated in monoplace hyperbaric chambers, but tolerance may not be as high as when treated in the multiplace chamber.     

Viewpoint: the type A- and the type B-variants of Decompression Sickness.

BACKGROUND: Symptoms of neurological decompression incidents (DCS/AGE) can be severe or mild. It is unknown if these differences of symptom presentation represent different clinical entities or if they represent just the spectrum of DCS/AGE. METHODS: 267 cases with DCS/AGE were compared retrospectively and classified into two subgroups, the Type A-DCS/AGE for cases with a severe and often stroke-like symptomatology and the Type B-DCS/AGE for those with milder and sometimes even doubtful neurological symptoms. The main outcome measures were the number of hyperbaric treatments (HTs) needed and the clinical outcome. RESULTS: 42 patients with DCS/AGE were classified as Type A- and 225 patients met the criteria for a Type B-DCS/AGE. Patients with Type A-lesions were more severely affected, needed more hyperbaric treatments and had a less favorable outcome than patients with the Type B-variant. CONCLUSIONS: The Type A- and the Type B-DCS/AGE are likely to be different entities with better clinical outcome in the Type B-variant and possibly significant differences in the underlying pathophysiologies of both variants. Future studies with a particular focus on the up to now inadequately investigated Type B-DCS/AGE are necessary to elucidate such differences in the pathophysiology.     

Complement levels before and after dives with a high risk of DCS.

BACKGROUND: Previously, complement activation has been associated with decompression sickness (DCS). However data, both in humans and in animals, are controversial. Hypothesis: Complement activation and depletion occurs after exposure to the hyperbaric environment and is associated with increasing risk of DCS. METHODS: We obtained serological samples from 102 dives (120-300 feet of seawater) with a constant partial pressure of O2 set at 1.3 ATA in thirty-five U.S. Navy diver volunteers. Blood was obtained within one hour of diving and within one hour of surfacing. Plasma was extracted and analyzed for complement depletion. The risk of DCS was estimated using a validated model of DCS risk. RESULTS: Pre-post dive concentrations of C3a were significantly related to estimated risk of DCS (Figure 1), but the variation in predicted DCS explained by C3a was small (correlation co-efficient (r2 = 0.19, p < 0.0001). CONCLUSIONS: There was a reduction in total Ca3 levels in divers after exposure to dives with a high estimated risk of DCS. This decomplementation appeared to increase as the estimated risk of DCS increased.     

Vestibular symptoms and otoneurological findings in retired offshore divers

INTRODUCTION: Inner ear barotraumas and decompression sickness (DCS) may cause acute vestibular symptoms in divers. The result may be irreversible damage to the vestibular end organs or their central connections. We examined a group of offshore divers in order to find out how many divers experience vestibular symptoms later in life and how this was related to occupational history and objective findings. METHODS: A questionnaire was sent to 230 offshore divers (mean age 52 yr) and 166 age-matched non-diving controls. Most of the divers had retired from diving. A subgroup (n=96) of the divers was referred for examination, including a clinical otoneurological examination, electronystagmography, bithermal caloric tests, and platform posturography. In addition, 42 of the controls were examined. RESULTS: The prevalence of dizziness (28%), spinning vertigo (14%), and unsteady gait (25%) was significantly higher in divers than controls (p < 0.0005). These symptoms were strongly associated with a previous history of DCS, particularly type I, which was reported by 61% of the divers. Symptoms were less strongly associated with the number of dives. In referred divers with dizziness, the prevalence of abnormal postural sway, nystagmus, canal paresis, or pathological smooth pursuit was 32%, 9%, 7%, and 11%, respectively. DISCUSSION: Reasons for the high prevalence of vestibular symptoms among the divers are discussed. The high exposure to DCS is probably an important factor.     

Delayed treatment of decompression sickness with short, no-air-break tables: review of 140 cases

INTRODUCTION: Most cases of decompression sickness (DCS) in the U.S. are treated with hyperbaric oxygen using U.S. Navy Treatment Tables 5 and 6, although detailed analysis shows that those tables were based on limited data. We reviewed the development of these protocols and offer an alternative treatment table more suitable for monoplace chambers that has proven effective in the treatment of DCS in patients presenting to our facility. METHODS: We reviewed the outcomes for 140 cases of DCS in civilian divers treated with the shorter tables at our facility from January 1983 through December 2002. RESULTS: Onset of symptoms averaged 9.3 h after surfacing. At presentation, 44% of the patients demonstrated mental aberration. The average delay from onset of symptoms to treatment was 93.5 h; median delay was 48 h. Complete recovery in the total group of 140 patients was 87%. When 30 patients with low probability of DCS were excluded, the recovery rate was 98%. All patients with cerebral symptoms recovered. Patients with the highest severity scores showed a high rate of complete recovery (97.5%). DISCUSSION: Short oxygen treatment tables as originally described by Hart are effective in the treatment of DCS, even with long delays to definitive recompression that often occur among civilian divers presenting to a major Divers Alert Network referral center.     

Altitude decompression sickness symptom resolution during descent to ground level

INTRODUCTION: Altitude decompression sickness (DCS) is a health risk associated with the conduct of high altitude airdrop operations, high altitude reconnaissance, future fighter operations, hypobaric chamber training, unpressurized flight, and extravehicular activity (EVA) in space. The treatment for DCS includes the provision of 100% oxygen (O2) at ground level (GLO) and/or hyperbaric oxygen therapy (HBO). In this paper we examine the effect of repressurization to ground level from hypobaric conditions on DCS symptoms. Timely recompression (descent at first recognition of any DCS symptom) may be a safe, effective treatment for the large majority of DCS symptoms. METHODS: Data from altitude chamber exposures recorded in the Air Force Research Laboratory (AFRL) Altitude DCS Database were reviewed to determine the level of recompression required for complete resolution of 1,699 observed symptoms. RESULTS: Of the 1,699 DCS symptoms reviewed, 66 (3.9%) resolved at altitude, 117 (6.9%) resolved at ground level, and 1,433 (84.3%) resolved during descent. Increasing the pressure by 138 mmHg from the altitude of exposure where symptoms occurred resolved roughly 50% of symptoms. Little resolution of symptoms was noted with recompressions of < 50 mmHg. The greatest rate of symptom resolution occurred with recompressions of 50-250 mmHg. CONCLUSION: These findings support the concept that descent and postflight, ground-level oxygen may be sufficient to relieve the majority of altitude DCS symptoms. HBO may be reserved for serious, recurring, delayed, or refractory symptoms. The findings also suggest a need for further study of DCS symptom resolution.     

Decompression sickness during simulated extravehicular activity: ambulation vs. non-ambulation

BACKGROUND: Extravehicular activity (EVA) is required from the International Space Station on a regular basis. Because of the weightless environment during EVA, physical activity is performed using mostly upper-body movements since the lower body is anchored for stability. The adynamic model (restricted lower-body activity; non-ambulation) was designed to simulate this environment during earthbound studies of decompression sickness (DCS) risk. DCS symptoms during ambulatory (walking) and non-ambulatory high altitude exposure activity were compared. The objective was to determine if symptom incidences during ambulatory and non-ambulatory exposures are comparable and provide analogous estimates of risk under otherwise identical conditions. METHODS: A retrospective analysis was accomplished on DCS symptoms from 2010 ambulatory and 330 non-ambulatory exposures. RESULTS: There was no significant difference between the overall incidence of DCS or joint-pain DCS in the ambulatory (49% and 40%) vs. the non-ambulatory exposures (53% and 36%; p > 0.1). DCS involving joint pain only in the lower body was higher during ambulatory exposures (28%) than non-ambulatory exposures (18%; p < 0.01). Non-ambulatory exposures terminated more frequently with non-joint-pain DCS (17%) or upper-body-only joint pain (18%) as compared with ambulatory exposures, 9% and 11% (p < 0.01), respectively. DISCUSSION: These findings show that lower-body, weight-bearing activity shifts the incidence of joint-pain DCS from the upper body to the lower body without altering the total incidence of DCS or joint-pain DCS. CONCLUSIONS: Use of data from previous and future subject exposures involving ambulatory activity while decompressed appears to be a valid analogue of non-ambulatory activity in determining DCS risk during simulated EVA studies.     

Treatment of decompression sickness in swine with intravenous perfluorocarbon emulsion

BACKGROUND: We examined an adjunctive treatment for severe decompression sickness (DCS) to be used when hyperbaric treatment is delayed or unavailable. HYPOTHESIS: It has been hypothesized that intravenous perfluorocarbon (PFC) emulsion combined with 100% inspired O2 would improve the outcome in severe DCS. METHODS: Swine (n = 45) were compressed to 4.9 ATA on air for 22 h and brought directly to 1 ATA at 0.9 ATA min(-1). The animals were then randomized to three groups. The first group breathed ambient air, the second group breathed 100% O2, and a third group received 6 ml x kg(-1) of perflubron emulsion (Oxygent) intravenously and breathed 100% O2. Outcomes of neurological and cardiopulmonary DCS and death were recorded. RESULTS: Animals that received PFC emulsion sustained less DCS (p < 0.01) than the other groups (53% vs. 93%). No animals in the PFC group sustained neurological DCS, which was present in 69% of the subjects in the other two groups. CONCLUSION: O2 breathing postdive did not significantly reduce morbidity or mortality in this model. Postdive treatment with PFC emulsion and 100% O2 decreased the incidence of DCS after nonstop decompression from saturation.     

Recompression treatment of Red Sea diving accidents: a 23-year summary.

OBJECTIVE: The growing popularity of diving sport has resulted in more diving accidents. Our objective was to characterize Red Sea divers requiring recompression treatment in Eilat, to recognize 23-year trends of diving accidents, and to facilitate appropriate administrative and treatment tools for diving accident in this area. DESIGN: Retrospective, uncontrolled study. SETTING: Recompression unit at a Red Sea medical center. PATIENTS: Charts of all divers treated at Eilat's recompression chamber from October 1976 to December 1999 were reviewed. INTERVENTIONS: Recompression treatment. RESULTS: During this period, annual crude numbers increased 5-fold, and a total of 453 patients were treated. Of them, 68% were Israelis and 32% tourists; 76% were males and 23% females; and 21.6% were diving buddies of injured divers (omitted decompression). The mean diving depth causing the accident was 30.2 +/- 13.1 m, and >50% of accidents occurred between 11 and 30 m. Over 42% suffered from decompression sickness (DCS) type 2, 26% from DCS type 1, and 7% from barotraumas. Women, unlike men, presented predominantly DCS type 2 (54% vs. 39%; P = 0.01) and sustained DCS at shallower waters (25.2 +/- 9.1 m) than men (31.8 +/- 13.8 m; P < 0.0001). Primarily, treatment followed recompression in alternating cycles of oxygen and air as stipulated in US Navy Tables 5 (18.1%) and 6 (37.5%). The 48-hour case fatality rate was 0.09%. CONCLUSIONS: This large survey of open sea diving accidents accentuated the need for a national registry of diving accidents and a national database of diving activities.     

CNS toxicity in closed-circuit oxygen diving: symptoms reported from 2527 dives

INTRODUCTION: Oxygen toxicity is a problem in diving and can have fatal consequences in the water. Various aspects of oxygen diving have been studied in dry hyperbaric chambers, but there is a lack of information on in-water diving using closed-circuit oxygen apparatus. METHOD: We collected 2527 dive reports from 473 closed-circuit oxygen divers (a mean of 5.2 reports per diver), and analyzed the relationships between various symptoms and their dependence on depth and diving time. RESULTS: No CNS oxygen toxicity-related symptoms were reported at a depth of 2 m seawater (msw), but their proportion increased at depths from 3 to 6 msw. We found that CNS oxygen toxicity-related symptoms appeared in 2.5% of dives conducted at a Po2 of 119 kPa. The main symptoms and signs reported were headache: 4.5%; nausea: 2.6%; hyperventilation: 2.6%; heavy breathing: 2.4%; dizziness: 1.6%; hiccups: 1.5%; bloody sputum: 1.4%; cold shivering: 1.1%; tinnitus: 0.9%; difficulty maintaining a steady depth: 0.9%; disorientation: 0.6%; tiredness: 0.5%; tingling in the limbs: 0.4%; hearing disturbances: 0.4%; a choking sensation: 0.4%; extreme effort: 0.4%; and loss of consciousness: 0.3%. DISCUSSION: Environmental factors, light vs. dark and temperature, had no effect on symptoms. The number of symptoms increased with diving time. Divers who experienced amnesia, facial twitching, hearing disturbances (p < 0.001), and disorientation (p < 0.014) were prone to suffer loss of consciousness. It was found that some divers are more sensitive to oxygen than others (p < 0.0001).     

Consensus factors used by experts in the diagnosis of decompression illness

INTRODUCTION: The diagnosis of decompression illness (DCI) is entirely based on clinical findings and DCI experts are rare. Of all the chambers reporting to Diver's Alert Network (DAN), 86% see less than 10 cases per year. Simulated diving injury cases (vignettes) were used to identify diagnostic factors important to 11 international experts attending the 2003 Undersea and Hyperbaric Medical Society symposium on DCI diagnosis. METHODS: There were 200 vignettes evaluated for the probability of DCS and/or arterial gas embolism (AGE). Vignettes were constructed from 141 factors that modeled information from DAN's emergency call system. Factor probability mirrored DAN's 2001 Report on Decompression Illness and Diving Fatalities. Factors included: diver characteristics, exposure characteristics, signs, symptoms, treatment, and response. Multiple linear regression with stepwise elimination identified and ordered the significant factors in terms of their importance to the experts. Results were confirmed with logistic regression. RESULTS: For DCS, the top five factors in order of importance were: 1) a neurological symptom as the primary presenting symptom; 2) onset time of symptoms; 3) joint pain as a presenting symptom; 4) any relief after recompression treatment; and 5) the maximum depth of the last dive. For AGE, the top five factors were: 1) onset time of symptoms; 2) altered consciousness; 3) any neurological symptoms as a presenting symptom; 4) motor weakness; and 5) seizure as the primary presenting symptom. Age, gender, or physical characteristics were not statistically important. CONCLUSIONS: The vignette concept may be useful in the development of consensus standards for DCI diagnosis.     

Prevalence of patent foramen ovale (PFO) and MRI-lesions in mild neurological decompression sickness (type B-DCS/AGE)

BACKGROUND: Neurological decompression sickness (DCS/AGE) may cover two variants with either severer and probably central nervous (Type A) or milder and sometimes doubtful neurological symptoms (Type B). The pathophysiology of the Type B-DCS/AGE might be different from the Type A-variant. In Type A-DCS/AGE a higher PFO-prevalence (patent foramen ovale) points towards an embolic origin of the Type A-symptomatology. This is not necessarily expected for the Type B-DCS/AGE if the pathophysiology here is micro-embolic or even non-embolic. METHODS: 18 patients with Type B-DCS/AGE were tested against matched controls for presence and size of a PFO with echocardiography and transcranial ultrasound with echo-contrast. Prevalence and number of Type A-brain lesions were visualized by cranial MRI as possible sequelae from gas-embolic events. RESULTS: PFO-prevalence in both groups, the patients with Type B-DCS/AGE (5/18) as well as the controls (7/18) was similar to published PFO-prevalences in normals without any difference between patients and controls (p = 0.725). Also the number of MRI-lesions (ACFs) was the same for Type B-DCS/AGE cases (15 ACFs in 5 patients) and controls (37 ACFs in 8 divers). CONCLUSION: Indirect findings suggesting embolic brain injuries are found with similar frequency in patients with Type B-DCS/AGE and normal controls, which is in contrast to data about Type A-DCS/AGE. This is compatible with different pathophysiological mechanisms involved in the Type A- and Type B-DCS/AGE.     

Prophylactic high dose methylprednisolone fails to treat severe decompression sickness in swine

INTRODUCTION: Controlled decompression from saturation conditions is not always an option, particularly in a disabled submarine scenario. Hypothesis Prophylactic high dose methylprednisolone (MP) would improve outcome in severe cases of decompression sickness (DCS). METHODS: Littermate pairs of male Yorkshire swine (n = 86, mean weight +/- SE = 19.3 +/- 0.2 kg) were randomized to one of three groups, then compressed on air to 4.3 ATA (33 msw) for 22 h and brought directly to surface pressure (1 ATA) at 0.9 ATA x min(-1). The MP-50 group received i.v. infusion of 50 mg x kg(-1) of MP dissolved in 60 cc normal saline (NS) immediately prior to the hyperbaric exposure. The NS group received 60 cc NS i.v. immediately prior to the hyperbaric exposure. The MP-10 group received i.v. infusion of 10 mg x kg(-1) MP dissolved in 60 cc NS during the hyperbaric exposure, 7 h before the decompression. RESULTS: Outcomes of severe DCS and death were recorded. NS group: 14 DCS, 4 died; MP-50 group: 19 DCS, 12 died; MP-10 group: 19 DCS, 10 died. Compared with the NS group, logistic regression analysis suggested that animals in the MP-10 group were more likely to get severe DCS and to die (p < 0.01) and animals in the MP-50 group were more likely to die from their disease (p < 0.01). DISCUSSION: Prophylactic high dose MP exerts no protective effect against severe DCS and actually worsens mortality in this model. An earlier group of untreated controls (UC, n = 44, 30 DCS, 11 died, mean weight +/- SE = 19.9 +/- 0.3 kg) exposed to the same profile was also available for analysis. Comparison of the UC and NS animals suggested that pre-dive NS treatment may protect against severe DCS.     

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.     

The relative risk of decompression sickness during and after air travel following diving

BACKGROUND: Decompression sickness (DCS) can be provoked by post-dive flying but few data exist to quantify the risk of different post-dive, preflight surface intervals (PFSI). METHODS: We conducted a case-control study using field data from the Divers Alert Network to evaluate the relative risk of DCS from flying after diving. The PFSI and the maximum depths on the last day of diving (MDLD) were analyzed from 627 recreational dive profiles. The data were divided into quartiles based on surface interval and depth. Injured divers (cases) and uninjured divers (controls) were compared using logistic regression to determine the association of DCS with time and depth while controlling for diver and dive profiles characteristics. These included PFSI, MDLD, gender, height, weight, age, and days of diving. RESULTS: The means (+/-SD) for cases and controls were as follows: PFSI, 20.7 +/- 9.6 h vs. 27.1 +/- 6.7 h; MDLD, 22.5 +/- 14 meters sea water (msw) vs. 19 +/- 11.3 msw; male gender, 60% vs. 70%; weight, 75.8 +/- 18 kg vs. 77.6 +/- 16 kg; height, 173 +/- 16 cm vs. 177 +/- 9 cm; age, 36.8 +/- 10 yr vs. 42.9 +/- 11 yr; diving > or = 3 d, 58% vs. 97%. Relative to flying > 28 h after diving, the odds of DCS (95% CI) were: 1.02 (0.61, 1.7) 24-28 h; 1.84 (1.0, 3.3) 20-24 h; and 8.5 (3.85, 18.9) < 20 h. Relative to a depth of < 14.7 msw, the odds of DCS (95% CI) were: 1.2 (0.6, 1.7) 14.7-18.5 msw; 2.9 (1.65, 5.3) 18.5-26 msw; and 5.5 (2.96, 1 0.0) > 26 msw. CONCLUSIONS: Odds ratios approximate relative risk in rare diseases such as DCS. This study demonstrated an increase in relative risk from flying after diving following shorter PFSIs and/or greater dive depths on the last day. The relative risk increases geometrically as the PFSI becomes smaller.     

Étude prospective sur les accidents de décompression ostéomyoarticulaires en plongée de loisir : leurs facteurs de risque et leur potentiel évolutif en ostéonécrose dysbarique

Objectives

Dysbaric osteonecrosis is a complication that can result from repetitive and prolonged hyperbaric exposures and the correlation with a previous type 1 decompression sickness described as a joint pain remains a controversial subject. The study was designed to determine the risk factors of type 1 decompression sickness in recreational divers and their potential to shortly evolve into osteonecrosis.

Methods

All the osteoarthromuscular decompression sickness treated between October 2004 and November 2005 in one of three hyperbaric centers assigned in the Provence-Alpes-Côte d'Azur region were analyzed in a prospective way of standardized collections, and the majority was explored with MRI in order to screen ischaemic osteomedullar damages.

Results

Eleven cases (8,5%) were inventoried amongst the 129 diving accidents treated during this period. These joint pains were mainly located in the shoulder area (81%) and involved a majority of male experienced divers after performing deep and long dives (90%) furthermore more than 50% of these divers had greater than one dive within a twelve hour period. The average age was 38,5 years with a body mass index of 27,5 kg/m². All dives were performed with a dive computer without omitted decompression. Ten injured divers (90%) were examined by MRI shortly after the accident, but only one diver (10%) had lesions compatible with osteonecrosis.

Conclusion

This preliminary study shows that osteoarthromuscular decompression sickness in recreational diving are essentially involved in dives considered to carry a high risk for bubble production. The conditions of occurence appear also to be related with some individual factors that must be specified in other studies. Nevertheless, the risk of early underlying dysbaric osteonecrosis development is quite low.     

Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops

OBJECTIVES: The French Navy uses the Marine Nationale 90 (MN90) decompression tables for air dives as deep as 60 msw. The resulting incidence of decompression sickness (DCS) for deep dives (45-60 msw) is one case per 3000 dives. METHODS: Three protocols with experimental ascent profiles (EAPs) were tested in the wet compartment of a hyperbaric chamber. For each protocol, eight subjects dove to 50 or 60 msw and ascended according to the standard MN90 table or an EAP. Precordial bubbles were monitored with Doppler sensors at 30-min intervals after surfacing. Protocol I went to 60 msw and used deep stops beginning at 27 msw. Protocol II was a repetitive dive to 50 msw with a 3-h surface interval; the EAP made the first deep stop at 18 msw. Protocol III again went to 60 msw, but the EAP used a single, shorter deep stop at 25 msw. RESULTS: For Protocol I, all divers developed bubbles at Spencer grade 2-3 and still had bubbles 120 min after surfacing; there was no statistical difference between bubbling for the MN90 and EAP, but one diver presented a case of DCS after the EAP. For Protocol II, the EAP produced severe bubbling for the eight divers. Those findings led to stopping the EAPs with the longer deep stops used in Protocols I and II. Protocol III again showed no difference between the standard and modified profiles. DISCUSSION: The addition of deep stops requires careful consideration. Two of our EAPs made no difference and one produced increased bubbling.     

Decompression sickness in women: a possible relationship with the menstrual cycle

BACKGROUND: Women are increasingly participating in recreational scuba diving and the professional roles of women are expanding in the fields of aviation, space, and diving. Evidence exists that there may be a relationship between altitude decompression sickness (DCS) and the menstrual cycle, although diving studies to support such findings are limited. The aim of the present study was to investigate the presence of any relationship between the development of DCS in female sports divers, the phase of the menstrual cycle, and the use of the oral contraceptive pill (OCP). METHOD: Personal, dive, symptom, and menstrual history details were collected by questionnaire from women treated with hyperbaric therapy for DCS in 23 treatment centers worldwide. RESULTS: There were 150 records suitable for analysis. The phase in the menstrual cycle of the DCS incident was estimated. The DCS incidents were unevenly distributed throughout the cycle (p = 0.001) with the greatest percentage of incidents occurring in the first week of the menstrual cycle. The variation in incidence across the cycle appeared to be greatest for the non-OCP users (p = 0.01), and when age was taken into account there was a significant difference between the OCP and non-OCP users with respect to risk of DCS across the menstrual cycle (p = 0.03). CONCLUSION: These data suggest that the risk of DCS may be dependent on the phase of the menstrual cycle and that the distribution of risk differs between OCP and non-OCP users.     

The effect of air and nitrox divings on platelet activation tested by flow cytometry

BACKGROUND: Nitrogen (N2) microbubbles activate the blood platelets and coagulaltion system. HYPOTHESIS: Breathing nitrox rather than air may reduce the level of platelet activation associated with decompression. METHODS: We tested platelet counts and the expression of functional membrane molecules on platelets in 10 divers subjected to saturated compression in nitrox at 4 ATA and in 9 divers subjected to compression in air at 2.8 ATA. Blood samples were taken before and immediately after the test. We measured the percentages of microplatelets, platelet aggregates and platelets bearing the activation marker C-D62P, and bearing molecules forming receptors for fibrinogen (CD61) and for von Willebrand factor (CD42b) using flow cytometry and specific monoclonal antibodies. Symptoms for DCS were also evaluated. RESULTS: DCS symptoms were not noted in either the nitrox or air group. In both groups we observed a marked increase in the percentage of activated platelets bearing CD62P molecules and an enhanced number of microplatelets and a marked drop in the platelets count in the blood of (divers in the air group. CONCLUSION: In all divers we observed certain changes in the platelet system, nevertheless decompression in nitrox resulted in a lesser degree of platelet activation. Though this study cannot exclude platelet activation as an etiological factor in DCS, the findings suggest platelet activation can occur in the absence of observable sign of DCS. Thus, platelet activation may be too sensitive a marker to serve as a predictor of DCS.