Aerobic exercise performance is reduced following prolonged cold-water immersion

Background

We tested the hypotheses that self-paced aerobic exercise performance is reduced following four hours of cold-water immersion when breathing air and further reduced when breathing 100% oxygen (O2). Nine healthy adults (four women; age 24 ± 3 years; body fat 17.9 ± 6.4%; VO2max 48±9 mL • kg • minute⁻¹) completed three visits: a no-immersion control trial and two experimental trials consisting of a four-hour cold-water immersion (20.1±0.3°C) either breathing air (FIO2 = 0.21) or O2 (FIO2 = 1.0). During the no-immersion control trial and following immersion in the experimental trials, subjects first completed a 60-minute ruck-march carrying 20% of body mass in a rucksack, immediately followed by an unweighted, self-paced 5-km time trial on a motorized treadmill. Core temperature, heart rate, and rating of perceived exertion were recorded every 1,000 meters during the 5-km time trial. Data are presented mean± SD. Time trial performance was reduced following immersion in both the 100% O2 trial (32±6 minutes; p=0.01) and air trial (32±5 minutes; p=0.01) compared to the control trial (28± 4 minutes). However, there was no difference between the 100% O2 and air trials (p=0.86). Heart rate, core temperature, and rating of perceived exertion increased during the time trial (time effect: p≺0.01), but were not different between trials (trial effect: p≥0.33). These findings suggest that prolonged cold-water immersion attenuates self-paced aerobic exercise performance, but does not appear to be further affected by breathing gas type.

Does diving deteriorate hearing functions?

Studies evaluating the hearing function of professional divers have yielded mixed results. In this study, we aimed to observe the effect of diving on hearing function by comparing the audiometry of experienced divers with a non-diver control group. Secondly, we aimed to compare the hearing function among divers according to the diving years and the number of dives in terms of diving exposure. Experienced divers who applied to the University of Health Sciences Gűlhane Training and Research Hospital Underwater and Hyperbaric Medicine Department between 2017-2021 for periodic fitness to dive examinations were included in our study. The control group was randomly selected from the non-diver population with similar ages and gender. The audiometry of the control group and the study group was compared. While the control group was found to be better only at 8,000 Hz in the left ear (p = 0.03), there was no difference between the study group and the control group in other frequencies and pure-tone averages. In conclusion, we did not find any evidence regarding the worsening effect of diving on the hearing functions of experienced divers. With the increased awareness of occupational safety in recent years, modern technologies, protective measures, and more conservative diving profiles may have minimized the possible adverse effects of diving on hearing function. Longitudinal studies on hearing functions in the same occupational diver groups should be conducted while observing the effect of different diving profiles and noise exposures.

Incidence of dental barotrauma and temporomandibular joint problems of divers in Turkey

Introduction

In this study, we aimed to examine dental barotrauma and temporomandibular joint (TMJ) complaints in a large group of divers.

Methods

This survey study included scuba divers older than 18. The questionnaire contained 25 questions about the demographic characteristics of divers, dental health behaviors, and diving-related dental, sinus and/or temporomandibular joint pain.

Results

The study group consisted of 287 instructors, recreational and commercial divers (mean age 38.96 years) (79.1% males). A total of 46% of divers reported a frequency of tooth brushing less than twice a day; 28% never receive a routine dental examination; 22.6% experienced dental pain after and/or during diving, mostly in the upper posterior teeth (40%); 17% required dental treatment; 77% of these cases are restoration fracture. TMJ symptoms after diving were statistically significantly higher in women (p=0.04). Jaw and masticatory muscle pain in the morning (p≺0.001) limitation of mouth opening (p=0.04) and joint sounds in daily life (p≺0.001) were recorded as exacerbated after diving; the results were found to be statistically significant.

Conclusion

In our study, the localization of barodontalgia was consistent with the distribution of caries and restored tooth areas in the literature. Dive-related TMJ pain was also more common in those with pre-dive problems such as bruxism and joint noise. Our results are important to remind us of the necessity of preventive dentistry practices and early diagnosis of problems in divers. Divers should take personal precautions, such as brushing their teeth twice a day and avoiding the need for urgent treatment. The use of a personalized mouthpiece is also recommended for divers to prevent dive-related temporomandibular joint diseases.

Cardiovascular risk assessment in divers: Toward safer diving

Similar to aviation, diving is performed in an environment in which acute incapacitation may lead to a fatal outcome. In aeromedicine, a pilot is considered "unfit to fly" when the cardiovascular event risk exceeds one percent per annum, the so-called 1% rule. In diving no formal limits to cardiovascular risk have been established. Cardiovascular risk of divers can be calculated using the modified Canadian Cardiovascular Society (CCS) Risk of Harm formula: risk of harm (RH: cardiovascular fatality rate per year during diving: number × 10-⁵/divers/year) = time diving (TD: number of dives × 10-⁴) × sudden cardiac incapacitation (SCI: cardiovascular diver event rate per year (number × 10-⁵/year). The SCI and thus the RH are strongly dependent on age. Using the CCS criterion for RH, 5 × 10-⁵ divers/year, and considering an average of 25 dives per year per diver, the calculated maximum acceptable SCI is 2%/year, consistent with current practice for dive medical examinations. If the SCI were to exceed 2%/year, a diver could be considered "unfit to dive," which could particularly benefit older (≥ 50 years) divers, in whom cardiovascular risk factors are often not properly treated. For the prevention of fatal diving accidents due to atherosclerotic cardiovascular disease, a dive medical examination is of limited value for young (≺ 50 years) divers who have no cardiovascular risk factors. Introducing a cardiovascular risk management system for divers may achieve a reduction in fatal diving accidents that result from cardiovascular disease in older divers engaged in both recreational and professional diving.

Unique challenges in naval military dentistry

Divers are regularly exposed to a unique and changing environment that dentists must consider when treating such patients. This review focuses around two case studies encountered in naval dentistry: (i) diving barotrauma (pressure-induced injury related to an air space); and (ii) scuba diving mouthpiece-related oral conditions. Each condition is described by its effect on the oral cavity and in particular the teeth. Then we generally review the latest literature on the different effects of scuba diving on the diver's head, face and oral regions and emphasize methods of dental disease prevention, diagnostic tools and treatment guidelines.

Hyperoxic exposure monitoring in diving: A farewell to the UPTD

Depending on pO2 and exposure time hyperoxic breathing gas may cause injury in many organs including the lungs. Pulmonary oxygen toxicity (POT) may be asymptomatic, but will initially present as a tracheobronchitis in symptomatic subjects. A number of objective measurements of POT have been investigated, but the decrement in vital capacity (VC) has remained the most accepted outcome measure. The unit pulmonary toxic dose (UPTD) has been established as the most common exposure index for POT in diving. UPTD is calculated based on the pO2 and exposure time. A literature search identified five models predicting POT, but no model would accurately predict VC change for the full range of pO2 variation and exposure time relevant for surface-oriented diving. Nevertheless, compared to UPTD, the K-index (K = t2*pO24.57, where t = time (hours) and pO2 = inspired pO2 (atm)) suggested by Arieli performed better for pO2 > 150 kPa and allowed estimation of recovery. We recommend that the Arieli K-index should replace UPTD as the POT exposure index for all surface-oriented diving. Based on the limited data available we suggest a daily threshold of K = 120 for a maximum of two diving days followed by two days of recovery. For five consecutive days of diving, we recommend that the threshold should not exceed K=70 and two recovery days should be allowed. For multiday diving without days of recovery, the daily exposure should probably be limited to K = 40-50.

Acclimatization to diving: a systematic review

Multiday hyperbaric exposure has been shown to reduce the incidence of decompression sickness (DCS) of compressed-air workers. This effect, termed acclimatization, has been addressed in a number of studies, but no comprehensive review has been published. This systematic review reports the findings of a literature search. PubMed, Ovid Embase, The Cochrane Library and Rubicon Research Repository were searched for studies reporting DCS incidence, venous gas embolism (VGE) or subjective health reports after multiday hyperbaric exposure in man and experimental animals. Twenty-nine studies fulfilled inclusion criteria. Three epidemiological studies reported statistically significant acclimatization to DCS in compressed-air workers after multiday hyperbaric exposure. One experimental study observed less itching after standardized simulated dives. Two human experimental studies reported lower DCS incidence after multiday immersed diving. Acclimatization to DCS has been observed in six animal species. Multiday diving had less consistent effect on VGE after hyperbaric exposure in man. Four studies observed acclimatization while no statistically significant acclimatization was reported in the remaining eight studies. A questionnaire study did not report any change in self-perceived health after multiday diving. This systematic review has not identified any study suggesting a sensitizing effect of multiday diving, and there is a lack of data supporting benefit of a day off diving after a certain number of consecutive diving days. The results suggest that multiday hyperbaric exposure probably will have an acclimatizing effect and protects from DCS. The mechanisms causing acclimatization, extent of protection and optimal procedure for acclimatization has been insufficiently investigated.

Nitric oxide in exhaled gas and tetrahydrobiopterin in plasma after exposure to hyperoxia

The fraction of nitric oxide in exhaled gas (FENO) is decreased after exposure to hyperoxia in vivo, although the mechanisms for this decrease is not clear. A key co-factor for nitric oxide synthase (NOS), tetrahydrobiopterin (BH4), has been shown to be oxidized in vitro when exposed to hyperoxia. We hypothesized that the decrease of FENO is due to decreased enzymatic generation of NO due to oxidation of BH4. The present study was performed to investigate the relationship between levels of FENO and plasma BH4 following hyperoxic exposure in humans. Two groups of healthy subjects were exposed to 100% oxygen for 90 minutes. FENO was measured before and 10 minutes (n = 13) or 60 minutes (n = 14) after the exposure. Blood samples were collected at the same time points for quantification of biopterin levels (BH4, BH2 and B) using LC-MS/MS. Each subject was his or her own control, breathing air for 90 minutes on a separate day. Hyperoxia resulted in a 28.6 % decrease in FENO 10 minutes after exposure (p < 0.001), confirming previous findings. Moreover, hyperoxia also caused a 14.2% decrease in plasma BH4 (p = 0.012). No significant differences were observed in the group measured 60 minutes after exposure. No significant correlation was found between the changes in FENO and BH4 after the hyperoxic exposure (r = 0.052, p = 0.795), this might be due to the recovery of BH4 being faster than the recovery of FENO.

Inner ear decompression sickness in Finland: a retrospective 20-year multicenter study

INTRODUCTION

Inner ear decompression sickness (IEDCS) is a condition from which only a minority of patients recover completely, the majority ending up with mild to moderate residual symptoms. IEDCS has been reported after deep technical dives using mixed breathing gases, and moderate recreational dives with compressed air as the breathing gas. Considering this and the high proportion of technical diving in Finland, a comparison between IEDCS cases resulting from technical and recreational dives is warranted.

METHODS

This is a retrospective examination of IEDCS patients treated at Hyperbaric Center Medioxygen or National Hyperbaric Centre of Turku University Hospital from 1999 to 2018. Patients were included if presenting with hearing loss, tinnitus, or vertigo and excluded if presenting only with symptoms of middle ear or cerebellar involvement. Patients were divided into technical and recreational divers, based on incident dive.

RESULTS

A total of 89 (15.6%) of all DCS patients presented with IEDCS, two-thirds treated during the latter decade. The most common predisposing factors were consecutive days of diving (47.2%), multiple dives per day (53.9%), and factors related to an increase in intrathoracic pressure (27.0%). The symptoms were cochlear in 19.1% and vestibular in 93.3% of cases, symptoms being more common and severe in technical divers. Complete recovery was achieved in 64.5% of technical and 71.4% of recreational divers.

CONCLUSION

The incidence of IEDCS in Finland is increasing, most likely due to changing diving practices. A comprehensive examination should be carried out after an incident of IEDCS in all cases, irrespective of clinical recovery.

Acclimatization to diving: a systematic review

Multiday hyperbaric exposure has been shown to reduce the incidence of decompression sickness (DCS) of compressed-air workers. This effect, termed acclimatization, has been addressed in a number of studies, but no comprehensive review has been published. This systematic review reports the findings of a literature search. PubMed, Ovid Embase, The Cochrane Library and Rubicon Research Repository were searched for studies reporting DCS incidence, venous gas embolism (VGE) or subjective health reports after multiday hyperbaric exposure in man and experimental animals. Twenty-nine studies fulfilled inclusion criteria. Three epidemiological studies reported statistically significant acclimatization to DCS in compressed-air workers after multiday hyperbaric exposure. One experimental study observed less itching after standardized simulated dives. Two human experimental studies reported lower DCS incidence after multiday immersed diving. Acclimatization to DCS has been observed in six animal species. Multiday diving had less consistent effect on VGE after hyperbaric exposure in man. Four studies observed acclimatization while no statistically significant acclimatization was reported in the remaining eight studies. A questionnaire study did not report any change in self-perceived health after multiday diving. This systematic review has not identified any study suggesting a sensitizing effect of multiday diving, and there is a lack of data supporting benefit of a day off diving after a certain number of consecutive diving days. The results suggest that multiday hyperbaric exposure probably will have an acclimatizing effect and protects from DCS. The mechanisms causing acclimatization, extent of protection and optimal procedure for acclimatization has been insufficiently investigated.

Nitric oxide in exhaled gas and tetrahydrobiopterin in plasma after exposure to hyperoxia

The fraction of nitric oxide in exhaled gas (FENO) is decreased after exposure to hyperoxia in vivo, although the mechanisms for this decrease is not clear. A key co-factor for nitric oxide synthase (NOS), tetrahydrobiopterin (BH4), has been shown to be oxidized in vitro when exposed to hyperoxia. We hypothesized that the decrease of FENO is due to decreased enzymatic generation of NO due to oxidation of BH4. The present study was performed to investigate the relationship between levels of FENO and plasma BH4 following hyperoxic exposure in humans. Two groups of healthy subjects were exposed to 100% oxygen for 90 minutes. FENO was measured before and 10 minutes (n = 13) or 60 minutes (n = 14) after the exposure. Blood samples were collected at the same time points for quantification of biopterin levels (BH4, BH2 and B) using LC-MS/MS. Each subject was his or her own control, breathing air for 90 minutes on a separate day. Hyperoxia resulted in a 28.6 % decrease in FENO 10 minutes after exposure (p < 0.001), confirming previous findings. Moreover, hyperoxia also caused a 14.2% decrease in plasma BH4 (p = 0.012). No significant differences were observed in the group measured 60 minutes after exposure. No significant correlation was found between the changes in FENO and BH4 after the hyperoxic exposure (r = 0.052, p = 0.795), this might be due to the recovery of BH4 being faster than the recovery of FENO.

Pulmonary fluid shifts occur as a result of scuba diving at NASA's Neutral Buoyancy Lab

INTRODUCTION

Pulmonary fluid shifts can occur while scuba diving. Such shifts, generally thought to be rare, may result in a life-threatening phenomenon known as immersion pulmonary edema (IPE). This study aims to better classify the normal physiology of diving using ultrasound (US) to determine if these fluid shifts occur routinely during commercial diving work at the NASA Neutral Buoyancy Laboratory (NBL).

METHODS

Chest US was performed on commercial divers prospectively pre- and post-dive to evaluate the presence of B-lines in a total of 12 intercostal points on the anterior, posterior, and lateral chest wall. The number of B-lines at each anatomic site was recorded and scored by two independent reviewers. An increase in the number of B-lines post-dive was considered a positive result.

RESULTS

There were 67 exposures; 39 (58%) had an increase of one or more B-lines post dive; 64% of the female exposures and 57% of the male exposures were positive for B-lines post-dive, suggesting no difference across gender (Fisher's exact; p = 0.763). After the dive, all divers remained asymptomatic.

CONCLUSION

From our results, fluid shifts can be viewed as a normal, transient, and physiologic process in commercial divers. This correlation can be compared to the formation of low-grade venous gas emboli (VGE) from decompression that does not result in decompression sickness. Further study of US B-lines in symptomatic divers may define the utility of field US in the diagnosis and management of IPE, and help identify associated risk factors.

Whole-body active heating does not preserve finger temperature or manual dexterity during cold-water immersion

BACKGROUND

Cold-water immersion impairs manual dexterity when finger temperature is below 15°C. This exposes divers to increased risk of error. We hypothesized that whole-body active heating would maintain finger temperatures and dexterity during cold-water immersion.

METHODS

Twelve subjects (six males) (22 ± 2 years old; BMI 23.9 ± 2.5; body fat 16 ± 6%) completed 60-minute head-out water immersion (HOWI) wearing a 7mm wetsuit and 3mm gloves in thermoneutral water (TN 25°C) and cold water (CW 10°C) while wearing a water-perfused suit (WP) with 37°C water circulated over the torso, arms, and legs. Gross (Minnesota Manual Dexterity Test [MMDT]) and fine (modified Purdue Pegboard [PPT]) dexterity were assessed before, during and after immersion. Core body and skin temperatures were recorded every 10 minutes.

RESULTS

MMDT (TN -25 ± 14%; CW -72 ± 23%; WP -67 ± 29%; p<0.05) and PPT (TN -16 ± 9%; CW: -45 ± 10%; WP: -38 ± 13%; p<0.05) performance decreased during immersion. MMDT and PPT did not differ between CW and WP. Immediately following immersion gross dexterity was recovered in all conditions. Post-immersion fine dexterity was still impaired in CW (p<0.01), but not WP or TN. Core and skin temperatures decreased during immersion in CW and WP (p<0.05) but did not differ between CW and WP.

CONCLUSION

Manual dexterity decreased during immersion. Dexterity was further impaired during cold-water immersion and was not maintained by water perfusion active heating. Warm water perfusion did not maintain finger temperature above 15°C but hand temperature remained above these limits, suggesting a need to reassess thermal thresholds for working divers in cold-water conditions.

Hyperoxic myopia: a case series of four divers

Hyperoxic myopia is a phenomenon reported in individuals who have prolonged exposure to an increased partial pressure of oxygen (PO2) and subsequently have a myopic (nearsighted) change in their vision. To date, there are numerous accounts of hyperoxic myopia in dry hyperbaric oxygen treatment patients; however, there have been only three confirmed cases reported in wet divers. This case series adds four confirmed cases of hyperoxic myopia in wet divers using 1.35 atmospheres (ATM) PO2 at the Navy Experimental Diving Unit (NEDU). The four divers involved were the first author's patients at NEDU. Conditions for two divers were confirmed via record review, whereas the other two divers were diagnosed by the first author. All subjects were interviewed to correlate subjective data with objective findings. Each subject completed five consecutive six-hour hyperoxic (PO2 of 1.35 ATM) dives with 18-hour surface intervals. Each individual was within the U. S. Navy Dive Manual's standards for general health. Visual acuity was measured prior to diving. Within three to four days after diving, the individuals reported blurry vision with an associated myopic refraction shift. Each diver had spontaneous resolution of his myopia over the next two to three weeks, with no significant residual symptoms. The divers in this case series were exposed to an increased PO2 (1.35 ATM for 30 hours over five days), a lesser exposure than that in other reports of hyperoxic myopia in wet divers diagnosed with hyperoxic myopia (1.3-1.6 ATM for 45-85 hours in 12-18 days). Furthermore, this pulse of exposure was more concentrated than typically seen with traditional hyperbaric oxygen therapy. Hyperoxic myopia continues to be a risk for those conducting intensive diving with a PO2 between 1.3-1.6 ATM. Additional investigation is warranted to better define risk factors and PO2 limits regarding ocular oxygen toxicity.

Carbon monoxide poisoning while scuba diving: a rare event?

Contamination of breathing gas is a risk for all divers. Some hydrocarbon contaminants will be sensed by the diver and the dive profile aborted. On the contrary, carbon monoxide may not be recognized by the diver and catastrophic consequences can result. Reported here is the fatal case of carbon monoxide poisoning while scuba diving, an event that has rarely been reported in the medical literature. A detailed review of other published cases of CO poisoning while scuba diving is included, attempting to identify causes in common and propose methods of prevention.

Proposal of a new scoring system for equalization problems during freediving

OBJECTIVE

Scuba diving and freediving are popular activities around the world, and their growth has increased the frequency of related pathology. A good ability to equalize is of paramount importance for diving. This is especially true for freediving, during which dive time is limited to just one breath. Even though equalization disorders are quite common in divers, a scoring system does not exist to date. In this paper we propose a new scoring system for equalization problems of freedivers: the EP score, shorthand for "equalization problems."

METHODS

We administered the EP score assessment to 40 Italian freediving spearfishermen who were divided in two groups: Group A comprised 20 freedivers complaining of equalization problems and multiple barotraumas but totally asymptomatic in their everyday lives. These individuals had already received medical treatment and nasal surgery without improvement and then had undergone Eustachian tube balloon dilation. Group B comprised 20 healthy freedivers without any history of equalization disorders. We performed a statistical analysis to evaluate the reliability of this scoring system and to evaluate its usefulness in diagnosis and follow-up.

RESULTS

Our data show substantial statistical differences between healthy freedivers and freedivers complaining of equalization disorders (Z-Score = -5.396 at p ⟨ 0.05); data do not show any statistical difference between healthy freedivers and patients successfully treated by Eustachian tube balloon dilation (U-value = 152.5 and Z-Score= -1.271 at p ⟨ 0.05).

CONCLUSION

The EP score assessment seems to be a reliable tool to quantify equalization disorders during freediving and to evaluate how the difficulty varies over time and after treatment. Since equalization disorders could be present in different populations, the EP score assessment could be applicable to a wider group.

Comparison of argon and air as thermal insulating gases in drysuit dives during military Arctic diving equipment development tests

INTRODUCTION

It is vital to protect divers from the cold, particularly in Arctic conditions. The insulating gas layer within the drysuit is crucial for reducing heat loss. The technical diving community has long claimed the superiority of argon over air as an insulating gas. Although argon is widely used, previous studies have shown no significant differences between the two gases. Owing to its lower heat conductivity, argon should be a better thermal insulating gas than air.

METHODS

The study aimed to determine whether argon is beneficial for reducing heat loss in divers during development of military drysuit diving equipment in Arctic water temperatures. Four divers completed 14 dives, each lasting 45 minutes: seven dives used air insulation and seven used argon insulation. Rectal and eight skin temperatures were measured from which changes in calculated mean body temperature (MBT) were assessed.

RESULTS

There was a significant reduction in area weighted skin temperature over time (0-45 minute) on air dives (ΔTskin = -4.16°C, SE = 0.445, P ⟨ 0.001). On argon dives the reduction was significantly smaller compared to air dives (difference between groups = 2.26°C, SE = 0.358, P ⟨ 0.001). There were no significant changes in rectal temperatures, nor was a significant difference seen between groups.

CONCLUSION

Compared to air, argon may be superior as a drysuit insulating gas in Arctic water temperatures for some divers. Argon used as insulating gas can make diving safer and may diminish the risks of fatal diving accidents and occupational hazard risks in professional diving.

Arrhythmogenicity of scuba diving: Holter monitoring in a hyperbaric environment

INTRODUCTION

About 26% of diving-related fatalities are caused by cardiac disease, part of which might be associated with fatal arrhythmias. This raises the question as to whether fatal arrhythmias are being provoked by hyperbaric conditions themselves or if exercise or stress provokes the fatal arrhythmias in cases of underlying (ischemic) cardiac disease.

OBJECTIVE

To measure the influence of hyperbaric conditions (50 msw) on cardiac conduction and arrhythmias in professional divers by means of ECG.

METHODS

This is a prospective study on military divers in a hyperbaric chamber with continuous ECG monitoring using Holter registrations. Supraventricular and ventricular ectopy was registered during hyperbaric conditions. RR, PR, QRS, QT and QTc intervals were calculated at 50 msw and compared with ECGs at rest.

RESULTS

Included were 17 male military divers who made 20 dives. A total of 10 PVCs, 45 PACs, four atrial runs and four atrial pairs were seen. Significant prolongation of the PR interval was seen and a decrease of in QRS duration at 50 msw. There was no significant change in the RR, QT and QTc intervals.

CONCLUSION

In these divers, no clinically relevant arrhythmias were observed during wet dives in a recompression chamber at 50 msw. We observed a small prolongation of PR interval that is probably not clinically relevant in divers without any known conduction disorders.

Hyperoxia and lack of ascorbic acid deplete tetrahydrobiopterin without affecting NO generation in endothelial cells

Nitric oxide (NO) may protect against gas bubble formation and risk of decompression sickness. We have previously shown that the crucial co-factor tetrahydrobiopterin (BH4) is oxidized in a dose-dependent manner when exposed to hyperoxia similar to diving conditions but with minor effects on the NO production by nitric oxide synthase. By manipulating the intracellular redox state, we further investigated the relationship between BH4 levels and production of NO in human endothelial cells (HUVECs). HUVECs were cultured with and without ascorbic acid (AA) and the glutathione (GSH) synthesis inhibitor buthionine sulfoximine, prior to hyperoxic exposure. The levels of biopterins and GSH were determined in cell lysates while the production of NO was determined in intact cells. Omitting AA resulted in a 91% decrease in BH4 levels (0.49 ± 0.08 to 0.04 ± 0.01 pmol/10⁶ cells, p⟨0.001) at 20 kPa oxygen (O2), and 88% decrease (0.24 ± 0.03 to 0.03 ± 0.01 pmol/10⁶ cells, p=0.01) after exposure to 60 kPa O2. The NO generation was decreased by 23% (74.5 ± 2.2 to 57.3 ± 5.6 pmol/min/mg protein, p⟨0.001) at 20 kPa O2, but no significant change was observed at 60 kPa O2. GSH depletion had no effects on the NO generation. No correlation was found between NO generation and the corresponding intracellular BH4 concentration (p=0.675, r=-0.055) or the BH4 to BH2 ratio (p=0.983, r=0.003), determined across 18 in vitro experiments. Decreased BH4 in HUVECs, due to hyperoxia or lack of ascorbic acid, does not imply corresponding decreases in NO generation.

Cold water submersion attenuates post-submersion aerobic performance and orthostatic tolerance irrespective of partial rehydration with water

PURPOSE

This study examined the independent effects of cold-water submersion and a rehydration strategy on an aerobic endurance performance and orthostatic tolerance following a four-hour dive in cold water (10°C).

METHODS

Nine male subjects completed a control (CON) performance and lower-body negative pressure test (LBNP) and two water immersion visits with either no rehydration (NR) or a post-immersion rehydration (RH) with 1 L of water. Following submersion, subjects ran to exhaustion and submitted to LBNP.

RESULTS

Core body temperature declined during submersion and remained reduced from baseline until the run (P ⟨ 0.001) and was not different between NR and RH (P = 0.13). Total urine output during submersion was not different between groups (1.69 ± 0.49 (NR), 1.75 ± 0.52 (RH) L; P = 0.74) eliciting a body mass reduction of -2.2 ± 0.3 and -0.8 ±; 0.3% (P ⟨ 0.01), respectively. Run duration was not different (547 ± 141 (NR), 566 ± 152 (RH) s; P = 0.79); however, both NR and RH run duration was shorter compared to CON (722 ± 170 s; P = 0.04). Cumulative stress index was suppressed in NR (534 ± 163 mmHg*min) and RH (591 ± 129 mmHg*min) compared to CON (707 ± 170 mmHg*min, P V#8804; 0.03), with no differences between submersion trials (P = 0.23).

CONCLUSION

Compared to a non-submersed state, run duration and orthostatic tolerance was reduced following a four-hour cold-water submersion. Rehydration with 1 L of water following submersion did not offer a performance advantage over no rehydration.

Understanding dive behavior of artisanal fishermen divers of the Yucatán Peninsula

INTRODUCTION/BACKGROUND

Artisanal fishermen dive for sustenance. The lifetime prevalence of decompression sickness (DCS) in this population is alarmingly high. We wanted to understand the level of decompression stress fishermen in this region of the Yucatán experience in their daily fishing effort. We used a mathematical model to quantify nitrogen-loading in a nine-tissue compartment model.

MATERIALS AND METHODS

Approved by the UCLA IRB 2 #13-000532, this study was conducted during fishing seasons 2012 through 2017. Diving fishermen were instructed to attach dive recorders to their waists every fishing day during the study period. Sensus Ultra dive recorders (ReefNet Inc.), with an accuracy of ±1 foot of seawater (fsw), 0.304 meters, and an activation depth of 10 fsw, 3.04 meters, were used to record dive parameters. Sampling interval was set to 10 seconds. A program in RStudio was created to extract the dive profiles of each fishing day and curtail into single-line outputs: pressure, time, date, start of dive and end of dive. An exponential decay formula was used to calculate the nitrogen-loading pressures for nine theoretical tissue compartments. Final nitrogen pressure, controlling compartments, decompression stop and time at stop were calculated.

RESULTS

Fishermen completed 4,961 dives over 1,758 diving days during the study period. The 40-minute compartment controlled most of the dives. The 80-minute compartment controlled 5%-20% of dives two through five. Decompression stop times for the last dive ranged from one minute to 190 minutes. Most of the required stop time observed was seen at depths of 1-15 fsw.

Updates in diving medicine: evidence published in 2017-2018

This report summarizes some of the most relevant studies during the 2017-2018 academic year of scientific literature for diving medicine. The article selection is the result of a PubMed search for "diving," as well as a manual review of the journals Undersea and Hyperbaric Medicine and Diving and Hyperbaric Medicine. Four articles were published reporting on new advances in decompression modeling. New consensus guidelines in the prehospital treatment of decompression sickness were published as well as a retrospective review of the efficacy of the U.S. Navy Treatment Tables. Several articles were published this year researching cardiovascular health and fitness to dive. A novel approach by one occupational medicine clinic for referral for hypertension may allow for early intervention of the "silent killer." Application of the Framingham risk score to commercial divers does not result in an excessive number of disqualifications. The controversy over screening and subsequent repair of a patent foramen ovale in divers was heavily researched this past year. Several groups reported their experience with closure and associated risks. Subjects diving with pre-existing conditions were surveyed and found to be fairly common, with seemingly little ill effect (albeit with a potential survivor bias). Recommendations for diving while using antidepressants were reported. Several articles were published utilizing point of care ultrasound in the diagnosis of immersion pulmonary edema (IPE). One case of a using sildenafil as a preventative medication in a triathlete with an extensive history of IPE may prove promising for further research. Finally, an extensive review article pertaining to hypercapnia in diving was published as well as the use of pulse oximetry as an early warning system to prevent hypoxia in rebreather divers.

Fatty acids and sphingolipids profile in the blood plasma of experienced divers in response to hyperbaric exposure

INTRODUCTION

Hyperbaric exposure mimics air-breathing scuba diving, which is reaching enormous popularity around the world. The diver's body is subjected to a broad range of divergent effects exerted by, e.g.: an increased partial pressure of inert gases, microclotting, oxidative stress and/or production of gas bubbles. However, very little is known regarding the impact of hyperbaric exposure on plasma fatty acids content and composition, together with the body's sphingolipids profile.

MATERIAL AND METHODS

The aim of this study was to investigate the contents of major fatty acids present in the plasma as well as sphingolipids, namely: sphingosine (SPH); sphingosine-1-phosphate (S1P); sphinganine (SPA); and ceramide (CER), after hyperbaric exposure corresponding to dives conducted to the depths of 30 and 60 meters of seawater. For the plasma lipids measurements, high-performance liquid chromatography together with gas-liquid chromatography were applied.

RESULTS

We demonstrated that hyperbaric exposure does not affect the content and composition of plasma fatty acids of experienced divers. Similarly, the amounts of major sphingolipids fractions were not influenced, as only the content of sphingosine-1-phosphate in the plasma was significantly decreased.

CONCLUSIONS

Observed lack of significant changes in plasma lipid profile after hyperbaric exposure suggests that the procedure might be considered as secure. However, decreased sphingosine-1-phosphate content in the plasma might possibly exert some adverse effects.

Effect of rehydration schedule after four-hour head-out water immersion on running performance and recovery

INTRODUCTION

Head-out water immersion (HOWI) results in diuresis, which could potentially limit performance after egress to land. We examined the effect of rehydration on endurance, cardiovascular stability, and overnight recovery following a four-hour thermoneutral HOWI on 12 subjects.

METHODS

Twelve males completed a crossover design consisting of no hydration, replacement of fluid loss during immersion (RD), and replacement of fluid after the immersion period (RA). Sixty minutes following immersion, subjects ran to exhaustion at ~80% maximum heart rate. After completing the run, each subject submitted to a head-up tilt test (HUTT). Vital signs and ECG were monitored overnight.

RESULTS

HOWI resulted in a transient diuresis in NH and RA, while it was sustained throughout immersion in the RD protocol, resulting in greater urine [l] output (1.27 ± 0.48 (NH), 1.18 ± 0.43 (RA), 2.32 ± 0.77 (RD) (p ⟨ 0.001). Body mass change (%) was greater in NH than RD, but not RA (-1.58 ± 0.56 (NH), -0.66 ± 0.47 (RD), and -0.92 ± 0.76 (RA)). Run times were 17% versus 20% in NH compared to RD and RA, respectively, but were not statistically different. Time to orthostasis during the HUTT did not differ by condition. Overnight heart rate variability and blood pressures were not different.

CONCLUSION

Rehydration during water immersion resulted in a large, sustained diuresis without improving performance or recovery after exiting the water. Loss of body water during thermoneutral HOWI was modest, and both rehydration strategies minimally affected aerobic performance and overnight recovery in young, healthy males.

The panic triangle: onset of panic in scuba divers

Panic arising from physical or psychological stress is a common issue in reported incidents and accidents in scuba diving. Due to its effect on perception, thinking and diver behavior, the panic reaction is often a significant factor in the generation or escalation of problems, potentially leading to injuries and fatalities. The instinctive behaviors associated with panic are incompatible with the constraints of scuba diving (e.g., flight response to threat, leading to rapid ascent). Although the dangers are well known, the psychological mechanisms of panic and the implications for prevention/risk reduction are not sufficiently highlighted to recreational divers. In applied psychology, there are grounded theoretical models which describe the onset and maintenance of anxiety and panic, and an evidence base for approaches to anxiety management. For example, these models are used within structured psychological approaches for people experiencing anxiety disorders; and panic attacks are resolvable. Based on these models and underlying theory, this article proposes a new, accessible model for panic in divers. The potential uses of the model are to: (1) provide a simple framework for divers to understand the onset of panic; (2) promote the need for adequate training; (3) describe the importance of staying within training standards, qualifications and personal limitations; (4) support diver and dive educator understanding of individual factors in panic reactions (e.g. psychiatric conditions) placing greater emphasis on psychological fitness to dive; and (5) draw attention to approaches to improved regulation of emotion and promote individual responsibility.

Can my patient dive after a first episode of primary spontaneous pneumothorax? A systematic review of the literature

INTRODUCTION

Patients with prior primary spontaneous pneumothorax (PSP) frequently seek clearance to dive. Despite wide consensus in precluding compressed-air diving in this population, there is a paucity of data to support this decision. We reviewed the literature reporting the risk of PSP recurrence.

METHODS

A literature search was performed in PubMed and Web of Science using predefined terms. Studies published in English reporting the recurrence rate after a first PSP were included.

RESULTS

Forty studies (n=3,904) were included. Risk of PSP recurrence ranged 0-67% (22 ± 15.5%; mean ± SD). Mean follow-up was 36 months, and 63 ± 39% of recurrences occurred during the first year of follow-up. Elevated height/weight ratio and emphysema-like changes (ELCs) are associated with PSP recurrence. ELCs are present in 59%-89% (vs. 0-15%) of patients with recurrence and can be detected effectively with high-resolution CT scan (sensitivity of 84-88%). Surgical pleurodesis reduces the risk of recurrence substantially (4.0 ± 4% vs. 22 ± 15.5%).

CONCLUSION2

Risk of PSP recurrence seems to decline over time and is associated to certain radiological and clinical risk factors. This could be incremented by the stresses of compressed-air diving. A basis for informed patient-physician discussions regarding future diving is provided in this review.

Cervicocranial artery dissection and scuba diving: Is there a link or is it serendipity?

INTRODUCTION

Numerous reports have documented cervicocranial artery dissection (CCAD) associated with scuba diving. The question remains as to whether there are risk factors unique to scuba diving related to the occurrence of CCAD.

OBJECTIVES

This article aims to perform an examination of the reported cases to demonstrate any commonality among the injured divers and association with known risk factors for CCAD.

METHODS

A PubMed search was performed utilizing the key words: carotid artery dissection, dissection, arterial dissection, cranial artery dissection, scuba, diving, scuba diving. Articles including reports, reviews, trials, case series, and letters were considered. Each report was critically dissected for information specific to the dive itself and the diver and analyzed for similarities and consistency with known risks.

RESULTS

Twelve (12) reports of CCAD associated with scuba diving were identified. Activities involved with scuba diving appear to be consistent with CCAD risk factors. It is unclear if hyperbaric stress and physiological changes during a dive present specific risk. Trauma - e.g., environmental protection and activities associated with diving - was identified as a common risk factor in all cases. Ten (10) cases involved arteries at anatomic sites commonly associated with dissections. Seven divers documented to have dive profiles suspicious of decompression sickness were identified.

CONCLUSIONS

There appears to be a correlation with minor traumas that occur with diving and CCAD. The inconsistency of the dive-related specific information reported makes it impossible for investigation of hyperbaric stress-related risk factors for CCAD to be analyzed.

A case-control questionnaire survey of decompression sickness risk in Okinawa divers

BACKGROUND

Decompression sickness (DCS) is a rare condition that is often difficult to diagnose in deep-sea divers. Because of this, prevention and early diagnosis are important. In this case-control study, we examined the risk and preventive factors associated with DCS.

METHODS

Our original questionnaire survey was conducted among 269 recreational divers in Okinawa. Divers who were diagnosed with DCS by a physician (n = 94) were compared with healthy recreational divers (n = 175). The questionnaire consisted of 30 items and included a dive profile. Odds ratios and multiple logistic regression analysis were used to estimate the relative risk of DCS.

RESULTS

Logistic regression analysis revealed the following risk factors for DCS: a past history of DCS, drinking alcohol the evening before diving, indicating decompression stops, cold exposure after the dive, and maximum depth. Preventive factors included hydration before the dive, deep stops, safety stops and using nitrox gas. The results were reliable according to the Hosmer-Lemeshow and omnibus tests.

CONCLUSION

We identified certain risk factors, together with their relative risks, for DCS. These risk factors may facilitate prevention of DCS among Okinawa divers.