Ceiling-controlled versus staged decompression: comparison between decompression duration and tissue tensions.

INTRODUCTION: In dissolved gas decompression algorithms, the ceiling is the depth at which the dissolved gas pressure in at least one tissue equals the maximum tolerated value defined by the algorithm. Staged decompression prescribes stationary stops in three-metre intervals so as to never exceed this maximum tolerated value. This keeps the diver deeper than the ceiling until the ceiling itself decreases to coincide with the next, three-metre shallower stage. Ceiling-controlled decompression follows the ceiling in a continuous ascent. METHODS: Mathematical simulations using the ZH-L16C decompression algorithm and gradient factors were carried out for several dive profiles to compare patterns of tissue gas supersaturation and overall decompression times for decompressions based on these approaches. RESULTS: During a stationary staged decompression stop the available pressure gradient for inert gas washout diminished as inert gas is washed out while inhaled inert gas partial pressure remained unchanged. Ceiling-controlled decompression, on the other hand, maintained the available pressure gradient for inert gas washout at its maximum tolerated level. Decompressions were 4-12% shorter using ceiling-controlled approaches but at the cost of exposing tissues with faster half times to higher levels of supersaturation than they would experience during staged decompression. CONCLUSIONS: Ceiling controlled approaches accelerate decompression but the effect of this on the risk of decompression sickness is unknown.

Health-Related Behaviors and Odds of COVID-19 Hospitalization in a Military Population.

INTRODUCTION: Understanding the impact of behaviors on COVID-19 severity can improve health promotion strategies. We investigated the association between health-related behaviors and odds of hospitalization for COVID-19 in a cohort of military personnel. METHODS: This case-controlled study compared all active-duty US Air Force service members hospitalized for COVID-19 between March 5, 2020, and March 10, 2021 (cases), with their geographically matched peers who had COVID-19 and were treated as outpatients (controls). We used logistic regression to compare cases and controls according to self-reported sleep duration, physical activity, dietary factors, binge alcohol consumption, and tobacco use - with and without adjustment for sociodemographic factors, body mass index, physical fitness level, pertinent disease history, and psychological distress - resulting in crude and adjusted odds ratios (ORs) with 95% CIs. The trend between sugar-sweetened beverage (SSB) consumption and hospitalization odds was assessed by using the Cochran-Armitage test. RESULTS: Ninety-three hospitalized cases were matched to 372 ambulatory controls. Adjusting for baseline characteristics and other health-related behaviors, cases were more likely than controls to report fewer than 7 hours of sleep, compared with 7 to 9 hours (OR = 1.84; 95% CI, 1.07-3.16), and were more likely than controls to consume 3 or more SSBs per week, compared with fewer than 3 SSBs (OR = 1.74; 95% CI, 1.03-2.92). In a dose-response relationship, higher SSB consumption was associated with greater odds of being hospitalized (P value for trend = .02). CONCLUSION: Interventions that address short sleep duration and SSB consumption may reduce morbidity from COVID-19 among military service members and potentially in the broader US population.

Disparities in COVID-19 Vaccine Initiation and Completion Among Active Component Service Members and Health Care Personnel, 11 December 2020-12 March 2021.

The objective of this study was to assess overall vaccine initiation and completion in the active component U.S. military, with a focus on racial/ethnic disparities. From 11 December 2020 through 12 March 2021, a total of 361,538 service members (27.2%) initiated a COVID-19 mRNA vaccine. Non-Hispanic Blacks were 28% less likely to initiate vaccination (95% confidence interval: 25%-29%) in comparison to non-Hispanic Whites, after adjusting for potential confounders. Increasing age, higher education levels, higher rank, and Asian/Pacific Islander race/ethnicity were also associated with increasing incidence of initiation after adjustment. When the analysis was restricted to active component health care personnel, similar patterns were seen. Overall, 93.8% of those who initiated the vaccine series completed it during the study period, and only minor differences in completion rates were noted among the demographic subgroups. This study suggests additional factors, such as vaccine hesitancy, influence COVID-19 vaccination choices in the U.S. military. Military leadership and vaccine planners should be knowledgeable about and aware of the disparities in vaccine series initiation.

Performance of life support breathing apparatus for under-ice diving operations.

INTRODUCTION: Single-hose scuba regulators dived in very cold water may suffer first- or second-stage malfunction, yielding complete occlusion of air flow or massive freeflow that rapidly expends a diver's air supply. PURPOSE: This study, conducted in Antarctica, evaluated the under-ice performance of a sampling of commercially available regulators. METHODS: Seventeen science divers logged a total of 305 dives in -1.86°C seawater under 6-meter-thick Antarctic fast-ice over two field seasons in 2008 and 2009. Dive profiles had an average depth of 30 msw and dive time of 29 minutes, including a mandatory three-minute safety stop at 6 msw. Sixty-nine unmodified regulator units (17 models) from 12 different manufacturers underwent standardized pre-dive regulator care and were randomly assigned to divers. Depths and times of onset of second-stage regulator freeflow were recorded. RESULTS: In 305 dives, there were 65 freeflows. The freeflows were not evenly distributed across the regulator brands. Regulator failure rates fell into two categories (⟨ 11% and ⟩ 26%). The regulators classified for the purpose of the test as "acceptable" (⟨ 11% failure rate: Dive-Rite Jetstream, Sherwood Maximus SRB3600, Poseidon Xstream Deep, Poseidon Jetstream, Sherwood Maximus SRB7600, Poseidon Cyklon, Mares USN22 Abyss) experienced only nine freeflows out of 146 exposures for a 6% overall freeflow incidence. Those classified as "unacceptable" (⟨ 26% failure rate) suffered 56 freeflows out of 159 exposures (35% freeflow incidence.). CONCLUSIONS: Contrary to expectations, the pooled incidences for the seven best performing regulators was significantly different by Chi-square test from the 10 remaining regulators (P ⟨ 0.001).

The incidence of decompression illness in 10 years of scientific diving.

BACKGROUND: The American Academy of Underwater Science (AAUS) constitutes the single largest pool of organizations with scientific diving programmes in North America. Members submit annual summaries of diving activity and any related incidents. METHODS: All diving records for a 10-year period between January 1998 and December 2007 were reviewed. Incidents were independently classified or reclassified by a four-person panel with expertise in scientific diving and diving safety using a previously published protocol. Subsequent panel discussion produced a single consensus classification of each case. RESULTS: A total of 95 confirmed incidents were reported in conjunction with 1,019,159 scientific dives, yielding an overall incidence of 0.93/10,000 person-dives. A total of 33 cases were determined to involve decompression illness (DCI), encompassing both decompression sickness and air embolism. The incidence of DCI was 0.324/10,000 person-dives, substantially lower than the rates of 0.9-35.3/10,000 published for recreational, instructional/guided, commercial and/or military diving. CONCLUSIONS: Scientific diving safety may be facilitated by a combination of relatively high levels of training and oversight, the predominance of shallow, no-decompression diving and, possibly, low pressure to complete dives under less than optimal circumstances.