Initial review of the U.S. Navy's pressurized submarine escape training outcomes.

The U.S. Navy reinstituted pressurized submarine escape training (PSET) for submarine sailors in 2009 after a nearly 30-year absence. This training addresses escape from a disabled submarine at depth with the use of the Beaufort, Ltd. Mk 10 Submarine Escape and Immersion Equipment (SEIE) suit. Training is classified as "high-risk" due to previous U.S. and foreign navy experience with training-associated morbidity and mortality, particularly from diving-related illness. To reduce risk, medical screening procedures are performed. During the first 39 months of training, 7,025 students screened for PSET with 32% completing all phases, including two pressurized ascents. The most common reason for screening disqualification was presence of upper respiratory congestion. During training, middle ear barotrauma was responsible for 53% of attrition, primarily during the test of pressure.

Assessment of cognitive function while on low-dose propranolol: implications for usage by survivors in a disabled submarine.

While awaiting rescue from a disabled submarine (DISSUB), survivors will likely endure an atmosphere of rising CO2 which will eventually be lethal. Previously, it was determined that low-dose propranolol reduces resting metabolic carbon dioxide production and therefore may increase survival time in this scenario. The actions and decisions survivors would carry out in a DISSUB situation would require an unaltered cognition state. Therefore, we wanted to determine if low-dose propranolol impairs cognitive function. Eight healthy males completed a counterbalanced, randomized, placebo-controlled, double-blinded crossover study in which each subject received propranolol (40 mg twice daily) or placebo (lactose pill twice daily) over a 72-hour period. The alternate condition was separated by a minimum 96-hour washout period. Subjects performed a series of 6 tasks from the Automated Neuropsychological Assessment Metrics (ANAM) battery and answered a self-report sleepiness scale each morning and afternoon. Subjects exhibited increased accuracy in one of the ANAM tasks while on propranolol compared to placebo, but showed no difference between treatments on the other 5 tasks and sleepiness scale. These results suggest that 40 mg of propranolol taken twice daily does not significantly impair cognitive function and may be a viable option for use in a DISSUB scenario.

Propranolol's potential to increase survival time in a disabled submarine.

BACKGROUND: While awaiting rescue from a disabled submarine, survivors will likely endure an atmosphere of rising CO2 that will result in CO2 toxicity once the available emergency CO2 scrubbing materials are exhausted. Propranolol is a beta-blocker that may increase survival time by reducing metabolic CO2 production (VCO2). The purpose of this study was to determine if propranolol reduces resting VCO2 in healthy men. METHODS: Eight healthy men completed a counterbalanced, randomized, placebo-controlled, double-blinded crossover study in which each subject received propranolol (40 mg twice daily) or placebo (lactose pill twice daily) over 72 h. The alternate condition was separated by a minimum 96-h washout period. Resting VCO2, oxygen consumption (VO2), ventilation (VE), respiration rate (RR), respiratory exchange ratio (RER), mean arterial pressure (MAP), heart rate (HR), and cardiac output (Q) were measured each morning and afternoon. RESULTS: When compared to placebo, propranolol significantly reduced VCO2 (-6.5%), MAP (-3.6%), HR (-10.4%), and Q (-8.2%); however, there were no significant differences in VO2, RR, VE, or RER. DISCUSSION: These results show that 40 mg of propranolol taken twice daily reduces resting VCO2 in healthy men and suggests that this treatment strategy may increase survival time in a disabled submarine scenario.

Vitamin D supplementation in underway submariners.

INTRODUCTION: We assessed the efficacy of vitamin D supplementation in maintaining normal calcium and bone homeostasis in underway submariners deprived of sunlight. METHODS: Serum 25-hydroxycholecalciferol (25(OH)D), 1,25-dihydroxycholecalciferol (1,25(OH)2D), calcium, parathyroid hormone (PTH), phosphate, osteocalcin, bone specific alkaline phosphatase, and urinary levels of N-telopeptide were examined in 51 subjects aboard a submarine. These levels were obtained prior to a 76-d deployment, before and after a 6-d liberty period (deployment day 49 and 55), and on return to homeport. There were 26 subjects who received 400-lU of vitamin D daily supplementation, and 25 who received placebo. RESULTS: Both groups exhibited significant reductions in 25(OH)D levels in the initial submergence (a decrease from 28.3 +/- 15 ng x ml(-1) to 24.1 +/- 10 ng x ml(-1) in the experimental group and 26.3 +/- 10 ng x ml(-1) to 20.7 +/- 9 ng x ml(-1) in the controls), an increase in 25(OH)D levels not significantly different from baseline during the liberty period, and decrements in 25(OH)D on repeat submergence (22.8 +/- 10 ng x ml(-1) in experimental and 21.4 +/- 10 ng x ml(-1) in controls). Both groups exhibited an increase in post-liberty osteocalcin (20.4 +/- 6 ng x ml(-1) to 24.5 +/- 5 ng x ml(-1) for experimental and 18.3 +/- 6 to 23.5 +/- 7 ng x ml(-1) for controls), and stable serum calcium levels throughout the patrol. CONCLUSIONS: 400-IU daily vitamin D supplementation was insufficient in maintaining serum vitamin D levels in underway submariners, engendering biochemical evidence of bone resorption and turnover. Six d sunlight exposure compensated for 49 d sunlight absence, supporting the enormous capacity of UV-B mediated vitamin D production.

Health experience of 122 submarine crewmembers during a 101-day submergence.

INTRODUCTION: The artificial environment encountered in submarine duty may affect the health of crewmembers. Previous studies of submariner health have not examined self-treatment habits or the incidence of minor health problems for which no care is sought from a health care provider. Our study examined patterns of minor medical problems and self-treatment among the crew of one submarine over a period of continued submergence for 101 d. METHODS: Study data were obtained from three self-administered serial surveys of 122 medically screened U.S. Navy personnel onboard a submerged nuclear-powered submarine at the beginning, middle, and end of the study. RESULTS: During the first half of the study, 82% had medical complaints, most commonly runny nose, difficulty sleeping, and backache. In the second half, 77% listed complaints, most commonly difficulty sleeping. Despite readily available medical care, self-medication for minor unreported health problems was common, with use of products such as non-steroidal anti-inflammatory drugs, multi-vitamins, health supplements, topical preparations, and antihistamine/decongestants. DISCUSSION: Planning for medical care in isolated environments should include consideration of inreported minor medical problems and self-treatment patterns.