UNDERSEA MEDICINE Session F Diving Performance and Medicine F 1 Test of cross corrections for altitude air/nitrox diving at 8,000, 10,000 and 12,000 feet Beck T, Weis T, Natoli M, Brown G, Gatrell A, Schinazi E, Walker A, Armstrong J, Howle L, Pieper C, Moon R Duke University Medical Center, Durham, North Carolina Submitting Author: Timothy Beck [email protected] Introduction / Background: This study tested current United States Navy procedures (Cross corrections: Bell RL, Borgwardt RE. Undersea Biomed Res 1976; 3:1-23) for adjusting decompression procedures during air and enriched O2 diving at altitude. Materials and Methods: After IRB approval and informed consent, three exposures were performed: (A) 60-fsw no-stop air dives for 30 minutes at 8,000 and 10,000 feet of altitude; (B) 100-fsw dives breathing 35% O2/N2 for 25 minutes at 10,000 feet and 20 minutes at 12,000 feet. Volunteer subjects ages 18-45 years were exposed to simulated altitude in a hypobaric chamber for 24 hours (8,000 feet) or 48 hours (10,000 and 12,000 feet). They then performed a single dive fully submersed while exercising moderately on an electrically braked ergometer. Following each dive the subjects were monitored for 12 hours at altitude for DCS symptoms and VGE using 2D echocardiography. After return to sea level they underwent a complete neurological exam with telephone follow-up the next day. Results: A total of 42 subjects have been studied (M/F=23/19, Caucasian=34, Asian=3, Hispanic=3, mixed race=2). Dives are summarized in the table. Summary / Conclusion: Preliminary results are consistent with adequacy of Cross corrections for these no-stop dives at 8,000-12,000 feet in altitude. Supported by NAVSEA Contract N0002418C4318 F 2 Initial evaluation of the efficacy of the O’Connor Tweezer Dexterity test as a metric of high pressure nervous syndrome Murphy FG U.S. Navy Experimental Diving Unit, Panama City Florida; Department of Mechanical Engineering and Material Science, Duke University, Durham, NC Submitting Author: F. Gregory Murphy, PhD [email protected] Introduction / Background: Saturation dives consist of a long, slow descent to storage depth followed by a hold during which work is performed. The slow descent was selected for its efficacy in preventing high pressure nervous syndrome (HPNS). HPNS is characterized by disorientation, nausea, dizziness, hand and arm tremors, microsleep, and convulsions. In past studies the Purdue Pegboard, Bennett Ball Bearing (BBB) Test, and electroencephalogram have all been used to detect HPNS. The U.S. Navy Experimental Diving Unit conducted an experimental saturation dive during which divers were compressed at an atypically fast rate to 450 fsw. Due to the rapid compression rate HPNS was a concern; however, the BBB test and an electroencephalogram were not readily available. Materials and Methods: Six divers underwent compression to 40 fsw on air at 40 fsw/minute. Following a brief stop for chamber system checks they continued compression to 450 fsw on helium at 40 fsw/minute. These six divers breathed from a constant 0.7 atm PO2 breathing source with 82% He/12% N2/6% O2 diluent during compression and for 40 minutes after compression until a safe breathable atmosphere had been established in the chambers. The O’Connor Tweezer Dexterity (OTD) test is a well-documented test for manual dexterity similar to the BBB test. Divers were tested for HPNS with the Purdue Pegboard and OTD test, 50 minutes, 160 minutes, and the following morning post compression. Results: One out of six divers showed a measurable performance decrement, taking 4.28 minutes longer to complete the OTD test than their average pre-dive completion time. The diver described tremors as starting just below the elbow and extending through the wrist. The diver also reported mild dizziness. All signs and symptoms had resolved the following morning. Summary / Conclusion: The OTD test is a suitable replacement for the BBB test to detect intentional tremors associated with HPNS. F 3 Characteristics of a cohort of older recreational divers with or without arrhythmias Buzzacott P1,2, Anderson G1,3, Tillmans F1, Grier J4, Denoble PJ1 1 Divers Alert Network, Durham, North Carolina 2 Prehospital, Resuscitation and Emergency Care Research Unit, School of Nursing, Midwifery and Paramedicine, Curtin University, Western Australia 3 The Warren Alpert School of Medicine at Brown University, Providence, Rhode Island 4 Biological Sciences, Dept., North Dakota State University, Fargo, North Dakpta Submitting Author: Peter Denoble, MD [email protected] Introduction / Background: Sudden cardiac death (SCD) accounts for 20-30% of all scuba fatalities. One suspected mechanism of SCD is acute arrhythmia triggering cardiac arrest. This study describes the prevalence of factors that may predispose divers to SCD. Materials and Methods: Sixty-eight certified scuba divers made 75 dive research trips and logged ≥920 dives. Diver characteristics, medical history and diving history were reported at enrolment. Before and after dive trips, 12-lead ECG recording and echocardiographic measurements were collected. Arrhythmias were identified and categorized by type. Results: No diver suffered SCD during this study. Compared to divers without any arrhythmias (n=48), those with arrhythmias recorded either pre- or post- diving (n=20) were 17% older (59 vs. 50 years), had been diving longer (20 vs. 10 years), but had made fewer dives in the previous six months (15 vs. 20). Their left ventricular mass wa s greater (176 vs. 153g) and was greater when indexed to body surface area (179 vs. 161g). Their relative wall thickness was 11% greater (0.48 vs. 0.43cm), and interventricular septum thickness was 8% greater (1.05 vs. 0.97cm). There were no meaningful differences between divers with arrhythmias compared to those without in the proportion who were past smokers, who were currently taking any prescription meds, or who had left ventricular hypertrophy. The arrhythmia group had a higher proportion of alcohol drinkers (92% vs. 82%), higher frequency of cholesterol diagnosis (38% vs. 22%), and more were taking cholesterol medications (32% vs. 16%). The incidence of arrhythmias changed between pre- and post- diving in 18/20 divers. Summary / Conclusion: Further studies of a more controlled, less exploratory, nature are warranted. We have developed and refined the protocols that could support such studies. This study, for the first time, characterizes a selected cohort of older recreational divers with cardiac arrhythmias, though this cohort may not be representative of older recreational divers generally. F 4 Hypoxia signatures in closed-circuit rebreather divers Kutz C, Carlile M, Brett K, Cespedes E, Powell F, Witucki P, Sadler R, Sadler C, Popa D Department of Emergency Medicine, Division of Hyperbaric Medicine; University of California - San Diego Health,San Diego, California Submitting Author: Craig J. Kutz, MD [email protected] Introduction / Background: Closed-circuit rebreather (CCR) diving has increased due to availability and advantages over scuba. Malfunctions or user error in CCR can lead to dangerous gradual hypoxia as a diver consumes available oxygen within the circuit. Hypoxia can cause underwater loss of consciousness, aspiration, drowning, and death. Studies of hypoxia in CCR divers are limited, and the question remains as to whether hypoxia training improves the ability to self-rescue. We hypothesize that CCR divers exhibit an individualized and reproducible constellation of symptoms from a gradual onset hypoxic exposure (“hypoxic signature”). Further, we hypothesize that by learning their hypoxic signature, divers will improve hypoxia recognition and self-rescue. Materials and Methods: We performed a single-blinded, cross-sectional study investigating 20 male and female divers certified in either CCR (n=8) or scuba (n=12). Subjects underwent a CCR oxygen malfunction with gradual onset hypoxia while simulating swimming on a cycle ergometer. Subjects played a distracting computer game while pointing to symptoms. Subjects underwent an initial known hypoxia trial, then three subsequent blinded (sham vs. hypoxia) trials. We instructed subjects to self-rescue if they perceived hypoxia. If they failed to perceive hypoxia, an alarm to self-rescue occurred at 75% oxygen saturation (hypoxia) or after six minutes (sham). Results: With randomization, subjects correctly identified the gas mixture in 52/60 trials (86.6%). Of the incorrect, three subjects incorrectly identified a hypoxic trial as sham; five subjects felt a sham trial was hypoxic. Of the subset who self-aborted, 30% on subsequent hypoxia trials were able to abort without prompting. Subjects undergoing blinded hypoxia identified similar symptoms to their known hypoxia trial in 19/20 trials (95%). Summary / Conclusion: Our preliminary evidence suggests that with known exposure to hypoxia, divers were able to recognize symptoms and self-rescue in subsequent blinded exposures. With further study, this initial work may reveal improvements in CCR safety through identification of divers’ “hypoxia signature.” F 4 Closed circuit rebreather diving: FiO2, PO2, ETCO2, and ETO2 during normobaric hypoxic hypoxia exposures Carlile M, Kutz C, Brett K, Moya Cespedes E, Powell F, Witucki P, Sadler R, Sadler S, Popa D, Department of Emergency Medicine, Division of Hyperbaric Medicine; University of California - San Diego Health,San Diego, California Submitting Author: Morgan Carlile, MD [email protected] Introduction