The United States Naval Sea Systems Command has awarded Duke Anesthesiology’s Richard Moon, MD, medical director of the Duke Center for Hyperbaric Medicine and Environmental Physiology, two grants totaling $1,237,073.
His first project, titled “Development of a Pulse Oximeter to Independently Monitor Oxygen Levels in Rebreather Divers,” is expected to increase the understanding of human performance under gradual hypoxia and ultimately create a safety device (for the military and diving industry) that could prevent the primary cause of death for rebreather divers.
Rebreather diving has one of the highest fatality rates per man-hour of any diving activity in the world. The leading cause of death is hypoxia, typically from equipment or procedural failures. Since the electronics responsible for controlling oxygen levels in rebreathers often control their alarm systems, frequently divers do not receive any external warnings.
The long-term objective of this proposal is the creation and characterization of a safety device that warns divers of hypoxia but also operates completely independently of the rebreather electronics. The safety device will be a modified, commercial-off-the-shelf (COTS) pulse oximeter, which is a well-established technology that measures the percentage of the subject’s blood that is saturated with oxygen. Previous research has already preliminarily demonstrated that a pulse oximeter can provide a useful amount of warning time to a rebreather diver with falling levels of inspired oxygen; however, the length of warning time available has not yet been fully characterized. The specific aims of this project include (1) modifying a COTS pulse oximeter for use underwater, (2) characterizing the warning time provided to the diver by the oximeter and (3) completing prototype deliverables to publish the results and enable the transfer of technology. The device will also be useful for civilian divers, among whom rebreathers are increasingly popular.
Dr. Moon’s second project, titled “Development of Altitude Decompression Tables,” is a series of studies that will provide testing of two different methods for altitude diving, where the Navy may have an operational need, but as of yet, no tested procedures. These data will also provide a series of depth-time excursions with outcomes that may facilitate development of a generalized decompression model from which a complete set of decompression procedures could be derived for multiple depths and times.
According to the research proposal, when diving at altitude, the reduced atmospheric pressure requires adjustment of the standard decompression tables such that for any given dive depth, either shorter dive times or longer decompression times are required. The U.S. Navy Diving Manual includes a method to modify standard air tables by applying an altitude correction procedure (“cross correction”). However, this method has never been formally tested and its safety is unknown.
This proposal aims to 1) investigate standard Navy corrections for a no-stop air dive at 8,000 and 10,000 feet altitude, 2) test a no-stop 100-foot dive using an enriched oxygen breathing mix at 10,000 and 12,000 feet and 3) investigate whether a period of high oxygen exposure causes immediate reversal of altitude acclimatization. Following the experiments, the Navy will know whether cross corrections are safe for a 60 feet of sea water (FSW) no-stop air dive at 8,000 and 10,000 feet altitude. A decompression procedure will also be developed for a 100 FSW no-stop enriched oxygen dive.
The study will also test whether a period of high oxygen exposure during a dive using enriched oxygen will reverse altitude acclimatization. In addition to the diving data, many of the experimental subjects will experience acute mountain sickness. To provide insights into this common condition, DNA, serum and urine samples will be routinely collected for future analysis.