DAN Research Updates

DAN's mission is recreational diving safety. The Research Department supports this mission through field, epidemiological and experimental studies that seek to shed light on the issues related to fatalities, injuries and the risks of decompression illness (DCI). Here are the findings from some of our recent projects.
DAN^® Research maintains an active surveillance program for dive fatalities. A recent investigation of 947 diving-related deaths from 1992 to 2003 found that the principal injuries preceding death were asphyxia (33 percent), arterial gas embolism, or AGE (29 percent), and cardiac incidents (26 percent).¹ Deaths due to asphyxia and AGE were associated with entrapment, insufficient gas, rapid ascent and equipment trouble. For cardiac incidents, associated factors were age and a history of cardiovascular disease.

A review of fatalities among insured DAN Members also provided some interesting insights, particularly regarding associations with the age of the diver.² Annual death rates for insured DAN Members were stable during 2000-2006, with a mean of 16.4 deaths per 100,000 members. Fatality rates increased dramatically with age. Among divers 15-25 years of age, the fatality rate was less than 10 per 100,000 members but increased to 30 per 100,000 among divers 65 years of age and older.

Women under the age of 55 were much less likely to die while diving than were men, but among divers 65 years of age and older, there was no difference in the death rate between the sexes.

To better understand the specific role of age in these deaths, we went back to the associated injury data and this time looked at the trends by dividing members into two age groups: over 50 and under 50. In this analysis, we found that older divers were three times more likely to die from asphyxia; four times more likely to die from AGE and 13 times more likely to die from cardiac events than the under-50 dive group.

The high association of cardiac incidents with older divers is of particular concern since the general diving population is aging. As a result of our findings, DAN Research has planned a two-and-a-half-day workshop for April 2010 to discuss the question of dive fatalities.
DAN fatality surveillance also tracks small, high-risk recreational diving populations such as cave and rebreather divers. Cave diving deaths decreased during 1969-2007 and now account for only about 5 percent of annual U.S. and Canadian fatalities reported to DAN. Rebreather fatalities, however, have increased since 2000 and now account for about 6 percent of known deaths.
Helping divers understand, avoid and find proper treatment for DCI was the primary reason for DAN's founding. DCI is a broad category of pressure-related injuries that includes both AGE and decompression sickness (DCS), with DCS — aka "the bends" — being the most common malady. DAN is notified of about 1,000 U.S. and Canadian DCI cases per year and processes insurance claims for approximately one-third of these.

Analysis of the DCS claims among DAN Members from 2000 to 2007 found an average rate of 217 cases per 100,000 insured members, with an annual decrease in claims of approximately 12 cases per 100,000 members during the period. The claims rate was very low for divers in their early teens, rose to 350-400 cases per 100,000 members for divers in their 20s and declined with age thereafter. For women, the claims rate was lower than for men by about 60 DCS cases per 100,000 members.

In future columns, we plan to bring you updates from ongoing DCI/DCS research projects including:

• a joint effort between DAN Research and DAN Medical Services to investigate first aid and therapy options that provide the best long-term outcomes for divers affected by DCI
the collection of depth-time profiles from recreational and technical divers to study the overall DCS incidence and identify profiles with the highest DCS probability

• the establishment of a center of excellence for DCS probability modeling in cooperation with Duke University's mechanical engineering department and the U.S. Navy.

Also in future columns: Look for updates on the experimental diving research under way in the chambers of the Duke Center for Hyperbaric Medicine and Environmental Physiology. Projects include:

• how immersion and exercise affects the DCS risks of flying after diving
• how elevated oxygen partial pressures affect carbon dioxide narcosis
• a recently completed study that found the prescription drug Cialis increased the risk of CNS oxygen toxicity in rats.³

References
1. Denoble P, Caruso J, Dear G, Pieper C, Vann R. "Common causes of open-circuit recreational diving fatalities." Undersea Hyperbar Med. 2008; 35(6):393-406.
2. Denoble P, Pollock N, Vaithiyanathan P, Caruso J, Dovenbarger J, Vann R. "Scuba injury death rate among insured DAN members." Diving and Hyperbaric Medicine. 2008; 38(4):182-8.
3. Demchenko I, Ruehle A, Allen B, Vann R, Piantadosi C. "Phosphodiesterase-5 inhibitors oppose hyperoxic vasoconstriction and accelerate seizure development in rats exposed to hyperbaric oxygen." J Appl Physiol. 2009; 106:1234-42.