title: Resolution and severity in decompression illness.
abstract: omegaWe review the terminology of decompression illness (DCI), investigations of residual symptoms of decompression sickness (DCS), and application of survival analysis for investigating DCI severity and resolution. The Type 1 and Type 2 DCS classifications were introduced in 1960 for compressed air workers and adapted for diving and altitude exposure with modifications based on clinical judgment concerning severity and therapy. In practice, these proved ambiguous, leading to recommendations that manifestations, not cases, be classified. A subsequent approach assigned individual scores to manifestations and correlated total case scores with the presence of residual symptoms after therapy. The next step used logistic regression to find the statistical association of manifestations to residual symptoms at a single point in time. Survival analysis, a common statistical method in clinical trials and longitudinal epidemiological studies, is a logical extension of logistic regression. The method applies to a continuum of resolution times, allows for time varying information, can manage cases lost to follow-up (censored), and has potential for investigating questions such as optimal therapy and DCI severity. There are operational implications as well. Appropriate definitions of mild and serious manifestations are essential for computing probabilistic decompression procedures where severity determines the DCS probability that is acceptable. Application of survival analysis to DCI data would require more specific case information than is commonly recorded.
authors.affiliation: Divers Alert Network, Center for Hyperbaric Medicine and Environmental Physiology, Duke University, Durham, NC 27710, USA. rvann@dan.org
authors.forename: Richard D
authors.initials: RD
authors.lastname: Vann
authors.forename: Petar J
authors.initials: PJ
authors.lastname: Denoble
authors.forename: Laurens E
authors.initials: LE
authors.lastname: Howle
authors.forename: Paul W
authors.initials: PW
authors.lastname: Weber
authors.forename: John J
authors.initials: JJ
authors.lastname: Freiberger
authors.forename: Carl F
authors.initials: CF
authors.lastname: Pieper
mesh_terms: D003665:Decompression Sickness / Q000175:diagnosis* / Q000534:rehabilitation; D004242:Diving / Q000009:adverse effects; D006801:Humans; D053208:Kaplan-Meier Estimate; D020127:Recovery of Function; D012720:Severity of Illness Index