Incidence of middle ear barotrauma in staged versus linear chamber compression during hyperbaric oxygen therapy: a double blinded, randomized controlled trial.

CONTEXT: Middle ear barotrauma (MEB) is common during chamber compression in hyperbaric oxygen therapy. However, little evidence exists on an optimal compression protocol to minimize the incidence and severity of MEB. OBJECTIVE: To compare the incidence of MEB during hyperbaric oxygen therapy using two different chamber compression protocols. DESIGN: Double-blinded, randomized controlled trial. SETTING: Hyperbaric Medicine Unit, The Townsville Hospital, Queensland, Australia, September 2012 to December 2014. PATIENTS: 100 participants undergoing their first hyperbaric oxygen therapy session. INTERVENTION: Random assignment to a staged (n=50) or a linear (n=50) compression protocols. Photographs of tympanic membranes were taken pre- and post-treatment and then graded. Middle ear barotrauma was defined as an increase of at least one grade on a modified TEED scale. RESULTS: The observed MEB incidence under the staged protocol was 48% compared to 62% using the linear protocol (P=0.12, exact one-sided binomial test), and thus the staged protocol did not show a significant improvement in MEB. However, the staged protocol resulted in significantly less severe deteriorations in MEB grades when compared to the linear protocol (P=0.028, exact one-sided Mann-Whitney type test). CONCLUSION: The use of the assessed staged compression protocol for the first hyperbaric oxygen treatment showed no significant effect on the overall incidence of MEB when compared to the gold standard linear protocol but resulted in a significant improvement in the severity of the experienced MEBs. Further studies are needed to elucidate an optimal compression protocol to minimize middle ear barotrauma.

Free-living tube worm endosymbionts found at deep-sea vents.

Recent evidence suggests that deep-sea vestimentiferan tube worms acquire their endosymbiotic bacteria from the environment each generation; thus, free-living symbionts should exist. Here, free-living tube worm symbiont phylotypes were detected in vent seawater and in biofilms at multiple deep-sea vent habitats by PCR amplification, DNA sequence analysis, and fluorescence in situ hybridization. These findings support environmental transmission as a means of symbiont acquisition for deep-sea tube worms.