Beating the Bends: Dolphin Thoracic Rete as a Natural Vascular Filter for Trapping Nitrogen Bubbles and Preventing Diving Decompression Sickness

The thoracic rete, a complex of interweaving vessels, is found in dolphins and other toothed whales (odontocetes). Its purpose is unclear, but proposed functions include: pressure‐damping central nervous system blood flow, reducing displacement stress of the thorax during diving‐induced lung collapse, or thermoregulation. The first two theories seem possible, but rete's location completely within the core of the body is not ideally positioned to function as a counter‐current exchanger or in radiating heat. Rather, we hypothesize that its dorsal location and complex anatomy make it suitable to serve as a bubble trap to filter bubbles circulating in the bloodstream. The gross anatomy of the thoracic rete was examined in ten fresh dead dolphin and porpoise specimens donated by the Cape Cod Stranding Network (Massachusetts). The rete is located laterally along the thoracic and upper lumbar vertebrae, ventral to the vertebral transverse processes, between the dorsal ribs (extending laterally and ventrally approximately to the mid‐axillary line), and is comprised of many small vessels that appear to have a random interweaved pattern.The rete vessels appear derived from intercostal arteries of the descending thoracic and upper abdominal aorta and likely drain into the azygos system of veins. Vessel positions and lumen sizes appear to permit functioning as a vascular filter to trap circulating nitrogen bubbles that have emerged from gas saturated blood during diving. Trapping bubbles in this central location prevents them from circulating to, and obstructing, the vessels supplying vital organs. It is hoped that these findings can direct development of a vascular filter to mitigate the effects of decompression sickness in human divers.