The Gradient Perfusion Model Part 1: Why and at what sites decompression sickness can occur

Introduction: Decompression sickness (DCS) is manifested by the quantity and location of bubbles in body tissues after reduction in ambient pressures. Models have been formulated to explain why bubbles form, but none provide satisfactory explanations as to why the findings of DCS occur as they do. This first of a three-part series explains why and at what sites DCS occurs. Materials and Methods: Over a 50-year span and 500 cases of DCS we have managed, it has become apparent that almost all "unexplained DCS" (i.e., cases with no obvious explanation as to how/why they occurred) have physiological explanations. The vagaries of the physiology of tissue perfusion and the physics of gradients as a cause of autochthonous bubble formation were analyzed. Findings: Perfusion is highly variable, with so-called "fast" tissues (i.e., tissues with a rapid rate of saturation) requiring a constant blood supply, "intermediate" tissues requiring a blood supply proportional to needs, and "slow" tissues having minimal perfusion requirements. The 5-liter blood volume in a vascular system with greater than a 20-liter capacity requires careful regulation. Disruptions in the regulation and/or overwhelming gradients explain why DCS Occurs. Conclusions: Our Gradient-Perfusion Model provides an explanation as to why disordering events account for almost all cases of unexplained DCS. We propose that this latter term be discarded and "disordering events" be used for DCS cases that have no obvious explanations.