The Myth of the Internal Nasal Valve.

According to ancient Greek myth, the Strait of Messina between Sicily and Calabria in southern Italy is home to Charybdis, a sea monster capable of bringing down the toughest ships by swallowing them whole. Of course, there was no monster and both ship and sailor fell victim to a whirlpool, an aquatic vortex resulting from a recirculating flow produced by the interaction of opposing currents. DaVinci described vortices within the human body, theorizing that the sinuses of Valsalva in the heart created vortices that prevented clot formation and facilitated aortic valve closure.1 Like Charybdis, there is a myth about the flow inside the nasal vault, and the historical description of the “internal nasal valve”2 fails to be either accurate or descriptive in light of what is now dogma in the field of aerodynamics. The archaic description of an angular region bounded by the inferior turbinate, septum, nasal floor, and upper lateral cartilage (ULC), poorly describes both the 3-dimensional (3D) structure and the flow.3 In fluid mechanics an inlet is a passage through which fluid first enters a machine or device.4 Similarly, gateways, described as archways built around a gate, are more apt descriptions for what the medical literature refers to as “valves”—terminology that is otherwise confusing to patients and nonsense to engineers. The fluid dynamics of the nose cannot be summarized with a single angular measurement. The anatomy is complex, with lateral attachments, overlying dilator musculature, and rigid nasal cavity structures contributing to the dynamic sidewall collapse as flow at high velocities generate considerable pressure differentials. Although imaging and computational fluid dynamics have accelerated our understanding immensely,5 there still exists a lack of means to reliably predict lateral wall collapse.6