Far from what you might think, the purr has a hemodynamic origin, and not an aerodynamic one, according to the American veterinarian WR Mc Cuistion. The expert explains that the noise originates in the chest , within the wall of the vena cava, as it passes through the liver and the diaphragm.
When blood flow is compressed as it passes through the diaphragmatic hiatus, a narrowing that connects the esophagus with the stomach, it causes turbulent oscillations in the blood as it enters the chest. That, as Cuistion points out, is what gives rise to perfectly audible vibrations that are transmitted and amplified through the air-filled bronchi and windpipe into the sinuses of the head.
