Physiological Mechanisms Underlying the Primary Respiratory Mechanism (PRM) and Cranial Rhythmic Impulse (CRI) in Osteopathy: A Narrative Review of the Literature

Cranial Rhythmic Impulse (CRI) or Primary Respiratory Mechanism (PRM), a rhythm felt by Osteopaths at the surface of the skin, is a fundamental concept that some of them in their practice for their diagnosis and treatment. However, the physiological basis of this phenomenon remains unclear. Sutherland, founder of cranial osteopathy, proposed in 1939 a theory that remained dogmatic, despite scientific advances that refuted it. Since 1990, some osteopaths have tried to find better explanations, such as those presented in a previous systematic review. In this narrative review, we first revisit each pillar of Sutherland’s theory, analyzing them in light of the latest scientific studies to assess whether contemporary research supports or challenges his ideas. After showing that this model is inconsistent with current scientific evidence, we explore the current knowledge of the physiological mechanisms underlying the PRM/CRI. The most plausible hypothesis to explain this is based on the variation in extracellular matrix and fascial texture, influenced by rhythmic oscillations in blood pressure (Traube Hering and Mayer waves), and the interplay of other physiological rhythms (ventilation, baroreflex, heart rate variability…). Finally, we discuss the relevance and practical applications of PRM in osteopathy. While Sutherland's model continues to hold sway in mainstream beliefs, the scientific literature has increasingly emphasized autonomic system activity as the leading hypothesis. This narrative analysis underscores the need for a paradigm shift regarding CRI/PRM in osteopathy, arguing for clearer communication of a model aligned with the latest scientific evidence.