Validation of subjective manual palpation using objective physiological recordings of the cranial rhythmic impulse during osteopathic manipulative intervention

Objective Reticular brain activity described by intermediate (IM) band physiology exhibits parallels to controversial concepts of cranial osteopathy (CO), the primary respiratory mechanism or cranial rhythmic impulse (CRI). Interestingly, evidence for PRM/CRI activity has been reported using manual palpation, yet with questionable validity. Validation is tested combining manual palpation, instrumented tracking, and algorithmic objectivation of frequencies and phases. Methods Using a standard CO intervention, Vault Hold (VH), two CO experts palpated and digitally marked CRI frequencies in 25 healthy adults. IM band autonomic nervous system activity was examined as momentary frequency of highest amplitude (MFHA) in examiner and participant forehead photoplethysmography (PPG). Palpation errors and frequency expectation bias during VH were examined using MFHA and CRI phases. Findings Palpated CRI frequencies matched those reported in the literature. Mean MFHA and CRI frequencies were highly correlated and showed constant low deviating 1:1 coupling in 77% of participants (responders), and high deviating 1:2 coupling in 23% of participants (non-responders). Both groups showed harmonic waves in (very) low and IM bands in >98% of palpated intervals. Phase analyses suggested synchronization between MFHA and CRI in responders but not in non-responders confirming that examiners palpated CRI activity in participants. Conclusions Decreases in forehead PPG of responders from IM activity (~0.14 Hz) to LF activity (0.072 Hz) suggest successful palpation may be explained by IM and LF activity, whereas CRI in non-responders was not associated with PPG activity.