Neurobiological aspects of the cranial rhythmic impulse
Cranial rhythmic impulse (also called primary respiratory mechanism) is a fundamental concept in cranial osteopathy. It is commonly assumed that this rhythmic motion is mechanically driven by variations in the pressure of the cerebrospinal fluid system and that it can be felt synchronously all over the body (Upledger & Vreedevoogt 1983).
Several difficulties have been pointed out with this concept:
1) If this motion is driven by pressure changes within the cerebrospinal fluid system, it is difficult to imagine that there is no time differential involved between cranial palpation of this rhythm and palpation at the legs and other body parts. Furthermore the often used concept of a purely mechanical tension transmission (of cranial movement to the sacrum via the dura mater) seems to be applicable only in a pre-stretched state of the dura, e.g. in spinal flexion. At least there should be some drastic differences in the transmission between different degrees of spinal flexion; yet this is usually not reported.
2) A review of scientific studies (MEDLINE search under "craniosacral") shows that most studies report a very poor interrater reliability, when 2 practitioners are palpating this pulse on different parts of the body.
More recent studies have been able to demonstrate a very close correlation of the cranial respiratory pulse with rhythmic changes in the circulatory system. Vasomotion (or venomotion, or Traube-Hering-Mayer oscillations) can be measured all over the body and seems to be the driving mechanism for what is felt as a cranial pulse. In other words, the 'primary respiratory mechanism' of cranial motion is now seen as a secondary effect of rhythmic changes within the blood vessels of the brain as well as in the rest of the body (Farasyn & Vanderschueren 2001, Nelson et al 2001). Another expression of the same phenomenon is heart rate variability, which has been shown to be a good indicator for health (e.g. patient with either no or diminished heart rate variability tend to have a 18 times higher likelihood of dying within one year).
Apparently there are at least two different oscillations in the cardiovascular system which coexist (Nelson et al. 2001). While one of these tends to be generally slower than respiration and seems to be associated with blood pressure variations, another vascular rhythm seems to be more closely related to respiratory sinus arrhythmia, i.e. heart rate variability in response to breathing cycles. For the slower vasomotor rhythm, Tasker and others stated that it is mostly controlled by the sympathetic nervous system (Tasker 1916). Yet Sahar et al. recently proposed that its amplitude might be influenced by both sympathetic and vagal influences (Sahar 2001).
Stephen Porges (who was involved in several of the scientific research around the effects of Rolfing) has been studying respiratory sinus arrhythmia for several decades and clearly demonstrated that these rhythmic changes express the state of regulation of the autonomic nervous system (ANS). His 'polyvagal
argues that these oscillations in the blood flow are an expression of the 'ventral vagus complex. Contrary to the 'dorsal vagus' (which is unmyelinated and of earlier phylogenetic origin) the ventral vagus complex is a more recent development of mammals and is characterized by a myelinated vagus that can rapidly regulate cardiac output to foster engagement and disengagement with the environment. It is neuroanatomically linked with the nucleus ambiguous and with cranial nerves that regulate social engagement via facial expression, head turning and vocalization, plus with the regulation of the neuropeptides oxytocin ('love hormone') and vasopressin which influence social bonding. Post traumatic stress disorders (PTSD) are usually characterized by significant changes within the ANS, which express in a shift from ventral vagus regulation to the older dorsal vagus system (which is involved with immobilization). This shift can be measured by a lowered 'vagal tone' (respiratory sinus arhytmia) as well as a lowering in the slower Traube-Hering-Mayer waves (Sahar 2001).
This new correlation of the cranial pulse with the ANS opens up some exciting perspectives for manual therapists:
Rather than focusing on questionable biomechanics (like in Upledger's pressure stat model) or seeing esoterically associated cosmic forces as the driving factors for cranial motion (as in the models of W. Sutherland, R. Becker and J. Jealous), Tasker's explanation as well as Porges' concept present us a more organic and more neurobiological foundation for further clinical research and application.
This new model includes the strong effects of manual therapy on the level of the ANS and emotion.
It offers clinical applications for PTSD and other stress disorders.
Via the existing vagal tone measurements (of respiratory sinus arrhythmia) it is easily possible, to conduct non invasive and inexpensive clinical research.
A further conclusion is that the treatment effectiveness of a cranial osteopathy session might be less dependent on the specificity of the biomechanical knowledge of the practitioner than on the interpersonal process skills as well as the practitioner's understanding and observation skills of ANS changes. If true, this should have some drastic consequences on the curriculum priorities of future osteopathy trainings.
While there haven't been any studies yet to correlate visceral motility with vasomotion, it seems quite likely that the rhythmic motions of visceral organs (which are taught to be independent of respiration, heart beat, or peristalsis) are also driven by biological rather than cosmic forces. Since visceral functioning is even more linked with the ANS than the cranium, it is most likely that visceral motility (as described by J.P. Barral and others) is an expression of vasomotor oscillations regulated by the ANS.
Farasyn A, Vanderschueren F 2001 The decrease of the cranial rhythmic impulse during maximal rhythmic exertion: an argument for the hypothesis of venomotion? Journal of Bodywork and Movement Therapies 5(1): 56-69
· Nelson KE et al.2001 Cranial rhythmic impulse related to the Traube-Hering-Mayer oscillation: comparing laser-Doppler flowmetry and palpation. J Am Osteopath Assoc, 101(3): 163-73
· Porges SW 2001 The polyvagal theory: phyolgenetic substrates of a social nervous system. Int J Psychophysiol 42(2):123-146
· Sahar T , Shalev AY , Porges SW 2001 Vagal modulation of responses to mental challenge in posttraumatic stress disorder. Biol Psychiatry, 49(7): 637-643
· Tasker DL 1916 Principles of Osteopathy
· Upledger JE, Vreedevoogt JD 1983 Craniosacral Therapy, Eastland Press, Chicago