Perceiving the Imperceptible

Sensing the Imperceptible: The human cranium

You see before you a dreamer – one who had to get away from the texts, as did Dr Still, and follow something he could not explain. Something that kept him digging into his dreams
‘William Garner Sutherland’

This particular post is intended for the reading eyes of the health professional, in particular osteopaths. Having studied osteopathic medicine for the past 5 years it has become obvious that there are contrasting styles in the way in which different individuals treat their patients. The most obvious difference being the divide between those who prefer a more structural approach to those who opt for the ‘gentler’ functional methods. The most controversial of these approaches seems to be techniques aimed at manipulating cranial bones (termed cranial osteopathy). I myself have modelled my treatments to the structural approach and have been highly sceptical of techniques aimed at influencing the articulations of cranial bones. Although I can’t help but wonder if this scepticism is justified, so I have decided to examine the cranial approach to see if it has any merit.

There is no doubting that the articulations between cranial bones (known as sutures) move. This has been proven again and again through research. The problem is that these movements are extremely small in amplitude (1mm and less). The contention of cranial osteopathy is that all of the cranial bones move at their sutures in a rhythmical fashion. This rhythm has been termed the cranial rhythmic impulse (makes sense). This too has been shown through research and even conventional medical textbooks agree that there is the presence of a slow oscillating rhythm. However, the debate begins to arise with the following questions:

What is causing this rhythmical movement?

Can we both palpate and therapeutically alter the movements of the cranial bones and hence influence the rhythm?

An Osteopath by the name of William Garner Sutherland was the first to describe these movements and hence was the first to propose a theory behind its cause. He concluded that a phenomenon known as the ‘Primary Respiratory Mechanism’ was the cause of these movements. The problem is that more than 60 years after Sutherland described the PRM we still don’t know what it actually is. I am also yet to be offered even a proposed theory as to what the PRM (after 3 months of classes). All I have been taught at university are 5 of its effects but nothing of its cause. This is a bit of a problem. If we are going to treat using this theory we need to at least develop a theory as to its cause. Luckily, through a bit of research of my own, I have come across some research papers which have looked at proposed causes for the PRM. It appears that there is a phenomenon in the body known as the traube-herring oscillation which just happens to share the same frequency as the Cranial rhythmical impulse (coincidence I think not). The traube-herring oscillation is defined as follows:

Slow oscillations in blood pressure usually extending over several respiratory cycles; related to variations in vasomotor tone; rhythmical variations in blood pressure.

This explanation for the cause of the PRM makes sense for the following reasons:

The PRM is proposed to be felt anywhere over the body (method of treatment in the field of biodynamics). The traube-herring oscillation is present throughout the entire body not just the cranium. I propose the following theory regarding treatment using cranial manipulation. If the traube-hering oscillation is a reflection of autonomic activity (variations in blood pressure and vasomotor tone reflect autonomic activity) then the PRM and the CRI is an expression of autonomic activity and hence cranial osteopathy deals with the treatment of the autonomic nervous system through manipulation this rhythm.

Ok, so I have attempted to put together an answer for the first question, now the next question. Can we both palpate and therapeutically alter the movements of the cranial bones and hence illicit a change in autonomic activity?

This has been the biggest problem for me to come to grasps with. Initially looking on the surface it would seem unlikely that we can perceive and manipulate such small movements. I can only speak from experience and say that I have definitely felt two rhythms. One that would correlate with pressure changes due to the cardiac cycle and a second more closely resembling the Traube-hering oscillation. Evidence also appears to back up that we can perceive this motion. Can we manipulate it? Given that the proposed contact required to manipulate these sutures are extremely light and small in nature to the normally structurally oriented practitioner it is difficult to grasp the concept of influencing these movements. I mean, if the cranium feels so firm and rigid to forceful contacts how will light contact illicit a change.

In order to better appreciate the possibility of manipulating the sutures let us consider the properties of water and how it may possibly relate to these articulations. When water is met with forceful contact it exhibits a rigid property, however, if we lightly caress the water it assumes a more malleable (and manipulable) state. It would make sense that sutures possess the same qualities. Rigid to force for protective and structural reasons and malleable to small forces for functional and physiological reasons.

The most important question of all is can we use this to illicit a therapeutic change in our patients? How would we do this? There is a current nomenclature in cranial osteopathy that deals with strain patterns and their correction, however, I think there is cause for another approach. This approach would involve illiciting an artificial frequency with our hands to alter the frequency of the traube-hering oscillation. This concept is usually termed entrainment and has been demonstrated in other physiological processes, most notably the menstrual cycle. By increasing frequency we would amplify the activity within the sympathetic nervous system and by decreasing the frequency we would dampen activity within the sympathetic nervous system. There has already been one study which has shown that cranial techniques improve latency to sleep which may be due to its effect on the autonomic nervous system (they did not use methods that would result in entrainment).

Some osteopaths use cranial osteopathy as their only means of treatment, I strongly disagree with this practice. Some osteopaths prefer a strictly structural approach. However, should we be distinguishing between a structural and functional approach? Shouldn’t manipulation of the cranial bones merely be viewed as simply another form of osteopathic technique rather than some specialised field of therapy? The only difference is you are working with the structure of the skull as opposed to the structure of the spine, shoulder, knee, ankle etc. In any case, I think the theoretical evidence behind cranial manipulation cannot be ignored and its acceptance will only come with clinical trial evidence, which for obvious reasons is difficult to obtain. Nevertheless, if you consider yourself to be an osteopathic physician in the true sense of the word, then you should not neglect the reciprocal nature of structure and function expressed by the cranium.