Cranial osteopathy (aka Cranial Therapy or Cranial-Sacral Therapy) is based on the fact that the central nervous system, including the brain and spinal cord, has subtle, rhythmic pulsations that are vital to health and can be detected and modified by a skilled practitioner.

“Osteopathy in the Cranial Field has gained a special position within the many dimensions of osteopathic medicine. The underlying causes of severe pathological disturbances are to be found in cerebrovascular insufficiency and impaired cerebrospinal fluid circulation. Throughout the early development of osteopathic medicine, Dr. Andrew Taylor Still, its founder, paid special attention to the cerebrovascular and cerebrospinal systems. The role of these systems was well known to him at the end of the XIX Century. He appreciated their respective dominance in body physiology. Another enlightened pioneer, Dr. William G. Sutherland, who advanced osteopathy into the cranial field, recognized the significance of slow fluctuations arising within the cranium, which could be responsible for skull bone motion.”^[1]

Dr. Sutherland defined this motion as the Primary Respiratory Mechanism in the 1930s. The PRM according to Sutherland “includes a number of structural or anatomical elements namely brain, blood vessels, meninges, the cranial bones with their delicate articular design of sutures and the reciprocal tension membrane of dura mater. Within the cranium there is the source of the special physical forces, which initiate the cranial rhythmic impulse and skull bone motion.”^[2]

“Experimental and clinical observations demonstrate that relations between main parameters specific for CV (cerebrovascular) and CSF (cerebral spinal fluid) systems are complex. … For example, in one combination of primary factors, if arterial volume increases, cerebral blood flow (CBF) increases together with increase of intracranial pressure (ICP), but if venous volume inside the cranium increases or outflow of CSF to spinal cavity is obstructed, increase of ICP will be accompanied by a decrease of CBF.”^[3]

Hence, osteopathic manual therapy to skull bones that encourages appropriate, balanced CSF flow (assessed through the cranial rhythmic impulse at 8-12 cycles/min) allows for the proper CBF (arterial and venous), normal ICP, and overall oxygenation and nourishment of the brain.

^[1] Moskalenko, Y., Frymann, V., Kravchenko, T., & Weinstein, G. (2003). Physiological Background of the Cranial Rhythmic Impulse and The Primary Respiratory Mechanism. The AAO Journal, 2003, V.13, No.2, P.21-33

^[2] Ibid

^[3] Ibid.

Regional brain blood supply is determined not only by hemodynamic factors but also by CSF mobility. Therefore, if resistivity of CSF pathways increases, the regional CBF will decrease, and this may be the explanation of some kinds of neurological deficit. Such a situation might be one of the consequences of brain injury. In this case the appropriate osteopathic techniques could increase the CSF circulation in the injured brain region.

Numerous experiments have determined that “slow fluctuation of cerebral blood flow closely correlate with local fluctuations of brain blood volume and oxygen availability in brain tissue.” Recent applications of spectral analysis have shown (Moskalenko 2000, Moskalenko et al. 2001) that slow fluctuations are composed of extracranial fluctuations of arterial pressure and respiratory chest movements, and of intracranial fluctuations namely redistribution of CSF volumes inside skull.

One key experiment has been to measure how CSF and CV flow during a single cardiac cycle using 2 different parameters. The most acceptable test is a “combination of simultaneous recordings of Bio-Impedance (B-Imp) and transcranial dopplerography (TCD), because these methods are based on different physical principles and, therefore, reflect different aspects of the functioning of CV and CSF systems. Indeed, B-Imp records the change of electrical conductivity between plate electrodes, placed on the human head, for high frequency (50-70 kHz) electrical current. Because electrical conductivity of blood and CSF are different (for blood it is about half that for CSF), their comparative volume changes will change the electrical conductivity between electrodes.”^[1]

The following figure compares the CSF flow (represented by t) of a healthy person, an athlete, and a TBI patient. It was found that “t”, translated as “CSF mobility” was greatest in the athlete, normal in the healthy person, and significantly smaller in the TBI patient.  In very simplistic terms, if we think of the CSF as an abundant river of fluid circulating the brain and spinal column, that river is stagnant and restricted in the TBI patient. See Figure 5.

Time shift between peaks of TCD and В-Imp is determined by the replacement of some portion of CSF out from (or into) zone of В-Imp electrodes. Thus, this time interval represents the mobility оf CSF inside the cranium during the pulse cycle. At this period no active processes could operate. Investigations under different conditions have shown that “t” reflects CSF mobility.

In sum, CSF motility (along with CV flow), can be assessed and addressed by the osteopathic practitioner via the CRI. The CRI can be felt as the subtle motion of the skull bones. Encouraging an improved CRI by the cranial osteopathic practitioner is a significant way to positively affect the primary respiratory mechanism and overall metabolic and neurovascular health of the brain.

^[1] Ibid.