The flow (and content) of the CSF is important for the homeostasis of the central nervous system and influencing that flow could have an impact on the patients’ health.
The production of CSF (renewed some 3 to 4 times per day) by the choroid plexi is believed to be relatively constant; however, the CSF secretion varies over the duration of a day with an average production of 650 ml and maximal production after midnight.
Absorption takes place from the subarachnoid spaces into the venous blood system through dural venous sinuses via cranial arachnoid granulations and into the lymph system via the nasal cribriform plate and the perineural sheaths.
The driving force of the convective flow is through the hydrostatic pressure gradients between the choroid plexus (high pressure) and arachnoid granulations (low pressure).
Beside the convective flow, there is the pulsatile flow. This pulsatile flow is a bidirectional movement in cranial and caudal direction along the spinal cord and in various directions in the brain.
The pulsatile flow is probably as well cardiac driven as respiratory driven.
The cardiac driven theory states that changes in blood volume are transmitted directly and indirectly to the CSF (blood vessel pulsations).
The respiratory-driven theory states that changes in the intrathoracic pressure are transmitted via the venous system to the CSF.
It is generally believed that inspiration elicits a cranial movement of CSF, while expiration elicits a caudal movement.
Both cranial and caudal CSF movements have been observed during inspiration as a result of epidural venous blood return to the thoracic spine from the cervical and lumbar spine.
The cardiac-driven force is thought to be responsible for the basic pulsatile CSF flow, while the respiratory-driven force is responsible for the large pulsatile CSF flow.
Read: Overgaard Wichmann T., Hasager Damkier H., Pedersen M. (2022) A Brief Overview of the Cerebrospinal Fluid System and Its Implications for Brain and Spinal Cord Diseases. Front. Hum.Neurosci. https://doi.org/10.3389/fnhum.2021.737217
My comment:
The above arguments are not in favor of the cranial techniques that are supposed to influence the CSF flow.
More important to influence the CSF flow is treating heart and lung dysfunctions as well with visceral, diaphragmic, thoracic musculoskeletal as autonomic nervous system techniques.
High cervical techniques can probably influence the transit of CSF between the cranial flow and the flow around the spinal cord.