engleski

Posture effects on cerebrospinal fluid pressure gradient and dynamics: does normal intracranial pressure has subatmospheric (negative) value?

It is generally believed that cerebrospinal fluid (CSF) pressure (CSFP) is regulated by rate of CSF secretion and resistance to circulation and absorption of CSF. However, it is not known which factors determine CSF pressure inside craniospinal system during body position changes. Body verticalization is followed by momentary decrease of hydrostatic CSF pressure inside cranium. This decrease is shown as transient, and is explained by sudden cranial fluids exchange. We hypothesized that these effects are not related to the cranial fluid volume changes, but depend on biophysical characteristics of cranial and spinal intradural space, as well as laws of fluid mechanics. Mentioned hypothesis was tested on cats and new artificial model of cranio-spinal space. CSF pressure changes in anaesthetized cats, with or without cervical stenosis, were compared with those in artificial model of CSF consisting of non-distensible „cranial“ and distensible „spinal“ part at the same recording points. Measuring cannulas were introduced into lateral ventricle (LV), cortical subarachnoid space (CSS) (4 cm from foramen magnum) and lumbar subarachnoid space (LSS) in cats fixed on a board in a prone position. Recording instruments were fixed on the board at the same hydrostatic level as the corresponding measuring cannula. In horizontal position the pressures were similar in cranial and lumbar regions in both animal and artificial model. In vertical position, CSFPs (cm H2O) of control animals in LV and CSS were similar (about -4), and in lumbar region it was about +32. Negative intracranial pressure was stable during recording in an upright position in cat as well as in artificial model. During postural changes, intracranial subatmospheric CSFP was not observed in animals with cervical stenosis. Results implicate that CSF pressure in cranium in upright position is determined by laws of fluid mechanics but not by changes of CSF and blood volume inside the cranium. Our results suggest that the cranial volume of blood and CSF remains constant in all body positions, which enables a good blood brain perfusion during everyday life activities. Hydrostatic CSFP gradient inside the cranium and LSS observed during changes of body position is not in accordance with the classical hypothesis of CSF physiology and unidirectional circulation. It seems that normal intracranial pressure in upright position in control animals has subatmospheric value.

cerebrospinal fluid ; cerebrospinal fluid pressure ; body position changes

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