Cerebrospinal fluid pressure in the anesthetized rat

Objective: The primary aims of this study were to determine the major frequencies and powers of oscillations in cerebrospinal fluid (CSF) pressure in the anesthetized rat, and determine whether the CSF pressure oscillations correlated with the major oscillation frequencies in the cardiovascular and respiratory systems as proposed by some chiropractic theories. Methods: The cardiac and ventilatory cycles, and CSF pressure were simultaneously recorded during spontaneous and positive-pressure mechanical ventilation in the anesthetized rat. Power spectra were generated from the raw data to identify the major oscillation frequencies in cardiorespiratory and CSF data sets. Entrainment of CSF pressure with ventilation was tested by mechanically pacing the ventilation over a range of frequencies. Results: The most powerful oscillation in CSF pressure was coincident with ventilatory chest movement during both spontaneous and mechanically paced ventilation. In 22 of 26 trials, there was also a very weak oscillation in CSF pressure that was entrained to heart rate. In addition, in 21 of 26 trials, it was possible to identify a low-frequency oscillation (<0.25 Hz) in CSF pressure that was coincident with a low-frequency oscillation in the power spectrum of the cardiac cycle. Conclusions: This study suggests oscillations in CSF pressure in the anesthetized rat are entrained to and driven by ventilation. The arterial pulse pressure makes little contribution to oscillations in CSF pressure in the immobile, anesthetized rat. This study provides normative, quantitative data on which to develop studies concerning the effects of vertebral movements and spinal posture on CSF dynamics.