Research Associate UW-Madison Madison, Wisconsin, United States
Introduction: Cerebral compliance reflects the ability of the cerebrospinal axis to buffer changes in volume. Compliance, and more specifically changes in compliance is a more critical issue than increasing ICP. Patients with decreased compliance may sustain greater increases in ICP from a given increase in volume than patients with adequate compliance. We propose new methods utilizing ICP waveform analysis to quickly estimate each patient’s compliance.
Methods: We built a test platform for generating ICP waveforms from simulated cardiac pulsations. The skull is simulated using a rigid chamber containing a latex balloon allowing the transmission of pulsations into the chamber. A second rigid chamber, communicating with the first one, represents the spinal canal. Cardiac pulsations are generated using a diaphragm pump interfaced with the balloon. Compliance is set by changing the total added air volume in continuity with the main rigid chamber. Baseline pressure is set by changing the fluid level in a reservoir column communicating with the main rigid chamber. Different combinations of compliance and baseline pressure were assembled to emulate different patient scenarios. A pressure transducer in the simulated brain/skull and spinal canal was placed for recording pressure. Each experiment was conducted over 1 min under changing physiologic parameters, including compliance, baseline pressure and pulse rate.
Results: We emulated ICP waveforms of over 30 patients under various compliance, baseline pressure, and pulse rates. Experiment results demonstrate that for a given pulse rate, brain compliance is linearly and inversely correlated with the area under curve (the area of ICP pressure above baseline pressure during each cardiac cycle). The R-squared is 0.985.
Conclusion : A method to estimate the brain compliance based on ICP waveform is developed. Our results indicate that brain compliance is linearly and inversely correlated with the area under curve.
