Pressure phase relationships between carotid arterial pressure and intracranial pressure: the 'violin' analogy of intracranial pulsations

  • Michael Egnor1Email author,

    Affiliated with

    • Mark Wagshul2,

      Affiliated with

      • Erin McCormack2,

        Affiliated with

        • Pat McAllister3,

          Affiliated with

          • Joe Madsen4,

            Affiliated with

            • Rui Zou4,

              Affiliated with

              • Lili Zhen5 and

                Affiliated with

                • Jeff Peng5

                  Affiliated with

                  Cerebrospinal Fluid Research20063(Suppl 1):S14

                  DOI: 10.1186/1743-8454-3-S1-S14

                  Published: 21 December 2006

                  Background

                  Many investigators have shown marked abnormalities of CSF and parenchymal pulse pressure in hydrocephalus, and Greitz, Bateman, and Egnor have proposed that abnormalities of pulsatility are at the root of the pathophysiology of hydrocephalus. Our work is aimed at a more rigorous understanding of pulsatility in the cranium. We have studied the phase relations between the carotid arterial pressure pulse and the intracranial pressure (ICP) pulse in dogs as a function of mean intracranial pressure.

                  Materials and methods

                  Carotid arterial pressure and intracranial pressure in 12 dogs were measured with progressive withdrawal and infusion of CSF to change intracranial pressure and compliance. The waveforms were recorded and synchronized in time. Phase between the carotid and ICP pulse was determined using the phase difference between the fundamental harmonics of the Fast Fourier Transform.

                  Results

                  The normal ICP pulse led the carotid arterial pulse by an about 50 degrees. With lowering of ICP, there was an increase in the lead of the ICP pulse with respect to the carotid pulse to about 100 degrees. Increasing ICP caused a progressive phase lag of ICP pulse with respect to carotid pulse, up to a maximum lag between arterial and intracranial pulse of approximately 30 degrees.

                  Conclusion

                  These data clearly show that there are conditions in which the ICP pulse precedes the carotid pulse. With raising and lowering of the mean ICP, the phase versus mean ICP curve is sigmoid-shaped, with the normal ICP phase is the inflection point of the sigmoid curve. The observation that the ICP pulse of the dog normally precedes the carotid arterial pulse is counterintuitive. It forces us to rethink our current understanding of the way in which the ICP pulse is generated. We propose that the ICP pulse is a standing wave, not a transmitted wave. Standing waves can be generated in chambers with elasticity, such as in the body of a violin. The vibrations from the violin strings excite the vibrations in the body of a violin, but the vibrations in the body of the violin can lead or lag the string vibrations. The concept that the ICP wave is a standing wave is important, because it suggests that the cranium can suppress (or accentuate) certain frequencies of arterial pulse entering it. This may shed new light on cerebral blood flow, the cerebral windkessel mechanism, and on the pathogenesis of hydrocephalus.

                  Authors’ Affiliations

                  (1)
                  Department of Neurosurgery, State University of New York at Stony Brook, Health Science Center
                  (2)
                  Department of Radiology, State University of New York at Stony Brook, Health Science Center
                  (3)
                  Department of Neurosurgery, Wayne State University School of Medicine
                  (4)
                  Department of Neurosurgery, Harvard University
                  (5)
                  Department Mechanical Engineering, State University of New York at Stony Brook

                  Copyright

                  © Egnor et al; licensee BioMed Central Ltd. 2006

                  This article is published under license to BioMed Central Ltd.

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