Pulse Pressure Waveform in Hydrocephalus: What It is and What It Isn't

Marek Czosnyka, Ph.D.; Zofia Czosnyka, Ph.D.; Nicole Keong, M.B., B.S., M.R.C.S.; Andreas Lavinio, M.D.; Piotr Smielewski, Ph.D.; Shahan Momjian, M.D.; Eric A. Schmidt, Ph.D.; Gianpaolo Petrella, M.D.; Brian Owler, Ph.D.; John D. Pickard, F.MED.SCI.

Disclosures

Neurosurg Focus. 2007;22(4):E1 

In This Article

Abstract and Introduction

Object: Apart from its mean value, the pulse waveform of intracranial pressure (ICP) is an essential element of pressure recording. The authors reviewed their experience with the measurement and interpretation of ICP pulse amplitude by referring to a database of recordings in hydrocephalic patients.
Methods: The database contained computerized pressure recordings from 2100 infusion studies (either lumbar or intraventricular) or overnight ICP monitoring sessions in patients suffering from hydrocephalus of various types (both communicating and noncommunicating), origins, and stages of management (shunt or no shunt). Amplitude was calculated from ICP waveforms by using a spectral analysis methodology.
Results: The appearance of a pulse waveform amplitude is positive evidence of a technically correct recording of ICP and helps to distinguish between postural and vasogenic variations in ICP. Pulse amplitude is significantly correlated with the amplitude of cerebral blood flow velocity (R = 0.4, p = 0.012) as assessed using Doppler ultrasonography. Amplitude is positively correlated with a mean ICP (R = 0.21 in idiopathic normal-pressure hydrocephalus [NPH]; number of cases 131; p < 0.01) and resistance to cerebrospinal fluid outflow (R = 0.22) but does not seem to be correlated with cerebrospinal elasticity, dilation of ventricles, or severity of hydrocephalus (NPH score). Amplitude increases slightly with age (R = 0.39, p < 0.01; number of cases 46). A positive association between pulse amplitude and increased ICP during an infusion study is helpful in distinguishing between hydrocephalus and predominant brain atrophy. A large amplitude is associated with a good outcome after shunting (positive predictive power 0.9), whereas a low amplitude has no predictive power in outcome prognostication (0.5). Pulse amplitude is reduced by a properly functioning shunt.
Conclusions: Proper recording, detection, and interpretation of ICP pulse waveforms provide clinically useful information about patients suffering from hydrocephalus.

Intracranial pressure is more than a number. Re corded ICP consists of a series of time-varying components derived from relatively fast changes in CBV. Pulsatile changes in arterial CBV evoke the pulse pressure waveform of ICP.[1] Changes in venous CBV due to variations in intrathoracic pressures are responsible for the respiratory component of ICP. Slower, intrinsic vasomotor changes in CBV are responsible for waves classified as B, C, plateau,[18] and other waves.

The intracranial pulse pressure waveform attracted the attention of many scientists approximately three decades ago and has maintained their interest until the present.[1,12] Relatively early it was postulated[8,16,23] that increased pulse pressure in ventricular CSF causes dilation of the ventricles. With the advent of dynamic MR imaging, pulsatile flow of CSF has been intensively studied. Most interest has been devoted to fast CSF flow through the aqueductus cerebri, reportedly increased in hydrocephalus.[4,14,22] However, there are conflicting reports regarding its role in prognostication following shunting, both enthusiastically supportive[4] and highly critical.[15] Some interesting theories on the development of communicating hydrocephalus, al though still awaiting conclusive documentation,[2,9,10,13,27] are largely based on MR imaging studies related to pulsatile CSF flow.

Pressure recording does not require strong magnets or complex machinery. Although invasive, it remains a frontline method of examination for hydrocephalus in many hospitals worldwide. Studies on the pulse pressure waveform[1,12,20,24] pioneered the understanding of CSF dynamics; however, clinical use of the data is not firmly established. A new generation of clinical neuroscientists continue in this direction, recently publishing a number of promising studies.[11,17,21]

We analyzed pulse pressure amplitude during CSF infusion studies[7] or overnight ICP monitoring sessions in hydrocephalic patients with or without shunts. Our intention was to summarize our subjective experience with the interpretation of ICP pulse pressure amplitude in different scenarios, in a predominantly observational manner.

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