Mechanisms behind altered pulsatile intracranial pressure in idiopathic normal pressure hydrocephalus: role of vascular pulsatility and systemic hemodynamic variables

Abstract

Background The dementia subtype idiopathic normal pressure hydrocephalus (iNPH) has unknown etiology, but one characteristic is elevated intracranial pressure (ICP) wave amplitudes in those individuals who respond with clinical improvement following cerebrospinal fluid (CSF) diversion. To explore the mechanisms behind altered ICP wave amplitudes, we correlated central aortic blood pressure (BP) and ICP waveform amplitudes (intracranial aortic amplitude correlation) and examined how this correlation relates to ICP wave amplitude levels and systemic hemodynamic parameters. Methods The study included 29 patients with probable iNPH who underwent continuous multi-hour measurement of ICP, radial artery BP, and systemic hemodynamic parameters. The radial artery BP waveforms were used to estimate central aortic BP waveforms, and the intracranial aortic amplitude correlation was determined over consecutive 4-min periods. Results The average intracranial aortic amplitude correlation was 0.28 ± 0.16 at the group level. In the majority of iNPH patients, the intracranial aortic amplitude correlation was low, while in about 1/5 patients, the correlation was rather high (average Pearson correlation coefficient > 0.4). The degree of correlation was hardly influenced by systemic hemodynamic parameters. Conclusions In about 1/5 iNPH patients of this study, the intracranial aortic amplitude correlation (IAAC AORTIC) was rather high (average Pearson correlation coefficient > 0.4), suggesting that cerebrovascular factors to some extent may affect the ICP wave amplitudes in a subset of patients. However, in 14/19 (74%) iNPH patients with elevated ICP wave amplitudes, the intracranial aortic amplitude correlation was low, indicating that the ICP pulse amplitude in most iNPH patients is independent of central vascular excitation, ergo it is modulated by local cerebrospinal physiology. In support of this assumption, the intracranial aortic amplitude correlation was not related to most systemic hemodynamic variables. An exception was found for a subgroup of the patients with high systemic vascular resistance, where there was a correlation. Keywords ICP wave amplitudes. Central aortic waveforms. Idiopathic normal pressure hydrocephalus. Autoregulation This article is part of the Topical Collection on Neurosurgery general

Neurofluids—Deep inspiration, cilia and preloading of the astrocytic network

“…However, experiments intending to prove the magnitude of this pulsatile effect through the aqueduct have found this effect to be too small for considerable efficacy (Holmlund et al., 2019). Although ICP overnight measurements in patients with iNPH have shown a normal amplitude pressure level, a higher pulsatility has been reported underlying the assumed mechanism, contradictory to the above cited observations (Evensen & Eide, 2020). Today, diagnostic workup mainly consists of tapping 30–40 ml CSF by lumbar puncture, simulating shunt therapy.…”

Functional analysis of the human perivascular subarachnoid space

“…In previous studies, we found that high correlation between intracranial and vascular pressure pulsatility in patients with subarachnoid hemorrhage was accompanied with worse outcome 34 . In subjects with iNPH, there was low correlation between intracranial and vascular pressure pulsatility in the majority of patients 35 . We suggest that elevated intracranial pulsatility due to underlying disease causes restriction on the arterial pulsatility, which in turn hampers the perivascular tracer transport.…”

Cerebral arterial flow dynamics during systole and diastole phases in young and older healthy adults

“…ICP monitoring, initially introduced by Lundberg [ 3 ], has been used for diagnosing and managing different brain diseases, such as hydrocephalus, idiopathic intracranial hypertension, traumatic brain injury, and cerebral haemorrhages [ 4 – 6 ]. Currently, only the mean ICP value is considered in clinical practice; however, a growing number of researchers are interested in studying the shape of the ICP pulse waveform [ 7 – 9 ] to better understand the pathology’s origin [ 10 ]. Typically, the ICP pulse is composed of three peaks, P1, P2, and P3, which in healthy cases, P1 predominates in amplitude over P2 and P3 [ 11 ].…”