The effect of body position change on noninvasively acquired intracranial pulse waves

Abstract

Objective. Craniospinal compliance (CC) is an important metric for the characterization of space-occupying neurological pathologies. CC is obtained using invasive procedures that carry risks for the patients. Therefore, noninvasive methods for acquiring surrogates of CC have been proposed, most recently based on changes in the head’s dielectric properties during the cardiac cycle. Here, we have tested whether changes in body position, which are known to influence CC, are reflected in a capacitively acquired signal (hereinafter referred to as W) originating from dynamic changes of the head’s dielectric properties. 
Approach. Eighteen young healthy volunteers were included in the study. After 10 minutes in supine position, subjects were tilted head-up (HUT), back to 0° (horizontal, control), and then head-down (HDT). Metrics related to cardiovascular action were extracted from W, including AMP, the peak-to-valley amplitude of the cardiac modulation of W. Computational electromagnetic simulations were performed to probe the association between intracranial volume change and W. 
Main results. AMP decreased during HUT (0°: 2869±597 arbitrary units (au); +75°: 2307±490 au, P=0.002) and increased during HDT (-30°: 4403±1428 au, P<0.0001). The same behavior was predicted by the electromagnetic model. 
Significance. Tilting affects the distribution of CC between cranial and spinal compartments. Cardiovascular action induces compliance-dependent oscillatory changes in the intracranial fluid composition, which causes corresponding variations in the head’s dielectric properties. These manifest as increasing AMP with decreasing intracranial compliance, which suggests that W may contain information related to CC, and that it might be possible to derive CC surrogates therefrom.

Automatic calculation for pulse wave morphology change: a rheoencephalographic study

“…Computerized noninvasive ICP monitoring was reported by [41,42]. In recent years, a few ICP pulse wave analysis publications have appeared, such as a patent [43], a device [17], a calculation of the P2/P1 ratio [18], and a device for measuring the head's dielectric properties (Cephalotec, Horgen, Switzerland), which is changing as a heartbeat-related pulse wave [44]. None of them performed comparative pulse wave morphology analyses, as we presented here.…”

Analysis of intracranial pressure pulse waveform in studies on cerebrospinal compliance: a narrative review

“…A modeling study confirmed that changes in the dielectric properties of the head correlate to the cardiac and respiratory cycles associated with changes in the volumes of cerebral blood and CSF (Karimi et al 2023). The signal provided by the device, denoted W, was shown through experimental hyperventilation studies to be, at least partially, of intracranial origin (Spiegelberg et al 2023) and the amplitude of its cardiac-related oscillations was demonstrated to change during head-up and head-down tilt testing in a way that reflects the alterations in blood and CSF volume induced by changes in body position (Boraschi et al 2023). The authors concluded that W may therefore contain meaningful information on craniospinal compliance; however, they have not yet reported comparative analyses between invasive and noninvasive methods of compliance assessment.…”

Influence of age on the relation between body position and noninvasively acquired intracranial pulse waves

“…Most recently, an approach based on the capacitive measurement of the dielectric properties of the head was introduced 13 . This method has been investigated so far only on young healthy volunteers below the age of 30 14 . Given that ageing affects the cerebrospinal fluid (CSF) system, for example by decreasing ICP 15 – 17 , it is expected that also the dielectric properties of the head change with age.…”

“…It has been shown through hyperventilation testing on healthy volunteers that W is, at least in part, of intracranial origin 13 . The peak-to-valley amplitude (AMP) of W associated with cardiovascular activity has been shown to decrease with head-up tilting and increase with head-down tilting in healthy subjects below the age of 30 14 . Tilt testing is a noninvasive maneuver known to change the relative contributions of the cranial and spinal compartments to CC 19 , 22 .…”

“…In this study, we acquired W in a cohort of healthy volunteers above 60 years of age and measured AMP, a metric potentially linked with CC, during tilt testing. We then compared the obtained AMP values and their change during tilting with those observed in a previously investigated cohort of younger (< 30 years) healthy subjects 14 .…”