RAQ: a novel surrogate for the craniospinal pressure–volume relationship

Abstract

OBJECTIVE The intracranial pressure-volume relation contains information relevant for diagnostics of hydrocephalus and other space-occupying pathologies. We aimed to design a noise-resilient surrogate for this relationship that can be calculated from intracranial pressure (ICP) signals. APPROACH The new surrogate, termed respiratory amplitude quotient (RAQ), characterizes the modulation of the cardiac pulse wave amplitude by the respiratory wave in the ICP time course. RAQ is defined as the ratio of the amplitude of the respiratory wave in the ICP signal to the amplitude of the respiration-induced variation in the course of the cardiac pulse wave amplitude. We validated the calculation of RAQ on synthetically generated ICP waveforms. We further extracted RAQ retrospectively from overnight ICP recordings in a cohort of hydrocephalus patients with aqueductal stenosis, age 55.8 ± 18.0 years, and a comparison group with hydrocephalus diagnosed by morphology in MRI, but not responsive to either external lumbar drainage or ventriculo-peritoneal shunting, age 72.5 ± 6.1 years. RAQ was determined for the full recordings, and separately for periods containing B-waves. MAIN RESULTS We found a mean difference of less than 2% between the calculated values of RAQ and the theoretically determined equivalent descriptors of the synthetic ICP waveforms. In the overnight recordings, we found significantly different RAQ values during B-waves in the aqueductal stenosis (0.86 ± 0.11) and non-responsive hydrocephalus patient groups (1.07 ± 0.20), p = 0.027. In contrast, there was no significant difference in other tested parameters, namely pressure-volume index, elastance coefficient, and resistance to outflow. Neither did we find significant difference when considering RAQ over the full recordings. SIGNIFICANCE Our results indicate that RAQ may function as a potential surrogate for the intracranial pressure-volume relation.

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

“…The respiratory peak was extracted in the frequency range of 0.14-0.33 Hz (corresponding to 8-20 breaths min −1 ) from both amplitude spectra, obtaining the amplitude of the respiratory wave in the W signal (A rp ) and the amplitude of the respiration-induced variation of AMP (AA vp ). The respiratory amplitude quotient (RAQ) was computed as the ratio of A rp to AA vp , as defined in Spiegelberg et al (2020).…”

Noninvasive Monitoring of Intracranial Pulse Waves

“…Thirdly, only AMP was calculated as a feature with possible association with craniospinal compliance. Other signal features that may be associated with compliance, such as the respiratory amplitude quotient [43], or B-waves (after adjustment of the frequency band) [44] should be considered as well.…”

A Deep Learning-Based Automated Framework for Subpeak Designation on Intracranial Pressure Signals

“…This is why different characterizations of cerebral compliance, based on a mathematical analysis of the ICP waveform, have been proposed in the literature [ 10 , 11 ]. Notably, the shape of heartbeat-induced pulses varies according to cerebral compliance [ 12 ].…”

“…Combined with the absolute value of the ICP, a measure of cerebral compliance could help guide the clinical management of intensive care patients [7][8][9]. This is why different characterizations of cerebral compliance, based on a mathematical analysis of the ICP waveform, have been proposed in the literature [10,11]. Notably, the shape of heartbeat-induced pulses varies according to cerebral compliance [12].…”