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Abstract
Intracranial pressure (ICP) includes the brain, optic nerve, and spinal cord pressures; it influences blood flow to those structures. Pathological elevation in ICP results in structural damage through various mechanisms, which adversely affects outcomes in traumatic brain injury and stroke. Currently, invasive procedures which tap directly into the cerebrospinal fluid are required to measure this pressure. Recent fluidic engineering modelling analogous to the ocular vascular flow suggests that retinal venous pulse amplitudes are predictably influenced by downstream pressures, suggesting that ICP could be estimated by analysing this pulse signal. We used this modelling theory and our photoplethysmographic (PPG) retinal venous pulse amplitude measurement system to measure amplitudes in 30 subjects undergoing invasive ICP measurements by lumbar puncture (LP) or external ventricular drain (EVD). We estimated ICP from these amplitudes using this modelling and found it to be accurate with a mean absolute error of 3.0 mmHg and a slope of 1.00 (r = 0.91). Ninety-four percent of differences between the PPG and invasive method were between − 5.5 and + 4.0 mmHg, which compares favourably to comparisons between LP and EVD. This type of modelling may be useful for understanding retinal vessel pulsatile fluid dynamics and may provide a method for non-invasive ICP measurement.
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Details
1 University of Western Australia, Lions Eye Institute, Centre for Ophthalmology and Visual Science, Perth, Australia (GRID:grid.1012.2) (ISNI:0000 0004 1936 7910)
2 University of Western Australia, Lions Eye Institute, Centre for Ophthalmology and Visual Science, Perth, Australia (GRID:grid.1012.2) (ISNI:0000 0004 1936 7910); Counties Manukau DHB, Department of Ophthalmology, Auckland, New Zealand (GRID:grid.416904.e) (ISNI:0000 0000 9566 8206)
3 University of Western Australia, Centre for Neuromuscular and Neurological Disorders, Perron Institute AU, Perth, Australia (GRID:grid.1012.2) (ISNI:0000 0004 1936 7910); Murdoch University, Institute for Immunology and Infectious Disease, Perth, Australia (GRID:grid.1025.6) (ISNI:0000 0004 0436 6763)
4 Sir Charles Gairdner Hospital, Neurosurgical Service of Western Australia, Nedlands, Australia (GRID:grid.3521.5) (ISNI:0000 0004 0437 5942); University of Western Australia, Medical School, Perth, Australia (GRID:grid.1012.2) (ISNI:0000 0004 1936 7910)
5 Sir Charles Gairdner Hospital, Department of Neurology, Nedlands, Australia (GRID:grid.3521.5) (ISNI:0000 0004 0437 5942)