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We would like to present our assessment and describe the accuracy of a retinal vein pulse amplitude photoplethysmographic (PPG) technique for non-invasively estimating intracranial pressure (ICP), which is a fundamental physiological parameter in neurological disease. Current ICP measurement techniques use external ventricular drain (EVD), pressure transducer implantation or cannulation of the lumbar cerebrospinal fluid space via lumbar puncture (LP) with risks of infection, haemorrhage and headache. Comparing LP to EVD pressure measures shows high concordance with SD of measured differences being just 2.1 mm Hg and 95% of differences falling between −5.1 to +2.6 mm Hg.1 We take PPG measures of venous pulse amplitude at varying intraocular pressure (IOP) to estimate the ICP/IOP balance point and hence the ICP. We present data from a cohort of neurological and neurosurgical patients comparing our estimates to invasive ICP estimates.
With institutional ethics approval, suitable neurosurgical patients with EVD and neurology patients within 2 days prior to undergoing LP were recruited. Suitability included being able to sit at a slit lamp for 10 min and being deemed fit for such examination by their clinical team. The PPG measurements were performed through an ophthalmodynamometry lens (Meditron, Volklingen, Germany) at a video slit lamp camera recording at 25 fps (Canon 5D mark III, Japan). A pulse oximeter was used to time the video-recordings in terms …
Contributors WHM: design and conceptualised study, examined patients. YJK: Examined patients, performed photoplethysmography analysis. AGK: performed lumbar puncture, design of study. CRL: performed EVD, study design and conceptualisation. MLH: study design, conceptualisation, designed harmonic analysis for study. KEP: designed and implemented modified broken stick data analysis. DYY: design and conceptualised study, manuscript preparation.
Funding National Health and Medical Research Council (NHMRC) of Australia grant APP107310
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
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