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Monitoring intracranial pressure (ICP) is vital for patients with elevated, or potentially elevated ICP. This pressure can be monitored using invasive procedures such as lumbar puncture manometry or various methods of direct measurement in or upon the brain, each with attendant complication risks. Measurement of naturally occurring tympanic membrane pulse (TMp) may provide an alternative non-invasive method of monitoring ICP, which would help the risks of invasive methodologies. This paper discusses a piezo based sensor (which we term the “brain stethoscope”) designed and tested to acquire TMp signals. In addition, the TMp signals were acquired from five human subjects where ICP was expected to vary. ICP was increased in this experimental model using head down positioning on a tilt table. Results showed that tympanic membrane waveform changed in morphology and amplitude with increased ICP. The lead time between the TMp signal and a reference signal (Ear lobe blood flow pulse) was found to increase as ICP increased using this model. We conclude that measurement of TMp changes may provide a new non-invasive, low cost and easy to perform technique for monitoring patients at risk of elevated ICP.

Hydrocephalus is a medical condition characterized by an excessive accumulation of cerebrospinal fluid (CSF) in the ventricles of the brain, typically causing an increase in patient intracranial pressure (ICP). The increased ICP can result in headache, nausea, vomiting, and even death. To combat this potentially dangerous elevated ICP, physicians often use surgically implemented brain shunt systems that drain excess CSF from the brain into the abdominal cavity. Monitoring of ICP in patients with hydrocephalus is crucial for the effective management of brain shunt systems. Currently, clinical ICP measurement approaches are typically invasive and are performed using intraventricular catheters placed through a drilled hole in the skull. Home monitoring of ICP may be advantageous for tracking patient clinical status. A noninvasive method would be particularly useful for ICP monitoring in the emergency department, doctor's office, home and other non-ICU settings. This study aims to explore the correlation between ICP and tympanometric parameters including static acoustic compliance, a measurement of middle ear pressure at maximum compliance. Tympanometry was performed on subjects who rested on a tilt table at varying tilt angles, which induces changes in ICP. Results suggested a correlation between tilt angles and pressure of the middle ear at peak compliance. Tympanometry may provide a noninvasive method for monitoring ICP.

Seismocardiography (SCG) is a non-invasive method that can be used for cardiac activity monitoring. This paper presents a new electrocardiogram (ECG) independent approach for estimating heart rate (HR) during low and high lung volume (LLV and HLV, respectively) phases using SCG signals. In this study, SCG, ECG, and respiratory flow rate (RFR) signals were measured simultaneously in 7 healthy subjects. The lung volume information was calculated from the RFR and was used to group the SCG events into low and high lung-volume groups. LLV and HLV SCG events were then used to estimate the subjects HR as well as the HR during LLV and HLV in 3 different postural positions, namely supine, 45 degree heads-up, and sitting. The performance of the proposed algorithm was tested against the standard ECG measurements. Results showed that the HR estimations from the SCG and ECG signals were in a good agreement (bias of 0.08 bpm). All subjects were found to have a higher HR during HLV $(\mathbf{HR}_{\mathbf{HLV}})$ compared to LLV $(\mathbf{HR}_{\mathbf{LLV}})$ at all postural positions. The $\mathbf{HR}_{\mathbf{HLV}}/\mathbf{HR}_{\mathbf{LLV}}$ ratio was $\mathbf{1.11}\pm \mathbf{0.07} \mathbf{1.08}\pm \mathbf{0.05},\ \mathbf{1.09}\pm \mathbf{0.04}$ , and $1.09\pm 0.04\ (\mathbf{mean}\pm \mathbf{SD})$ ) for supine, 45 degree-first trial, 45 degree-second trial, and sitting positions, respectively. This heart rate variability may be due, at least in part, to the well-known respiratory sinus arrhythmia. HR monitoring from SCG signals might be used in different clinical applications including wearable cardiac monitoring systems.