Graphical and statistical analyses of the oculocardiac reflex during a non-invasive intracranial pressure measurement

Purpose. This study aimed to examine the incidence of the oculocardiac reflex during a non-invasive intracranial pressure measurement when gradual external pressure was applied to the orbital tissues and eye. Methods. Patients (n = 101) and healthy volunteers (n = 56) aged 20–75 years who underwent a non-invasive intracranial pressure measurement were included in this retrospective oculocardiac reflex analysis. Prespecified thresholds greater than a 10% or 20% decrease in the heart rate from baseline were used to determine the incidence of the oculocardiac reflex. Results. None of the subjects had a greater than 20% decrease in heart rate from baseline. Four subjects had a greater than 10% decrease in heart rate from baseline, representing 0.9% of the total pressure steps. Three of these subjects were healthy volunteers, and one was a glaucoma patient. Conclusion. The incidence of the oculocardiac reflex during a non-invasive intracranial pressure measurement procedure was very low and not associated with any clinically relevant effects

Example spectrograms of pulse waves of blood flow in the ophthalmic artery collected by a transcranial Doppler using different external pressure steps.

<p>(A) 0 mmHg; (B) 48 mmHg. HR—heart rate.</p

Histogram of HR_diff (parameter for the detection of the oculocardiac reflex) for subjects from all groups and 870 external pressure steps applied during all of the non-invasive intracranial pressure measurements.

<p>Histogram of HR_diff (parameter for the detection of the oculocardiac reflex) for subjects from all groups and 870 external pressure steps applied during all of the non-invasive intracranial pressure measurements.</p

Schematic representation of the non-invasive intracranial pressure (ICP) measurement equipment Vittamed 205.

<p>(A) Relevant orbit and brain anatomy in contact with the ICP measurement device. (B) Block diagram of the system control unit. ICA—internal carotid artery; IOA—intracranial part of the ophthalmic artery; EOA—extracranial part of the ophthalmic artery; TCD—transcranial Doppler; Pe—external pressure applied to the ocular globe.</p

Protocol parameters for the non-invasive intracranial pressure measurement according to group.

<p>Protocol parameters for the non-invasive intracranial pressure measurement according to group.</p

Demographic data of the included subjects in this retrospective study.

<p>Demographic data of the included subjects in this retrospective study.</p

Typical heart rate variation.

<p>(A) A heart rate variation in a healthy volunteer. (B) A pressure increase of 4 mmHg per pressure Pe(t) step (time period of approximately 30 sec each) was used on the ocular globe from 0 mmHg to 48 mmHg.</p

Heart rate (HR) variation at every external pressure step (Pe) applied on the ocular globe in the case of a 10% decrease in the MHR compared to the BHR.

<p>(A) Healthy subject. (B) Glaucoma patient. (C) Healthy subject. (D) Healthy subject.</p