Abstract
Purpose :
There is increasing evidence that intracranial pressure (ICP) plays a significant role in the development and progression of glaucoma through both physical and neural interaction with intraocular pressure (IOP). However, very little is known about transient ICP fluctuations due to the invasiveness required for accurate measurement. Here, we utilized the TSE-Systems Stellar total implant to wirelessly record and quantify ICP fluctuations of non-human primates (NHPs).
Methods :
Continuous ICP data were collected from 7 NHPs via a pressure transducer implanted in the brain parenchyma at the level of the optic nerve head as a surrogate for retrobulbar cerebral spinal fluid pressure (CSFP). Data were collected at 250 Hz for a 33% duty cycle in 3 NHPs and at 200 Hz for a 10% duty cycle in 5 NHPs, with one NHP providing data for both. ICP transducers were calibrated monthly via a Codman ICP Express microsensor inserted into the parenchyma via a titanium port. ICP data were subjected to a dual-band finite impulse response (FIR) filter with a lower band of 0.5-3 Hz to detect shorter transient fluctuations and an upper band of 5-10 Hz to detect longer transient fluctuations. Transient ICP fluctuation magnitudes were sorted and binned hourly to quantify the average magnitude of transient ICP fluctuations during waking (6AM-6PM) and sleeping hours (6PM-6AM). The area under the ICP vs time curve was used to define the relative % transient energy contribution to the overall ICP waveform.
Results :
The distribution of ICP fluctuations during both waking and sleeping hours showed a higher prevalence of transient ICP fluctuations <5 mmHg. ICP fluctuations >5 mmHg occurred primarily during waking hours. On average, transient ICP fluctuations occurred ~7200 times per waking hour and ~5300 times per sleeping hour, which translates to ~26% more transient ICP fluctuations during waking hours. During waking and sleeping hours the average % transient energy across animals was ~27% and ~16%, respectively. This is likely due to increased heart rate, respiration, and activity during waking hours.
Conclusions :
Similar to IOP, ICP is variable and fluctuates moment-to-moment. However, ICP fluctuations occur less often than IOP fluctuations (~10,000 per waking hour) and are not as prevalent at higher magnitude. Cardiac pulse was the most prominent feature in ICP. Future work will quantify ICP fluctuations in glaucomatous versus untreated fellow eyes.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.