Short-term Ocular Perfusion Pressure (OPP) Can Be As Low As 4-8 mmHg via 24-hour Telemetry in Nonhuman Primates (NHP)

Abstract

 

Purpose

 

To test the hypothesis that the distribution of 5-minute-window averages of bilateral OPP differs between NHPs as characterized via continuous radio telemetry of bilateral IOP and aortic blood pressure (BP).

 

Methods

 

We have developed and validated an implantable IOP telemetry system that wirelessly records 500 measurements per second for up to 2-1/2 years (IOVS 52(10):7365-75). Using an enhanced version of this system, continuous bilateral IOP, bilateral electro-oculogram (EOG), and aortic blood pressure (BP) were recorded 24 hours/day for a period of 45 days in four young adult male rhesus macaques aged 3-6 years old. Bilateral IOP measurements were taken in 3 NHPs and unilateral measurements acquired in 1 NHP. The IOP transducers were calibrated directly via anterior chamber manometry, and OPP was calculated 500 times per second as: central retinal artery (CRA) BP - IOP. The CRA systolic and diastolic BPs were calibrated directly to the aortic systolic and diastolic BPs recorded by the telemetry system via ophthalmodynamometry, by visualizing the IOPs at which the CRA begins to flutter (diastolic) and fully collapse (systolic). OPP data was corrected for signal drift, averaged in non-overlapping 5-minute windows for each 24-hour period, and compared between animals.

 

Results

 

As seen in the Figure, the distribution of 5-minute-window averages of OPP was consistent between contralateral eyes but varied widely between animals. One NHP had a significant number of 5-minute periods in which average OPP was 4-8 mmHg, while another animal had none below 40 mmHg. The modes of the daily 5-minute-window average distributions were 15-20 mmHg, 30-40 mmHg and >40mmHg for 2, 1, and 1 NHP, respectively.

 

Conclusions

 

Short-term OPP, calculated as non-overlapping 5-minute-window averages, is consistent between contralateral eyes within NHPs, but shows a broad distribution within NHPs. Two of four NHPs exhibited a significant number of daily 5-minute periods with relatively low OPP (<15 mmHg), which may put these animals at risk for periodic, recurring ischemic damage at lower IOP levels.  

 

OPP calculated from continuous bilateral IOP and aortic blood pressure telemetry for 4 NHPs. Data for 45, 24-hour recording periods are plotted as the daily average distributions of 5-minute-window averages with standard deviations.