Nycthemeral Rhythm of Bilateral Ocular Perfusion Pressure (OPP) via 24-hour Telemetry in Nonhuman Primates (NHP)

Abstract

 

Purpose

 

To characterize the nycthemeral rhythm of bilateral OPP 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 12 days in a 14-day period in both eyes of three young adult male rhesus macaques aged 3-6 years old. The bilateral IOP transducers were calibrated directly via anterior chamber manometry, and bilateral 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 collapses (systolic). OPP and IOP data were corrected for signal drift, and averaged for each hour across all 12 days.

 

Results

 

As seen in the Figure, both OPP was consistent between contralateral eyes but varied widely between NHPs (means of 52, 44, and 24 mmHg, respectively). OPP was highest at night, and decreased significantly (~4 mmHg) upon waking in all three NHPs. In one NHP (9140), mean OPP for the first 24-hour period was 47 mmHg but steadily decreased to 36 mmHg by the end of the 12-day recording period. OPP was very consistent over time in the other two NHPs. The nycthemeral rhythm in OPP was driven by IOP in all NHPs.

 

Conclusions

 

OPP: 1) varies widely between NHPs; 2) is consistent between contralateral eyes within NHPs; 3) can vary widely within NHPs over time; 4) is highest at night, and 5) is lowest upon waking. The nycthemeral rhythm in IOP drives the nycthemeral rhythm in OPP.

 

 

Bilateral OPP (top) and IOP (Bottom) calculated from continuous bilateral IOP and aortic blood pressure telemetry for 3 NHPs. Data are plotted as mean hourly averages with standard deviations from midnight to midnight, averaged over all twelve 24-hour recording periods for each eye. Note that time is plotted on the 24-hour scale; waking hours are hours 7-18, and lights-out are hours 1-6 and 19-24.

 

Keywords: 436 blood supply • 627 optic disc • 568 intraocular pressure