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Kevin J Byrne, Lisa A Hethcox, Christopher A Girkin, J Crawford C Downs; Nycthemeral Rhythm of Bilateral Ocular Perfusion Pressure (OPP) via 24-hour Telemetry in Nonhuman Primates (NHP). Invest. Ophthalmol. Vis. Sci. 2014;55(13):2947.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the nycthemeral rhythm of bilateral OPP via continuous radio telemetry of bilateral IOP and aortic blood pressure (BP).
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.
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.
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.
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