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John Markert, Jessica V Jasien, Daniel Turner, Christopher A Girkin, J Crawford C Downs; The Relationship between IOP, IOP Transient Impulse, Ocular Perfusion Pressure (OPP), and Average Blood Pressure (BP) in Nonhuman Primates (NHP) Instrumented with Telemetry. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5323.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the relationships between IOP, BP, OPP, and IOP transient impulse.
We have developed and validated an implantable telemetry system that wirelessly records 500 measurements of IOP per second continuously for up to 2-1/2 years (IOVS 52(10):7365-75). Using an enhanced version of this system, bilateral IOP and arterial BP were continuously recorded in 7 eyes of 4 young adult male rhesus macaques, aged 3-6 years old. Ten days of continuous telemetric data from each eye was used in the analysis. IOP transient impulse was defined as the percentage of the total IOP signal that is due to IOP transients <0.5 s duration alone, and OPP was defined as BP-IOP (calculated continuously). IOP, BP, OPP, and IOP transient impulse were then averaged into one-hour periods over ten randomly chosen days for each NHP, with each day of data obtained two days post-calibration to ensure the most accurate result. BP data are not calibrated but relative change during short time periods is accurate; analyses were restricted to 24-hour periods during which the BP transducer is unlikely to drift. Relationships between the variables under study were then analyzed for each 24-hour period using linear regression.
Over the course of ten 24-hour periods, IOP transient impulse and average BP showed the most significant relationship, as shown by high R^2 values and high significance across most days in all NHPs. The relationships between IOP and IOP transient impulse, and IOP and OPP also had slight positive trends, but exhibited lower R^2 and varying significance, suggesting a more complex relationship. There was no relationship between hourly IOP and BP.
There is a significant positive relationship between the frequency and/or size of IOP transients (IOP transient impulse) and average BP. A possible explanation of this finding is that higher BP is associated with increased activity, and a greater number of blinks and saccades (the primary sources of IOP transients).
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Figure: IOP transient impulse and average blood pressure relationships within ten 24-hour periods by eye and NHP.
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