OXYGEN KINETICS IN THE VITREOUS SUBSTITUTE PERFLUOROTRIBUTYLAMINE - A F-19 NMR-STUDY INVIVO

Perfluorocarbon (PFC) vitreous substitutes yielded promising results in the surgical management of retinal detachments. This success is due primarily to their useful physical properties. However, oxygen kinetics in PFC in vivo have not been investigated. The oxygen flux in the vitreous substitute perfluorotributylamine (FTBA) was assessed in the rabbit eye by monitoring the partial oxygen pressure (PO2) in real-time using Fluorine-19 nuclear magnetic resonance spectroscopy (F-19 NMR). The spin-lattice relaxation rate (T1)-1 of the CF, resonance of FTBA is a rapid and sensitive index of PO2. T1-derived PO2 from the FTBA-filled rabbit eye was followed at regular time intervals under different oxygenation protocols. In the first series of experiments, FTBA in the vitreous space was oxygenated by ventilating the rabbit with a mixture of 95% 02 and 5% CO2. The oxygen uptake profile could be approximated by a simple exponential function with a time constant of 159 +/- 110 min (mean +/- SD, n = 3). A more reproducible correlate was obtained by performing an initial rate analysis on the first hour of ventilation with high oxygen levels. This analysis showed that the rate of increase in FTBA PO, was 2.34 +/- 0.67 mm Hg/min (mean +/- SD, r2 = 0.99, n = 7). After the animal was removed from the 95% O2/5% CO2 gas and was ventilated with room air, the oxygen clearance profile could be approximated in all cases by a single exponential with a time constant of 59.8 +/- 9.6 min (mean +/- SD, n = 4). To assess whether or not ventilating the animal with 95% 02/5% CO2 could have influenced the O2 clearance rate, FTBA was preoxygenated with 100% 02 immediately before injecting the compound into the vitreous cavity. The animal was continuously ventilated with room air. A single exponential profile was again obtained with a time constant of 69.6 +/- 12.6 min (mean +/- SD, n = 4) which does not differ statistically from the above mean (p = 0.4). This work represents the first to characterize oxygen kinetics in a perfluorocarbon vitreous substitute in vivo. These experiments provide a basis for future investigations to determine the possible beneficial effects of oxygenated PFC when used as vitreous substitutes during vitreoretinal surgical conditions.