Simultaneous measurement of pO₂ and perfusion in the rabbit kidney in vivo

Recently, a combined probe has been developed capable of simultaneous measurement of local tissue pO₂ (fluorescence oximetry) and microvascular perfusion (laser Doppler flux) within the same local region. The aim of the current study was to test the utility of these combined probes to measure pO₂ and perfusion in the kidney. Studies were performed in anesthetized, artificially ventilated rabbits (n=7). Baseline measurements of renal medullary perfusion and pO₂ obtained using combined probes (537± 110 units & 28.7± 6.1mmHg, respectively) were indistinguishable from those obtained using independent probes (435± 102 units & 26.9± 6.4mmHg). Baseline measurements of renal cortical pO₂ were also similar between combined (9.7± 1.6mmHg) and independent probes (9.5± 2.3mmHg). Baseline levels of cortical perfusion however, were significantly greater when measured using independent probes (1130± 114units) compared to combined probes (622± 59units; P<0.02). Relative changes in perfusion and pO₂ resulting from graded stimulation of the renal nerves were not significantly different when measured using combined probes to those obtained using independent probes. We conclude that combined probes are equally suitable to independent probes for tissue pO₂ and microvascular perfusion measurement in the kidney. Our results raise some concerns regarding the accuracy of these OxyLite fluorescence probes for pO₂ measurement in the kidney, particularly within the renal cortex.