Neofox

To assess the arterial partial pressure of oxygen (P_aO₂) in real-time, we used a calibrated ruthenium-tipped oxygen-sensing probe (Foxy AL300, OceanOptics, Dunedin, USA) that was advanced to the ascending aorta. The PO₂ probe was connected via a fiberglass cable to a server unit (NeoFox, OceanOptics, Dunedin, USA). This PO₂ measurement based on the principle of fluorescence quenching of oxygen by the multi-frequency phase fluorimetry (MFPF) method has been previously published [26 (link)]. PO₂ values were digitally sampled with a temporal resolution of 10 Hz and stored on a personal computer.

The grafts were perfused using an original MP system (Fig 1) [15 ]. This system consists of the hepatic artery (HA) and portal vein (PV) perfusion circuits. Each circuit consists of a roller-type pump (MasterFlex7520-40; Cole-Parmer, Bunker Court Vernon Hills, IL, USA), an electrical flow meter (VN05; Aichi Tokei, Japan for PV; FD-SS02, Keyence, Osaka, Japan for HA), a ceramic capacitance pressure sensor (KL76; Nagano Keiki, Nagano, Japan), and a custom-made air trap. An oxygenator (HP0-06 H-C; Senko Medical Instrument, Tokyo, Japan) was installed in the circuit for the PV and HA. Two optical oxygen sensors (NeoFox; Ocean Optics, Seattle, FL, USA) were installed to measure the oxygen concentration of the perfusate in the PV circuit. The temperature of the perfusate was controlled by a heat exchanger and ice-cold water. The flow rate of the PV was 0.22 mL/min/g (liver) and that of the HA was 0.06 mL/min/g (liver).

PEC measurements were performed in a three-electrode glass cell with a quartz window containing an aqueous solution of 1 M Na₂SO₄. Pt foil was used as the counter electrode and Ag/AgCl as the reference electrode. A 300-W Xenon lamp was used as the light source. A long-pass filter (>420 nm) was used to obtain visible light for PEC measurement. The fluorescence-based O₂ sensor (Neofox, Ocean Optics) was used to test the dissolved oxygen in reaction solution. An N₂-gas was used to purge the O₂ of reaction solution before illumination.

A ruthenium-covered probe was inserted via the femoral artery introducer (Foxy-AL300, Ocean Optics, USA) as previously reported [13 (link), 14 (link)]. The tip of the probe is covered with ruthenium-based fluorescent molecules, whose fluorescence is quenched by the presence of molecular oxygen. A fiber optic bundle sends blue LED light to the sensor and the resulting fluorescence is relayed back through the bundle to the detector (NeoFox, Ocean Optics, USA). The decay profile of the fluorescent molecules changes in the presence of molecular oxygen, and arterial PaO₂ is calculated automatically by the dedicated software with a time resolution of up to 10 Hz.

We investigated the capacity of an in-house, custom-built fibre optic $P_{{\text{O}}_2}$ sensor to detect rapid $P_{{\text{O}}_2}$ oscillations in blood in vitro. This sensor is made by coating the end section of a silica fibre with a Pt(II) doped polymer sensing material, poly(methyl methacrylate) (PMMA). This PMMA sensor is based on the principle of fluorescence quenching of the platinum complex by oxygen, and is compatible with clinical application. Further technical details about the sensor have been reported previously (Chen et al., 2012a ). The Foxy-AL300 fibre optic $P_{{\text{O}}_2}$ sensor was used as a control for comparison with the PMMA sensor. Each sensor was calibrated in blood at 0 and 50 kPa before each experiment. The two sensors were connected to a phase measurement system (NeoFox, Ocean Optics, Dunedin, FL, USA), and interfaced to a computer through an A/D board sampling at 10 Hz (USB-6251, National Instruments, Austin, TX, USA). In order to compare our data with those reported in the literature (Baumgardner et al., 2002 (link), Shi et al., 2011 (link)), the AL300 sensor was also connected to a light intensity measurement system (USB 2000 spectrometer, Ocean Optics, Dunedin, FL, USA), interfaced to a computer through the A/D board. Data were recorded on a computer by means of a custom program (LabView, National Instruments, Austin, TX, USA).