The PMMA sensor captured the whole of the 45 kPa (338 mmHg) PO2PO2 step change even at the highest simulated RR (60 bpm); whereas the AL300 was able to record only 60% of the actual PO2PO2 oscillation at 60 bpm. Similarly, Fig. 2 illustrates PO2PO2 values recorded by the PMMA and AL300 sensors 5 h after they had been continuously immersed in flowing blood at 39 °C. The PMMA

sensor still captured ∼90% of the 45 kPa (338 mmHg) PO2PO2 step change, even at the highest simulated RR, where the AL300 sensor only captured ∼49% of the actual PO2PO2 oscillation. The slow increasing and decreasing tails of the AL300 sensor are even more evident here as RR is increased. Fig. 3A shows the relative PO2PO2 oscillation amplitude (defined as ΔPO2 recorded by the sensor, divided by the actual ΔPO2 set by the test (i.e. 45 kPa [338 mmHg]) for the RG7204 mouse PMMA and the AL300 sensors, as a function of simulated RR in flowing blood at 39 °C. Twenty minutes after the sensors were immersed in blood, the PMMA sensor recorded the entire PO2PO2 oscillation even at the highest VE-821 order RR (i.e. 60 bpm). The AL300 recorded the entire PO2PO2 oscillation at the lowest RR, but it recorded smaller than actual PO2PO2 oscillations as RR increased.

The difference between the two sensors was statistically significant for each RR (p < 0.05). Fig. 3B shows the values recorded after 5 h of continuous immersion in flowing blood at 39 °C. The PMMA sensor still recorded most of the actual PO2PO2

oscillation at each RR, apart from at 60 bpm, where it recorded 83% of the actual PO2PO2 oscillation. Five hours after immersion in flowing blood, the difference between the PMMA and AL300 sensors was statistically significant for RRs of 30, 40, 50, and 60 (p < 0.05). The surfaces of four PMMA sensors were free from deposits of organic material following insertion in the animal, non-heparinised, flowing blood for 24 h. The results of one sensor are shown below, but all four demonstrated the same apparent immunity from organic deposits. Fig. 4 shows scanning electron microscopy (SEM) images of one PMMA sensor prior to insertion into the non-heparinised anaesthetised Monoiodotyrosine animal (Fig. 4A), and 24 h after continuous immersion in arterial (Fig. 4B) and venous blood (Fig. 4C). On a microscopic scale, there was no visible evidence of clotting on the sensors’ surfaces. Fig. 4D–F shows relative quantities of materials observed by EDX analysis on the surface of the sensors shown in Fig. 4A–C respectively. Carbon, silicon and oxygen were the elements predominantly detected (i.e. the component parts of the sensor’s material itself). There was no apparent difference in observed elements between the clean and used sensors with respect to the carbon spectrum, indicating no adsorption of organic material.