A fibre-optical sensor has been developed based on the fluorescent indicator 8-hydroxyl-1,3,6-pyrene trisulphonic acid trisodium salt (HOPSA) for monitoring physiological pH values. Dowex-1 strongly basic anion exchange resin is used as the medium to immobilise the indicator on the end of an optical fibre. Polyurethane is coated on the sensor as the permeable membrane for H+. The properties of HOPSA in solution, as well as when immobilised on the sensor, are studied and found to have the potential for monitoring physiological pH values.

The first in vivo evaluation of a pO2 sensor constructed with a novel copolymer is described. The performance of the sensor is assessed under dynamic conditions in vitro and in vivo. This sensor is more stable and reliable than the control sensor with a heparin-treated polyethylene membrane.

When a mechanical model of the rat aortic input impedance is perfused with a pulsatile pump, the computed values of the impedance components vary linearly with flow rate and are interactive. When the model is perfused by an isolated rat heart, the total load upon the left ventricle consists of the model and coronary impedances in parallel. Adenosine triphosphate induces changes in coronary impedance, and the redistribution of cardiac output from the model to the coronary circulation causes flow-related changes in the model impedance. Thus, the mechanical model does not provide a constant load for the isolated heart, because of variations in both the model and coronary impedances.

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