CHALLENGE: Some signals are not easy to measure directly either because access is limited or because the specific device required is not available. We encountered two such situations in isolated heart experiments (i) coronary flow (not easy to access) and (ii) left ventricular volume (specific device not available).

SOLUTION: The principal was simple: to contruct the required signals from available information. To achieve this, we added a new functionality to iox2 software, enabling the creation of input signals as mathematical formulas using existing digitized analog signals. These new calculated signals then become available either for display or real-time analysis. In (i), two flow probes were placed to record from the ascending aorta (AO) and the pulmonary vein (PV). Coronary flow was obtained by a simple mathemetical operation: PV - AO. In (ii), we decided to use the signals from segment-length crystals (sonomicrometry technique). The signals for 3 axes were used in a formula based on a heart ellipsoid model to calculate the left ventricular volume.

RESULTS:
The coronary flow was displayed and analysed in real-time. The coronary vascular resistance could also be calculated by addition of a pressure catheter. Volume was displayed and used to generate pressure/volume loops.