Continuous measurement of arteriovenous oxygen difference and VO2 by microcomputer

Abstract

We have developed a microcomputer-based system to measure the arteriovenous oxygen difference [(a-v)O2] continuously in whole blood and to compute the oxygen consumption rate of an organ. The system consists of a pair of flow-through cuvettes perfused with arterial and venous blood, a simple electronic circuit to illuminate the cuvettes and to measure the intensity of the transmitted light, an analog-to-digital converter, and an Apple II+ computer. The computer samples the intensities of the light transmitted through the arterial and venous cuvettes, digitizes an electromagnetic blood flow signal, and computes both the arteriovenous oxygen difference and the oxygen consumption rate. The computed variables are sent via a digital-to-analog converter to a multichannel recorder. By comparing our spectrophotometric determinations of the (a-v)O2 with conventional O2 content measurements, we found our (a-v)O2 computer to yield an accurate, linear measurement of the (a-v)O2. This spectrophotometric method for determining the (a-v)O2 offers the advantages of a rapid, continuous measurement. It eliminates the labor and errors involved in multiple, discontinuous sampling, thus freeing the investigator for other tasks, and it provides the investigator almost immediate feedback regarding the oxygen consumption rate of his preparation. Furthermore, the system could also be used (with minor modifications to the program) for the continuous measurement of cardiac output if whole-body oxygen consumption were determined from expired gases.