| Popis: |
Microcomputer assisted processing of data from the vascular laboratory has proved useful in the interpretation and reporting of a number of widely used investigations. A series of programs have been written which enable traces obtained from Doppler ultrasound, foot vein pressures, photoplethysmography and strain gauge plethysmography to be displayed on the screen of a BBC microcomputer, stored on disc, analysed and printed by matrix printer or plotter. Programs have been written in sections separating the functions of data acquisition, storage, analysis and hard copy. All data is read into the microcomputer by an eight channel analogue to digital converter plugged into the 1 MHz bus (Interbeeb, MCP Developments Ltd). The A D converter has a level shifting and gain adjusting pre-amplifier for each channel (PMS Instruments Ltd, Maidenhead, Berks). This arrangement means that the switching between different input devices (Doppler, PPG etc.) can be achieved by software alone. Most of the software has been written in BBC BASIC since some sections require much mathematical manipulation. The Doppler ultrasound input section has, however, been written in 6502 assembly language compiled to machine code because the A D converters must be read every 10 ms for good trace resolution. This program enables the traces from each of the eight limb vessels to be displayed, updated and stored on disc. The remaining programs generally have much lower speed requirements and read input data at 400 ms intervals for each channel. This can easily be accomodated by the standard BBC BASIC. Mathematical and statistical techniques have been used to overcome the difficulties of analysis of plethysmography traces. In general an exponential curve will fit the sections to be analysed and the program achieves this using a simple ‘least squares’ technique. Hardcopy of the traces can be obtained in colour on a plotter or in black and white on a matrix printer. The finished document is intended as a definitive report. This software has been found to facilitate these investigations considerably and much less chart recorder paper has to be examined to arrive at the final result. |
