Computerised graft monitoring.

Many vascular disorders require surgical procedures to overcome failing blood supply. Deficient arteries are replaced by prosthetic or vein bypass grafts to recover normal blood flow. However some grafts fail after operation. Therefore graft surveillance programs are important to increase the patency rate of grafts. Although there are a number of methods for medium and long term graft surveillance, these are not suitable for monitoring grafts immediately after operation to detect early graft failures which account for 20% of the total. This dissertation describes a computerised graft monitoring system which is suitable for continuous or intermittent monitoring of grafts immediately after surgery. The system comprises a floating point DSP board, an IBM compatible computer and a purpose built CW Doppler board. The Doppler board is designed to be installed in the computer. The possibility of implementation of DSP algorithms for obtaining directional information is extensively discussed. This study shows that digital techniques outperform their analogue counterparts. Therefore in this system, apart from the quadrature demodulation of the Doppler signals all processes are implemented digitally. Maximum frequency envelope detection algorithms are also discussed. The results obtained from monitoring seven patients are presented and practical difficulties encountered during the monitoring process are highlighted.