Development of Simple Flow Measurement in the Vascular Access Conduit Based on the Bernoulli's Theory

ABSTRACT

PURPOSE: Early detection of arteriovenous fistula (AVF) dysfunction in hemodialysis patients and prompt corrective procedures reduces the AVF thrombosis rates and lengthens access survival. We tried to develop a new simple and cheap bedside measurement technique based on the Bernoulli's theory. METHOD: From a total of 20 case of vascular accesses for hemodialysis, of at least 3 months of construction, we twicely measured the AVF flow rate (QD) with Doppler ultrasonography and vascular conduit pressure. Four kinds of pressure were measured tubing set free from dialysis machine and positioned on the patient's bed (PrF), two kinds of artificial stenosis made with tourniquet (PrS1, PrS2), pump flow rate at 100ml/min (Pr100), and pump off (Pr0). We calculated the flow rate of vascular conduit (QF) with PrF and mean arterial pressure on Bernouli's equation, and QF was compared with QD. RESULT: AVF was 26.0+/-28.6 (3~108) months after operation, with five cases (including 2 PTFE grafts) using brachial artery. PrF was closely correlated with Pr100 (R2=0.914), and inversely correlated with QD (R2=-0.026). QF was poorly correlated with QD (R2=0.003). There was no statistical difference in the double pressure measurement (P>0.05), but there was differenence in QD (P<0.05). When artificial stenosis was made, the pressures increased, and the calculated flow rates decreased in every patients. Thrombosis or stenosis was detected in all patients with decrement of QF, but not in all with decrement of QD. CONCLUSION: Pressure measurement and calculated flow rate in dialysis vascular conduit represent alterations of AVF flow rate. However its value in long-term follow up awaits further study with accurate constant number.