1. ¹Department of Electronics, Systems and Computer, University of Bologna, Bologna, Italy
2. ²Foundation 'Graziano Frigato pro-centro emodialisi', Paderno Dugnano (MI), Italy
3. ³R&D Monitor Division, Gambro Dasco S.p.A., Medolla (MO), Italy
4. ⁴Nephrology Division, San Carlo Clinic, Paderno Dugnano (MI), Italy

Correspondence: Silvio Cavalcanti, DEIS, Viale Risorgimento, 2, Bologna I-40136, Italy. E-mail: silvio.cavalcanti@unibo.it

Received 24 December 2007; Revised 24 September 2008; Accepted 9 October 2008; Published online 3 December 2008.

Abstract

We tested a new bedside method to determine the function of native arteriovenous fistula in 16 patients performed during hemodialysis without stopping the treatment. We initially measured vascular access flow (Q_a) in each patient using the Transonic HD01^plus device. We then measured the pressure in arterial and venous drip chambers at different blood pump flow rates (Q_bset=0, 50, 100, 250, 300, 350 ml/min). The intravascular blood pressure gradient (P_f) between arterial and venous puncture sites was estimated by a mathematical model. P_f was positive for low Q_bset, but became negative when Q_bset overcame the threshold value (Q_Inv). Such critical flow showed a high correlation with Q_a, even if it was systemically lower. Computer analysis of fluid dynamics showed that when the blood pump flow overcame the Q_Inv threshold, a critical transition from laminar flow to vortex circulation took place downstream of the venous needle, causing a dangerous shearstress on the vessel wall. Our results show that Q_Inv provides an indication of the maximal blood pump flow rate needed to be reached to maximize blood flow supply in order to limit hemodynamic stress on the vascular access.