title: Volume blood flow, static pressure ratio and venous conductance in native arterio-venous fistulae: three surveillance methods compared.
abstract: OBJECTIVE
  Dialysis venous pressure monitoring has been widely recommended as a surveillance method but has not been shown to improve access outcomes in randomised controlled trials. The method has been impaired by the need to either turn off the blood pump or to derive the static venous pressure from the venous pressure measured with the dialysis pump running. We have developed a unique algorithm which converts Doppler-shifted spectral information derived from unscaled pulsatile blood flow waveforms into an estimate of mean blood pressure (MBP) at the point of ultrasound insonation.
  
  
  METHODS
  We have devised the unique expression shown here: MBP = MAP/(1 + Pff/Vff) where MAP is the mean arterial pressure, Pff = (systolic - diastolic)/MAP measured on the contralateral arm and Vff = spectral maximum - minimum/mean. Venous conductance (VC) can be measured by combining this pressure data with Duplex ultrasound blood flow data. A new device BlueDop™ has been used to illustrate the potential clinical value of non-invasive static pressure ratio (SPRn) in a monitoring role. Duplex and BlueDop™ technology were tested in an arterio-venous fistula (AVF) study in which VC, Q and SPRn were compared. Thresholds used for detection of ≥60% venous stenosis were VC <10 mL min-1 mm Hg-1, Q <500 mL min-1, SPRn >0.56.
  
  
  RESULTS
  The following accuracy was achieved: VC = 96%, Q = 92%, SPRn = 76% with similar accuracy in predicting premature thrombosis.
  
  
  CONCLUSIONS
  A new algorithm has been described and its in vivo accuracy in estimating mean 'pressure from flow' has been confirmed. Two new variables and a new dedicated instrument BlueDop™ have been demonstrated in clinical use.
authors: 1 Renal Unit, Broomfield Hospital, Chelmsford, Essex - UK.
authors: David H
authors: DH
authors: King
authors: William D
authors: WD
authors: Paulson
authors: Mo
authors: M
authors: Al-Qaisi
authors: Michael G
authors: MG
authors: Taylor
authors: Yiannis
authors: Y
authors: Panayiotopoulos
authors: Sumith
authors: S
authors: Abeygunarsekara
authors: Anthony
authors: A
authors: Chan
authors: Galil
authors: G
authors: Ali
authors: Eric S
authors: ES
authors: Chemla
mesh_terms: D000465:Algorithms; D000818:Animals; D062186:Arterial Pressure; D001166:Arteriovenous Shunt, Surgical / Q000009:adverse effects; D001783:Blood Flow Velocity; D001795:Blood Pressure Determination / Q000379:methods*; D004285:Dogs; D006083:Graft Occlusion, Vascular / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology; D006801:Humans; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D006435:Renal Dialysis; D015203:Reproducibility of Results; D012307:Risk Factors; D012815:Signal Processing, Computer-Assisted; D013927:Thrombosis / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology; D013997:Time Factors; D016896:Treatment Outcome; D018615:Ultrasonography, Doppler, Color; D018616:Ultrasonography, Doppler, Duplex / Q000379:methods*; D014654:Vascular Patency; D014690:Venous Pressure