Bruit-enhancing phonoangiogram filter using sub-band autoregressive linear predictive coding.

Subjective analysis of bruits has long been an element of vascular access physical exams. Digital recordings of blood flow bruits-phonoangiograms (PAGs)-may provide an objective, non-imaging measure of vascular access stenosis. We have analyzed the long-term stability in PAGs from typical dialysis patients with arteriovenous fistulas and grafts and found that typical patients have correlated PAG spectra. PAGs can be analyzed using nonlinear, sub-band frequency-domain linear prediction to produce both bruit-enhanced recordings and a bruit-enhanced power envelope. This approach is novel over prior methods because it adaptively predicts signal envelopes based on physiologic properties of blood flow determined from chronic dialysis recipients. Our results indicate that a generalized bruit-enhancing filter can be developed for dialysis vascular access. Outputs from this filter may be analyzed to determine vascular physiology, including re-stenosis risk.