Vascular access dysfunction is the leading cause of hospitalization for hemodialysis patients and accounts for the most medical costs in this patient population. Vascular access flow is commonly hindered by blood vessel narrowing (stenosis). Current screening methods involving imaging to detect stenosis are too costly for routine use at the point of care. Noninvasive, real-time screening of patients at risk of vascular access dysfunction could potentially identify high-risk patients and reduce the likelihood of emergency surgical interventions. Bruits (sounds produced by turbulent blood flow near stenoses) can be interpreted by skilled clinical staff using conventional stethoscopes. To improve the sensitivity of detection, digital analysis of blood flow sounds (phonoangiograms or PAGs) is a promising approach for classifying vascular access stenosis using non-invasive auditory recordings. Here, we demonstrate auditory and spectral features of PAGs which estimate both the location and degree of stenosis (DOS). Auditory recordings from nine stenosis phantoms with variable DOS and hemodynamic flow rate were obtained using a digital recording stethoscope and analyzed to extract classification features. Autoregressive modeling and discrete wavelet transforms were used for multiresolution signal decomposition to produce 14 distinct features, most of which were linearly correlated with DOS. Our initial results suggest that the widely-used auditory spectral centroid is a simple way to calculate features which can estimate both the location and severity of vascular access stenosis.

Vascular access is the “Achilles Heel” of hemodialysis, as maintaining high flow characteristics (access patency) is critical to achieving efficient dialysis treatment. Thus, monitoring of vascular access is essential for maintaining long-term dialysis success. Blood sounds change in the presence of stenosis and can be analyzed digitally as phonoangiograms (PAGs) to determine changes in hemodynamic flow. We propose a multi-channel PAG recording sensor suitable for rapid, non-invasive vascular access monitoring. Here we present the initial design and characterization of sensors appropriate for recording PAGs from the skin surface. An optimized sensor size and backing material was selected to improve sensitivity and to provide a neutral frequency response. The sensor performance was finally compared with a conventional stethoscope on a controlled blood flow stenosis benchtop phantom.

Eine nicht gleichmäßige Verteilung des radioaktiven Tracers 42K wird durch teilweises Maskieren einer Glasprobe mit Cd und nachfolgendes Bestrahlen mit thermischen Neutronen erzeugt.

A nonuniform distribution of a radioactive tracer was produced within a glass specimen by partially masking it with Cd and irradiating it with thermal neutrons. The calculated distribution of the tracer in the given geometry agreed reasonably well with the measured distribution. The latter, in turn, served as the initial condition for a self‐diffusion experiment which gave results consistent with previous studies. This technique avoids problems associated with interfaces in conventional diffusion couples.

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