Continuous acoustic monitoring for dialysis access
A low-cost wearable that listens to a dialysis patient's fistula around the clock, and notices when it starts to change.
Meet the deviceThe lifeline
When kidneys fail, a machine has to clean the blood. To reach it, a surgeon joins an artery directly to a vein in the arm. That joint, the arteriovenous fistula, is used two to three times a week, for years. When it begins to narrow, it does so silently, between visits, where no one is listening.
of fistulas stay open without any intervention through their first year.1
Narrowing (stenosis) is the most common cause of fistula dysfunction, and it can lead to clotting and loss of access.2
of hemodialysis patients surveyed in India travel more than 50 km to reach their dialysis centre.3
of continuous fistula monitoring in routine care. Guidelines rely on regular physical examination by a trained practitioner.4
Continuous · Personal · Affordable
The device
A soft, low-profile shell designed to be worn over the fistula for long periods, with a status light that breathes with the signal.
An ESP32: dual-core, up to 240 MHz, with Wi-Fi and Bluetooth. It samples, transforms and scores every recording on the patch.
A MAX9814 microphone amplifier with automatic gain control (40, 50 or 60 dB). It captures the bruit, the sound of blood rushing through the fistula.
An ADXL345 three-axis MEMS accelerometer, up to ±16 g at 13-bit resolution. It feels the fistula's vibration and knows when the arm is moving.
An acoustic coupling layer that seals against the skin over the anastomosis and outflow segment, where narrowing most often begins.5
Industrial design concept. The working prototype uses the same three sensing modules.
How it listens
The microphone records the bruit over the anastomosis and outflow segment.
The accelerometer records the thrill, the fistula's vibration, as a second, independent signal.
If the arm is moving, the recording is discarded. Only still, clean windows are scored.
A Fast Fourier Transform turns sound into frequencies and measures energy against a research-informed 600–800 Hz reference.
Every fistula sounds different. PRAVAH first learns this patient's own baseline.
A machine-learning model learns the fistula's acoustic and vibration pattern over days, not a single fixed threshold.
When the pattern moves significantly away from normal, the patient is told early, while there is time to act.
The physics
Push the same flow through a smaller opening and it has to move faster: flow equals area times velocity. Halve the diameter and the jet moves four times as fast. Fast jets break into turbulence, and turbulence is sound. As the vessel tightens, the sound's energy climbs into higher frequencies.6
The evidence
Illustration · 28 days of one fistula's sound spectrum. As the vessel narrows, energy climbs into 600–800 Hz.
JMIR Formative Research · 2026
Pilot study, 29 patients over three months. All stenotic recordings came from one patient, and the authors call their threshold exploratory. PRAVAH uses this band as a reference, not a diagnosis.7
npj Digital Medicine · 2023
A vision transformer reading spectrograms of digital stethoscope recordings detected stenosis at a level comparable to a physical exam by a nephrologist.8
The sound is there. The tools that hear it are expensive, occasional, and in the clinic. PRAVAH puts them on the arm.
For the patient
Is my fistula okay? The patch answers in plain language, compared with the patient's own normal, not a population average. No numbers to interpret. No waiting for the next visit.
Interface concept.
Built for India
government dialysis centres under the Pradhan Mantri National Dialysis Programme, across 751 districts.9
median one-way distance patients travel to a dialysis centre in a national geospatial study.10
retail cost of the three core sensing modules in India today. No Doppler machine. No specialist required to wear it.11
Roadmap
ESP32, MAX9814 and ADXL345. Real-time frequency analysis, motion rejection, personal baseline and a live interface.
Test the patch against reference recordings and a flow phantom with controlled narrowing.
Wear-testing alongside routine care at a dialysis centre, with ethics approval and Doppler as reference.
One flexible board, a sealed shell and a battery that lasts between sessions.
Why
“My late grandfather developed AV fistula stenosis. It was caught and treated only because it was noticed early. Had it progressed, it could have meant a failed access, an emergency procedure, or a missed dialysis session.”
Most patients don't have someone noticing early.
PRAVAH is built to be that someone.
Listen to the lifeline.
Read the research