The goal of this clinical trial is to learn whether transcutaneous auricular vagus nerve stimulation (taVNS) works to treat refractory constipation in adults. It will also learn about the safety and tolerability of taVNS. The main questions it aims to answer are:
Does taVNS improve constipation symptoms, as measured by the change in complete spontaneous bowel movements per week (ΔCSBMs/week) from baseline to post-treatment? What medical problems or side effects do participants have when receiving taVNS? Does taVNS reduce the need for rescue laxatives? Researchers will compare active taVNS to sham taVNS to see if taVNS works to treat refractory constipation.
Participants will:
Be randomly assigned (double-blind) to receive active taVNS or sham taVNS for 20 days Receive stimulation twice daily, 30 minutes per session, with a 12-hour interval between sessions Receive stimulation at 30 Hz with 200 μs pulse width, delivered to the left cymba conchae Keep a daily diary of bowel habits and symptoms, including CSBMs, and rescue laxative use (bowel movements occurring within 24 hours after rescue laxative use will not be counted as CSBMs)
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Parallel
transcutaneous auricular vagus nerve stimulation
DeviceParticipants will receive active transcutaneous auricular vagus nerve stimulation (taVNS) delivered to the left cymba conchae using the study device. Stimulation will be administered twice daily for 20 consecutive days, with two 30-minute sessions per day separated by approximately 12 hours. Stimulation parameters will be 30 Hz with a 200 μs pulse width (single pulse width 200 μs).
Placebo
DeviceParticipants will receive a sham taVNS procedure designed to mimic active stimulation while not providing effective vagal nerve stimulation. Sham sessions will follow the same schedule and duration as the active arm: twice daily for 20 consecutive days, with two 30-minute sessions per day separated by approximately 12 hours. The sham condition will use an identical-appearing device and procedures to maintain blinding.
Predictive Value of Baseline EEG for Treatment Response (Area Under the Curve)
The ability of baseline EEG spectral power (specifically alpha band power) to classify patients as Responders vs. Non-Responders. Responders are defined as patients with an increase of ≥1 CSBM/week. The performance will be assessed using Receiver Operating Characteristic (ROC) analysis.
Change from baseline in weekly frequency of spontaneous bowel movements (SBM)
Change in Complete Spontaneous Bowel Movements per Week (ΔCSBMs/week)
Primary efficacy outcome is the change in weekly complete spontaneous bowel movements (CSBMs) from baseline to end of treatment. A CSBM is defined as a spontaneous bowel movement accompanied by a sensation of complete evacuation. Weekly CSBMs will be derived from daily bowel diaries. Bowel movements occurring within 24 hours after use of rescue laxatives will not be counted as CSBMs.
Proportion of participants using polyethylene glycol (PEG) as rescue medication
Change from baseline in Patient Health Questionnaire-9 (PHQ-9) score
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