Gastric Focused Ultrasound Stimulation

This exploratory pilot study will investigate whether noninvasive gastric focused ultrasound (FUS) stimulation is associated with changes in postprandial gastric electrical activity and gastrointestinal symptoms in adult patients with gastroparesis or clinically significant symptoms of delayed gastric emptying. A total of 12 participants ages 18 to 70 years will complete two study visits in a randomized crossover design. During one visit, participants will receive active gastric focused ultrasound stimulation; during the other visit, they will receive sham stimulation. The order of active and sham stimulation will be randomized. The two visits will be separated by at least 48 hours to reduce potential carryover effects. When possible, visits will be scheduled at a similar time of day. Participants will fast for at least 6 to 8 hours before each visit, except for water and medications permitted by their treating physician. At each visit, nine electrogastrography (EGG) electrodes will be placed on cleaned skin over the upper abdomen and stomach region. Participants will complete approximately 10 minutes of fasting baseline EGG recording, consume up to two bottles of Ensure or Glucerna nutritional drink within approximately 15 minutes as tolerated, and complete approximately 10 minutes of post-meal EGG monitoring. Participants will then receive active FUS or sham stimulation according to their randomized visit assignment. Active stimulation will be delivered noninvasively through the abdominal skin over the stomach region using an ultrasound transducer and coupling gel. Active stimulation will use a center frequency of 650 kHz and pulse repetition frequency of 1 kHz. Each pulse will consist of 200 microseconds on and 800 microseconds off, corresponding to a 20% pulse-level duty cycle. Pulsed ultrasound will be delivered in repeated blocks of 500 milliseconds on and 500 milliseconds off throughout a total FUS session of 600 seconds. During the sham condition, transducer placement, coupling gel, device setup, and study procedures will be the same, but no active ultrasound energy will be delivered. EGG signals will be recorded continuously during stimulation or sham and during approximately 10 minutes of post-stimulation recovery monitoring. Participants will report discomfort, warmth, tingling, nausea, pain, dizziness, or other symptoms. Study procedures may be paused or stopped at any time at the participant's request or if the study team identifies a safety concern. Gastrointestinal symptom severity will be assessed using the Total Symptom Score questionnaire. The Total Symptom Score sums ratings of nausea, vomiting, early satiety, bloating, postprandial fullness, and abdominal pain. Each symptom is rated from 0 to 4, with a total score ranging from 0 to 24; higher scores indicate worse symptom severity. Symptom ratings will be collected at the past-two-week baseline assessment, immediately before stimulation, after meal consumption, immediately after FUS or sham stimulation, and 30 minutes after stimulation completion. The study will evaluate EGG signal characteristics, including gastric slow-wave rhythm, dominant frequency, amplitude or power, and percentage of time in normal gastric rhythm, and will compare within-participant changes between active FUS and sham conditions. The study is intended to assess feasibility and preliminary physiological effects and is not designed to establish clinical efficacy.