Modulation of the rat micturition reflex with transcutaneous ultrasound
Daniel P. Casella, Anne G. Dudley, Douglass B. Clayton, John C. Pope, Stacy T. Tanaka, John Thomas, Mark C. Adams, John W. Brock, Charles F. Caskey
Neurourology and Urodynamics 2017, 36, 1996-2002 · 10.1002/nau.23241
Abstract
Introduction Low intensity focused ultrasound has recently been identified as a novel method of stimulating targeted neurons. We hypothesized that ultrasound stimulation of the posterior tibial nerve would inhibit bladder contractions in an established rat model of rhythmic bladder contractions. Methods Cyclical detrusor contractions were initiated by placing a transurethral catheter in female rats and infusing saline into the bladder. Transcutaneous ultrasound pulses were then delivered to the lower extremity of a rat (overlying the posterior tibial nerve) using a single element spherically focused 250 kHz transducer. Sixty-three cycles were repeated at 2 kHz for 300 ms at peak negative pressure of 900 kPa pulsed at 0.5 Hz. Results We report successful suppression of bladder contractions using ultrasound stimulation in 10 animals. The average latency between the initiation of ultrasound and suppression of bladder contractions was 3 min 23 s (±51 s), the average time of contraction suppression was 13 min and 50 s (±2 min 25 s) and the average time from the end of ultrasound to return of contractions was 9 min 37 s (±2 min and 30 s). Conclusion In this work, we demonstrate the ability of targeted transcutaneous ultrasound to inhibit rhythmic bladder contractions in anesthetized rats. Due to its non-invasive nature and ease of application, we believe ultrasound mediated suppression of the micturition reflex is potentially an ideal outpatient treatment of overactive bladder and dysfunctional elimination.
Abstract via europepmc.
Exposures
Exposure 1: Transcutaneous ultrasound stimulation of the posterior tibial nerve
Target: tibial nerve — “posterior tibial nerve”
Device: Sonic Concepts · Sonic Concepts · H-115MR ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 250 | ✓✓✓ |
| Pulse duration (ms) | 0.252 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 2,000 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 50.4% | |
| Sonication duration (s) | 0.3 | ✓✓✓ |
| Free-field pressure (kPa) | 950 | ✓✓✓⚑ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | ⚑ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported | |
| Isppa, domain unspecified (W/cm²) | 28 | ✓✓✓ |
| Ispta, domain unspecified (W/cm²) | 2.1 | ✓✓✓ |
Ultrasound pulses consisted of 63-cycle 250 kHz bursts repeating at a rate of 2 kHz over a total duration of 300 ms; this 300 ms pulse was itself repeated every 2 s. Stimulation was delivered in set time intervals of 5-10 min, and if bladder contractions were unchanged by the end of a period, the probe was repositioned by 1-2 mm and the cycle repeated; total ultrasound exposure time was 5 min (n=6), 10 min (n=3) or 15 min (n=1) per animal. After the initial stimulation, pulses were reapplied at 15, 20, 30, 40, 53 and 70 min to test for a refractory period.
Flags from extraction
exposures[0].free_field.pressure_kpa— Abstract states a slightly different peak negative pressure of 900 kPa ('peak negative pressure of 900 kPa pulsed at 0.5 Hz'), while Methods states 950 kPa measured in a free water field; the Methods value is used here and the discrepancy is flagged.exposures[0].free_field.isppa_w_cm2— Domain (free-field vs in-situ) is not explicitly stated for these Isppa/Ispta figures; classified as free_field because they are derived from the pressure explicitly measured 'in a free water field'.exposures[0].timing.pulse_duration_ms— 0.252 ms obtained via the sanctioned cycles-per-pulse ÷ frequency conversion (63 cycles / 250 kHz); paper does not state pulse duration directly in ms.