Figure 2.

US does not excite the sciatic nerve using numerous parameters. (A) Single pulse stimulation patterns were used for the US experiments, where the duty cycle was defined as the PD divided by the TD and stimulation on time was defined as PD. (B) Single pulse paradigms, in which PDs at 1, 10, and 100 ms were tested with a variety of duty cycles and TDs. (C) Single pulse paradigms, in which PDs were exponentially chosen from 10 µs to 500 ms for 1 s TDs. The red lines indicate the maximum pressures usable to minimize potential damage to the transducers. The longest PDs tested at the highest pressures of US were 20, 75, and 75 ms for 0.22, 0.52, and 1 MHz, respectively. Different TDs of 0.5 and 3 s were also tested, in which the PDs were halved for 0.5 s TD. (D) Multiple pulse stimulation patterns were used for the US experiments, where duty cycle was defined as PD over the reciprocal of PRF and stimulation on time (per trial) was defined as PD times number of pulses per trial (N). (E) Multiple pulse paradigms, in which PRFs at 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, and 5 kHz were tested with 50% duty cycle when US was presented for 20, 75, and 75 ms per trial (1 s TD) at the highest pressures of 2, 1.3, and 5 MPa for 0.22, 0.52, and 1 MHz transducer, respectively. None of these displayed paradigms elicited a CAP or any activity in SC, indicating that direct excitation of the sciatic nerve with US is not readily possible. These parameters (B, C, and E) were tested across ten animals. The maximum intensities tested for US stimulation substantially exceeded levels recommended in the FDA guidance for diagnostic ultrasound (I_SPTA of 62.48 W/cm², I_SPPA up to 833 W/cm², and mechanical index of 5 exceeding limits of 0.72 W/cm², 190 W/cm², and 1.9, respectively), yet still did not excite the nerve. Further description and equations for these intensity parameters are provided in Materials and Methods.