Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve
Ning Ji, Yuanheng Li, Jingjing Wei, Fei Chen, Lisheng Xu, Guanglin Li, Wan-Hua Lin
Journal of Neural Engineering 2022 · 10.1088/1741-2552/aca8cd
Abstract
Objective. Our previous study has shown that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve could modulate blood pressure (BP), but its underlying mechanisms remain unclear. We hypothesized that low-intensity FUS of the vagus nerve would regulate autonomic function and thus BP. Approach. 17 anesthetized spontaneously hypertensive rats were treated with low-intensity FUS of the left vagus nerve for 15 min each trial. Continuous BP, heart rate, respiration rate (RR), and core body temperature were simultaneously recorded to evaluate the effects on BP and other physiological parameters. Heart rate variability (HRV), systolic BP variability, and baroreflex sensitivity were computed to evaluate the autonomic modulation function. A Control-sham group without stimulation and another Control-FUS group with non-target stimulation were also examined to exclude the influence of potential confounding factors on autonomic modulation. Main results. A prolonged significant decrease in BP, pulse pressure, RR, the normalized low-frequency power of HRV, and the low-to-high frequency power ratio of HRV were found after the low-intensity FUS of the left vagus nerve in comparison with the baseline and those of the control groups, demonstrating that activities of the sympathetic nervous system were inhibited. The prolonged significant increase of the normalized high-frequency power of HRV suggested the activation of parasympathetic activity. Significance. Low-intensity FUS of the left vagus nerve effectively improved the autonomic function by activating parasympathetic efferent and inhibiting sympathetic efferent, which contributes to BP reduction. The findings shed light on the hypotensive mechanism underlying FUS.
Abstract via europepmc.
Exposures
Exposure 1: FUS of the left cervical vagus nerve
Target: vagus nerve — “left vagus nerve”
Device: not reported
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 3,700 | ✓✓✓ |
| Pulse duration (ms) | 2 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 100 | ✓✓✓ |
| Duty cycle (%) | 20pulse duration × PRF gives 20% | ✓✓✓ |
| Sonication duration (s) | 1 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 18 | ✓✓✓ |
| Free-field Ispta (W/cm²) | 0.6 | ✓✓✓⚑ |
| 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 |
100 Hz PRF, 20% duty cycle, 2 ms tone burst, 1 s sonication, inter-stimulation interval of 6 s; each trial had 10 min baseline, 15 min ultrasound stimulation and 30 min recovery. Control-sham: transducer placed on the nerve with FUS off; Control-FUS: FUS to the left upper leg.
Flags from extraction
n_subjects— 50 rats were allocated to three groups; 21 (Control-sham) received no ultrasound, 12 received FUS at the leg and 17 at the vagus nerve. Value is enrolled total.exposures[0].free_field.ispta_w_cm2— Stated Ispta 0.6 W/cm2 is not what 20% duty cycle times 18 W/cm2 would give; the 1 s on / 6 s interval pattern may explain it. Recorded as stated.auditory_control— Paper states the control groups were meant to exclude auditory and non-target confounds; no dedicated auditory control (masking, deafening) is described.exposures[0].device.family— Transducer maker not named; described only by frequency, diameter and focal length; refers to a previous paper.n_sessions_per_subject— Trials are counted per group (25, 25, 15 trials) and not per rat.