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Diaphragm motor unit activation with temporal interference stimulation
Author(s) -
Sunshine Michael,
Fuller David
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.02416
Subject(s) - stimulation , motor unit , diaphragm (acoustics) , biomedical engineering , motor unit recruitment , medicine , neuroscience , electromyography , anatomy , physics , biology , physical medicine and rehabilitation , acoustics , loudspeaker
Breathing requires repeated periodic contraction of the diaphragm muscle, and this is impaired in many neuromuscular diseases. Respiratory neuroprostheses can restore ventilation by activating phrenic motor neurons using surgically implanted epidural wires. Historically these devices use square‐wave (SQ) stimulation patterns that require large currents to target deep structures. We recently demonstrated that temporal interference (TI) stimulation, delivered through epidural electrodes, can very effectively activate phrenic motor neurons. A successful respiratory neuroprosthesis must be able to elicit repeated diaphragm contractions without fatigue. Further, the motor unit recruitment patterns could have an impact on gas exchange and force generation. Here we examined diaphragm motor unit recruitment during TI stimulation and compared this to recruitment during square wave stimulation. Diaphragm motor units were recorded in anesthetized rats using a multi‐electrode array. An average of 22 motor units were evaluated in each experiment. Epidural stimulation was delivered at a rate of 50 pulses per second, on for 0.5 s and off for 0.5 s. Temporal interference stimulation was delivered using two sinewaves with frequencies of 5000 Hz, and 5001 Hz. Both types of stimulation produced initial motor unit discharge rates similar to firing during spontaneous bursts, but both stimulation method had lower average discharge rates (spontaneous = 24,TI = 15; SQ = 11 spikes/sec). During spontaneous and evoked bursts, motor recruitment pattern was assessed using a shuffle index. Spontaneous bursts had an average shuffle index of 21, indicating that there is a 21% variability in the unit recruitment order. Both types of stimulation increased the shuffle index, though TI stimulation had less of an impact (TI = 27, SQ = 33). Finally, we calculated cycle triggered histograms to assess the pattern in which motor unit were recruited relative to the compound diaphragm bursts. TI stimulation, but not square‐wave stimulation, recruited more units within the center of the burst resulting in a modulated breath pattern similar to spontaneous bursts. Taken together these results suggest TI stimulation could be used as an alternative method for pacing the diaphragm.