Objective
The levator ani muscles (LAMs) are integral to pelvic floor support, but our ability to evaluate the neuromuscular integrity of this muscle complex is limited. Magnetomyography is a novel tool to measure passively the electromagnetic field activity that is generated by depolarization activity of muscles and provides a functional map of muscle activity patterns. Magnetomyography signals record the skeletal muscle contraction mechanisms that are produced by the same ionic currents that give rise to electromyography signals. Magnetomyography allows detection of lower ranges of magnetic fields with higher spatial resolution when compared with electromyography, because surface electromyography is considered highly sensitive to the geometry and the conductivity properties of the volume conductor. Thus, electrical fields are disrupted by the different layers of tissue between the source and the skin surface, whereas these tissues are not disruptive to magnetic fields. Magnetomyography records electrophysiological signals that are related to primary currents as opposed to surface electromyography that records the secondary currents that reach the surface of the skin. The goal of our project was to establish the feasibility of measuring magnetomyography signals of the LAM complex to provide simultaneous functional and anatomic assessment of the pelvic floor.
Study Design
We collected magnetomyography data from a single nulligravid woman using the Superconduction Quantum Interference Device Array for Reproductive Assessment (SARA) system, which noninvasively detects biomagnetic signals that are related to the electrical activity generated in muscle tissue using 151 magnetomyography sensors. Previous clinical assessment demonstrated that our participant was able to correctly perform voluntary LAM contraction. We collected magnetomyography data during moderate intensity Kegels in intervals with intervening rest periods (each 10 seconds duration). We collected data during purposeful isolated abdominal and thigh contractions to define these magnetomyography patterns and allow for identification of accessory muscle recruitment/artifact during Kegels. To validate that the detected magnetomyography signals corresponded to LAM activation, we performed simultaneous vaginal manometry with an intravaginal balloon pressure catheter placed in the mid/distal vagina. We also used concurrent body-surface (electromyography) to evaluate for accessory-muscle recruitment and artifact by placing a pair of electromyography surface electrodes on the perineum (LAM), abdomen (rectus abdominus), and upper lateral/posterior thigh (gluteus muscles). We collected repeated measures to establish reliability, using a sampling rate of 625 Hz that used the lowermost SARA sensors, given their proximity to the LAMs. Cardiac signals and artifacts were removed by advanced signal processing techniques. Kegel and rest periods were identified, and average power spectrum density (PSD) was calculated for each of these segments in the bandwidth of 20–200 Hz (selective for skeletal muscle) with a frequency resolution of 1 Hz. To measure the correlation between signals in the frequency domain, coherence was calculated between electromyography and magnetomyography signals from the lower sensors of the SARA array during Kegel contraction.
Study Design
We collected magnetomyography data from a single nulligravid woman using the Superconduction Quantum Interference Device Array for Reproductive Assessment (SARA) system, which noninvasively detects biomagnetic signals that are related to the electrical activity generated in muscle tissue using 151 magnetomyography sensors. Previous clinical assessment demonstrated that our participant was able to correctly perform voluntary LAM contraction. We collected magnetomyography data during moderate intensity Kegels in intervals with intervening rest periods (each 10 seconds duration). We collected data during purposeful isolated abdominal and thigh contractions to define these magnetomyography patterns and allow for identification of accessory muscle recruitment/artifact during Kegels. To validate that the detected magnetomyography signals corresponded to LAM activation, we performed simultaneous vaginal manometry with an intravaginal balloon pressure catheter placed in the mid/distal vagina. We also used concurrent body-surface (electromyography) to evaluate for accessory-muscle recruitment and artifact by placing a pair of electromyography surface electrodes on the perineum (LAM), abdomen (rectus abdominus), and upper lateral/posterior thigh (gluteus muscles). We collected repeated measures to establish reliability, using a sampling rate of 625 Hz that used the lowermost SARA sensors, given their proximity to the LAMs. Cardiac signals and artifacts were removed by advanced signal processing techniques. Kegel and rest periods were identified, and average power spectrum density (PSD) was calculated for each of these segments in the bandwidth of 20–200 Hz (selective for skeletal muscle) with a frequency resolution of 1 Hz. To measure the correlation between signals in the frequency domain, coherence was calculated between electromyography and magnetomyography signals from the lower sensors of the SARA array during Kegel contraction.
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