Title: Novel approaches to assess the neuromechanical control of involuntary pelvic floor muscle activation
Thesis Supervisors: Dr. Tania Lam, Dr. Jean-Sébastien Blouin
Committee Member: Dr. Bill Sheel
Chair: Dr. John (Kip) Kramer
Abstract:
The pelvic floor muscles (PFM) form the base of the abdominopelvic cavity. A key aspect of PFM function is to contract and prevent urinary incontinence upon increased exertion, which is associated with an elevation in intra-abdominal pressure commonly seen during postural perturbation, dynamic activities, and respiratory maneuvers. PFM activation in these scenarios often occur in the absence of any volitional effort to engage this muscle group. As the neural control of posture, breathing, and micturition converges in the brainstem, we hypothesize that descending control of involuntary PFM activation, if present, should be of subcortical origin. However, previous research suggests that PFM activation is subject to an additive effect of intra-abdominal pressure and visceral loading due to gravity, and associated with concomitant trunk and gluteal muscle activation. As a result, there lacks an experimental paradigm to selectively elicit and examine involuntary PFM activity. Therefore, the overarching objective of my thesis is to address this gap by (1) developing a novel model to assess involuntary PFM activation in the absence of confounding activity of the trunk and gluteal muscles, and (2) exploring candidate neural pathways underlying the involuntary PFM activation.
Leveraging an industrial robotic arm (KUKA KR500-3), we will systematically examine resting tonic PFM activation using surface electromyography in various whole-body orientation with respect to gravity in healthy, continent adults (Study 1). We hypothesize that the amplitude of resting PFM activity will be higher in an orientation where the PFM are under greater visceral loading due to gravity. We will also characterize and compare PFM activity in response to passive whole-body linear translations (anterior-posterior, lateral, vertical) in a seated (Study 2) versus body-extended (Study 3) posture. We hypothesize that in both postures, the whole-body translation stimuli will consistently and selectively elicit responses in the PFM, and there will be greater PFM activation when the translation is along an axis parallel to gravity and has higher speed and acceleration. For abovementioned studies, we will also explore the role of intra-abdominal pressure in orientation- and motion-related PFM response in a subset of participants. Considering the parallel features of the motion stimuli provided by the robot and the sensory information processed by the vestibular system, Study 4 will examine the vestibular contribution to motion-evoked PFM activation. We will first characterize PFM responses elicited by mechanical whole-body pitch, roll, and yaw rotations provided by the robot, then use electrical vestibular stimulation to deliver virtual motion signals equivalent to the mechanical rotation stimuli. We hypothesize that compared to mechanical motion, the virtual motion will still elicit responses in the PFM, but the activation will be of smaller amplitude. This work will advance our understanding of the neuromechanical factors contributing to involuntary PFM activation, and offer a new perspective on potential therapeutic interventions targeting the PFM in rehabilitation.