Clinical translation of optical quantification of muscle function to aid pelvic floor muscle rehabilitation following partial spinal cord injury


Background: Spinal cord injury (SCI) compromises muscle function; when the pelvic floor muscles (PFM) are involved continence is affected. Women with partial injury rely on PFM rehabilitation therapy (PFMT) to aid continence, but the current lack of absolute measures to quantify training effects by monitoring changes in muscle oxygenation and perfusion hampers rehabilitation. We report clinical translation of a near infrared spectroscopic (NIRS) system to enable women with partial SCI to apply transvaginal optical detection of physiologic changes during PMFT as a point of care tool to quantify the effects of their PFM rehabilitation. Methods: The NIRS interface incorporates a circumferential grid of 6 LED emitters and 4 photodiode receivers with interoptode distances of 20 and 35 mm. The system was developed iteratively by engineers working with clinicians and patient care advocates to be clinically applicable for women following spinal cord injury. The continuous wave system uses 2-wavelengths (nominal 760nm, 850nm) and a sampling rate of 50Hz. Placed in the vagina during PMFT, the system monitors changes in oxy and deoxy-hemoglobin concentration (O2Hb/HHb) in real time at multiple points in the PFM. The slope of reoxygenation recovery post contraction is a measure of muscle oxidative capacity. Results: A point of care system was successfully developed that provides a means of detecting chromophore change occurring in the PFM during muscular contraction. The chromophore changes monitored also allow an absolute measure, HbDiff half-recovery time (½RT) to be derived. Comparison of these data over time provides a means of evaluating PMFT regimens for a training effect. In preparation for application in subjects with SCI, the reproducibility of SMVCs was monitored successfully in a pilot study where a volunteer conducted a series of 4 SMVCs on 15 occasions. Discussion: Skeletal muscle recovery from exercise-induced oxygen deficit indicates oxidative capacity; this equates with muscular fitness. SMVC is a robust measure of muscle strength and endurance, and HbDiff in occlusion free ½RT analysis reflects metabolic changes within muscle better than O2Hb. This clinical translation of NIRS provides a hand held system for women to use to quantify physiologic changes in their PFM; this will aid women with partial spinal cord injury in whom PFM function may either be too weak to be detected by physical exam or manometry, and may only be present unilaterally. Hence the merit of an optical system able to provide quantifiable measures of reoxygenation recovery as a measure of PFM fitness. A quantitative physiologic measure for evaluating for PMFT training effect is currently lacking Conclusions: The collaborative development of this self-contained transvaginal NIRS system, and prior proof that optical detection of a validated quantifiable oxygenation parameter is feasible in the pelvic floor, now allows clinical evaluation using this point of care system to aid women with partial spinal cord injury. The aim is to enable them to use this system to optimize their PFM rehabilitation therapy as means of enhancing their continence and quality of life.

Clinical Biophotonics II