Application of a NIRS-derived measure to quantify reoxygenation of the pelvic floor muscles in women following sustained maximal voluntary contraction

Background: Near infrared spectroscopy (NIRS) is used to quantify multiple physiologic measures; several of these are applied to optimize muscle training regimens in elite athletes. However, pelvic floor muscle training (PMFT), the definitive therapy for urge urinary incontinence (UUI) due to PFM damage/dysfunction in women, lacks quantifiable measures beyond simple pressure manometry. A NIRS interface able to transvaginally monitor the PFM bilaterally has been developed; we now describe a method to quantify oxygen kinetics in the PFM. Methods: The NIRS interface (interoptode distance 20 mm) enables dual-channel monitoring at 10 Hz during PFM sustained maximal voluntary contraction (SMVC) with a 4-wavelength (766nm, 861nm, 906nm 971nm) continuous wave instrument. Changes in oxy and deoxy-hemoglobin concentration (O2Hb/HHb) in the right and left PFM were used to derive HbDiff (O2Hb - HHb). Established HbDiff half-recovery time (½RT) methodology was then applied to quantify PFM reoxygenation commencing on cessation of SMVC. Results: SMVCs were monitored successfully in 15 asymptomatic women; contraction strength and duration varied; post- SMVC reoxygenation HbDiff (½RT) was quantified for both the right and left sides of the PFM. Conclusions: 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 pilot study shows the feasibility of using transvaginal NIRS data to derive a quantitative measure of PFM oxygen kinetics relevant to improving the evaluation PFM dysfunction in UUI and the efficacy in PMFT.