The effect of repair on contractile properties of single permeabilized muscle fibers from congenitally‐clefted goat palates

We hypothesize that differences in levator veli palatini (LVP) muscle characteristics prior to surgery play a critical role in the prevalence of velopharyngeal insufficiency (VPI) after cleft palate repair. Physiologic differences in single muscle fibers from LVP muscles of congenitally‐clefted (CP) and normal palates (NP) exist: CP consist of predominately type II fibers and have increased fatigability that may result in VPI. We compared contractile properties of 5 single permeabilized muscle fibers from each of three 2 mo old CP goats prior to and 6 mo post cleft palate repair (RP) and one 2 mo NP goat. The cross‐sectional area (CSA), maximum isometric force (F 0 ), and rate of force development (k tr ) were measured, and specific force (sF 0 ) and normalized power (nP max ) were calculated for CP (n=15), RP (n=15), and NP (n=5) fibers. Using k tr to determine the fiber type composition, NP was 100% type I compared to 100% type II in CP. Two of the three RP shifted to 100% type I fibers, while one RP remained 100% type II fibers. The difference in fiber type was the only factor contributing to the increases in CSA, F o , and nP max between the groups. There was no difference in sF 0 between the groups or fiber types. These data show that in 30% of the RP, surgical repair did not result in a shift to type I fibers. This persistent state of type II fibers will lead to increased fatigue in the LVP of these subjects and may lead to VPI. Grants: P30 AG 13283.