title: Analysis of fiber type transformation and histology in chronic electrically stimulated canine rectus abdominis muscle island-flap stomal sphincters.
abstract: Dynamic skeletal muscle flaps are designed to perform a specific functional task through contraction and relaxation of their muscle fibers. The most commonly used dynamic skeletal flaps today are for cardiomyoplasty and anal or urinary myoplasty. Low-frequency chronic stimulation of these flaps enables them to use their intrinsic energy stores in a more efficient manner through aerobic metabolic pathways for increased endurance and improved work capacity. The purpose of this study was to (1) determine whether fiber type transformation from fatigue-prone (type II) muscle fibers to fatigue-resistant (type I) muscle fibers could be demonstrated in the authors' chronic canine stomal sphincter model where the rectus abdominis muscle was used to create a functional stomal sphincter, (2) assess whether there is any correlation between the degree of muscle fiber type transformation and the continence times, and (3) examine the long-term effects of the training regimens on the skeletal muscle fibers through histologic and volumetric analysis. Eight dynamic island-flap sphincters were created from a part of the rectus abdominis muscle in mongrel dogs by preserving the deep inferior epigastric vascular pedicle and the most caudal investing intercostal nerve. The muscular sphincters were wrapped around a blind loop of distal ileum and trained with pacing electrodes. Two different training protocols were used. In group A (n = 4), a preexisting anal dynamic graciloplasty training protocol was used. A revised protocol was used in group B (n = 4). Muscle biopsy specimens were obtained before and after training from the rectus abdominis muscle sphincter. Fiber type transformation was assessed using a monoclonal antibody directed against the fatigue-prone type II fibers. Pretraining and posttraining skeletal muscle specimens were examined histologically. A significant fiber type conversion was achieved in both group A and group B animals, with each group achieving greater than 50 percent conversion from fatigue-prone (type II) muscle fibers to fatigue-resistant (type I) muscle fibers. The continence time was different for both groups. Biopsy specimens 1 cm from the electrodes revealed that fiber type transformation was uniform throughout this region of the sphincters. Skeletal muscle fibers within both groups demonstrated a reduction in their fiber diameter and volume. Fiber type transformation is possible in this unique canine island-flap rectus abdominis sphincter model. The relative design of the flap with preservation of the skeletal muscle resting length and neuronal and vascular supply are important characteristics when designing a functional dynamic flap for stomal continence.
authors.affiliation: Division of Plastic and Reconstructive Surgery, Department of Surgery, University of Louisville, Ky 40292, USA.
authors.forename: Ramsey K
authors.initials: RK
authors.lastname: Majzoub
authors.forename: Janou W J M
authors.initials: JW
authors.lastname: Bardoel
authors.forename: Claudio
authors.initials: C
authors.lastname: Maldonado
authors.forename: John H
authors.initials: JH
authors.lastname: Barker
authors.forename: Wayne K
authors.initials: WK
authors.lastname: Stadelmann
mesh_terms: D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D005242:Fecal Incontinence / Q000601:surgery; D007150:Immunohistochemistry; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology*; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology*; D017568:Rectus Abdominis / Q000166:cytology* / Q000601:surgery; D013524:Surgical Flaps; D054047:Surgical Stomas