Techniques, Models, and Variables of Interest in Studies of Intrinsic Laryngeal Muscle Fiber Types: A Bibliometric Analysis.

Introduction: Laryngeal muscle physiology is integral to many speech, voice, swallowing, and respiratory functions. A key determinant of a muscle's contractile properties, including its fatigue profile and capacity for force production, is the myosin heavy chain (MyHC) isoform that predominates in the muscle. This study surveys literature on the MyHC compositions of mammalian intrinsic laryngeal skeletal muscle to illustrate trends and gaps in laryngeal muscle fiber typing techniques, models, and concepts.

Methods: The Embase, Scopus, Medline, Web of Science, and Cochrane databases were systematically searched for studies of mammalian intrinsic laryngeal muscle MyHC composition. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews, 1531 non-duplicate papers were identified; 146 were selected for full-text screening. One hundred twenty papers were included in the final bibliometric analysis, which aimed to highlight key concepts in the literature.

Results: Publication of intrinsic laryngeal MyHC studies peaked in the early 2000s and has since declined. Although early research predominantly used histochemical techniques and large mammalian models (cow, sheep, dog, horse, etc), practice has evolved to focus on electrophoretic, immunohistochemical, and transcriptomic fiber typing techniques in rats and humans. Comparatively few studies have examined how experimental manipulations affect laryngeal muscle MyHC composition.

Discussion: Three areas of laryngeal muscle physiology lack a large body of supporting literature: (1) MyHC responses to stimuli such as training and disease, (2) MyHC plasticity across the lifespan, and (3) MyHC heterogeneity within muscle fibers (MyHC polymorphisms) and across muscle fibers (topographical MyHC distribution). We propose new avenues for research, education, and discussion in these three subdomains.