Fiber-type composition and fiber size of the human cricopharyngeal muscle and the pharyngeal constrictor muscle.
BACKGROUND
Despite a similar density of nicotinic acetylcholine receptors, the upper esophageal sphincter is sensitive to partial neuromuscular block, whereas the pharyngeal constrictor muscle is more resistant. In order to postulate possible mechanisms behind this difference in pharmacological response, basic knowledge of morphological and physiological features of these muscles is needed. The aim of this study was to compare the muscle fiber-type composition, the size and the morphology of the muscle fibers of the cricopharyngeal muscle, the main component of the upper esophageal sphincter, with that of the pharyngeal constrictor muscle.


METHODS
Muscle specimens were obtained from five patients undergoing surgery with laryngectomy. Muscle fiber type was determined by myosin heavy chain immunohistochemistry and the muscle fiber cross-sectional area was measured for each fiber type by planimetry. Morphology of muscle fibers was evaluated by histochemistry.


RESULTS
The muscle fiber cross-sectional area was generally smaller in the cricopharyngeal muscle compared with the pharyngeal constrictor muscle (P < 0.001). The composition of fiber types showed a large interindividual variability with no distinct difference between the studied muscles. Aberrant histological features were common in both the cricopharyngeal muscle and the pharyngeal constrictor muscle.


CONCLUSIONS
The main morphological difference between the neuromuscular blocking agents sensitive cricopharyngeal muscle and the more resistant pharyngeal constrictor muscle is a uniformly smaller size of contributing fiber types in the cricopharyngeal muscle than in the pharyngeal constrictor muscle. The muscle fiber-type composition does not differ between the two studied muscles.
Sundman
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Department of Anesthesiology and Intensive Care, Karolinksa Hospital and Institute, Stockholm, Sweden. Eva.Sundman@kirurgi.ki.se
Ansved
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Margolin
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Kuylenstierna
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Eriksson
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D000328:Adult; D000368:Aged; D004943:Esophagogastric Junction / Q000166:cytology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007150:Immunohistochemistry; D007825:Laryngectomy; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000145:classification / Q000166:cytology*; D018995:Myosin Heavy Chains; D010609:Pharyngeal Muscles / Q000166:cytology*
D018995:Myosin Heavy Chains