In a macroscopical study the dimensions of the adult laryngeal skeleton of man and sheep were compared. In both species the data for male and female were evaluated separately. In contrast to pronounced differences in size between male and female human larynges, the dimensions of both sexes in sheep proved to be very similar. In respect of 7 size values, the sheep larynx falls in the range between the male and female human larynx. This applies to most values for height, the antero-posterior diameter and the inferior breadth of the thyroid cartilage. In the sheep cricoid, the height of the lamina and the inner transverse diameter correspond closely to the human counterpart. The most conspicuous differences vis-à-vis the human larynx are the narrowing of the upper portion, the absent upper incisure of the thyroid and the relatively large dimensions of the arytenoid cartilages in sheep. Since in sheep the dimensions at the level of the glottis and of the subglottic space are within the range of the human larynx, the suitability of the sheep larynx as a model for experimental clinical laryngology is discussed.

Isomyosin analyses by biochemical, immunochemical, and histochemical investigations have been carried out in five sheep following unilateral recurrent laryngeal nerve paralysis and direct functional electrostimulation of the denervated cricoarytenoid posterior muscle. Myosin light chains were identified by two-dimensional gel electrophoresis. Myosin heavy chains were analyzed by one-dimensional SDS-polyacrylamide gel electrophoresis. Slow myosin heavy chain was identified by orthogonal peptide mapping and immunochemistry. The stimulation effect at cellular level was determined using adenosine triphosphatase (ATPase) histochemistry. A dramatic increase of the type 1 fiber area (slow, fatigue-resistant fibers) could be seen after many weeks of an increasing regime of low-frequency direct electrical stimulation. Biochemically, the amount of slow myosin was always higher than in normal muscles. Some muscles were transformed almost completely to the slow type. At the time they were studied and with the methods employed, the expression of embryonic isomyosin was not observed. In conclusion, after numerous weeks of maintained functional activity, elicited by direct electrostimulation, the denervated muscle regionally showed areas of hypertrophy or at least lack of atrophy of slow myofibers without major signs of muscle damage.

Four laryngeal muscles of human male, human female and sheep female cadavers were evaluated by histological, histochemical and quantitative techniques. The muscle fibre sizes showed significant differences between human male, female and sheep. Fibre diameters of male human laryngeal muscles were 2 to 4 microns larger than in female human and 11 to 13 microns larger than in sheep muscles. In the group of human laryngeal muscles, the posterior cricoarytenoid muscle contained the highest percentage (65%) of type I fibres. In sheep, the homologous muscle consists only of 45% type I fibres. On the other hand, in sheep the cricothyroid muscle showed significantly more type I fibres (58%) than the human counterpart (43%). In both species the vocal muscles had a rather low content of type I fibres (26 to 37%).

Electromyograms (EMG) of the PCM and the diaphragm were evaluated in 6 sedated female sheep. Corresponding pneumatograms were recorded simultaneously by means of thermocontrolled respiration flowmeter. Evidence was obtained on considerable intra- and inter-individual differences in the duration of respiratory cycles as well as PCM- and diaphragmatic activity. Most of the evaluated respiratory periods showed either a phase coincidence between the PCM and the diaphragm, or a leading edge of about 40-80 ms of the posticus muscle. Due to this minimal phase shift, the diaphragmatic myogram seems to be a valuable trigger for an external PCM stimulation unit in bilateral recurrent nerve palsy.

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