Effect of unilateral nasal obstruction on tongue protrusion forces in growing rats

Abstract

Mouth breathing caused by nasal obstruction affects the normal growth and development of craniofacial structures, including changes in the orofacial muscles. Tongue muscles play an important role in patency of the pharyngeal airway, and changes in the breathing pattern may influence tongue function. The purpose of this study was to evaluate the effect of unilateral nasal obstruction during growth on contractile properties of the tongue-protruding muscles. Sixty 6-day-old male Wistar albino rats were divided randomly into control (n = 30) and experimental (n = 30) groups. Rats in the experimental group underwent a unilateral nasal obstruction after cauterization of the external nostril at the age of 8 days, and muscle contractile characteristics were measured at 5, 7, and 9 wk of age. The specific parameters measured were twitch force, contraction time, half-decay time, tetanic force, and fatigue index. Repeated-measures multivariate analysis of variance was used for intergroup and intragroup statistical comparisons. Twitch contraction force and half-decay time were significantly increased in the experimental group at all ages. Tetanic forces at 60 and 80 Hz were significantly higher in the experimental group at all ages. The fatigue index was decreased significantly in the experimental group at the age of 5 wk. These results suggest that early unilateral nasal obstruction may increase the contraction force of the tongue-protruding muscles and prolong the duration of muscle contraction, which may influence the shape and development of the craniofacial complex.

Unilateral Nasal Obstruction during Later Growth Periods Affects Craniofacial Muscles in Rats

“…In previous studies, it has been reported that unilateral nasal obstruction before maturation of the respiratory function is well tolerated and affects the craniofacial complex (Otani-Saito et al, 2001), such as JOR (Funaki et al, 2014) and the contractile properties of the tongue-protruding muscles (Uchima Koecklin et al, 2015). Unilateral obstruction also induces atrophy of the ipsilateral olfactory bulb, associated with olfactory deprivation in rats (Meisami, 1976; Baekey et al, 2009).…”

“…In our previous studies, we performed unilateral nasal obstruction in neonatal rat pups at 8 days of age, before the stabilization of SpO 2 levels (Funaki et al, 2014; Uchima Koecklin et al, 2015). The maturation of JOR was altered (Funaki et al, 2014) and the force of the tongue-protruding muscles increased (Uchima Koecklin et al, 2015).…”

“…The rat was placed onto a stage with the body and head fixed, and the tongue extended at a preloaded force of 3 g (Figure 2A), as described previously (Uchima Koecklin et al, 2015). …”

“…We applied a bilateral electrical stimulation to the medial branches of the hypoglossal nerves by 0.1-ms rectangular pulses at a supramaximal current (generally ~500 μA), as described in previous studies (Uchima Koecklin et al, 2015). Electrical stimulation was supplied by an electric stimulator (SEN-7203, Nihon Kohden, Tokyo, Japan) with two tungsten electrodes (0.010-inch-length, 250-μm-diameter, epoxylite insulation, 9 MΩ of impedance measured at 1000 Hz; FHC, Bowdoin, ME, USA).…”

“…With regard to masticatory function (Hsu and Yamaguchi, 2012; Ikenaga et al, 2013), previous studies have shown that oral breathing reduces masseter muscle activity (Ferla et al, 2008), and increases suprahyoid muscle activity and hypotonia of the lips and buccinator muscle (Valera et al, 2003). In our previous electrophysiological study, we suggested that unilateral nasal obstruction during early periods of growth reduces the response properties of the jaw-opening reflex (JOR; Funaki et al, 2014), increases the contraction force of the tongue-protruding muscles, and prolongs the duration of muscle contraction (Uchima Koecklin et al, 2015). The JOR plays an important role in the regulation of jaw movement during mastication (Lund, 1991).…”