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

Abstract

Nasal obstruction can occur at different life stages. In early stages of life the respiratory system is still under development, maturing during the growth period. Previous studies have shown that nasal obstruction in neonatal rats alters craniofacial function. However, little is known about the effects of nasal obstruction that develops during later growth periods. The aim of this study was to investigate the effects of nasal obstruction during later periods of growth on the functional characteristics of the jaw-opening reflex (JOR) and tongue-protruding muscles. In total, 102 6-day-old male Wistar rats were randomized into either a control or experimental group (both n = 51). In order to determine the appropriate timing of nasal obstruction, the saturation of arterial oxygen (SpO2) was monitored at 8 days, and at 3, 5, 7, 9, and 11 weeks in the control group. Rats in the experimental group underwent unilateral nasal obstruction at the age of 5 weeks. The SpO2 was monitored at 7, 9, and 11 weeks in the experimental group. The electromyographic responses of JOR and the contractile properties of the tongue-protruding muscles were recorded at 7, 9, and 11 weeks. In the control group, SpO2 decreased until 5 weeks of age, and remained relatively stable until 11 weeks of age. The SpO2 was significantly lower in the experimental group than in the control. In the experimental group, JOR changes included a longer latency and smaller peak-to-peak amplitude, while changes in the contractile properties of the tongue-protruding muscles included larger twitch and tetanic forces, and a longer half-decay time. These results suggest that nasal obstruction during later growth periods may affect craniofacial function.

Changes in maxillofacial morphology due to improvement of nasal obstruction in rats

“…In the present study, we performed unilateral nasal obstruction with reference to the method of Uchima et al Figure shows that there were no significant differences in the body weight among all groups, findings that were similar to those of Uchima et al Although the age of the rats and methods in our study differed, mild respiratory disorders over long periods of time do not seem to affect body weight, findings that are consistent with those of Funaki et al Therefore, we believe that this method is suitable for investigating the effects of unilateral nasal obstruction on changes in the craniofacial morphology.…”

“…Humans breathe through their mouth when the nostrils on both sides are blocked, while rats cannot breathe through their mouth . Therefore, we blocked the nose unilaterally in rats.…”

Alveolar Bone Density Reduction in Rats Caused by Unilateral Nasal Obstruction

“…Previous research demonstrated that oral breathing induces chewing activity (24), but whether the decrease in chewing activity will reduce the bone density of alveolar bones remains unclear. Oral breathing is known to affect craniofacial muscle activity (6,8,9,10). Nonetheless, further studies are needed to explore the relationship between craniofacial muscle activity and the density of alveolar bones.…”

“…Oral breathing has an important impact on the growth and development of craniofacial structures (1,2,3,4,5). Animal experiments demonstrated that changes in breathing patterns from the nasal cavity to the oral cavity can induce changes in craniofacial muscle activity (6,7,8,9,10,11). Recent studies have focused on the effect of oral breathing on the morphology of maxillofacial (12,13).…”

Histological and contractile changes in the genioglossus muscle after nasal obstruction in growing rats

“…Our previous studies showed an increase in the tongue-protruding forces after unilateral nasal obstruction in growing rats, by changing the muscle contractile properties, while oxygen saturation levels were also lower after nasal obstruction 13 , 14 . It has been suggested that the muscle force and contractile properties are affected by the cross-sectional area of muscle fiber 15 .…”