Effects Of Chronic Electric Stimulation Using Low And Physiologic Frequencies On Genioglossus Structure And Function In Rabbits With OSAHS

Obstructive sleep apnea hypopnea syndrome (OSAHS) is that occurred upper airway obstruction and intermittent apnea/hypopnea during sleep,which symptome is snoring or breath holding in sleep, headache or dizziness in daytime. Because of hypoxemia and sleep disorder at night, the morbidity of cardiovascular and cerebrovascular diseases in OSAHS patients are increased. OSAHS which has attracted widespread attention in recent years is considered independent risk factor of high blood pressure,heart infarction and acute cerebral accident, impacting the quality of human life and survival time seriously.The main etiological factors of OSAHS are upper airway stenosis and partial collapse of soft tissue[1]. Research has found the airway resistance of OSAHS patients compared with normal is 3 times higher during sleep[2].It has been generally accepted the upper airway muscle contraction capacity is an important factor of the upper airway in patients with OSAHS [3]. Genioglossus is the main upper airway dilator.When genioglossus contract, tongue moves forward to prevent pharyngeal narrowing, resistance against the flow and maintain an open airway.Confirmed by clinical and basic researches [4,5], genioglossus dysfunction can lead to upper airway collapse and is the most important reason of OSAHS.Therefore, improving contractile function of genioglossus is an effective and reasonable treatment of OSAHS .Domestic and international study found that [6,7,8], when apnea occured during sleep at night, gived acute electrical stimulation of genioglossus to OSAHS patients, genioglossus contracted to improve the immediate ventilation and terminate apnea. But the treatment with stimulation frequency 50Hz or so is a kind of short-term acute electrical stimulation modality, will not rule out injury on genioglossus and will not prevent apnea in long-term. Therefore, for the purpose of preventing apnea and improving the ventilation and long-term life quality of OSAHS patients, we need to find a more scientific and effective electrical stimulation modality to reconstruction genioglossus fibers .Electric stimulation using various frequencies may cause adaptive changes of skeletal muscles. Skeletal muscle fiber type can be changed with a high plasticity[9]. Reports indicate[10] that rabbits genioglossus were increased in the proportion of type I fibers after stimulation with 10Hz in 7 days.However, if the electrical stimulation of genioglossus to increase the proportion of type I fibers, the problem is that muscle contraction strength, speed and response capacity will be reduced, obviously this is not the demand of the best muscle fiber remodeling for clinical treatment of OSAHS. In previous studies, we found that [11] low and physiologic frequencies stimulation of the diaphragm can improve muscle fibers, while enhancing the ability of anti-fatigue and contraction intensity. According to the above we speculate that low and physiologic frequencies electrical stimulation may be the best electrical stimulation modality to improve the proportion of genioglossus muscle fibers, increase resistance to fatigue and muscle contractility .Currently, there is no similar domestic and foreign research reported.In this study, the features and patterns of adaptive changes in genioglossus structure, energy metabolism and muscle mechanics was observed in rabbit models of OSAHS subjected to electric stimulation using low frequencies and low and physiologic frequencies.The aim of which was to elucidate the mechanism by which chronic electric stimulation using low and physiologic frequencies (10+40Hz) prevents and treats genioglossus fatigue and to provide theoretical basis for the using low and physiologic frequencies electric stimulation genioglossus to prevent and treat OSAHS.The main contents of this study are as follows:(I) Establishment and evaluation of rabbit models of obstructive sleep apnea syndrome.1. Rabbit models of OSAHS were established through hypobaric hypoxia2. Changes in upper airway structure of OSAHS rabbit models(assayed by X-ray computer tomography).3. Changes in respiratory airflow in sleep of OSAHS rabbit models(assayed by using the Rm6240 multi-channel physiological signal collecting and processing system). 4. Changes in arterial blood gas of OSAHS rabbit models.5. Changes in pathology of pharyngeal and genioglossus tissue of OSAHS rabbit models.(II)Experimental observation on changes in myosin heavy chain (MHC) of genioglossus of OSAHS rabbit models following chronic electric stimulation using low and physiological frequencie.1. Changes in genioglossus MHC subtypes (assayed by SDS-PAGE).2. Changes in the expression of mRNA in genioglossus MHC subtypes (assayed by RT-PCR).(III)Experimental observation on changes in mechanics and Ca2+-ATPase activity of genioglossus of OSAHS rabbit models following chronic electric stimulation using low and physiological frequencies.1.Changes in the mechanic properties of genioglossus (assayed by using the Rm6240 multi-channel physiological signal collecting and processing system).2. Changes in sarcoplasmic reticulum Ca2+-ATPase activity (SERCA) of genioglossus (assayed by using the Ca2+-ATPase kit manufactured by Nanjing Jiancheng Bioengineering Institute).Main results1. Showed by CT scan of upper airway: in hyoid bone plane, the posterior pharyngeal wall thickness of OSAHS rabbit models group showed have significant thicked(P<0.01), the anteroposterior diameter (P<0.01)and cross-sectional area (P<0.05)have significant decreased compared with that of the control group; In middle of soft palate plane, the soft palate of OSAHS rabbit models group showed have significant thicked, the anteroposterior diameter have significant decreased compared with that of the control group (P<0.05).2. While sleeping monitoring, apnea/hypopnea index (AHI) of OSAHS rabbit models group was more than control group (P<0.01), breathing rate of OSAHS rabbit models group was faster than control group (P<0.01), expiratory/inspiratory of OSAHS rabbit models group was higher than control group (P<0.01) and mean respiratory depth was deeper than control group (P<0.05) . 3. Arterial oxygen pressure (PaO2) of OSAHS rabbit models group has degraded (P<0.05) and partial pressure of carbon dioxide in arterial blood (PaCO2) has heightened (P<0.05) compared with that of the control group.4. In pathological examination of OSAHS rabbit models group, the pharyngeal epithelium was cornified and proliferated, with proliferation of glandular organ. The genioglossus was collapsed.5. Following chronic electric stimulation using 10Hz and 10+40Hz, the percentage of MHC-I was significantly increased, while that of MHC-IIa was significantly decreased (P<0.05). Compared with the two chronical electical stimulation groups, the change in (10+40)Hz electical stimulation group was remarkably(assayed by SDS-PAGE).6. Following chronic electric stimulation using 10Hz and 10+40Hz, the mRNA expression of MHC-I in 10Hz electrical stimulation group was slightly increased (P > 0.05); the mRNA expression of MHC-I in (10 +40) Hz electrical stimulation group was increased significantly (P <0.05); the mRNA expression of MHC-â…¡a, MHC-â…¡b, and MHC-â…¡x was no significant difference betweem groups.(assayed by RT-PCR).7. In the observation experiment of genioglossus mechanical characteristics, the fatigue tolerance were increased significantly in 10Hz electrical stimulation group(P <0.05), but genioglossus inotropy in 10Hz electrical stimulation group did not improve significantly (P > 0.05); the notropy and the fatigue tolerance of OSAHS rabbits genioglossus were both increased significantly in (10 +40) Hz electrical stimulation group(P <0.05).8. In the observation experiments of genioglossus SERCA, genioglossus SERCA in 10Hz electrical stimulation group was significantly lower (P <0.05); genioglossus SERCA in (10 +40) Hz electrical stimulation group was slightly higher (P > 0.05).Conclusions1. The hypobaric hypoxia condition can be used to produce rabbit models of OSAHS. The physiology and the pathology of rabbit models similar changes in patients with OSAHS.2. Chronic electric stimulation using low and physiologic frequencies may transform MHC of genioglossus form typeâ…¡a fibers into typeâ… fibers, that is from fast to slow .The adaptive changes in structure of genioglossus is the foundation of changes in function.3. Chronic electric stimulation using low and physiologic frequencies increase inotropy and the fatigue tolerance of OSAHS rabbits genioglossus. And it enhance genioglossus SERCA, improve E-C coupling. It indicate that chronic electric stimulation using low and physiologic frequencies may be the optimal frequency mode for treatment of OSAHS patients.