The maximum tongue pressure during oral breathing was significantly

greater than that during nasal breathing in both the upright and the supine positions. Changes in body position significantly affected the maximum tongue pressure during oral breathing. The GG EMG activity Caspase inhibitor changed significantly with different breathing modes and body positions. Changes in the position of the hyoid bone produced by changes in the breathing mode and body position appear to play a critical role in determining tongue pressure. This assumption was supported by an MRI study in normal awake subjects during nasal breathing [36]. In the retropalatal region, there was a significant decrease in the lateral dimension in the lateral recumbent position compared with that in the supine position. The cross-sectional area in the retroglossal region was significantly increased in both the “supine with the head rotated” and

the “lateral recumbent” positions. This change was accompanied by significant volumetric changes in the retroglossal region. Thus, the anatomical change in UA configuration GSK1210151A in vivo is in concert with functional change in GG activity. As indicated above, some GG fibers run perpendicular to the pharynx, and therefore activation of these fibers may result in both advancement of the base of the tongue and enlargement of the UA. Previous physiological studies have shown that the fibers of UA dilator muscles have faster contractile properties and less resistance to fatigue than those of the diaphragm [37] and [38]. In addition, the GG muscle contains type I, type IIa, and type IIb fibers [38] and [39]. However, it is not yet clear which type of motor unit is responsible for the respiratory-related activity of the GG muscle. It has

recently been shown that there are at least two types of motor units with respiratory-related activity in the human GG muscle [40]: inspiratory motor units (IMUs), which show phasic firing during inspiration; and inspiratory/expiratory motor units (IEMUs), which fire during both inspiration and expiration, with a greater instantaneous firing frequency during inspiration. Their different patterns of firing activity indicate that these two types of motor units play different physiological roles with regard to respiratory-related control of tongue movement, but it is unclear whether the diglyceride IMUs and IEMUs are heterogeneous. Unitary spike activity of GG respiratory-related motor units were recorded in healthy subjects [41]. The mean interspike interval and the SD of successive spikes were calculated for IMUs and IEMUs, respectively. Scattergrams of the mean interspike interval versus SD were constructed for the two groups of motor units (Fig. 4). The effects of changes in head position on the firing activity and the patterns of distribution of the mean interspike interval versus its SD were significantly different between IMUs and IEMUs.