Submental scanning Before the measurement of dynamic changes, participants will be given time to practice the maneuvers under instruction. Forced inspiration will be desired to approach the inspiratory reserve volume by maximal effort of inspiration within 3 sec. Mullers maneuver (reverse valsalva) will be performed by an attempt at vigorous inhalation with the mouth and nose closed. To localize measurement, two strategies will be applied. First, no shoulder and head movement will be allowed during the maneuver. We will measure the airspace 3 times in every participant based on the same level of US-structure composed of tongue, hypoglossal muscle and geniohyoid muscle and the final recorded value will be mean of the three values.