“…The pressure in the mouthpiece and its relation to the upstream steady pressure have been investigated (Bouhuys, 1965;Yoshikawa, 1995;Fletcher and Tarnopolsky, 1999). Stroboscopy (Martin, 1942;Copley and Strong, 1996;Yoshikawa and Muto, 2003) and high-speed video (Newton et al, 2008;Bromage et al, 2010) have been used to study the motion of the lips directly. The electrical impedance across the lips has been used to study it indirectly (Wolfe and Smith, 2008;Scavone, 2011, 2013), although a variable delay between the variations in electrical impedance across the lips and the lip aperture (Boutin et al, 2014;H ezard et al, 2014) makes it difficult to draw firm conclusions.…”