(1) Subglottal pressure can be varied by changes in the pattern of innervation of the muscles of respiration.
(2) Variations of subglottal pressure may be caused by variations in the glottal-supraglottal resistance (or, equivalently, in the rate of air flow). In plosive production the main variations of glottal-supraglottal resistance occur at the closing of the articulators and the articulatory release.
(3) If the glottis is partially open during a period of articulatory and velopharyngeal closure, changes in the supraglottal cavity volume (Ie in Figure 2.4.2) may produce changes in subglottal pressure.
The variations of subglottal pressure caused by changes in glottal-supraglottal resistance or in supraglottal cavity volume (2 and 3 above) can be thought of as passive responses resulting from the processes of articulation and phonation. In Chapter 4 we will consider the extent to which subglottal pressure is affected by these factors in simple-released-plosive production when a constant respiratory muscle innervation is assumed.