FIG. 2.

Ventilatory function of subjects at study enrollment. (A) Although all subjects required full-time invasive ventilation, baseline maximal inspiratory pressure (MIP) varied appreciably between children. MIP values were >60% reduced from expected age- and sex-matched unaffected children. Solid and dashed lines represent average and upper/lower limits of age-predicted normal values for MIP. (B) Maximal voluntary ventilation (MVV) is influenced not only by respiratory muscle strength, but also by pulmonary mechanics, upper airway patency, and chest wall restrictive disease. MVV of the subjects was reduced >80% from healthy references. Unfilled bars represent the age, sex, and height-predicted reference value for each child. (C) The maximal-effort, unassisted tidal volumes of subjects fell short of the expected range of resting tidal volume in unaffected individuals (dashed lines).