This discussion emphasizes the importance of inspiratory collapse, despite some literature that has emphasized the importance of expiratory collapse in OSA.7 We believe that inspiratory narrowing is an important phenomenon in OSA and would suggest that protective reflexes (eg, negative pressure reflex8) can help to maintain pharyngeal patency from diaphragm-generated inspiratory negative pressures. That is, the activation of pharyngeal dilator muscles, such as the genioglossus, occurs in response to negative intrapharyngeal pressure,8 and individuals with impaired reflexes should be susceptible to inspiratory collapse. Indeed, we and others have observed evidence of marked negative effort dependence (Fig 1), such that inspiratory flows are markedly diminished with increasing driving pressures both within and across breaths. These findings are in contrast to the classic Starling resistor model, in which constant flows are seen across a range of driving pressures.9-11 The mechanism underlying negative effort dependence remains unknown, but may involve the complex geometry of the upper airway, such as axial coupling (eg, movement of one structure near the larynx might affect the mechanics of the airway behind the tongue) or movement of a large structure such as the tongue, where it behaves as an axially lumped object rather than a tube whose area at any point is only determined by the pressure locally at that point. These kinds of behaviors/structures cannot be well represented by a simple floppy tube model. Regardless, although negative effort dependence is well described in the flow limitation literature, we would emphasize the magnitude of the decline seen with increasing respiratory efforts across breaths, at least in some individuals, and would speculate that airway length in the setting of poor upper airway protective reflexes may contribute to this negative effort dependence finding.