External mechanical loading in conscious humans: role of upper airway mechanoreceptors.

To determine whether upper airway mechanoreceptors partly subserve the ventilatory response to external mechanical loading in conscious humans, we studied 11 laryngectomized subjects. The oropharynx (OP) or tracheostomy was selectively loaded (in random order) by attaching the mouth or tracheal tube to a special pressure-generating apparatus, and steady-state ventilatory responses were recorded. Phasic negative pressure changes generated at the OP to simulate inspiratory resistive loading, expiratory resistive unloading, and elastic loading resulted in trivial prolongation of inspiratory duration by 12, 9, and 4%, respectively; other ventilatory variables were not significantly altered. Phasic positive pressure changes at the OP that simulated inspiratory resistive unloading and expiratory resistive loading had little effect on breathing pattern. When the above loads were applied via the tracheostomy, using pressures of similar magnitude, ventilatory responses were qualitatively similar and quantitatively not significantly different from those of normal healthy controls. The results suggest that the OP does not make an important contribution to ventilatory responses during external mechanical loading in conscious humans. Loading responses to conventional mechanical loads are preserved in the absence of afferent information from the upper airways.