Mechano- and chemoreceptor modulation of respiratory muscles in response to upper airway negative pressure.

To investigate the influence of phasic pulmonary stretch receptors (n = 6) and chemoreceptors (n = 7) on the reflex response of the genioglossus (GG) muscle and diaphragm (DIA) to upper airway (UAW) negative pressure, we measured the response of the GG and DIA electromyogram (EMG) to three challenges: 1) negative pressure applied to the UAW during normoxia and hypercapnia, 2) end-expiratory tracheal occlusion, and 3) application of UAW negative pressure simultaneous with tracheal occlusion in spontaneously breathing tracheotomized anesthetized cats. Peak GG EMG was greatest when UAW negative pressure and end-expiratory tracheal occlusion were combined. No GG EMG activity was seen when UAW negative pressure was applied alone unless the animal was vagotomized or hypercapnic. DIA EMG increased in response to UAW negative pressure combined with occlusion. However, the increase in peak GG EMG was significantly greater than for the DIA with the same challenge. DIA EMG amplitude increased in response to occlusion alone but did not change when UAW negative pressure was applied alone. In the cat, phasic feedback from phasic pulmonary stretch receptors is a potent inhibitor of reflex activation of the GG in response to negative pressure applied to the UAW, which can be overridden by an increase in chemoreceptor drive.