In one embodiment, a method for modulating a person's autonomic function comprises interfacing a valve system to the person's airway, the valve system being configured to decrease or prevent respiratory gas flow to the person's lungs during at least a portion of an inhalation event. The person is permitted to inhale and exhale through the valve system, wherein during inhalation the valve system functions to produce a vacuum within the thorax to transiently decrease intrathoracic pressure and thereby modulate the person's autonomic function.