Systems and methods are provided for decreasing intracranial pressure and enhancing circulation, as well as for increasing the respiratory rate and encouraging spontaneous respiration. According to such methods, a valve system is coupled with a person's airway. The valve system has an exhalation valve and an patient port that interfaces with the person's airway. The exhalation valve includes a diaphragm having a textured surface. The diaphragm is positioned across an exhalation valve seat and contacts a distal end of the exhalation valve seat, and is configured to prevent or impede respiratory gas flow to the person's lungs until an expiratory pressure equals or exceeds an opening pressure of the exhalation valve, at which time the diaphragm moves away from the distal end to create an open exhaust channel.