The VRG contains both inspiratory and expiratory neurons. It can be inspiratory, expiratory or biphasic, although it is usually heard during inspiration. Peak inspiratory pressure increases with any airway resistance. The paroxysmal cough precedes a crowing inspiratory sound characteristic of pertussis. As a rule, extrathoracic airway obstruction produce inspiratory sounds. It is measured during an inspiratory pause on the mechanical ventilator. Paroxysms of cough followed by inspiratory whoop and vomiting suggests pertussis. Obstructed venous return and quick inspiratory gasp can occur. Tachypnea, respiratory distress, and inspiratory crackles over lower lung fields often are present. Sometimes fine inspiratory crackles can be heard at the lung bases on auscultation. Consequently, airflow is either reduced or compensated for through an increase in inspiratory efforts. The pressure is constant during the inspiratory time and the flow is decelerating. The longer, deeper inspiratory flows by the patient will result in a larger tidal volume. Both methods offer a set inspiratory pressure. The patient is then asked to make an inspiratory effort.