When an inspiratory effo is made against a closed airway, all the pressures inside the thorax fall including the pulmonary vascular pressures. The other choices are incorrect: During inspiration, the tension in the diaphragm increases, external not internal intercostal muscles become active, intrapleural pressure becomes more negative, and alveolar pressure will fall equally with intrapleural pressure if lung volume does not change. If lung volume does increase slightly, intrapleural pressure will fall more than alveolar pressure.