<prompt> A 3-year-old child is admitted to the emergency department with a particularly severe attack of asthma. Which of the following is the most important factor in increasing the intrathoracic capacity in inspiration?Pump handle movement of the ribs-thereby increasing anterior-posterior dimensions of the thoraxBucket handle movement of the ribs-increasing the transverse diameter of the thoraxStraightening of the forward curvature of the thoracic spine, thereby increasing the vertical dimensions of the thoracic cavityDescent of the diaphragm, with protrusion of the abdominal wall, thereby increasing vertical dimensions of the thoracic cavity  <response>: Contraction of the diaphragm descent pulls the dome inferiorly, increasing the vertical dimension of the thorax. This is the most important factor in inspiration for increasing the internal pulmonary volume and concomitantly decreasing intrathoracic pressure. The contraction of intercostal muscles is usually involved in forced inspiration, resulting in increases in the transverse and anteroposterior dimensions of the thoracic cavity. 