Final answer:
Grunting is heard during exhaling and occurs as the child exhales against resistance. During exhalation, the diaphragm relaxes and moves upward, decreasing the volume of the thorax.
Step-by-step explanation:
Grunting is heard during exhaling and occurs as the child exhales against resistance. During exhalation, the diaphragm relaxes and moves upward, decreasing the volume of the thorax. This causes the air pressure inside the lungs to increase, which forces air out of the lungs. If exhalation is forced, internal intercostal and abdominal muscles may help move the air out of the lungs.