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Intercostal retractions occur when the muscles between the ribs pull inward. The movement is most often a sign that the person has a breathing problem. Intercostal retractions are a medical emergency.
Relevance. Rating Newest Oldest. Best Answer: Increase. When the intercostal muscles and the diaphragm contract they increase the size of the thoracic cavity, causing negative pressure in the lungs, causing inspiration.Source(s): Dr. T Â· 7 years ago.ating Newest Oldest. Best Answer: Increase. When the intercostal muscles and the diaphragm contract they increase the size of the thoracic cavity, causing negative pressure in the lungs, causing inspiration.