Final answer:
Spirometry is the diagnostic test used to ascertain airway obstruction in children with mandibular hypoplasia, with the FEV1/FVC ratio providing insight into whether the condition is restrictive or obstructive.
Step-by-step explanation:
To determine the presence and severity of airway obstruction in children with mandibular hypoplasia, spirometry is the diagnostic test commonly used. Spirometry measures the rate and volume of air inhalation and exhalation. The ratio of FEV1 (the amount of air that can be forcibly exhaled in one second after taking a deep breath) to FVC (the total amount of air that can be forcibly exhaled) helps distinguish between restrictive and obstructive lung diseases.
In obstructive lung disease, which is related to airway obstruction, the FEV1/FVC ratio is characteristically lower (<69 percent). On the other hand, in restrictive lung disease, this ratio is typically higher (88 to 90 percent) because the primary problem is a reduction in lung volume, rather than an obstruction in air flow.