Table 3.

Pulmonary Function Tests and Their Indications for Patients With Congenital Muscular Dystrophy

Pulmonary Function Test	Indication
Forced vital capacity sitting and supine, forced   expiratory volume in first second, ratio of forced   expiratory volume in first second and forced vital   capacity, maximal expiratory pressure, maximal   inspiratory pressure, peak cough flow	Obtain during routine evaluation, performed at each   clinic visit, at least annually
Nocturnal oximetry	Obtain if patient shows increased work of breathing,   tachypnea, retractions, restless sleep, decreased functioning   during the day, recurrent chest infections, poor weight gain,   morning headache, forced vital capacity <60% predicted, or   >20% difference between sitting forced vital capacity and   supine if sitting forced vital capacity <80%
Nocturnal CO2 monitoring	Obtain if oximetry has a low baseline of <94% on room air   when patient is awake or asleep and/or oximetry drops below   90% on room air for >5 min with a low of at least 85% or >30%   of total sleep time spent at <90% saturation
Blood gas	Obtain if there is an acute onset of respiratory distress, if noninvasive   CO2 monitoring is not available, or to correlate with end-tidal CO2   and transcutaneous measurements obtained
Polysomnography that includes CO2 monitoring	Obtain to differentiate between central apneas, obstructive sleep apneas,   hypopneas, seizures, and gas exchange abnormalities; hypoventilation   is present if >25% of the total sleep time is spent with CO2 >50 torr;   obtain if symptoms listed as indication of nocturnal oximetry persist   with normal overnight oximetry recording (drop in saturation can trigger   an arousal inducing sleep fragmentation); also helpful to titrate best settings   for noninvasive ventilation