RESPIRATORY MECHANICS IN ADOLESCENTS WITH IDIOPATHIC SCOLIOSIS

Publisher Website
Google Scholar
Abstract
Mechanisms causing the reduction in lung capacity commonly found in adolescents with idiopathic scoliosis (IS) have not been understood. In 29 patients with typical thoracic-curvatures of mild to moderate degree (< 60.degree.), total lung capacity (TLC) was a mean 75 .+-. 13% (SD) of predicted. The patients could generate only -70 .+-. 26 cm H2O (SD) maximal inspiratory airway pressure at functional residual capacity, as comapred with -102 .+-. 28 cm H2O in 21 normal control subjects (P < 0.001). Studies of lung mechanics in 15 of the patients showed that maximal transpulmonary presure at TLC was also reduced. Static pressure volume curves were shifted to the right, and both static and dynamic lung compliance were significantly reduced. Although both upstream conductance per TLC and anatomic dead space per TLC were abnormally high, relationships between maximal expiratory flow and static lung recoil were appropriate for age, indicating a normal growth of airway dimensions. From results of the single-breath nitrogen washout procedure, amounts of trapped nitrogen were also normal, indicating that the low compliance is not caused by airway closure. After a 5-min period of positive pressure (25 cm H2O) breathing, dynamic compliance increased by a mean of 34% in subjects with low TLC, and by a significantly smaller (P < 0.05) mean increase of 14% in subjects with normal TLC. The 15 patients were restudied 1 yr after corrective surgery by the Harrington procedure. Maximal inspiratory airway pressures increased by a mean 14 cm H2O (P < 0.01), and peak expiraotry flows increased in all 15 patients (by a mean of 32%). Reduction in lung capacity in IS is associated with alteration of pulmonary pressure volume characteristics similar to those prevously found during experimental low lung volume breathing in normal subjects. Evidently, low lung capacity in adolescents with mild to moderate IS is caused partly by defective mechanism coupling between inspiratory muscles and the chest cage.