Ventilatory patterns during hypoxia, hypercapnia, and exercise in adolescents with mild scoliosis

Adolescents with mild, asymptomatic scoliosis (thoracic curvature less than 35 degrees) may have little or no impairment of resting lung volumes. Progression to more severe disease may, however, be accompanied by lung restriction, impaired exercise tolerance, and respiratory failure with CO2 retention. We wished to see whether adolescents with mild scoliosis and minimally abnormal resting pulmonary mechanics had impairment of their responses to hypercapnia, hypoxia, and progressive cycle exercise. Forty-four adolescents with idiopathic scoliosis were studied. The mean forced vital capacity (FVC), expressed as a percentage of the predicted value, was 94.3 +/- 2.2 (SE). The mean ventilatory response to hypercapnia (2.57 +/- 0.24 L/min/mm Hg) was within the normal range but was achieved with a tidal volume response (1.87 +/- .17% vital capacity [VC]/mm Hg) that was significantly lower than that previously reported in healthy young adults. Ventilatory responses to exercise were also within the normal range, the mean dyspnea index (VE-max/maximal voluntary ventilation) = 0.92 +/- 0.04. However, at a ventilation of 30 L/min, the tidal volume was 0.38 +/- 0.01% FVC, which was considerably lower than predicted. The tidal volume response to hypoxia was also abnormally low, the mean response being 0.52 +/- 0.059% VC/% decrease in arterial O2 saturation. These findings indicated that, even when scoliosis is asymptomatic and associated with minimal impairment of resting pulmonary function, abnormal patterns of ventilation occur during exercise or in response to chemical stimuli.