Spirometry and Chest Wall Dimensions in Achondroplasia

Standard values for pulmonary function in short-limbed dwarfism are not available. Therefore, chest diameters and expiratory spirograms were measured in 58 female and 44 male subjects between 7 and 60 years of age with achondroplasia, the most common form of dwarfism. Standing height in adults was 49.6 ± 3.2 (SD) inches with a sitting/standing height ratio of 0.66 (normal 0.52–0.53). Despite extremely short stature, only AP chest diameters in males were smaller than control subjects of similar age. The following equations were derived for forced vital capacity (FVC): males (under 25 years), FVC(L)= −3.56 + 0.162 × sitting height (in) +0.067 × age (yrs); males (over 25 years), FVC(L)= −0.73 + 0.162 × sitting height (in) −0.047 × age (yrs); females (under 20 years), FVC(L) = − 3.56 + 0.150 × sitting height (in) + 0.067 × age (yrs); females (over 20 years), FVC(L)= −1.92 + 0.150 × sitting height (in) −0.016 × age (years). Similar prediction equations were derived for FEV1, and FEF25-75%: FEV1/FVC % was 84.2 (±6.5) for females and 88.0 (±6.5) for males. We also compared the observed FVC measurements to values calculated using standing heights derived from the subject's sitting height, assuming a normal body proportion. The observed vital capacity in achondroplasia was only 67.6 (± 19.2) percent of that predicted for normally proportioned females and 72.4 (±13.6) percent for males, suggesting reduced vital capacity in achondroplasia, due to reduced chest wall compliance or abnormal lung growth.