DEVELOPMENTAL-CHANGES IN CHEST-WALL COMPLIANCE IN INFANCY AND EARLY-CHILDHOOD

Development of chest wall stiffness between infancy and adulthood has important consequences for respiratory system function. To test the hy pothesis that there is substantial stiffening of the chest wall in the first few years of life, we measured passive chest wall compliance (C w) in 40 sedated humans 2 wk-3.5 yr old. Respiratory muscles were rela xed with manual ventilation applied during the Mead-Whittenberger tech nique. Respiratory system compliance (Crs) and lung compliance (CL) we re calculated from airway opening pressure, transpulmonary pressure, a nd tidal volume. Cw was calculated as 1/Cw = 1/Crs - 1/CL during manua l ventilation. Mean Cw per kilogram in infants <1 yr old was significa ntly higher than that in children >1 yr old (2.80 +/- 0.87 vs. 2.04 +/ - 0.51 ml cmH(2)O(-1) kg-l; P = 0.002). There was an inverse linear re lationship between age and mean Cw per kilogram (r = -0.495, slope -0. 037; P < 0.001). In subjects with normal CL during spontaneous breathi ng, Cw/spontaneous CL was 2.86 +/- 1.06 in infants <1 yr old and 1.33 +/- 0.36 in older children (P = 0.005). We conclude that in infancy th e chest wall is nearly three times as compliant as the lung and that b y the 2nd year of life chest wall stiffness increases to the point tha t the chest wall and lung are nearly equally compliant, as in adulthoo d. Stiffening of the chest wall may play a major role in developmental changes in respiratory system function such as the ability to passive ly maintain resting lung volume and improved ventilatory efficiency af forded by reduced rib cage distortion.