Rapid structural changes in the lungs and chest wall during early childhood lead to lower respiratory system resistance (R) and elastance (E = 1/Compliance). Although R and E depend on tidal volume (VT) and breathing frequency (f), how development affects these dependencies is unclear. We studied 14 healthy children (age: 3d-27m; weight (Wt): 2.5-14 kg), anesthetized and mechanically ventilated with constant inspiratory flow and I: E ratios (1:2). We estimated R and E, assuming a series R-E topology, from tracheal pressure and flow measured at three VT (≈ 6, 10, 14 ml/Kg) at each of three f (10, 20, 30/min). Wt, VT and f-dependencies of R and E were determined by stepwise multivariate analysis. As expected, R and E decreased with increasing Wt (Figure), given the larger airway diameters and lung volumes, respectively. R was not significantly changed with VT, but decreased substantially with f probably due to stress adaptation of respiratory tissues. E did not depend on f, but was systematically lower at increasing VT presumably due to the nonlinear Pressure-Volume relationships of the lungs and chest wall. Although the magnitude of f-dependence of R and VT-dependence of E were smaller as weight increased, the fractional changes of these dependencies were not dissimilar throughout the range of weights. To our knowledge this study is the first to quantify, simultaneously, the effects of VT and f on R and E in growing children. These data are useful when comparing healthy children to those with lung disease who are studied at varying VT and f.

figure 1

Figure 1