Shape changes in static V-P loops from children's lungs related to growth

Sixty-eight sets of deflation data from the left lungs of children who had died from non-pulmonary causes were analysed by the exponential equation model to derive theoretical values of Pst(1) for 50, 60, and 90% of the observed maximum inflation volume. The resultant P50, 60, and 90 values were compared to the same values measured from graphic displays of the V-P data. The graphically derived Pst(1) data at 50, 60, and 90% of TLC were then plotted against the crown-heel length to demonstrate a shape change related to physical growth. It was found that the form of the deflation curve in preterm infants did not fit an exponential model as satisfactorily as did the deflation curve from older children. The exponential model should be used with caution in small infants where Pst(1) values below P90 are sought. A maximum inflation pressure of +30 cm H2O was found to produce a Vmax within 98% of the hypothetical VINF value.