Maturation of pulmonary input impedance spectrum in infants and children with ventricular septal defect.

To determine whether pulmonary vascular disease can be detected in infants with ventricular septal defect (VSD) by the presence of an increase in the frequency of the impedance modulus minimum of the pulmonary input impedance spectrum, as has been implied for older children, spectra of 25 infants (2 years or younger) (group 1) were compared with spectra of 20 children (ages 2 to 7 years) (group 2). Groups were subdivided according to mean pulmonary artery (PA) pressure: those with moderate pressure levels (35 mm Hg or less, groups 1A and 2A) and those with high pressure levels (at least 40 mm Hg, groups 1B and 2B). Pulmonary vascular resistance, characteristic impedance and frequency of the modulus minimum were significantly lower in group 2A than in group 1A. The decrease in pulmonary vascular resistance and characteristic impedance with increasing age was consistent with body surface area increases; however, the shift in frequency of the modulus minimum could be more easily related to a decrease in the pulse wave velocity than to a shift in the primary reflection site. Pulmonary vascular resistance, characteristic impedance and the frequency of the first modulus minimum were comparable in groups 1B and 2B; however, none of the patients in group 1B had evidence of pulmonary damage, whereas 3 of 4 group 2B patients had microscopically apparent pulmonary vascular disease.(ABSTRACT TRUNCATED AT 250 WORDS)