Pulmonary input impedance spectra in models of chronically altered pulmonary hemodynamics

Pulmonary input impedance spectra were estimated in one-month-old lambs whose circulation had been altered during the first few days of life to mimic the pulmonary. hemodynamic states observed in infants and children with left-to-right shunts (high flow) and /or pulmonary vascular obstructive disease (high pressure). Spectral results obtained from the animal models were compared with those obtained from a computer simulation based on morphometric and hemorheologic data compiled for the 4 kg cat. Spectral features examined included the frequency of the first modulus minimum (indicative of the pulse wave reflection and/or pulse wave velocity) and characteristic impedance (average resistance to pulsatile flow). High flow (shunt-open/shunt-closed ratio>2.1) resulted in a slight spectral shift to the right with little change in characteristic impedance in both the lamb and the passive computer simulation models. High pressure (mean pulmonary artery pressure >28 mmHg) in the lamb model resulted in a marked shift to the right with a doubling of characteristic impedance