Input Impedance of the Pulmonary Arterial System in Normal Man: Effects of Respiration and Comparison to Systemic Impedance

Input impedance of the pulmonary arterial system was determined in 10 subjects undergoing elective cardiac catheterization. No cardiovascular or pulmonary disease was found in these patients. In five of the subjects, systemic arterial input impedance was also obtained, so that both systems could be compared. Pulmonary and systemic peripheral resistances were 79 ± 9 dynes sec/cm (mean ± SEM) and 1016 ± 50 dynes sec/cm, respectively. Characteristic impedance of the pulmonary circulation was lower than the characteristic impedance of the systemic circulation20 ± 1 dynes sec/cm vs. 47 ± 9 dynes sec/cm, respectively. Pulmonary pressure and flow spectra for both systems are also presented. The amplitudes of the harmonics of pressure and flow are smaller for the pulmonary circulation, which is consistent with the lower pressures and more rounded waveforms of the normal pulmonary circulation. In all 10 subjects, input impedance of the pulmonary system was examined during both the inspiratory and expiratory phases of respiration. There was no difference between inspiration and expiration in either pulmonary vascular resistance (77 ± 10 dynes sec/cm vs. 80 ± 9 dynes sec/cm, respectively), characteristic impedance (20 ± 1 dynes sec/cm vs. 20 ± 1 dynes sec/cm) or in the overall impedance spectrum. Quiet respiration, thus, has no effect on the pulmonary arterial load, and changes in pressure and flow must result from alterations in right ventricular performance.