Effects of pneumonectomy on pulmonary input impedance

The long-term effects of pneumonectomy on the pulmonary circulation quantifiable through pulmonary input impedance analysis were studied. Excision of the left lung was performed in purebred beagle dogs aged 6 to 10 weeks (n = 6 group I) or 1 year (n = 8 group II). Unoperated beagles served as controls (n = 8 group III). When the dogs were 5 years of age, pulmonary pressure and flow were measured and the impedance spectra calculated. Characteristic impedance (Zo) (indicative of changes in proximal vessel physical properties) and pulmonary vascular resistance (PVR) (indicative of the distal response) were estimated. In group III the cardiac output (CO) was 1.7 +/- 0.4 L/min, mean pressure 16 +/- 5 mm Hg, PVR 605 +/- 448 dyne-sec/cm, and Zo 204 +/- 76 dyne-sec/cm. Group I results exhibited bimodal distributions that were not statistically different from results of groups II or III; four dogs had spectra comparable to those of group III, while two dogs had developed moderate hypertension and high PVR and Zo. Group II results were more normally distributed, and comparison with group III indicated statistically significant differences (P less than 0.05) in CO (1.1 +/- 2 L/min), PVR (1396 +/- 573 dynes-sec/cm), and Zo (543 +/- 273 dynes-sec/cm). Doubling of PVR and Zo in group II indicated that proximal vessel compliance and peripheral perfusion radius had not increased following pneumonectomy in adult beagles. Group I results indicate that marked facilitory adaptation can occur when pneumonectomy is performed in puppies; however, the adaptation may not be based on true lung growth and, therefore, may not be sustained indefinitely.