Cardiopulmonary hypoxic response 5 years postpneumonectomy in beagles.

Ventilatory hypoxia was used to study the effects on pneumonectomy on the right heart and pulmonary vascular bed in purebred beagle dogs. Operated animals underwent pneumonectomy at 6 to 10 weeks of age (six, group I) or at 1 year (eight, group II). Eight unoperated adult beagles served as controls (group III). Five years following pneumonectomy, exposure to 10% O2 ventilation indicated that group I animals were more reactive to hypoxia than either group II or III. Increases in pulmonary flow were recorded as group I, 0.79 +/- 0.58 liter/min; II, 0.32 +/- 0.54 liter/min; III, 0.04 +/- 0.24 liter/min (P = 0.006, I vs III, two-tailed test). Also, the peak first derivatives of power and blood flow and the external work of the right ventricle increased significantly in group I compared to group III but not in group II compared to group III. On the contrary, hypoxic stress produced similar changes in pulmonary vascular resistance and characteristic impedance in all groups. It is concluded that the hyperdynamic response of the group I animals, those undergoing pneumonectomy as puppies, can be attributed to a primary change in pump characteristics.