Changes in physiological activity following bilateral lung transplantation in dogs

There have been a number of unsolved problems in lung transplantation with regard to preservation, immunosuppression and pathophysiological alterations, for which much time and effort was, and still is, expended in solving. The purpose of this paper is to report the results obtained in our serial studies concerning hemodynamic characteristics following bilateral lung auto- and allotransplantation in dogs. The one-stage bilateral lung autotransplantation employed in our studies showed the critical entity of different degrees of pulmonary edema in both lungs in the early postoperative period. Some experimental animals with bilateral lung grafts succumbed to respiratory failure showing gradual decrease in PaO ₂ caused by pulmonary edema but some other animals recovered from these pathologic states within 10 days postoperatively. Hemodynamic characteristics of lung transplantation include high pulmonary vascular resistance, occurring in the early postoperative period and returning to near preoperative values in later periods. There have been few answers to the question concerning how pulmonary vascular beds change with abrupt alteration of pulmonary blood flow in this model. Our approach to this question was to inject plasma expander consecutively via intraatrial catheter in order to increase pulmonary flow and to determine simultaneously Ppa and cardiac output in the bilaterally transplanted animal. During the course of increased cardiac output both Ppa and TPVR linearly increased until the lung transplant became edematous, while TPVR decreased despite increase in Ppa in the control animals. It should be noted that these results may indicate the change in mechanism of pulmonary circulation in the transplanted lungs, i.e. suggesting the characteristics of lung denervation. In regard to the ventilatory effects of CO ₂ inhalation, it was associated with a similar increase in minute ventilation and tidal volume in both control and bilaterally reimplanted animals. However, the transplanted dogs showed no change in respiratory rate in the control animals. It is difficult to explain entirely this loss of rate alteration during CO ₂ inhalation in the bilaterally transplanted dogs. Previous work has established that the Hering-Breuer reflex is lost for several years after surgery and it seems reasonable to assume that this phenomenon is responsible for the loss of rate alteration with CO ₂ inhalation.