ALTERED REGULATION OF BREATHING AFTER BILATERAL LUNG TRANSPLANTATION

In our previous animal studies on dogs, regulation of breathing was fo und to be altered after en bloc transplantation of the heart and both lungs. During carbon dioxide (CO2) inhalation the minute volume was in creased due to an increase of tidal volume after transplantation where as before transplantation both respiratory frequency and tidal volume increased. The success of the heart-lung transplantation was based on experiments on baboons as no long-term survivors were obtained in dogs . It was thought that the regulation of breathing is different in dogs and primates. We therefore decided to study the regulation of breathi ng in humans after bilateral lung transplantation during CO2 stimulati on. The regulation of breathing was tested 2 to 4 months after bilater al lung transplantation in six patients. Six healthy subjects with int act lungs were tested as controls. The test persons were allowed to br eathe first room air, then 5% CO2 in air for 4 min and then room air a gain. The frequency of respiration, tidal volume and minute ventilatio n were recorded using a phneumotachograph. Simultaneously samples of a rterial blood were drawn from a cannulated brachial artery for analysi s of pressure of arterial oxygen (PaO2), pressure of arterial carbon d ioxide (PaCO2), base excess (BE) and pH. During inhalation of CO2 for 4 min the minute volume doubled in both transplant patients and in con trols. The tidal volume of the transplant patients increased significa ntly more than that of the controls (P < 0.005) whereas respiratory fr equency increased significantly only in the controls with intact lungs (P < 0.05). It is concluded that bilateral lung transplantation, due to denervation of the lungs and switch off of the pulmonary receptors with afferent pathways in vagal nerves, alters the regulation of breat hing in humans, too.