[Functional respiratory physiology and physiopathology of lung transplant patients]

Lung transplantation results in dramatic improvement in pulmonary function which allows the patients to resume a normal lifestyle. When the lung allograft is free of infection and rejection, lung volumes and gas exchange are within normal limits after heart-lung and double lung transplantation, both at rest and during exercise. After single lung transplantation, lung volumes remain below predicted values and some patients show mild oxygen desaturation with exercise. Infection, acute rejection, and chronic rejection (bronchiolitis obliterans) produce an obstructive ventilatory defect. In addition, there is a bronchial hyperreactivity to cholinergic stimulation; this hyperreactivity might be related to airway denervation and upregulation of muscarinic receptors or might be triggered by the bronchial inflammation induced by rejection. Control of breathing is normal at rest, during exercise, in response to CO2 rebreathing, and during sleep. This indicates that pulmonary afferents play a negligible role in the control of breathing in adult humans. Most transplanted patients show a significant reduction in maximum oxygen consumption and have an early anaerobiosis during exercise; this response may be accounted for, at least in part, by a persistent state of physical deconditioning, and by an inadequate adaptation of cardiac output in heart-lung transplant recipients.