The effect of human heart-lung transplantation upon breathing at rest and during sleep.

We have assessed the contribution of intrathoracic pulmonary nerves to the control of breathing in humans. During relaxed wakefulness and during sleep the level, pattern and variability of breathing have been quantified in 8 healthy patients 1 month to 2 years after combined heart--lung transplantation. These data have been compared with similar data from both of 2 matched control groups; either healthy normal controls, or healthy patients after heart transplantation alone. We found no significant differences in the mean levels of respiratory variables between the 3 groups either during relaxed wakefulness or sleep. There were no significant differences between groups (other than would be expected by chance alone) either in the variability of breathing, or in the shapes of the frequency distributions of respiratory variables during these states. There were no respiratory disorders associated with sleep nor any disturbances in blood gases in any group. We conclude that in man breathing is remarkably normal, during relaxed wakefulness and during sleep, after chronic pulmonary denervation. When the ventilatory demands are minimal the human ventilation system functions normally in the absence of a control loop involving pulmonary proprioceptors and the medullary respiratory centres.