[Ventilatory control in lung transplantation].

Heart/lung transplantation offers a unique opportunity for studying the role of pulmonary innervation on control of breathing. In heart/lung transplant patients the pattern of breathing has been found to remain unaffected at rest and when asleep. In contrast, CO2 breathing studies have yield conflicting results. In heart/lung transplant recipients with normal pulmonary function, the hypercapnic ventilatory response was not different from that seen in control subjects, whereas heart/lung transplant recipients with moderate restriction had a profound depression in the ventilatory response to CO2. These results suggested that pulmonary vagal afferent fibers may have a facilitating effect on the hypercapnic ventilatory response in patients with restriction. This result is in opposition with data from airway anesthesia studies. In studies of the effects of exercise in transplant patients, control of breathing was affected in the same way as in normal subjects with anesthetized airways: transplant patients had an appropriate level of ventilation with a disproportionate increase in tidal volume. In normal subjects after suppression of inspiratory activity by mechanical hyperventilation, hypercapnia at which inspiratory activity muscle recruitment appeared was lower when arterial CO2 was raised by decreasing ventilator ventilation rather than by adding CO2 in the inspiratory line. This was not the case in double lung transplant subjects. These findings suggest that pulmonary afferent nerves have an inhibitory effect on inspiratory activity in humans. In conclusion, pulmonary afferent play a negligible role in the control of breathing of human at rest but are important in regulating the pattern of ventilation during stress conditions and large tidal volume conditions.