Frequency of mechanical ventilation and respiratory activity after double lung transplantation

Abstract

We investigated the contribution of pulmonary afferent nerve fibers to the control of inspiratory activity in awake humans. Eight double lung transplant outpatients and eight normal subjects were hyperventilated with a mechanical ventilator. Respiratory frequency was increased until no respiratory activity was detectable. Then, by either adding CO 2 in the inspired gas or decreasing respiratory frequency, end-tidal P CO 2 ( PET CO 2 ) was increased until respiratory activity ( i.e. change in inspiratory airway pressure peak and/or time profile) was detected. In normal subjects, PET CO 2 threshold for inspiratory muscle recruitment was significantly lower when frequency was decreased than when CO 2 was added (31.3 ± 6.8 Torr vs. 38.2 ± 8.1 Torr respectively, P<0.005). This was not the case in the double lung transplant group (31.5 ± 6.5 Torr vs. 32.9 ± 5.8 Torr). These findings suggest that pulmonary afferent nerves have an inhibitory effect on inspiratory activity in humans.