Vagal feedback in the entrainment of respiration to mechanical ventilationin sleeping humans

We studied the capacity of four "normal" and six lung transplant subjects t o entrain neural respiratory activity to mechanical ventilation. Two transp lant subjects were studied during wakefulness and demonstrated entrainment indistinguishable from that of normal awake subjects. We studied four norma l subjects and four lung transplant subjects during non-rapid eye movement (NREM) sleep. Normal subjects entrained to mechanical ventilation over a ra nge of ventilator frequencies that were within +/-3-5 breaths of the sponta neous respiratory rate of each subject. After lung transplantation, during which the vagi were cut, subjects did demonstrate entrainment during NREM s leep; however, entrainment only occurred at ventilator frequencies at or ab ove each subject's spontaneous respiratory rate, and entrainment was less e ffective. We conclude that there is no absolute requirement for vagal feedb ack to induce entrainment in subjects, which is in striking contrast to ane sthetized animals in which vagotomy uniformly abolishes entrainment. On the other hand, vagal feedback clearly enhances the fidelity of entrainment an d extends the range of mechanical frequencies over which entrainment can oc cur.