Modulation of the corticospinal control of ventilation by changes in reflex respiratory drive

We have determined whether changes in PCO2 above and below eucapnia modulate the precision of the voluntary control of breathing. Twelve trained subjects performed a compensatory tracking task in which they had to maintain the position of a cursor (perturbed by a variable triangular forcing function) on a fixed target by breathing in and out of a spirometer (ventilatory tracking; at 10 l/min). Before each task, subjects hyperventilated for 5 min, and the end-tidal PCO2 (PET(CO2)) was controlled; tracking was then performed separately at hypocapnia, eucapnia, and hypercapnia (PET(CO2) ~25, 37, and 43 Torr, respectively). Ventilatory tracking error was unchanged during hypocapnia (P > 0.05) but was significantly worse during hypercapnia (P <0.003), compared with eucapnia; arm tracking error, performed as a control, was not significantly affected by PET(CO2) (P > 0.05). In conclusion, ventilatory tracking performance is unaffected by the eucapnic PCO2. From this, we suggest that resting breathing in awake humans may be independent of chemical drives and of the prevailing PCO2.