Phase-dependence of breathing and finger tracking movements during normocapnia and hypercapnia

The coordination between breathing and other motor activities usually impli es that the respiratory rhythm has become entrained by the rhythm of the si multaneous movement. Our hypothesis was that by increasing the respiratory drive, e.g. by hypercapnia, we would be able to reduce the subordination of breathing to other movements and, on the other hand, enhance effects of br eathing on those movements. We investigated interactions between breathing and finger flexion movements in a visually controlled step-tracking procedu re which allowed us to distinguish the mutual effects and to detect the dep endence of these effects on the phase-relationship between breathing and mo vement. In contrast to our hypothesis, we found no large increase of the re spiratory influences on finger movements during hypercapnia. A noteworthy d ifference to normocapnia was a shortening of the finger flexion time during the final stage of expiration which was associated with an increased frequ ency of coincidence between the end of flexion time and the transition from expiration to inspiration. On the other hand, the response of breathing to the finger movement increased when the tracking signal was presented at th e beginning of inspiration. The results of the study disproved our hypothes is and demonstrated that, during hypercapnia, breathing can be even more su sceptible to influences originating from motor control. Thus, they are in a greement with the findings of a previous study that the coordination betwee n breathing and rhythmic limb movements becomes closer during hypercapnia.