Respiratory response to passive limb movement is suppressed by a cognitive task.

Feedback from muscles stimulates ventilation at the onset of passive movement. We hypothesized that central neural activity via a cognitive task source would interact with afferent feedback, and we tested this hypothesis by examining the fast changes in ventilation at the transition from rest to passive leg movement, under two conditions: 1) no task and 2) solving a computer-based puzzle. Resting breathing was greater in condition 2 than in condition 1, evidenced by an increase in mean +/- SE breathing frequency (18.2 +/- 1.1 vs. 15.0 +/- 1.2 breaths/min, P = 0.004) and ventilation (10.93 +/- 1.16 vs. 9.11 +/- 1.17 l/min, P < 0.001). In condition 1, the onset of passive movement produced a fast increase in mean +/- SE breathing frequency (change of 2.9 +/- 0.4 breaths/min, P < 0.001), tidal volume (change of 233 +/- 95 ml, P < 0.001), and ventilation (change of 6.00 +/- 1.76 l/min, P < 0.001). However, in condition 2, the onset of passive movement only produced a fast increase in mean +/- SE breathing frequency (change of 1.3 +/- 0.4 breaths/min, P = 0.045), significantly smaller than in condition 1 (P = 0.007). These findings provide evidence for an interaction between central neural cognitive activity and the afferent feedback mechanism, and we conclude that the performance of a cognitive task suppresses the respiratory response to passive movement.