Received July 30, 2004
Revised October 4, 2004
Accepted after revision January 19, 2005

¹ University of Toronto
² University of Groningen

^* To whom correspondence should be addressed. E-mail: j.duffin{at}utoronto.ca.

	Abstract

Increased wakefulness is known to suppress the initial ventilatory response to passive movement, and the steady-state ventilatory response to exercise. However, the effect of increased wakefulness upon the integrated ventilatory response at exercise onset is not known. We hypothesized that increasing wakefulness via a cognitive task would attenuate the initial ventilatory response to exercise, and so we examined the response to active leg extensions under two conditions: with and without concurrently solving a puzzle. At rest before exercise, subjects demonstrated greater minute ventilation while solving a puzzle (mean ± SEM = 12.38 ± 0.55 l min^-1 versus 10.12 ± 0.51 l min^-1, p < 0.001), due to a higher mean breathing frequency (mean ± SEM =17.1 ± 0.93 br min^-1 versus 13.6 ± 0.59 br min^-1, p <0.001). At the start of exercise, subjects did not increase their ventilation significantly while solving the puzzle (p = 0.170), but did by a mean ± SEM of 6.16 ± 1.12 l min^-1 (p < 0.001) when not puzzle solving. The ventilation achieved at the start of exercise in absolute terms was also lower while solving the puzzle (14.6 ± 1.1 vs. 16.3 ± 1.3 l·min^-1, p = 0.047). Despite differences in the rapid ventilatory response to exercise between conditions, the steady-state responses were not different. We conclude that the performance of a cognitive task decreases the initial phase of exercise hyperpnoea, and suggest that this might occur because of either a competitive interaction between drives to breathe, or a behavioral distraction from the 'task' of exercise.

Key Words: Breathing, Exercise, Respiratory control