Overview of ventilatory control during exercise.

Practically every respiratory physiologist of the last 100 years has studied the ventilatory response to exercise. Yet we still do not know the cause of increased ventilation associated with exercise. This overview considers the problem from a broad observational point of view. Data from studies combining exercise with continuous inspired CO2 and "slug" CO2 breathing imply a feed-forward/feed-back structure for the ventilatory controller. The feed-forward stimulus is correlated to CO2 production. Feed-back senses arterial CO2 tension and acts to minimize the effects of correlation errors and correlation slope errors in the feed-forward path. This feed-forward/feed-back structure yields a regulated arterial CO2 and a tight coupling of ventilation to CO2 production. The feed-back mechanism acts via the carotid body, and indirectly via the central chemoreceptor. A variety of mechanisms are discussed that may be involved in providing the feed-forward stimulus. In particular, the intravenous loading experimental results are considered in terms of an appropriate feed-forward stimulus.