1)
We have calculated the effects on amplitude and shape of arterial CO 2 (P•.C02) oscillations of varying cardiac output and inspired CO 2 fraction, and of exercise, under various constrained respiratory patterns.
(2) The amplitude of the oscillations is highly frequency dependent and therefore unsuitable for a feed-forward variable.
(3) The up-going slope of the CO 2 oscillation is linearly dependent on CO 2 output, and therefore highly suitable for feed-forward. (4) An additive combination of feed-forward of up-going slope plus negative feed-back with classical CO 2 -0 2 interaction equations neatly simulates the steady-state effects of CO 2 breathing, exercise, and a combination of both.
(5) It is postulated that the classical CO 2 -0 2 interactive relations may act to calibrate the feed-forward drive, rather than primarily to provide drive. (6) Under certain described conditions, humoral signals may be transmitted faster than the blood. If a detector is rate-sensitive and the chemical signal oscillates, a response occurring with time-lag shorter than the relevant circulation time need not automatically imply a neural method of signal transmission.