Carotid Arterial Blood Gas Oscillations and the Phase of the Respiratory Cycle During Exercise in Man: Testing a Model

The time relationship of the arrival centrally of bursts of activity in carotid body afferents and the phase of the respiratory cycle affects the reflex respiratory response in the cat as first shown by Black and Torrance1,2,3. In man, too, there is evidence that small changes in the time profile of alveolar CO2 oscillations, induced by tube- or simulated tube-breathing can be detected4,5. It has, therefore, been proposed that the respiratory “centres” are particularly sensitive to afferent activity when it arrives in certain parts of the cycle. If this were so then we could add another kind of control by blood gases to those commonly considered: the system besides being sensitive to the mean level and perhaps also to the magnitude and frequency of the oscillations of PaC02 6,7, would also respond to changes between optimal, suboptimal and “pessimal” in the phase relations of the oscillation at the carotid bodies and the respiratory movement. This ideal was elaborated into a model from which certain tentative predictions were made regarding the breath-by-breath control of breathing8.