Effect on respiration of changes in the form of the naturally occurring oscillation in arterial pH.

We have previously shorn that the respiratory control system in the cat has the requisite sensitivity and speed to respond to changes in arterial pH which are equal to, or smaller than, the normal fluctuations in pH with respiration. A respiratory response was only observed when the changes in pH were produced by alterations in PCO2 and not when they were induced by non-gaseous acids. We describe now the respiratory effect produced by various procedures which modify or abolish the naturally occurring arterial pH oscillations before they reach the peripheral chemoreceptors. The pH oscillations were abolished by a mixing chamber, whilst their phase relationship to respiration was altered by delay coils; by presenting a moving plastic surface to the arterial blood stream it was possible to distort the shape of the oscillations without increasing the transport lag between lung and peripheral chemoreceptors. All manoeuvres produced a brief period of respiratory stimulation which was greater than could occur by chance. We were particularly concerned in these experiments with the possibility of artefacts in our experimental design. We feel that we have excluded respiratory effects due to changes in arterial pressure, blood temperature and mean pH. We are less confident that we have excluded changes in ventilation resulting from the release of a substance (or substances) from the contact of blood with plastic or glass surfaces. This problem is discussed in relation to experiments on the control of breathing where blood, which is perfusing the chemoreceptors, has been in contact with artificial surfaces.