The effects of breathing of alternate breaths of air and a carbon dioxide rich gas mixture in anaesthetized cats

Abstract

SUMMARY1. An in vivo pH electrode was used to assess the effect in anaesthetized cats of the administration of 5 % CO2 (21 % 02, balance N2) and air as alternate inspirates upon the time course of the carotid arterial pH, and by inference, the Pco2.2. This method of administration of CO2 and air resulted in a lowering of the recorded pH with the production of oscillations of twice the duration seen on air alone. These larger oscillations had a period of two respiratory cycles and their amplitude was approximately twice that of normal oscillations.3. The respiratory response consisted in all cases of an increase in mean tidal volume and ventilation, and in 50-60 % of recorded runs, of a highly specific sequence of tidal volume changes. The specific sequence was composed of alternately larger and smaller breaths which persisted while the larger oscillations continued.4. The use of the in vivo pH electrode made it possible to determine whether or not the tidal volume alternation was a result of sensitivity to carotid arterial Pco, oscillations. By diverting the carotid arterial blood through a mixing chamber the amplitude of the double (respiratory) period oscillations was, in some cases, reduced but not eliminated. In these cases the specific pattern of tidal volume changes was still present in 60 % of trials. In the cases where the pH fluctuations were completely eliminated the specific respiratory pattern was never present.5. Average breath to breath differences in tidal volume seen during control runs with large oscillations present ranged in size from 3X6 to 8-6 % of the mean tidal volume. When the oscillations were completely eliminated by means of the mixing chamber the breath by breath differences * Present address: Physiology Department, Guy's Hospital Medical School, London, S.E.1. only ranged from 0.2 to 2*7 % of mean tidal volume. The change was highly significant.

Alveolar Gas Pressure Changes with Resistive Loads in Man

“…However, rapid changes in airway CO2 have been shown to produce small changes in expiratory duration (T^) as ear ly as the first breath [Cunningham et al, 1977]. The timing and direction of the changes in Te were consistent with their being initiated reflexly, by COj-sensitive receptors in the airways [Mustafa and Purves, 1972;Wolff. 1977], Recently, Bowes et al [1982] showed that in con scious dogs a single inspiration of 3-9% CO2 could shorten the test breath T^.…”