Fluxes of CO₂ in the lung gas studied by continuously recorded arterial pH

Arterial blood pH, measured continuously in anesthetized, paralyzed dogs, was used to investigate time dependent factors in gas exchange. When the ventilatory pump was stopped at the end of inspiration, there was often a rise of pH before the fall brought on by CO₂ accumulation. This rise or 'hump' was more pronounced when the animal breathed a helium oxygen mixture. When the ventilation was changed from the usual end expiratory pause pattern to a pattern with end inspiratory pauses, the hump phenomenon could no longer be elicited by a breath hold and there was a gradual rise of mean pH of the blood, indicating better clearance of CO₂. Apparently the effectiveness of a breath, so far as CO₂ exchange is concerned, can be improved upon because of better mixing if the breath remains in the lung for a time, rather than being immediately expelled as in ordinary expiratory pause breathing.