Changes in ventilation, breathing pattern and acid-base balance of conscious rabbits following intravenous almitrine

Five conscious rabbits each received a single injection of almitrine bismesylate via a marginal ear vein. Measurements were made of ventilation and breathing pattern using a barometric method, and blood gases, pH and lactate concentration ([Lac]) were measured from arterial blood samples throughout the hour following the injection. Almitrine caused an immediate increase in ventilation through an increase in tidal volume (VT), frequency (f) showing a small decline. After 15 min f increased to above control level and VT declined. Slower, deeper breathing was reinstated by 40 min post-injection. Large changes in blood gases occurred in the first 15 min, with PO2 raised by 30 Torr and PCO2 lowered by 20 Torr. These recovered to be within 10 and 7.5 Torr of control at the end of 1 h. [Lac] increased steeply at first, then declined towards control levels. The acid-base situation was mixed, comprising a respiratory alkalosis, resulting from CO2 washout, and a metabolic acidosis from high [Lac]. These results are discussed in the context of assessing the primary and secondary effects of almitrine and recognition of the possibility that the drug may act at more than one site to alter respiration.