[Pharmacological properties of almitrine dimesylate. Effects on the ventilation-perfusion ratio].

Animal studies performed in various species have shown that the compound induces different effects depending on dosage: At high doses, almitrine bismesylate specifically stimulates the aortic and carotid chemoreceptors, with subsequent increase in ventilation and improvement in arterial blood gases. At low doses, almitrine bismesylate increases arterial oxygen pressure (PaO2) in the anaesthetized dog without any ventilatory change. The only effect occurring simultaneously with the increase in PaO2 is transient vasoconstriction of the pulmonary vascular bed. Dissociation between PaO2 and ventilation has also been observed in clinical trials performed in patients with chronic bronchitis and has been attributed to a normalization of ventilation/perfusion (VA/Q) ratios. Animal pharmacological studies were undertaken in order to elucidate the mechanism underlying the improvement of the VA/Q ratios by almitrine bismesylate. Results suggested that both redistribution of ventilation and perfusion concurred to improve alveolar gas and pulmonary circulation matching and thus alveolar blood-gas exchanges.