Almitrine decreases the distensibility of the large pulmonary arteries in man.

Almitrine improves blood gas values in patients with COPD, primarily through better ventilation-perfusion matching. The improvement comes largely from a vasomotor effect of the drug. The vasomotor mechanism is unknown. We suspected that decreased distensibility of the large pulmonary arteries was one probable effect of the drug. If present, reduced distensibility would explain many of the hemodynamic alterations produced by almitrine. To test this idea, we measured the diameter of the right pulmonary artery during systole and diastole both before and after almitrine administration in nine patients who were undergoing pulmonary cineangiography. Our calculations of the distensibility of the right pulmonary artery showed that almitrine caused a 60 percent decrease. This significant alteration in the stiffness of the large pulmonary arteries can account for the rise in systolic pressure, a change that would be expected to redistribute pulmonary blood flow upwards and thereby improve ventilation-perfusion balance.