Effects of Almitrine on Diaphragm Contractile Properties in Young and Old Rats

Background: Diaphragm muscle force and fatigue are key factors in the development of respiratory failure. Almitrine is used to improve ventilatory drive and ventilation-perfusion matching in respiratory failure. Recently, it has also been shown to improve diaphragm muscle force and endurance in young rats, but it is not known if this effect persists with ageing. Objectives: To determine the effects of almitrine on diaphragm contractile properties in young and old rats. Methods: In young and old rats, isometric contractile properties were measured in strips of isolated diaphragm muscle in physiological saline solution at 30°C with or without almitrine. Results: In young animals, almitrine increased twitch tension, reduced half-relaxation time and increased endurance, but had no effect on tetanic tension, contraction time or tension-frequency relationship. Ageing had no effect on endurance, but did reduce twitch and tetanic tension and contraction and half-relaxation time. Almitrine had no effect on contractile tension and kinetics, tension-frequency relationship or on endurance in the old animals. Conclusions: Ageing negates the beneficial effects of almitrine on diaphragm muscle force and endurance.