Inhaled olprinone improves contractility of fatigued canine diaphragm

Inhaled milrinone for the improvement of contractility of fatigued diaphragm in dogs: a dose-ranging study

The present study was undertaken to evaluate the efficacy of inhaled milrinone on contractility of fatigued diaphragm in dogs. Animals were divided into four groups of seven each. In each group, diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. Immediately after the end of a fatigue-producing period, Group I received inhaled vehicle; Group II received inhaled milrinone 0.1 mg/ml (1 mg); Group III received inhaled milrinone 0.2 mg/ml (2 mg); Group IV received 0.5 mg/ml (5 mg). Study drug was administered for 30 min. Diaphragmatic contractility was assessed by transdiaphragmatic pressure (Pdi). After the fatigue-producing period, in each group, Pdi at low-frequency (20 Hz) decreased from baseline values (P<0.05), and Pdi at high-frequency (100 Hz) stimulation did not change. In Groups III and IV, during milrinone inhalation, Pdi at both stimuli increased from fatigued values (P<0.05). The increase in Pdi was more in Group IV than in Group III (P<0.05). Compared with Group I, Pdi to each stimulus did not change in Group II. In conclusion, inhaled milrinone, in doses more than 0.2 mg/ml, is effective for improving contractility of fatigued diaphragm in dogs.

The effect of inhaled colforsin daropate on contractility of fatigued diaphragm in dogs

We studied the effect of inhaled colforsin daropate, a water-soluble forskolin derivative, on the contractility of fatigued diaphragm in dogs. Animals were divided into 3 groups of 8. In each group, diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20-Hz stimulation applied for 30 min. Immediately after the end of the fatigue-producing period, Group 1 received inhaled vehicle, Group 2 received inhaled colforsin daropate 0.1 mg/mL, and Group 3 received inhaled colforsin daropate 0.2 mg/mL. We assessed diaphragmatic contractility by transdiaphragmatic pressure (Pdi). After fatigue was produced, in each group, Pdi at low-frequency (20-Hz) stimulation decreased from baseline values (P < 0.05), and there was no change in Pdi at high-frequency (100-Hz) stimulation. In Groups 2 and 3, during colforsin daropate inhalation, Pdi at both stimuli increased from fatigued values (P < 0.05). The increase in Pdi was significantly larger in Group 3 than in Group 2. The integrated electrical activity of the diaphragm did not change in any group. We conclude that inhaled colforsin daropate causes an increase in contractility of fatigued canine diaphragm in a dose-related fashion.

IMPLICATIONS

Diaphragmatic fatigue may contribute to the development of respiratory failure. Inhaled colforsin daropate improves, in a dose-dependent manner, the contractility of fatigued diaphragm in dogs.