The American review of respiratory disease
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Am. Rev. Respir. Dis. · Jul 1992
Effects of broxaterol and theophylline on fatigued canine diaphragm in vivo. A randomized, controlled study.
Since broxaterol, a new beta 2-agonist, has been shown to improve contractility of fatigued canine diaphragm in vitro, a controlled, randomized study was designed to assess its effects on fatigued canine diaphragm in vivo, and compare these to the expected inotropic effects of aminophylline. Diaphragm fatigue was induced in 21 dogs using electrophrenic stimulation at 20 Hz until transdiaphragmatic pressure (Pdi) at 20 Hz was reduced to about 50% of its original value. After stabilization of fatigue, animals were randomized in three groups. ⋯ In contrast, broxaterol administration resulted in a significant (p less than 0.05) and long-lasting increase in Pdi at low stimulation frequencies. Pdi at 20 Hz thus increased by 20 +/- 16% 90 min after the first bolus, and by 36 +/- 18% 90 min after the second dose. We conclude that (1) broxaterol promotes recovery of low-frequency fatigue in a dose-dependent way, and (2) theophylline does not improve the force output of fatigued canine diaphragm in vivo.