[Salbutamol improves diaphragmatic contractility in chronic airway obstruction]

Chronic airflow obstruction in conditions such as chronic obstructive pulmonary disease is associated with respiratory muscle dysfunction. Our aim was to study the effects of salbutamol-a beta-adrenergic agonist known to improve muscle strength in physiologic and pathologic conditions-on diaphragm contractility in an animal model of chronic airway obstruction achieved by tracheal banding.

Twenty-four Sprague-Dawley rats were randomized into a control group and 3 tracheal banding groups, 1 that received acute salbutamol treatment, 1 that received chronic salbutamol treatment, and 1 that received nothing. Arterial blood gases, acid-base balance, and in vitro diaphragmatic contractility were evaluated by measuring peak twitch tension, contraction time, contraction velocity, half-relaxation time, relaxation velocity, and force-frequency curves.

The 3 study groups had significantly reduced arterial pH and increased PaCO2 and bicarbonate levels compared to the control group (P<.05). The untreated tracheal banding group had significantly reduced peak twitch tension and contraction velocity, and a significantly lower force-frequency curve in comparison with the other groups (P<.05). The chronic treatment group had a higher relaxation velocity than the untreated study group (P<.05). The mean (SE) peak twitch tension values were 6.46 (0.90)N/cm(2) for the control group, 3.28 (0.55)N/cm(2) for the untreated tracheal banding group, 6.18 (0.71)N/cm(2) for the acute treatment group, and 7.09 (0.59)N/cm(2) for the chronic treatment group.

Diaphragmatic dysfunction associated with chronic airflow obstruction improves with both the acute and chronic administration of salbutamol. The mechanisms involved in respiratory muscle dysfunction warrant further study.