Abstract
OBJECTIVE: To determine if muscle fibre injury, reduced force output and fatigue of the diaphragm accompanied hyperinflation induced by experimental emphysema.DESIGN: Controlled and randomized.ANIMALS: Adult male golden Syrian hamsters: seven control and seven experimental emphysema hamsters were studied.INTERVENTIONS: Following anesthesia, experimental emphysema hamsters received a transtracheal injection of elastase. They also received injections of β-aminopropionitrile every other day for five weeks. After five weeks, all hamsters we re anesthetized , and their diaphragm and lungs were excised.MAIN RESULTS: Measurements of the excised lungs showed an increased residual volume. functional residual capacity and total lung capacity in experimental emphysema hamsters. In vitro physiological study of diaphragm strips showed no difference in force output but a greater fatiguability during repetitive stimulation for 5 mins in experimental emphysema hamsters than in control hamsters. Histological examination did not show significant muscle injury in the diaphragm of experimental emphysema hamsters.CONCLUSION: The greater fatiguability and absence of muscle injury in the diaphragm of emphysematous hamsters may result from hyperinflation decreasing diaphragmatic load. Alternatively, muscle damage not detectable at the light microscopic level may have contributed to increased fatiguability of the diaphragm of experimental emphysematous hamsters.
Highlights
CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) IS charactcriZL'.d by increased airway resistance leadi ng Lo hyperinflation and placement of the inspi ratory muscles at shortened lengths, with the d iaphragm affected to the greatest degree
The ventilatory loads imposed on the diaphragm may he greater because it is forced to pump more frequently in a less fun ctional position
The purpose of this study was to determ ine if muscle fibre injury, reduced force output and fatig ue of the diaphragm accompanied hyperinflation induced by experimental emphyse ma
Summary
An animal model of increased resistive loading by tracheal banding hamsters was developed and marked diaphragm da mage and infl ammation were fo und (3) Another animal model, experimental emphysema, leads to profound hyperinflation and fla ttening of the diaphrag m (4) but li llle change in pulmonary resistance (5). The purpose of this study was to determ ine if muscle fibre injury, reduced force output and fatig ue of the diaphragm accompanied hyperinflation induced by experimental emphyse ma. The effects of this type of loading on the diaphragm were assessed by exa mining: fi rst, muscle morphology using light microscopy; and second. The effects of this type of loading on the diaphragm were assessed by exa mining: fi rst, muscle morphology using light microscopy; and second. in vitro phys iologica l function of costal diaphragm strips
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