Response of the rabbit diaphragm to tendon vibration

To evaluate the potential role of diaphragmatic muscle spindles in the act of breathing, we have recorded the electromyograms of the diaphragm and the external intercostal muscle in the third interspace during high-frequency mechanical vibration (50 Hz) of the central tendon in eight anesthetized, s pontaneously breathing rabbits. Vibration induced a consistent, clear-cut i ncrease in the inspiratory activity recorded from the external intercostal, thus indicating that the mechanical stimulus applied to the diaphragm was strong enough to trigger muscle spindles at distant sites. However, vibrati on did not elicit any alteration in costal or crural diaphragmatic activity in any animal. Similarly, when vibration was applied during hyperventilati on-induced apnea, activity was recorded in the external intercostal but not in the diaphragm. These observations support the traditional view that the diaphragm is poorly endowed with muscle spindles and that these play littl e or no significant role in the act of breathing. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.