Ventilatory responses to muscular vibrations in healthy humans

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Abstract
In healthy humans the effects of high-frequency mechanical vibrations, applied unilaterally to the tendon of the biceps or triceps brachialis, on ventilation and the breathing pattern were studied. This stimulus preferentially activates the muscle spindle afferents. Increase in respiratory frequency and changes in the ventilatory timing started at the 1st or 2nd inspiration during tendon stimulation and no adaptation occurred as long as the vibrations continued. The tidal volume and mean inspiratory flow rate were only enhanced in individuals having high-frequency breathing during eupnea. The changes in ventilatory variables were observed when the motor response to vibrations was tested under isometric or isotonic conditions. Various experimental procedures induced a tonic reflex contraction in the vibrated muscle or the antagonist or no reflex contraction in either group of muscles. In all cases the increase in minute ventilation was identical. These changes in breathing pattern were not associated with a significant decrease in alveolar CO2 pressure and did not seem to be responsible for important variations in respiratory gas exchanges. The response to high-frequency vibrations was also studied after ventilation was increased with added dead space. The magnitude of hyperventilation and the pattern of ventilatory response produced by tendon stimulation did not change with increased ventilation. Stimulation of muscle spindles in humans induces changes in ventilation and pattern of breathing. The occurrence of a reflex muscular contraction does not seem necessary to obtain such effects.