Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis.

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

Diaphragmatic fatigue produced by constant or modulated electric currents.

In anesthetized rabbits the efficiency of phrenic nerve stimulation with trains of electric current was studied either when ventilation was effected entirely by bilateral nerve stimulation (electrophrenic ventilation) or during unilateral nerve stimulation when animals were ventilated with a pump and open chest. Trains of rectangular electric pulses (RPT) with constant amplitude and frequency or sine waves, both the amplitude and frequency of which were modulated and controlled by a computer (MSWT), were used with each animal. MSWT closely reproduced the physiological shape of transdiaphragmatic pressure waves. Diaphragm fatigue, as determined from the decrease in the maximal relaxation rate of twitches, occurred after 20 minutes of bilateral or unilateral nerve stimulation with RPT, but only after 60 min (unilateral stimulation) or 98 min (bilateral stimulation) with MSWT. These data show the importance of the motor signal pattern in long-lasting nerve stimulation.

[Trial of a new technic of transcutaneous diaphragmatic electrostimulation in man]. / Essai d'une nouvelle technique d'électrostimulation diaphragmatique transcutanée chez l'homme.

A new method of diaphragmatic pacing by transcutaneous electrical stimulation, using alternative currents with frequency and amplitude modulations, was tested in 12 subjects: 3 were normal and awake (group I); 4 were studied in acute respiratory failure while under mechanical ventilation and central apnea (group II) and 5 were studied while anaesthetized for peripheral venous surgery and breathing spontaneously (group III). Stimulation was performed either during spontaneous ventilation (groups I and II) or during short periods of respiratory depression (group III). Tidal volume was measured by pneumotachography. A positive correlation was found between stimulus intensity and inspired volume. This effect was not due to voluntary control alone, since diaphragmatic stimulation could support 24% of the theoretical minute ventilation in group II subjects and 64% in group III subjects. These preliminary results demonstrate the relative efficacy of this new method of diaphragmatic pacing using computerized alternative currents.

Ventilatory responses to muscular vibrations in healthy humans.

In healthy humans, we studied the effect of high-frequency mechanical vibrations applied unilaterally to the tendon of the biceps or triceps brachialis on ventilation and the breathing pattern. This stimulus preferentially activates the muscle spindle afferents. Increase of respiratory frequency and changes in the ventilatory timing started at the first or second 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 enabled us to induce a tonic reflex contraction in either the vibrated muscle or the antagonist of no reflex contraction in either group of muscles. In all cases the increase in minute ventilation was identical. These changes in breathing pattern was 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 an the pattern of ventilatory response produced by tendon stimulation did not change with increased ventilation. In conclusion, the stimulation of muscle spindles in human induces changes in ventilation and pattern of breathing , and the occurrence of a reflex muscular contraction does not seem necessary in order to obtain such effects.