Neuromuscular adaptations in rats trained by muscle stretch-shortening

The aim of this study was the analysis of neurophysiological, mechanical and histochemical parameters to demonstrate muscle adaptation with training. If the parameters studied were to show correlated changes, it would be possible to propose that the neural and the muscle components of motor units are both affected by the training programme used. The training consisted of repeated stretch-shortening cycles known to use extensively fast fibres. After the training period electromyographical reflex activities of the ankle plantar-flexors were recorded in awake rats and then mechanical and histochemical measurements were made on isolated soleus muscles of the control and trained rats. The reflexes studied were the H-response to electrical stimulation of the sciatic nerve and the T-response to an Achilles tendon tap. The H-response analysis indicated a decrease in reflex excitability of the trained muscles. The trained soleus muscle also presented a higher contractility as demonstrated by significantly smaller twitch contraction times and higher maximal velocities of shortening measured during tetanic contractions. The reflex and contractile muscle changes were accompanied by relative increases in the number of type II fibres. The T-response was not significantly modified by training despite the decrease in motoneuron excitability demonstrated by the decrease in H-response. This would suggest that the peripheral components of the reflex pathway such as tendon stiffness and/or spindle sensitivity might be modified by training. This would imply that both the motor and the sensory parts of a muscle are affected by training.     

Influence of plyometric training on the mechanical impedance of the human ankle joint

The objective of this work was to study the effects of plyometric training on the mechanical properties of the ankle joint in humans. Changes in the mechanical parameters of this musculo-articular structure were quantified with the aid of a sinusoidal perturbation technique. This technique allowed the expression of the mechanical impedance of the musculo-articular system in terms of stiffness, viscosity and inertia. Measurements were performed under passive conditions and when the subject performed plantar flexion. A 7-week period of training induced a decrease in the slope of the relationship between stiffness and plantar flexion torque, whereas passive stiffness was increased. A slight decrease in viscosity and an invariability in inertia were also found. These results are interpreted in terms of the possible adaptations of the musculo-articular structure and ultrastructure involved in the performance of plantar flexion. Accepted: 11 April 1997     

Implications of Deep Electrode Insertion on Cochlear Implant Fitting

Using long Med-El Combi40+ electrode arrays, it is now possible to cover the whole range of the cochlea, up to about two turns. Such insertion depths have received little attention. To evaluate the contribution of deeply inserted electrodes, five Med-El cochlear implant users were tested on vowel and consonant identification tests with fittings with first one, two, and up to five apical electrodes being deactivated. In addition, subjects performed pitch-ranking experiments, using loudness-balanced stimuli, to identify electrodes creating pitch confusions. Radiographs were taken to measure each electrode insertion depth. All subjects used each modified fitting for two periods of about 3 weeks. During the experiment, the same stimulation rate and frequency range were maintained across all the fittings used for each individual subject. After each trial period the subject had to perform three consonant and three vowel identification tests. All subjects showed deep electrode insertions ranging from 605° to 720°. The two subjects with the deepest electrode insertions showed significantly increased vowel- and consonant-identification performances with fittings with the two or three most apical electrodes deactivated compared to their standard fitting with all available electrodes activated. The other three subjects did not show significant improvements in performance when one or two of their most apical electrodes were deactivated. Four out of five subjects preferred to continue use of a fitting with one or more apical electrodes deactivated. The two subjects with the deepest insertions also showed pitch confusions between their most apical electrodes. Two possible reasons for these results are discussed. One is to reduce neural interactions related to electrodes producing pitch confusions. Another is to improve the alignment of the frequency components of sounds coded by the electrical signals delivered to each electrode to the overall pitch of the auditory perception produced by the electrical stimulation of auditory nerve fibers.     

Joint medico-psychological consultation for patients suffering from tinnitus

Because no effective treatment against tinnitus is available, all sorts of approaches have been developed. We believe the care of tinnitus patients concerns mainly ENT medical doctors. In order to take care of such patients, we started in 1993 a joint medico-psychological consultation (JMPC) to dispense adequate care for patients and training to the ENT residents. Every patient visiting our clinic for a tinnitus consultation benefits first from a comprehensive audiological examination. Once all objective causes of tinnitus are excluded, those patients who were not able to accept their auditory disorder or who insist on focusing on the annoyance caused by the perception of their tinnitus are invited by the doctor to the JMPC. The intolerance caused by tinnitus is enhanced by psychological and social aspects. These aspects are considered and discussed during the JMPC. The patients talk about their tinnitus bringing additional information on professional, familial and relational issues. In the JMPC, the therapists try to help the patients to void the affective irritation and the internal tension they clearly demonstrate. When the patients notice that the therapists accept their distress, they usually talk more calmly about their hearing irritation and even consider it tolerable. The medical and psychological information given during the JMPC helps the patients to understand the links between tinnitus and the disturbing elements of their current life. During the JMPC, the medical residents have been able to observe how somatic complaints can lead to complaints of another nature, to distress, to aggressive or angered behaviors. They have acknowledged the way the psychologist deals with the attitudes of these patients. This learning process became mandatory to all our residents specializing in ENT. At the end of their training they should have learned how to help the patient accept the tinnitus and the irritation it causes. They should be able to help tinnitus patients to stop searching for a treatment that does not exist in the so-called specialized centers, which often do not fulfill their expectations.     

Benefits and costs of universal hearing screening programme

Hearing loss affects 1-3 out of 1000 newborns. A programme of universal newborn hearing screening (UNHS) was implemented in our ENT department in February 2000. In 2001, the programme was extended to all the hospitals of the canton Geneva. The programme is based on the recording of transient evoked otoacoustic emissions (TEOAE) from all newborns. In addition, automated auditory brainstem responses (aABR) are recorded in high-risk neonates. In the report, we compare the mean age at which rehabilitation of hearing was undertaken during a 5-year period before and after the screening programme was instituted. We also identify some causes of delayed diagnosis and intervention and the pitfalls of universal hearing screening. The price of the UNHS programme is estimated at 26 Swiss francs (17 Euros; 21 US dollars) per infant screened, including the material required, the personal involved to run the programme, and the follow-up.     

Partial withdrawal of deeply inserted cochlear electrodes: observations of two patients

Three patients implanted in our department received the preformed Clarion S-Series cochlear implant with the electrode Positioning System (EPS). The EPS is a device designed to bring the electrode array closer to the modiolus and deeper into the cochlea. Two of these patients still complained because they were perceiving too low pitch sounds, and because of the presence of echoes and poor discrimination after 3 years of implant use and many tuning sessions. We hypothesized that the electrode array was too deeply inserted and could be stimulating overlapping populations of neurons in the low frequency range. The EPS was removed through a transcanal tympanotomy under local anesthesia and the array was pulled 2–3 mm out of the cochlea. The angle of electrode insertion into the cochlea and the patients’ performances on consonant identification tests were evaluated before and after the removal surgery and over the long term, 3 years after the surgery. Immediately after the removal surgery the angle of insertion of the electrode array decreased from 720° to 485° in one case and from 675° to 485° in the other. Both patients reported subjective improvements after the removal which were confirmed by tests of performance at the long term by one of the patients. These observations show that (1) the electrode array can be moved without deterioration of performances even several years after being implanted; revision surgery may be beneficial in some cases, (2) neighboring electrodes might stimulate overlapping populations of neurons, inducing a deterioration of performances; for anatomical reasons, this is most likely to occur in the apex of the cochlea and (3) tuning of the external processor should be a customized procedure.     

Effects of stretch-shortening cycle training on mechanical properties and fibre type transition in the rat soleus muscle

The effects of exercise training on mechanical properties and fibre type transitions have been investigated in rat soleus muscle. The exercise was a repetition of stretch-shortening cycles. A method of dual controlled releases was applied to obtain tension/extension curves, which characterize the elastic behaviour of the series elastic component (SEC), and the force/velocity relationship characterizing the contractile elements. Other contractile measurements included: contraction time (t _c), half-relaxation time (t _1/2) and twitch/tetanus ratio (P _t/P _o). Additionally, the muscle fibre type composition was determined by a classical histochemical method. A 12-week period of training induced a significantly higher percentage of fast-twitch fibres and a lower percentage of slow-twitch fibres (P<0.01). This fibre adaptation led to a significant (P<0.01) decrease in t _c and an increase in maximum shortening velocity (V _max). An increase in compliance of the SEC was also observed. This elastic adaptation is interpreted in terms of modification of the active components of the SEC. All the histochemical and mechanical data presented in this study show that rat soleus muscles trained by stretch-shortening cycles acquired faster characteristics. Thus the results confirm that a slow-twitch to a fast-twitch fibre transition is obtainable in mature rats.     

Changes in stiffness induced by hindlimb suspension in rat Achilles tendon

The aim of this study was to measure the effects of hindlimb suspension on mechanical properties of the rat Achilles tendon. Adult male Wistar rats were randomly assigned to groups to be either suspended, or a control. After 21 days, Achilles tendons were removed for mechanical analysis. Classical tests of tensile performance were made, and mechanical parameters were derived from a stress-strain relationship. The tendons of animals that had been suspended presented values for maximal stress and tangent modulus which were 37.5% (P < 0.01) and 41% (P < 0.01), respectively, lower than the tendons of the control rats. In a similar way, the energy absorption capacity had largely decreased in animals that had been suspended. However, the maximal strain was similar in the two groups. These results showed that hindlimb suspension in rats has an important detrimental effect on mechanical properties of the Achilles tendon. Differences in tendon stiffness obtained here, along with those found by other investigators, encourage the hypothesis that homeostatic responses of soft tissues are due to changes in limb loadings. This study may be useful in providing a better understanding of the adaptation of human skeletal muscle when exposed to microgravity. Accepted: 3 September 1999