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Biomedical subjects

J L Pepin

Publications and source records attributed to J L Pepin.

31 records · Page 2Linked to original sources
PubMed1994

Circadian changes of left ventricular ejection fraction in normal subjects.

Sleep has a specific physiology with related cardiovascular changes. We have previously found in respiratory patients [chronic obstructive pulmonary disease (COPD) and sleep apnea syndrome (OSAS)] an unexpected decrease in left ventricular ejection fraction (LVEF) at waking in the morning when compared with the rest period during the day. Whether this observation was linked to the consequences of the respiratory abnormalities or reflected physiological fluctuations related to the changes in autonomic nervous system tone remained unknown. Thus, we have set out to analyze the changes in LVEF with sleep in normal individuals. Eight healthy young men had LVEF measured before and after submaximal exercise, at rest before bedtime, and on waking in the morning. Technetium-99m with in vivo red cell labelling was used. Sleep parameters were assessed using classical polysomnography. In order to detect any influence of autonomic nervous system stimulation on LVEF, sympathovagal tone (SVT) was also assessed during night-time LVEF measurements using spectral analysis of RR intervals. LVEF at rest was within the normal limits for all the subjects (range 51-62%). On submaximal exercise, the LVEF increased in four subjects, was unchanged in two, and decreased in two. The main result concerns the changes in LVEF overnight. In the morning, LVEF decreased dramatically in three subjects and reached a level of < 30% in four. These decreases in LVEF were not related to changes in SVT or sleep structure. LVEF values returned to normal in 30 min. The LVEF changes during exercise are in accordance with previous data in the literature. The dramatic decrease in LVEF observed in the morning could be related either to vascular resistance changes or to nocturnal variations in cardiac contractility, which both need further studies to be established.

Adult↗
PubMed1993

The audiospinal reaction in parkinsonian patients reflects functional changes in reticular nuclei.

Audiospinal facilitation using the soleus H-reflex as a test was compared in 16 control subjects and 23 parkinsonian patients. In the patients, facilitation was significantly reduced during the 75 to 150 msec after the conditioning stimulation. This reduction was seen bilaterally even in patients with a hemisyndrome. It was corrected by L-dopa but not by anticholinergic agents. Facilitation at the 75-msec delay showed an inverse linear correlation with the bradykinesia intensity (r = -0.7, p < 0.01). The results argue in favor of a reduced excitability of the nucleus reticularis pontis caudalis from which a reticulospinal tract emanates as effector of the audiospinal facilitation. This would represent another example of dysfunction of reticular nuclei in Parkinson's disease.

Acoustic Stimulation↗
PubMed1992

Facilitation of responses to motor cortex stimulation: effects of isometric voluntary contraction.

In 7 normal subjects we compared the facilitatory effect of isometric contraction of the tibialis anterior on the size of electromyographic responses evoked in this muscle by electric stimuli applied over the cervical column and by electric and magnetic percutaneous stimulation of the motor cortex. No significant difference was found between the degrees of facilitation of the responses to any of the stimuli. Using collision techniques, we also showed that the pyramidal fibers activated by spinal and cortical stimuli are the same. Facilitation induced by isometric contraction (20% maximum) was of similar or greater magnitude than that found with constant vibration of the tendon of the target muscle. In cases where vibration and contraction had equal facilitatory effects, there was no further facilitation of the responses when both conditions were applied together. These findings indicate that the facilitatory effect of isometric contraction of the target muscle essentially originates at a spinal level rather than in the motor cortex.

Adult↗
PubMed1992

Percutaneous magnetic stimulation of the motor cortex in migraine.

We have used transcranial magnetic stimulation of the motor cortex interictally in 12 patients with unilateral classic migraine with sensorimotor auras and 10 patients with common migraine and unilateral headache. In classic migraine, the threshold of activation of the FDI muscle by the cortical stimulus was significantly increased on the side of the auras, when compared to the unaffected side (P less than 0.01) and to normal subjects (P less than 0.01). The amplitude of EMG responses was also reduced in FDI on the affected side when compared to normals (P less than 0.02). Responses obtained in common migraine patients were normal on both sides. We suggest that some permanent subclinical dysfunction of the motor cortex might play a role in the pathogenesis of attacks of classic migraine with sensorimotor auras.

Adolescent↗
PubMed1992

Somnofluoroscopy, computed tomography, and cephalometry in the assessment of the airway in obstructive sleep apnoea.

BACKGROUND: Assessments of the upper airways in patients with the obstructive sleep apnoea syndrome are usually carried out on awake patients who are upright. The dynamics of the airway in a patient who is asleep and lying down may be different. METHODS: Somnofluoroscopy, computed tomography of the upper airway, and cephalometry were carried out in 11 patients with the obstructive sleep apnoea syndrome (10 male; mean (SD) age 53 (10) years) to examine the airway while they were awake and asleep. RESULTS: At somnofluoroscopy 10 patients were in stage 2 sleep and only one in REM sleep. At least five obstructive events were visualised by lateral fluoroscopy in each patient. Imaging allowed observation of the dynamics of airway collapse, which began in the oropharynx in all cases, progressing to the hypopharynx in 10 cases and to the laryngopharynx in five. At fluoroscopy the soft palate was seen to hook up during airway occlusion in 10 patients, thereby increasing its cross sectional area. It was then sucked down into the hypopharynx. Somnofluoroscopic and cephalometric findings agreed, eight of the 10 patients with hypopharyngeal collapse shown by somnofluoroscopy having an inferiorly placed hyoid bone according to cephalometry (distance from the mandibular plane to the hyoid bone (MP-H distance) increased); the one patient with no hypopharyngeal collapse had a normal MP-H. By contrast, six of the 11 patients had a normal or supranormal hypopharyngeal cross sectional area of the airway on the computed tomogram. CONCLUSIONS: Somnofluoroscopy allows examination of the dynamics of airway closure in this disorder and shows the important role of the soft palate in acting as a plug in the oropharynx. Dynamic studies are required to determine the pattern of pharyngeal obstruction in obstructive sleep apnoea.

Adult↗
PubMed1991

Short-latency autogenic inhibition in patients with Parkinsonian rigidity.

The spinal Ib interneuron efficacy has been compared in 11 control subjects and 19 patients with parkinsonian rigidity. In normal subjects, gastrocnemius medialis nerve stimulation induces an inhibition of the soleus H reflex for 3 to 8 msec with a peak at 5 msec of 83.72 +/- 7.28% of the control value of H reflex. In parkinsonian patients, inhibition is reduced or even replaced by facilitation, which also peaks at 5 msec. The departures from normal values correlate with rigidity intensity assessed by the Webster scale. Increase in rigidity is associated, first, with a reduction of inhibition and, from a score of 2 or more, with facilitation replacing the normal inhibition. In addition to providing an electrophysiological index of rigidity, reduction in autogenic inhibition might be one of the neurophysiological mechanisms underlying rigidity. In association with the known hyperactivity of the Ia inhibitory interneuron in Parkinson's disease, reduction of activity of Ib interneuron could be explained by an increased activity in the reticularis gigantocellularis nucleus; its efferent tracts both inhibit Ib interneurons and activate Ia interneurons.

Aged↗
PubMed1991

The influence of contralateral primary afferents on Ia inhibitory interneurones in humans.

1. Contralateral influences on short latency reciprocal inhibition between wrist extensor and flexor muscles were investigated in twenty-two healthy volunteers. Reciprocal inhibition, probably mediated through the Ia inhibitory interneurone, was measured by conditioning the flexor carpi radialis (FCR) H reflex by weak stimulation of the ipsilateral radial nerve. Maximum reciprocal inhibition occurring at a precise delay between conditioning and conditioned stimulations was taken as the test level of inhibition. 2. Contralateral median or radial nerves were stimulated at short intervals before the onset of reciprocal inhibition. The latter was increased by 8.6% after median nerve stimulation and decreased by 16.5% after radial nerve stimulation. 3. The contribution of sensory fibres in the two nerves to contralateral effects was investigated by stimulating purely sensory branches of the nerves. No clear modification of the contralateral reciprocal inhibition was observed. The effects produced by mixed nerve stimulation are thus likely to have been mediated by Ia fibres. 4. In three hemiplegic patients where reciprocal inhibition was reduced unilaterally, stimulation on the spastic side produced contralateral effects similar to those observed in normal subjects. This result indicates that contralateral effects are not mediated through the Ia inhibitory interneurone ipsilateral to the conditioning stimulus. 5. Since contralateral effects occur after short delays (2 ms, median nerve; 3 ms, radial nerve), we suggest a functional scheme in which the excitability of Ia inhibitory interneurones is modified by contralateral primary afferents via the interneurones activated by group I fibres, probably Ia fibres. The short delays indicate that the interneurone transmitting primary afferent influences to the contralateral side is probably excitatory.

Adolescent↗
PubMed1991

Magnetic stimulation of the motor cortex in cervical spondylosis.

We report a new technique of transcranial magnetic stimulation of the motor cortex to measure conduction within central motor pathways of 67 patients with cervical spondylosis or disk herniation. There were upper motor neuron signs in 34 patients (51%) and x-ray evidence of cervical cord compression in 44 (66%). Muscle action potentials (MAPs) to cortical stimulation were abnormal in 84% of patients with, and 22% of those without, radiologic signs of cervical cord compression. Median nerve somatosensory evoked potentials were altered in only 25% of patients. The frequency of MAP alterations correlated with upper motor neuron signs. In 5 (11%) of the 44 patients with x-ray evidence of cervical cord compression, subclinical cord compression was disclosed by cortical stimulation. In 10 patients restudied 3 months after surgical decompression, normalization of central motor conduction time did not occur, indicating permanent damage to the cervical cord.

Action Potentials↗
PubMed1990

[Parkinsonian rigidity: clinical and physiopathologic aspects].

Neurophysiologic mechanisms responsible for parkinsonian rigidity are poorly understood. In any case, they have to fit all the clinical data which are first reviewed before discussing 2 theories which are proposed to interpret rigidity. The first theory postulates that increased resistance to mobilization is due to hyperactivity in a long loop reflex pathway which originates at the neuromuscular spindles and relays in the motor cortex. This theory is based on the largely accepted finding that, in parkinsonian patients, M2 response is increased when a voluntary movement is abruptly stopped. Although popular this hypothesis is far from explaining all the clinical facts, namely that rigidity is equal in extensor and flexor, proximal and distal muscles. Based on a reflex set by primary afferent discharges, it is incompatible with the lack of rigidity reinforcement after faster passive mobilization. The second theory rests on data obtained from electrophysiological studies of some spinal interneurones. Both IA and IB inhibitory interneurones are functionally modified but not in the same direction. While the IA inhibitory interneurone is facilitated, the IB inhibitory interneurone is less active. Disappearance of autogenic inhibition can explain rigidity at rest and the tonic stretch reflex. In addition, interneurones intervening in the flexor reflex disclose a modified excitability. It is possible to interpret these facts by postulating an abnormal influence transmitted through descending reticulospinal pathways. This abnormal influence would result from modified activation of reticular nuclei by afferents projecting from the basal ganglia. Such a hypothesis is open to experimental testing through the startle reaction. The latter facilitates the H reflex by the reticulospinal pathways, the influence of cortex--if any--being negligible.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiology↗
PubMed1990

[Can oximetry contribute to the detection of apnea? The use of a mathematical analysis of the oximetry signal].

The aim of this study was to test the efficacy of nocturnal oximetry as a means of continuous recording of SaO2 in the identification of apnoeic events in the recognition of non-apnoeic desaturation. The oscillations of SaO2 in relation to successive periods of apnoea during the course of the sleep apnoea syndrome (SAS) or with apnoeic episodes in patients with chronic airflow obstruction (BPCO) or restricted disease, were identified using a new delta index quantifying the variations of SaO2 during the night. 26 successive patients in whom there was an indication for nocturnal oximetry were included in a prospective study comparing nocturnal oximetry and polysomnography during 34 nights. In the apnoeic patients we found a strong correlation (r = .85. p. less than .01) between the apnoeic period and the delta index. In BPCO the number of apnoea was correlated with the delta index (r = .96. p. less than .01). A minimal threshold of the delta index fixed at 1.5 was satisfactory for detecting apnoea if the initial SaO2 was less than 93%. The value of the adequate for affected detection ought to be fixed at .8 (95% sensitivity) when the initial SaO2 was greater than 93%. A detection of apnoeic events thus seems possible by this method.

Apnea↗
PubMed1988

Reinforcement of reciprocal inhibition by contralateral movements in man.

A reduction of flexor carpi radialis H reflex size was produced by submotor threshold stimulation of the radial nerve. This reduction reflects reciprocal inhibition exerted by the inhibitory IA interneuron. The effects of contralateral movements on IA reciprocal inhibition were studied in eight normal subjects. Active contralateral arm movement appeared to significantly increase the degree of reciprocal inhibition without affecting the unconditioned reflex. A minor enhancement of reciprocal inhibition was also noted after passive mobilization. Results are discussed in terms of contralateral segmental afferent fibers influencing IA interneuronal excitability. They strongly suggest that contralateral muscular IA afferents may reinforce reciprocal inhibition in man.

Adult↗