Many clinicians believe exercise associated muscle cramps (EAMC) occur because of dehydration and electrolyte losses. Experimental research supporting this theory is lacking. Mild hypohydration (3% body mass loss) does not alter cramp threshold frequency (TF), a measure of cramp susceptibility, when fatigue and exercise intensity are controlled. No experimental research has examined TF following significant (3-5% body mass loss) or serious hypohydration (>5% body mass loss). TF and blood variables of ten subjects were measured pre-post exercise. Subjects exercised in an environmental heat chamber alternating between upper arm ergometry and non-dominant leg cycling every 15 minutes until they lost 5% of their body mass or were too exhausted to continue. Significant (n=5) or serious hypohydration (n=5) did not alter cramp TF, cramp intensity, or cramp EMG amplitude. Significant and serious hypohydration with moderate electrolyte losses does not alter cramp susceptibility when fatigue and exercise intensity are controlled.

Goals of this study were to identify and characterize effects of neurokinin A (NKA) in isolated guinea pig hearts. Bradycardia, augmentation of ventricular contractions, and reduction of perfusion pressure were prominent responses to bolus injections of NKA (0.25-25 nmol). NKA was more potent than substance P (SP) in causing bradycardia but did not differ in potency for lowering perfusion pressure. Doses of SP of 25 nmol or less decreased ventricular force, whereas 100 nmol caused a biphasic response. The percent decrease in heart rate produced by 25 nmol NKA was reduced from 58.0 ± 4.8 to 39.6 ± 3.5% in the presence of μM atropine (n = 5). The positive inotropic response to 25 nmol of NKA in spontaneously beating hearts was replaced by a negative inotropic response during pacing (22.5 ± 3.3% increase vs. 11.7 ± 1.7% decrease, n = 5). Reserpine pretreatment did not affect the positive inotropic response to NKA. Specific binding sites for (125)I-labeled NKA were localized to intracardiac ganglia and coronary arteries but not to myocardium. It was concluded that 1) negative chronotropic responses to NKA involve cholinergic and noncholinergic mechanisms, and 2) the positive inotropic response is an indirect action.

Summary: The effects of clonidine, a central alpha2 agonist, on changes in blood pressure caused by muscle afferent nerve (ergoreceptor) activation and baroreceptor manipulation were studied in cats. Prolonged isometric contractions (ergoreceptor activation) of the gastrocnemius and plantaris muscles increased mean arterial pressure by 53 mmHg. This pressor response was not altered by naloxone (0.5 μmol·litre-1) but was eliminated by clonidine (0.5-2.0 μg) when injected into the cerebral aqueduct. Brief occlusion of the carotid artery (15-30 s) caused mean arterial pressure to increase by 32-42 mmHg at rest. Neither naloxone nor clonidine altered the magnitude of the reflex pressor response to carotid occlusion. Similar increases in pressure were measured when occlusion was applied during fatiguing isometric contractions; thus baroreceptor induced increases in pressure were superimposed on the ergoreceptor induced blood pressure changes. Naloxone did not affect the changes in pressure caused by either reflex response. Clonidine continued to eliminate the pressor response to muscular contraction but did not affect the pressure increase when the carotid occlusion was applied during contractions. Electrical stimulation of the carotid sinus nerve caused blood pressure to decrease by 36 mmHg during rest and by 41 mmHg during fatiguing isometric contractions. Clonidine did not alter the depressor response to carotid sinus nerve stimulation. These data may indicate that separate pathways centrally mediate the changes in blood pressure caused by ergoreceptor and baroreceptor afferent activation. The integration of the ergoreceptor pathway may involve a catecholaminergic-opioidergic system but the present results do not suggest a similar interaction for the baroreceptor integration.

Fragmented QRS (fQRS) is a marker of conduction block due to myocardial scar that presents in electrocardiography (ECG) as an additional one or more R wave (R') or notching in the S wave nadir in contiguous leads. However, fQRS description on premature ventricular contractions (PVCs) has not been previously described. We describe a case of a 67-year-old male with a past medical history of prediabetes, hypertension and coronary artery disease who presented after an ophthalmic procedure with asymptomatic PVCs and episodes of bigeminy. Initial ECG showed an isolated fQRS in V2. However, during PVCs significant extrasystoles fragmentation was seen in other coronary territories. Upon reviewing his most recent cardiac catheterization, it showed a 40% ostial and 70% distal left anterior descending stenosis with a mid-segment patent stent, 95% first diagonal stenosis and totally occluded proximal right coronary artery. Identification of diffuse fQRS known to be associated with myocardial scar, sustained arrhythmic events and sudden cardiac death, particularly when seen in the inferior leads, became extremely relevant in our patient. We noted that ejection fraction reduction from 52% to 34% on his last coronary intervention was crucial to decide if an implantable cardioverter-defibrillator would be needed. PVC fragmentation might be a new ECG marker that could uncover both scar and arrhythmia potential in patients at risk of adverse cardiac events.

<p> The interrelationship of force, surface elecrograms (EMG) and joint position for static voluntary contractions of Quadriceps Femoris muscle group in man were investigated before and during partial curarization induced by d-tubocurarine. </p> <p> Four normal male volunteers were studied. Each performed a series of brief isometric contractions (by extension of the lower leg against resistance) at different levels of force and at three knee-joint positions while lying in the supine position. All series were repeated for both a normal state and a partially paralyzed state under the :influence of curare. Torque generated about the knee-joint was measured with a Cybex isokinetic system and the nyoelectric activity of three quadriceps muscles was monitored using bipolar surface electrodes. </p> <p> Traditional parameters of nyoelectric activity (mean-rectified-EMG [MRE], and root-mean-squared-DG [RMSE]) were calculated using a minicomputer (PDPll/34), which had also acquired and processed the data. In addition, EMG power spectra were computed by Fast Fourier Transform techniques in an attempt to provide further insight into the effects of curare on human muscle. </p> <p> In order to provide a basis for comparison of the normal state with the parially curarized state, force-EMG relationships were computed for each subject, muscle, knee-joint angle, and condition. Statistical methods (three-way ANOVA' s) were then employed to both quantify any differences that may have existed between the two states and to identify sources of differences within each state. A similar statistically- based comparison of the power spectra was undertaken utilizing several indices that described the shape of the spectra. A general description of the activities of the quadriceps femoris muscles followed after collating all the information that the surface DIG provided in conjunction with the external forces measured. </p> <p> It was concluded that curare did not have any significant effects on the force-EMG relationship. There appeared to be a slight effect of curare on the power spectra however, with a general trend of increasing lower frequency power. The greatest source of variation of force-EMG relationships and power spectra was attributed to the position of the knee-joint. </p> / Thesis / Master of Engineering (MEngr)

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The effects of aging on the muscle length (as inferred by joint angle)-tension relationship was studied in the ankle dorsiflexors of male and female subjects aged 20-40 years (x=25.3; 15d, 159) and 60-80 years (x=68.8; 15d, 159) at 10 joint angles {15°0 through 30°P, in 5° increments). Isometric twitches, voluntary contractions, and 1-sec evoked tetanic contractions {20, 50 & 80 Hz) were measured in the R-tibialis anterior muscle. The resting joint angle for the ankle dorsi flexors was similar between elderly and young adults {13°P ± 3.44). On average, evoked and voluntary torque output increased upon muscle lengthening beyond resting length, and decreased upon shortening. Evoked single twitches of the TA revealed that peak total torque occurred at the extreme of plantarflexion (30°P} in both elderly and young adults. Most importantly, elderly individuals produced similar twitch torque values at all joint angles compared to young adults. Maximal voluntary torque was stronger at the more plantarflexed compared to the dorsiflexed angles, for all subjects, regardless of age, with maximum torque plateauing at 15°P. Elderly subjects demonstrated much reduced MVC torque values compared to young adults at all joint angles (ave.= 18% reduction, p<O.Ol) while maintaining no less than 96% motorunit activation (MUA) . Stimulation of the dorsiflexors at 20, 50, & 80 Hz revealed that the 1-sec peak tetanic torques declined from a maximum at 30°P through to 15°0 for all subjects. Elderly adults produced significantly less tetanic torque at all joint angles compared to young adults (p<0.05). There was no difference between the elderly and young adults in the rate at which the rise in tetanic torque was developed at all joint angles, but elderly adults displayed a significantly greater twitch/tetanus ratio as compared to young adults (p<0.005). In conclusion, these results suggest that there is no age-associated change in the elastic properties of the ankle dorsiflexors, and thus, the length-tension relationship of this muscle group is similar between elderly and young adults. / Thesis / Master of Science (MSc)

L’accouchement prématuré est l’un des problèmes majeurs en obstétrique. Par suite, il a été un sujet d'intérêt pour de nombreux chercheurs. Parmi les nombreuses méthodes utilisées pour enregistrer la contractilité utérine, le plus utilisé est l'EHG abdominal, comme étant un outil facile à utiliser et non invasif. De nombreuses études ont indiqué que l'utilisation de ce signal pourrait être un outil très puissant pour surveiller la grossesse et pour détecter le travail. Il permet en effet d'accéder à l'utérus ainsi que la synchronisation de l'activité utérine, en utilisant des signaux multiples. Il a été démontré que l'analyse de connectivité des signaux EHG a donné des résultats prometteurs en application clinique, comme la classification des contractions de travail et de grossesse. Cependant, dans presque toutes les études antérieures, les matrices de corrélation EHG étaient souvent réduites en ne gardant que leur moyenne et les écarts-types, ce qui a peut aboutir à perdre des informations pertinentes en raison de ce moyennage, ce qui peut induire le taux de classification relativement faible jusqu'à présent. Pour caractériser précisément la matrice de corrélation et quantifier la connectivité associée, nous avons proposé dans cette thèse d'utiliser une technique de mesure de réseau basée sur la théorie des graphes. Selon cette approche, la matrice de corrélation obtenue peut être représentée sous forme de graphiques constitués d'un ensemble de nœuds (électrodes) interconnectés par des arêtes (valeurs de connectivité / corrélation entre électrodes). La nouvelle procédure de l'analyse des signaux EHG enregistrés pendant la grossesse et le travail se base sur la caractérisation de la corrélation entre les activités électriques utérines et sur sa quantification précise en utilisant l'approche de la théorie des graphes. Le pipeline de traitement inclut i) l'estimation des dépendances statistiques entre les différents signaux EHG enregistrés, ii) la quantification des matrices de connectivité obtenues à l'aide de l'analyse théorique des graphes et iii) l'utilisation clinique des mesures de réseau pour la surveillance de la grossesse ainsi que la classification entre les éclosions d'EHG de grossesse et de travail. Une comparaison avec les paramètres déjà existants utilisés pour la détection du travail et la détection d’accouchement prématuré sera également effectuée. Nous étudions également une nouvelle méthode pour étudier la connectivité source EHG, afin de surmonter le problème du calcul de la connectivité au niveau de la surface abdominale. Les résultats de cette thèse montrent que cette approche basée sur la théorie de graphe est un outil très prometteur pour quantifier la synchronisation utérine, lorsqu'elle est appliquée à l'abdomen, pour une meilleure surveillance de la grossesse. Nous espérons que cette approche soit utilisée pour le suivi de la grossesse et contribuerait ainsi à la prédiction précoce de l’accouchement prématuré. / Preterm birth remains a major problem in obstetrics. Therefore, it has been a topic of interest for many researchers. Among the many methods used to record the uterine contractility, the most used is the abdominal EHG, as being an easy to use and a non-invasive tool. Many studies have reported that the use of this signal could be a very powerful tool to monitor pregnancy and to detect labor. It indeed permits to access the uterine as well as the synchronization of the uterine activity, by using multiple signals. It has been shown that the connectivity analysis gave promising results when using EHG recordings in clinical application, such as the classification labor/pregnancy contractions. However, in almost all previous studies EHG correlation matrices were often reduced keeping only their mean and standard deviations thus relevant information may have been missed due to this averaging, which may induce the relatively low classification rate reported so far. To characterize precisely the correlation matrix and quantify the associated connectivity, we proposed in this thesis to use a network measure technique based on graph theory. According to this approach, the obtained correlation matrix can be represented as graphs consisting of a set of nodes (electrodes) interconnected by edges (connectivity/correlation values between electrodes). The new framework, to analyze the EHG signals recorded during pregnancy and labor, is based on the characterization of the correlation between the uterine electrical activities and on its precise quantification by using graph theory approach. The processing pipeline includes i) the estimation of the statistical dependencies between the different recorded EHG signals, ii) the quantification of the obtained connectivity matrices using graph theory-based analysis and iii) the clinical use of network measures for pregnancy monitoring as well as for the classification between pregnancy and labor EHG bursts. A comparison with the already existing parameters used in the state of the art for labor detection and preterm labor prediction will also be performed. We also investigate a new method to study the EHG source connectivity, to overcome the problem of computing the connectivity at the abdominal surface level. The results of this thesis showed that this network-based approach is a very promising tool to quantify uterine synchronization, when applied at the abdominal level, for a better pregnancy monitoring. We expect this approach to be further used for the monitoring of pregnancy and would thus help for the early prediction of preterm labor.

Afin d’être représentatif d’un niveau d’effort musculaire, le signal électromyographique (EMG) est exprimé par rapport à une valeur d’activation maximale. Comme l’épaule est une structure articulaire et musculaire complexe, aucune contraction volontaire isométrique (CVMi) proposée dans la littérature ne permet d’activer maximalement un même muscle de l’épaule pour un groupe d’individus. L’objectif de ce mémoire est de développer une approche statistique permettant de déterminer les CVMi optimales afin de maximiser les niveaux d’activation d’un ensemble de muscles de l’épaule. L’amplitude du signal EMG de 12 muscles de l’épaule a été enregistrée chez 16 sujets alors qu’ils effectuaient 15 CVMi. Une première approche systématique a permis de déterminer les 4 CVMi parmi les 15 qui ensemble maximisent les niveaux d’activation pour les 12 muscles simultanément. Ces 4 contractions ont donné des niveaux d’activation supérieurs aux recommandations antérieures pour 4 muscles de l’épaule. Une seconde approche a permis de déterminer le nombre minimal de CVMi qui sont nécessaires afin de produire un niveau d’activation qui n’est pas significativement différent des valeurs d’activation maximales pour les 16 sujets. Pour 12 muscles de l’épaule, un total de 9 CVMi sont requises afin de produire des valeurs d’activation qui sont représentatives de l’effort maximal de tous les sujets. Ce mémoire a proposé deux approches originales, dont la première a maximisé les niveaux d’activation qui peuvent être produits à partir d’un nombre fixe de CVMi tandis que la deuxième a permis d’identifier le nombre minimal de CVMi nécessaire afin de produire des niveaux d’activation qui ne sont pas significativement différentes des valeurs d’activation maximales. Ces deux approches ont permis d’émettre des recommandations concernant les CVMi nécessaires à la normalisation de l’EMG afin de réduire les risques de sous-estimer l’effort maximal d’un ensemble d’individus. / As a means to provide information on the intensity of the muscle activity, the electromyographic (EMG) signal must be expressed as a percentage of a maximum activation value. Because of the anatomical complexity of the shoulder, no single maximum voluntary isometric contraction (MVIC) has been found to maximally activate the same muscle for a group of subjects. The objective of this study is to develop a statistical approach to determine the optimal MVICs that can maximise the activation levels for several shoulder muscles. The amplitude of the EMG signal of 12 shoulder muscles was recorded as 16 subjects performed 15 MVICs in standardised positions. A first systematic approach was used to determine the optimal 4 MVICs amongst 15 that could maximise the activation levels of 12 shoulder muscles simultaneously. The activation levels produced by these 4 MVICs were significantly higher than those produced by previous recommendations. A second approach was adopted to identify the minimum number of MVICs that were required to produce muscle activation levels that did not significantly differ from the maximum activation values. For 12 shoulder muscles, 9 MVICs were necessary to produce muscle activation levels that were representative of the maximum effort of all 16 subjects. This study proposed two novel approaches, the first of which maximised the EMG activation levels that can be produced by a fixed number of MVICs while the second approach identified the minimum number of MVICs required to produce EMG activation levels that were not significantly different from the maximum values of activation. These two approaches provided guidelines with regards to the MVICs that are necessary to normalize the EMG signals of 12 shoulder muscles while reducing the risks of underestimating the maximum capacity of each individual.

La réalisation d’une action motrice implique l’activation simultanée des muscles agonistes et antagonistes contrôlés par le système nerveux central. Un traumatisme médullaire détériore la moelle épinière, entrainant une déficience motrice et des modifications du contrôle des activations musculaires. Ce travail étudie la réorganisation des activations musculaires, des activations corticales et des interactions corticomusculaires (ICM) d’un groupe traumatisé médullaire cervical (SCI) et d’un groupe contrôle (AB) lors de flexions et d'extensions isométriques autour de l’articulation du coude. En extension, nos résultats ont mis en évidence une altération des capacités de force maximale chez les SCI, associée à une augmentation des activations musculaires, une activation corticale identique aux AB et une diminution de l’implication du M1 dans le contrôle des activations musculaires. En flexion, la force développée, les activations corticales et les ICM étaient similaires chez les SCI et AB, mais les activations antagonistes et la difficulté à inhiber la contraction étaient plus importantes chez les SCI. Pour l’ensemble des participants, les ICM en flexion étaient différentes selon la fonction des groupes musculaires. Ces résultats suggèrent une altération du contrôle cortical des mécanismes inhibiteurs spinaux de la contraction musculaire après un traumatisme médullaire mais indiquent que le cortex moteur reste fonctionnel pour contrôler un acte moteur malgré l’atrophie des muscles extenseurs. Ces résultats pourraient trouver des applications cliniques pour l’élaboration de neuroprothèses nécessitant un contrôle simultané de différents groupes musculaires. / The realization of a motor action involves simultaneous activation of both agonist and antagonist muscles controlled by the central nervous system. Following spinal cord injury, damage to the spinal cord causes both a loss of motor efficiency and changes in the control of muscle activations. In the present work, we studied the reorganization of muscle activations, cortical activations and corticomuscular interactions (ICM) in spinal cord injured (SCI) and able-bodied (AB) participants during voluntary isometric contractions in flexion and extension around the elbow joint. In extension, our results showed altered capacity of maximum force production in SCI participants, associated with increased muscle activations, similar cortical activation and decreased involvement of M1 in the control of muscle activations when compared to AB participants. In flexion, the force capacities, cortical activations and ICM were similar between SCI and AB participants, but the activation of antagonistic muscles and the difficulty to inhibit the contraction were greater in SCI participants. For all participants in flexion, ICM were different depending on the function of the muscle groups. Taken together, these results suggest an alteration of the cortical control of spinal inhibitory mechanisms following a spinal cord injury, but suggest that the motor cortex remain functional to control a motor act despite the atrophy of the extensor muscles. These results could find clinical applications for the development of neuroprotheses involving simultaneous control of different muscle groups.