Enhanced fatigue resistance of rat muscles with lowered contents of high-energy phosphates (1994)

Les paraplégiques ont une aptitude physique réduite en raison de leur moindre masse musculaire fonctionnelle et des moins bonnes qualités aérobies des muscles des membres supérieurs. Le niveau de l'atteinte médullaire conditionne la masse musculaire fonctionnelle ainsi que l'étendue des perturbations neurovégétatives associées. L'interruption des efférences sympathiques est responsable de troubles vasomoteurs, qui, associés à la perte de la fonction pompe des muscles des membres inférieurs est responsable d'une stase sanguine sous-lésionnelle. La diminution du retour veineux est responsable d' un moindre volume de précharge et volume d'éjection systolique, le débit cardiaque étant maintenu par cardio-accélération. La contention veineuse permet de réduire le volume de stase et done d'améliorer le remplissage cardiaque. Nous avons étudiél' effet de la contention veineuse sous-lésionnelle sur l' adaptation cardiaque à l'effort et sur la performance physique des blessés médullaires. Quatorze sujets paraplégiques et dix sujets témoins ont été évalués au cours d'un exercice maximal des bras, effectué sans contention et avec contention des membres inférieurs et de l'abdomen par pantalon antigravité. La consolation maximale d'oxygène (VO2max) des sujets valides de 24 ± 5.8mL·min−1·kg−1 sans contention, n'était pas modifiée par la contention, leur profil de fréquence cardiaque à l'effort était superposable dans les deux situations. La VO2max des blessés médullaires de 21.5 ± 6.5mL·min−1 kg−1 sans contention, était significativement améliorée par la contention, atteignant 23,8 ± 6,3 mL·min−1·kg−1 (p < 0,01). La fréquence cardiaque diminuait de façon significative aux différents paliers (p < 0,005). Les désordres cardiocirculatoires peuvent donc constituer un facteur limitant de la performance des blessés médullaires; le portd'une contention veineuse sous-lésionnelle penmet d'augmenter la réserve de débit cardiaque et d'améliorer les performances. II existe cependant une variabilité individuelle des réponses, pouvant être en rapport avec le niveau lésionnel, l'ancienneté de la paraplégie, le degré de spasticité.Paraplegics have low aerobic capacity because of the spinal cord injury. Their functional muscle mass is reduced and usually untrained. They have to use upperbody muscles for displacements and daily activities. Sympathic nervous system injury is responsible of vasomotricity disturbances in leg vessels and possibly abdominal vessels, proportionally to level injury. If cord injury level is higher than T5, then sympathic cardiac efférences may be damaged. Underbody muscles atrophy and vasomotricity disturbances contribute to phlebostasis. This stasis may decrease verrous return, preload and stroke volume (Starling). To maintain appropriate cardiac output, tachycardia is necessary, especially during exercise, Low stroke volume, all the more since it is associated with cardio-acceleration disturbances, may reduce cardiac output reserve, and so constitutes a limiting factor for adaptation to exercise. The aim of this study was to verify if use of an underlesional pressure suit may increase cardiac output reserve because of lower venous stasis, and increase performance. We studied 10 able-bodied and 14 traumatic paraplegic subjects (table I). Able-bodied subjects were 37 ± 6 years old, wellbeing, nor especially trained with upperbody muscles: there were 2 women and 8 men. Paraplegics were 27 ± 7 years old, wellbeing except paraplegia, five of them practiced sport regularly (athletism or basket for disabled), and the others just daily propelled their wheelchair; there were 5 women and 9 men. For 8 of them, cord injury levels were located below T7, between T1 and T6 for the 6 others. The age of disability varied from 6 months to 2 years for 9 of them, it was approximatively five years for 4 of them, and 20 years for one. We used a maximal triangular arm crank exercise with an electro-magnetic ergocycle Gauthier frame. After five minutes warm up, it was proceeded in one minute successive stages until maximal oxygen consumption is raised. VO2, VCO2, RER were measured by direct method with an Ergostar analyser every 30 seconds. Heart rate was registered continuosly using a cardio-frequence-meter Baumann, and ECG was observed on a Cardiovit electro-cardiograph. Each subject reached maximal exercises on diffèrent days: one without any contention, and the other one with abdomen and legs contention using an antigravity suit, inflated to 45–50 mm Hg for legs and 30–40 mm Hg for abdomen (fig 1). The able-bodied subjects V02 peak was 24 ± 5.8 mL·min−1·kg−1 without any change on pic VO2 and on cardiac frequency when pressure suit was used (figs 2.3). Results were different for paraplegics: peak VO2 was significantly higher (21.5 ± 6.5 mL·min−1·kg−1 without contention and 23.8 ± 6.3 mL·min−1·kg−1with contention), heart rate was significantly lower at all stages of exercise with antigravity suit and comfort was better during exercise and rest (figs 2. 4.5). In our study, contention contributed to increase paraplegics's performances, but responses depend also on spinal cord level, injury, age, spasticity. Therefore, testing paraplegics using an antigravity suit may be useful to determine if neurovegetative disturbances significantly modify their cardiac adaptation and capability. If gravity suit is efficient, contention tights might be prescribed, with respect to subject's legs measurements. But, because these tights are very difficult to put on, their efficiency has to be proved before, the motivation of the subject is essential too.