Search

Background Sensorimotor control of axial segments, which develops during childhood and is not mature until adolescence, is essential for the development of balance control during motor activities. Children with cerebral palsy (CP) have deficits in postural control when standing or walking, including less stabilization of the head and trunk which could affect postural control. Research question Is dynamic stabilization of axial segments during an unstable sitting task deficient in children with CP compared to typically developing children? Is this deficit correlated with the deficit of postural control during standing? Method Seventeen children with CP (GMFCS I-II) and 17 typically-developing children from 6 to 12 years old were rated on the Trunk Control Measurement Scale (TCMS). In addition, posturography was evaluated in participants while they maintained their balance in stable sitting, unstable sitting, and quiet standing, under “eyes open” and “eyes closed” conditions. In sitting tasks, the participants had to remain stable while being prevented from using the lower and upper limbs (i.e. to ensure the involvement of axial segments alone). Results Children with CP compared to TD children had significantly larger surface area, mean velocity and RMS values of CoP displacements measured during the unstable sitting task and the standing task, under both “eyes open” and “eyes closed” conditions. No significant group effects were observed during the stable sitting task. The TCMS total score was significantly lower, indicating trunk postural deficit, in the CP group than in the TD group and was significantly correlated with postural variables in the sitting and standing tasks. Significance Children with CP indeed have a specific impairment in the postural control of axial segments. Since the postural control of axial segments is important for standing and walking, its impairment should be taken into account in rehabilitation programs for children with CP.

Equinus and toe walking are common locomotor disorders in children with cerebral palsy (CP) walking barefoot or with normal shoes. We hypothesized that, regardless of the type of footwear, the plantar flexors do not cause early equinus upon initial foot contact but decelerate ankle dorsiflexion during weight acceptance (WA). This latter action promoted by early flat-foot contact is hypothesized to be functional. Hence, we performed an instrumented gait analysis of 12 children with CP (Gross Motor Function Classification System class: I or II; mean age: 7.2 yr) and 11 age-matched typically developing children. The participants walked either barefoot, with unmodified footwear (4° positive-heel shoes), or with 10° negative-heel shoes (NHSs). In both groups, wearing NHSs was associated with greater ankle dorsiflexion upon initial foot contact, and greater tibialis anterior activity (but no difference in soleus activity) during the swing phase. However, the footwear condition did not influence the direction and amplitude of the first ankle movement during WA and the associated peak negative ankle power. Regardless of the footwear condition, the CP group displayed 1) early flattening of the foot and ample dorsiflexion (decelerated by the plantar flexors) during WA and 2) low tibialis anterior and soleus activities during the second half of the swing phase (contributing to passive equinus upon foot strike). In children with CP, the early action of plantar flexors (which typically decelerate the forward progression of the center of mass) may be a compensatory mechanism that contributes to the WA's role in controlling balance during gait.NEW & NOTEWORTHY Adaptation to walking in negative-heel shoes was similar in typically developing children and children with cerebral palsy: it featured ankle dorsiflexion upon initial contact, even though (in the latter group) the soleus was always spastic in a clinical examination. Hence, in children with cerebral palsy, the early deceleration of ankle dorsiflexion by the plantar flexors (promoted by early flattening of the foot, and regardless of the type of footwear) may have a functional role.

Summary Background Singers are unique musicians because they use their whole body as a musical instrument. Posture and proprioception are key components for a robust and healthy voice. Objective This study aimed to analyze the postural control of lyric singers in different sensorimotor conditions. Methods Seventeen lyric singers were compared to a control group of 12 participants in static postural control test in eyes open (C1) and eyes closed (C2) conditions. Postural control of singers was also assessed in four specific singing conditions: singing posture eyes open (C3) and eyes closed (C4), vocalization (C5) and free aria (C6), low values being representative of good postural control. Singers also completed the Singing Voice Handicap Index (SVHI) French version, low scores reflecting a good SVHI result. Results No significant difference was observed between the two groups in C1 and C2. Postural control of singers was more accurate in C3 than in C1. Increased values in all postural parameters were seen in the singing conditions. Scores obtained at the SVHI were correlated to the area covered by the center of foot pressure in C5, low scores at the SVHI being correlated with low area values in this postural condition. Conclusions Singing is a multitask situation which involves several movements including breathing, and management of factors such as stress. This can affect balance and so rigorous work on posture and proprioception is required as soon as a singer begins to perform in order to take care of the voice.

Postural control continues to develop during middle childhood as shown by the decrease in body sway in stance between the ages of 5 and 11. Although head and trunk control is crucial for balance control during both static and dynamic activities, evaluating its specific development and its contribution to overall postural control is methodologically challenging. Here, we used an unstable sitting device adapted to ensure that only the axial segments could control the balance of the device and thus the balance of the upper body. This study aimed to assess the development of the postural stabilization of axial body segments during middle childhood. Thirty-six children (in three age groups: 6-7yo, 8-9yo, and 10-11yo) and 11 adults sat on the unstable sitting device and had to stabilize their axial segments under several conditions: a moderate vs. high level of balance challenge, and eyes open vs. eyes closed. Upper-body postural sway (area, mean velocity and root mean square (RMS) of the center of pressure (CoP) displacement) decreased progressively with age (6-7yo > 8-9yo > 10-11yo > adults), and this effect was accentuated when the balance challenge was high (for CoP area) or in the “eyes closed” condition (for CoP area and RMS). The stabilization strategies were assessed by anchoring indexes computed from three-dimensional kinematics. A progressive shift was showed, from an “en bloc” pattern at 6–7 years of age toward a more articulated (i.e. adult-like) pattern at 10–11. A head-on-space stabilization strategy first emerged at the age of 8–9. Middle childhood is an important period for the development of axial segment stabilization, which continues to mature until adulthood. This development might be related to the introduction and progressive mastery of feedforward sensorimotor processes and might contribute strongly to the development of overall postural control.

International audience; We reviewed neural control and biomechanical description of gait in both non-disabled and post-stroke subjects. In addition, we reviewed most of the gait rehabilitation strategies currently in use or in development and observed their principles in relation to recent pathophysiology of post-stroke gait. In both non-disabled and post-stroke subjects, motor control is organized on a task-oriented basis using a common set of a few muscle modules to simultaneously achieve body support, balance control, and forward progression during gait. Hemiparesis following stroke is due to disruption of descending neural pathways, usually with no direct lesion of the brainstem and cerebellar structures involved in motor automatic processes. Post-stroke, improvements of motor activities including standing and locomotion are variable but are typically characterized by a common postural behaviour which involves the unaffected side more for body support and balance control, likely in response to initial muscle weakness of the affected side. Various rehabilitation strategies are regularly used or in development, targeting muscle activity, postural and gait tasks, using more or less high-technology equipment. Reduced walking speed often improves with time and with various rehabilitation strategies, but asymmetric postural behaviour during standing and walking is often reinforced, maintained, or only transitorily decreased. This asymmetric compensatory postural behaviour appears to be robust, driven by support and balance tasks maintaining the predominant use of the unaffected side over the initially impaired affected side. Based on these elements, stroke rehabilitation including affected muscle strengthening and often stretching would first need to correct the postural asymmetric pattern by exploiting postural automatic processes in various particular motor tasks secondarily beneficial to gait.

International audience; A method based on the coupling of a calixarene column used for the preconcentration of actinides to a quadrupole ICP-MS was developed for the separation of actinides and their on-line detection. First, a flow injection system was developed for aqueous U, Pu and Am on-line ICP-MS analysis. Then, chromatography parameters such as the column diameter and flow rates were optimised using the theoretical plate model. The detection limits achieved are 0.6 ng (7 μBq) for 238U, 16 pg (37 mBq) for 239Pu and 0.21 pg (27 mBq) for 241Am. The signal improvement achieved by this coupling method was discussed and compared to "dilute and shoot" analysis. Finally, this method was validated on certified reference materials of 238U, 239Pu and 241Am, at concentration levels close to the detection limits. © The Royal Society of Chemistry 2016.

Patellofemoral pain is likely due to compressive force acting on the patella related in turn to knee extension moment. The latter variable was assumed to be (i) reduced during short-distance free walking in case of patellofemoral pain syndrome and (ii) increased after therapeutic pain reduction. Peak knee extension moment at beginning of stance phase was recorded by three-dimensional gait analysis in 22 controls and in 23 patients with patellofemoral pain syndrome before and after rehabilitation of knee extensors and flexors to reduce the pain. Pain would occur mainly in stressful activities such as stair negotiation or squatting and was quantified by the anterior knee pain scale. Peak knee extension moment was significantly reduced in all the patients before treatment (n = 23) compared to controls, although no one had pain during free walking. In the 17 patients who experienced significant postrehabilitation pain reduction in their stressful activities, the peak knee extension moment was significantly reduced before treatment compared to controls and significantly increased after treatment, reaching values similar to control values. The peak knee extension moment during free walking appears to be a good kinetic variable related to a compensatory mechanism limiting or avoiding anterior knee pain and may be of interest in assessing knee dynamics alteration in patients with PFPS.

Introduction L’AVC desorganise la fonction posturale et l’equilibre affectant la verticalite et les capacites de marche. L’hemicorps sain se trouve privilegie. Posture et mouvement sont intimement associes, comme Sherrington l’evoquait « la posture suit le mouvement comme son ombre ». Comment reintegrer l’hemicorps lese au sein des strategies motrices indispensables a la deambulation ? Bobath [1] ou Brunnstrom [2] evoquent des les annees 1950 l’importance de la fonction posturale dans la structuration et l’organisation de la motricite. Elles proposent des methodes globales s’inspirant du developpement psychomoteur de l’enfant. Plus tardivement les NEM decrits par M. Le Metayer [3] chez l’enfant sont repris chez l’adulte neurologique. L’evolution, entre autre, des connaissances dans le domaine des neurosciences depuis les annees 1980 a fait evoluer la reeducation du patient hemiplegique adulte [4] . Pour autant, certains reeducateurs continuent a s’inspirer des NEM ou positions intermediaires pour leur reeducation. Cette approche therapeutique est-elle toujours d’actualite en 2016 ? Materiel, population et methode Les bases de donnees consultees relevent peu d’articles traitant la question ; pour autant, le recoupement d’informations, les echanges avec des professionnels « experts » du domaine de la neurologie ont permis de retenir 3 publications francaises de F. Laurent [5] , [6] , [7] pour, leurs conclusions et l’importance des echantillons (n = 354) et 2 articles parus en 2015 [8] , [9] . Resultats Les articles concluent a l’amelioration des capacites de marche chez le patient hemiplegique adulte apres entrainement dans des positions intermediaires [5] , [8] . Une forte correlation entre d’une part les capacites segmentaires, capacites posturales et capacites a la marche et d’autre part l’entrainement dans des positions nommees « paliers » [5] est notee. L’etude controlee randomisee de R. Cabanas-Valdes [8] incluant 80 patients met aussi en evidence l’amelioration des capacites a la marche apres realisation d’exercices de gainage dans des positions intermediaires. Conclusion ou discussion Le faible niveau de preuve, le nombre reduit d’etudes, les differences de protocole et de positions utilisees ne permettent pas de proposer aux reeducateurs des situations d’exercices types. Pour autant, les resultats ne peuvent qu’inciter les reeducateurs a s’interesser et a s’inspirer de ces travaux afin d’approfondir la question et demontrer l’interet de ces positions pour l’hemiplegique adulte, et ce, en accord avec les exigences de l’EBP.

Introduction Les enfants atteints de paralysie cerebrale (PC) presentent des difficultes de controle des segments axiaux qui pourraient expliquer certains deficits locomoteurs tels que le freinage excessif lors l’appui initial. Tandis que les interventions therapeutiques classiques se centrent majoritairement sur les membres inferieurs, cette etude visait a determiner si l’amelioration du controle du tronc des enfants PC, grâce a une reeducation axiale accentuee, pouvait entrainer des repercussions favorables sur le freinage initial lors de la marche. Materiel et methodes Treize enfants PC (8 ans ± 2,4), ont suivi en cross-over deux phases de reeducation de 3 mois, l’une de reeducation habituelle et l’autre ciblant davantage les segments axiaux (reeducation axiale accentuee, RAA). Avant et apres chaque phase de reeducation, ont ete realisees (1) une evaluation de la stabilisation des segments axiaux via un dispositif d’assise instable et via l’echelle Trunk Control Measurement Scale (TCMS) et (2) une analyse quantifiee de la marche. Les performances initiales des enfants PC etaient comparees a celles de 16 enfants controles (EC). Resultats Les enfants PC avaient davantage de difficultes pour stabiliser le tronc que les EC (score inferieur au TCMS et surface de deplacement du CoP superieure sur assise instable). Apres RAA, ces performances posturales etaient ameliorees et le freinage initial lors de la marche etait significativement moins important. La reeducation habituelle ne montrait pas d’effet significatif. Discussion/Conclusion Incorporer des activites challengeant les segments axiaux semble pertinent pour ameliorer le controle postural mais aussi la locomotion des enfants atteints de PC.

Hip dynamics in the intact limb during the beginning of stance phase in unilateral trans-tibial amputees (TTA) was studied to evaluate its contribution to compensatory function. We hypothesized (1) an increase in hip total work during H1 power phase (0-30% of gait cycle) including an initial negative phase and (2) an intensification of the hip work in response to uncomfortable gait induced by prosthesis misalignment. Three-dimensional gait analysis was conducted in 17 unilateral TTA and 15 healthy subjects walking at the same self-selected speed in three prosthetic alignments: initial alignment (IA); IA altered either by 6 degrees of internal rotation (IR) or by 6 degrees of external rotation. Patients reported best comfort of gait in IA condition and discomfort mainly in IR condition. During the H1 power phase, in intact limbs a consistent initial flexion movement of the hip (0-8% gait cycle) was associated to negative work and was followed by hip extension and positive work whereas in both prosthetic and control limbs only hip extension and positive work occurred (except in one healthy individual). Absolute value of hip work during H1 phase was significantly higher in intact and prosthetic limbs compared to control limbs in IA condition and was further significantly increased in IR condition only in intact limbs demonstrating a compensatory function of the latter. In intact limbs, early hip negative work contributed to energy absorption in addition to the knee joint probably to compensate the lower energy absorption exerted by the prosthetic limbs.

Resume Objectifs Exposer la place de l'exploration situationnelle de l'activite locomotrice et l'interet des methodes d'analyse ambulatoire. Decrire les capteurs, les variables mesurees, les systemes de monitorage a disposition. Materiel et methode Revue de la litterature et experience personnelle. Pour chaque methode et technique d'exploration ambulatoire, les principes, les objectifs et les limites sont decrits. Resultats Les monitorages d'activites d'origine accelerometriques tendent a s'imposer compte tenu de la richesse des informations contenues dans la variable « acceleration », de leur fiabilite et des applications aujourd'hui developpees. Leur pertinence clinique est accrue lorsque les resultats sont associes a un monitorage d'effort (frequence cardiaque). Les podometres et actimetres, d'utilisation plus simple, peuvent apporter des reponses quantifiees et resultantes de l'activite locomotrice. Leur choix et leur modalite d'utilisation doivent etre adaptes au probleme prealablement defini avec precision. Conclusion Les monitorages d'activite et de longue duree constituent un progres considerable en parfaite coherence avec la medecine physique et de readaptation : mesurant la performance ils sont les temoins de l'activite et de la participation. La connaissance simultanee des conditions environnementales de l'activite en ameliorerait l'interpretation.

Degenerative osteoarthritis in subtalar and midtarsal joints occurring after tibiotalar arthrodesis may be related to biomechanical factors. For patients with tibiotalar arthrodesis walking with their everyday shoes, the ground reaction force is posterior at heel-off and the maximal foot-tibia dorsiflexion is at its upper limit. We hypothesized that increasing the instep of the shoes would improve these abnormalities. Three-dimensional gait analysis was done in nine patients with ankle arthrodesis fused in the neutral position and for 10 control subjects. Four conditions of walking were tested: barefoot, wearing everyday shoes, wearing everyday shoes with the instep increased by 1 cm, and wearing everyday shoes with the instep increased by 2 cm. In the arthrodesis group, the two modified delayed heel-off shoe conditions shifted the ground reaction force closer to the metatarsal heads at heel-off to a normal range, and reduced the maximal foot and tibia dorsiflexion angle. Based on these results, patients with a tibiotalar arthrodesis in the neutral sagittal position may be advised to choose shoes with an instep of approximately 25 mm.

Resume Introduction. – Les resultats fonctionnels des reimplantations apres amputation traumatique de main sont consideres comme bons en depit des frequents troubles de mobilite des doigts longs et des troubles de la sensibilite quasi constants. Objectifs. – Evaluer la recuperation et les compensations mises en œuvre a l’origine des performances de la prehension. Materiel et methodes. – Etude prospective de huit sujets masculins droitiers amputes distaux du membre superieur gauche reimplante depuis plus de deux ans. Groupe temoin de huit sujets apparies selon l’âge, le sexe, la lateralite. Evaluation des recuperations sensitive (monofilaments), motrice (TAM) et fonctionnelle (Box and Blocks test et 400 points) et de la reinsertion socioprofessionnelle. Evaluation cinematique par systeme opto-electronique et cube dynamometrique : sequences temporelles de la prehension lors d’une tâche de saisie–transport, deplacements du tronc et des membres (bras, avant-bras, main). Etudes des correlations entre les resultats fournis par les epreuves cliniques et fonctionnelles et les donnees cinematiques. Resultats. – La replantation se caracterise par une recuperation remarquable de la duree absolue et relative des differentes phases decrites lors de la prehension physiologique. Seule la phase de saisie est significativement allongee chez les reimplantes en rapport avec les difficultes motrices et sensitives residuelles comme en temoignent les correlations avec les tests cliniques. La dependance au controle visuel est accrue, probablement en raison des troubles sensitifs superficiels et profonds. Les compensations portent sur une deviation globale de l’ensemble du membre superieur reimplante, semblant a rapporter principalement a une deviation du tronc dans le plan lateral. Conclusion. – Le patient ampute et reimplante de main developpe une strategie de deplacement homogene du tronc et de la ceinture scapulaire de facon a compenser le raccourcissement et la reduction de la mobilite active de la main. Cette amplification d’une strategie observee chez le sujet sain aboutit a une compensation efficace, respectant les caracteristiques des phases de la prehension normale.

Introduction L’indice d’ancrage (IA), proposee par Assaiante et Amblard (1993), permet d’identifier les differentes strategies de stabilisation segmentaire adoptee par l’enfant pendant la marche selon son developpement moteur. A notre connaissance, aucune etude n’a analyse les IA pendant la marche d’enfants atteints de paralysie cerebrale (PC) qui presentent pourtant des retards de developpement au niveau des synergies durant la posture debout statique (Woollacott et al., 1998). Materiel et methodes Les IA de la tete et du tronc ont ete calcules sur 9 cycles de marche a vitesse spontanee pour 59 enfants PC separes en 3 groupes : atteinte bilaterale symetrique (ABS) ( n = 25 ; 11,6 ± 3,2 ans), atteinte bilaterale asymetrique (ABA) ( n = 18 ; 11,5 ± 2,8 ans) ou atteinte unilaterale (AU) ( n = 16 ; 11,1 ± 2,9 ans). Resultats Le resultat le plus remarquable etait l’IA negatif de la tete dans le plan frontal pour les enfants du groupe ABS, differant significativement des indices positifs releves pour les deux autres groupes. La tete se comporte donc en bloc avec le thorax dans le plan frontal lors d’une ABS. En revanche, pour tous les groupes, le thorax n’etait pas ancre sur le bassin. Discussion–conclusion La strategie en bloc de la tete avec le thorax dans le plan frontal observee chez l’enfant PC seulement lors d’une ABS pose la question de son origine (retard developpemental, compensation) alors que l’enfant de developpement typique de plus de 7 ans, stabilise la tete par rapport a l’espace, dans les 3 plans de l’espace, meme lors d’une marche d’equilibre difficile. L’absence d’ancrage du thorax sur le bassin chez les enfants PC pourrait en partie etre imputee a la marche en Trendelenburg frequemment observee chez ces patients.

Introduction Le controle de la posture et de l’equilibre en station debout implique les afferences visuelles, vestibulaires, proprioceptives et exteroceptives. Le role de la position des yeux dans la posture chez des personnes ayant des troubles orthopediques du tronc et/ou des membres inferieurs est etudie. Materiel et methodes Lors d’une consultation medicale pour troubles orthopediques, des patients etaient selectionnes sur une periode continue. Une stabilometrie debout avec le placement des pieds a 15° d’ouverture sur plateforme de force a 4 quadrants etait realisee (51 s) en fixant le regard droit devant soi et la repartition des appuis droit et gauche etait mesuree. Sur des photographies de face, l’alignement vertical des pupilles par rapport au centre de la ligne intermalleolaire et aux centres des articulations tibiotarsiennes ainsi que l’inclinaison de la ligne biscapulaire par rapport a l’horizontale etaient analyses. Resultats Parmi les 99 patients etudies (62 scolioses 7 attitudes scoliotiques), le centre intermalleolaire etait aligne verticalement avec l’œil droit (n = 57) ou l’œil gauche (n = 42) et les appuis bipodaux etaient symetriques pour ces 2 groupes. Lors de l’alignement du centre intermalleolaire avec l’œil droit, l’œil gauche s’alignait par rapport a la tibiotarsienne gauche pour 88 % des cas associes a une inclinaison biscapulaire moyenne marquee. Lors de l’alignement du centre intermalleolaire avec l’œil gauche, l’œil droit s’alignait par rapport a la tibiotarsienne droite dans 79 % des cas associes a une inclinaison biscapulaire moyenne moderee. Discussion–conclusion De facon remarquable, le centre intermalleolaire s’aligne constamment verticalement avec un œil, avec un alignement frequent du 2e œil avec le centre de l’articulation tibiotarsienne homolaterale, chez des personnes ayant des troubles orthopediques touchant le tronc et/ou les membres inferieurs. Cette asymetrie posturale est cependant associee a une symetrie des appuis bipodaux. Le choix d’un œil directeur pour organiser la posture est discute.

Introduction Lors de la marche spontanee, la retraction des ischio-jambiers est un facteur de flexion excessive du genou lors du contact initial (CI) chez l’enfant ayant une paralysie cerebrale (PC). En effet, la longueur des ischio-jambiers est maximale au CI quand la difference entre la flexion de hanche et la flexion de genou (DFH-FG) est maximale. Nous avons teste si la marche a grands pas peut augmenter la DFH-FG chez l’enfant PC et l’enfant sain. Materiel et methodes Chez 47 enfants PC (GMFCS I et II, diplegiques (n = 34) et hemiplegiques (n = 13), 12 ± 3 ans) et 10 enfants sains (9 ± 1 ans), l’angle poplite a vitesses lente et rapide etait mesure pour estimer la retraction et la spasticite des ischio-jambiers. Une analyse 3D de la marche spontanee et a grands pas etait realisee pour evaluer entre les 2 conditions la variation de longueur des pas et la variation de DFH-FG (ΔDFH-FG). Resultats Deux sous-groupes d’enfants PC etaient clairement observes, ceux avec ΔDFH-FG Discussion–conclusion Alors que les angles poplites etaient comparables entre les 2 sous-groupes d’enfants PC, la marche a grands pas a permis de distinguer les enfants PC capables d’allonger les ischio-jambiers. Cette condition de marche apparait utile pour orienter une decision therapeutique pour les ischio-jambiers.

Objective Postural control and standing balance involve visual, vestibular, proprioceptive and exteroceptive afferents. The role of the position of the eyes in posture in people with orthopedic disorders of the trunk and/or lower limbs is studied in correlation with the podal supports. Material/patients and methods In a medical consultation for orthopedic disorders, patients were selected over a continuous period. A standing stabilometry (platform of force with 4 quadrants-51sec-feet at 15°), performed by fixing the right gaze in front measures the distribution of the supports right/left. In frontal photographs, the vertical alignment of the pupils with the center of the intermalleolar line, the centers of the tibiotarsal joints and the inclination of the biscapular line with the horizontal line were analyzed. Results Of the 99 patients studied (62 scoliosis 7 scoliotic attitudes), the intemalleolar center was aligned vertically with the right eye ( n = 57) or the left eye ( n = 42). The bipodal supports were symmetrical for these two groups. When the right eye was vertically aligned with the intermalleolar center, the left eye was aligned with the left tibiotarsus for 88% of cases with a marked biscapular inclination. When the left eye was aligned with the intermalleolar center, the right eye was aligned with the right tibiotarsus in 79% of cases with a moderate average biscapular inclination. Discussion, conclusion Remarkably, the intermalleolar center constantly aligns vertically with one eye, with a frequent alignment of the second eye with the center of the homolateral tibiotarsal joint, in people with orthopedic disorders affecting the trunk and/or the lower limbs. This postural asymmetry, however, is associated with symmetric loading on feet. Why does the subject not detect this postural shift centered on an eye as fixed point? The role of the action of the eye in this configuration with permanent shift action on the body is source of distance stresses, pain and deformations (Wolf and Delpech's laws and soft tissue adaptation-retraction). The choice of a director's eye organizing the posture is discussed. This might explain correlations between the alignment of the second eye on the left and scoliosis in women.

The aim of the study was to describe the pattern of respiratory oscillation mechanics and responses to positive end-expiratory pressure (PEEP) in bronchiolitis. Six infants were studied during the course of mechanical ventilation. A 20 Hz sinusoidal pressure variation was applied at the endotracheal tube where flow was measured with a pneumotachograph. Resistance and reactance obtained from the complex pressure-flow ratio were separated during inspiration (R(rs,i); X(rs,i)) and expiration (R(rs,e); X(rs,e)), and the differences between R(rs,i) and R(rs,e) (deltaR(rs)) and X(rs,i) and X(rs,e) (deltaX(rs)) were calculated. The data were corrected for the mechanical characteristics of the endotracheal tube. The measurements were repeated while PEEP was varied between 0 and 8 hPa. Two infants were found to have normal R(rs) and near-zero X(rs) and both parameters exhibited little change within the respiratory cycle or with varying PEEP. Four infants had high R(rs) at zero PEEP. In two, R(rs,i) was markedly elevated (108.5 and 85.2 hPa.s/L, respectively), and X(rs,i) was markedly negative (-25.0 and -22.5 hPa.s/L, respectively) at zero PEEP, while deltaR(rs) and deltaX(rs) were small. R(rs,i) and the absolute value of X(rs,i) decreased with increasing PEEP. This pattern of oscillation mechanics was consistent with low lung volumes and atelectasis, being reversed by increasing PEEP. In the remaining two subjects, R(rs,i) was moderately elevated (57.8 and 53.6 hPa.s/L, respectively) and X(rs,i) moderately negative (-12.5 and -7.7 hPa.s/L, respectively) at zero PEEP. DeltaR(rs) (-59.8 and -56.5 hPa.s/L, respectively) and delta(rs) (28.1 and 48.7 hPa.s/L, respectively) were large, but were dramatically reduced by increasing PEEP. These patterns were consistent with expiratory airflow limitation. Measurements of respiratory impedance are, therefore, informative in regard to the pathophysiological mechanisms occurring in bronchiolitis during mechanical ventilation, and they may be helpful in setting the level and assessing the effect of PEEP.

The upper airways may contribute to increases in airway resistance in response to a bronchial challenge, and thus decrease the specificity of such challenge tests to diagnose airway hyperresponsiveness when forced oscillation techniques are used to evaluate changes in respiratory system resistance (Rrs). A concomitent decrease in respiratory system reactance (Xrs) may indicate a change in the intrathoracic airways and/or lung parenchyma, provided that extrathoracic airway wall motion is prevented. To test the value of Xrs in the evaluation of bronchial hyperresponsiveness, we studied the respiratory impedance response to methacholine in 38 children with a history of asthma (aged 6-14.5 years), and compared the results to changes in the forced expiratory volume in one second (FEV1). Rrs and Xrs were measured by the forced oscillation technique with pseudorandom (11 subjects) or sinusoidal (27 subjects) pressure variations applied around the child's head to minimize upper airway wall motion. Changes in Rrs and in Xrs at 12 Hz (Rrs12, Xrs 12) correlated significantly with changes in FEV1 (P or = 20% was observed in 23 subjects. When these 23 subjects were compared with the 15 children who did not show significant changes in FEV1, the responding group had larger mean +/- SEM changes in Rrs (116.0 +/- 13.2% vs 60.4 +/- 11.4%, P < 0.006) and in Xrs (-2.1 +/- 0.4 hPa.s/L vs -0.9 +/- 0.3 hPa.s/L, P < 0.03) than the nonresponders. The receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic value, i.e., specificity and sensitivity, of different levels of change in Rrs and Xrs, with reference to FEV1. The overall incidence of false results was similar for Rrs and Xrs. The optimum diagnostic value for Rrs was a 70% increase, which corresponded to a sensitivity of 87% and a specificity of 67%. For Xrs the optimum decision level was -1 hPa.s/L, corresponding to a sensitivity of 70% and a specificity of 80%. It is concluded that Xrs may improve the specificity of the forced oscillation technique in interpreting the airway response to methacholine. This may be of particular interest in young children unable to perform forced expirations.

Introduction Le controle de la posture et de l’equilibre en station debout implique les afferences visuelles, vestibulaires, proprioceptives et exteroceptives. Le role de la position des yeux dans la posture chez des personnes ayant des troubles orthopediques du tronc et/ou des membres inferieurs est etudie. Materiel et methodes Lors d’une consultation medicale pour troubles orthopediques, des patients etaient selectionnes sur une periode continue. Une stabilometrie debout avec le placement des pieds a 15° d’ouverture sur plateforme de force a 4 quadrants etait realisee (51 s) en fixant le regard droit devant soi et la repartition des appuis droit et gauche etait mesuree. Sur des photographies de face, l’alignement vertical des pupilles par rapport au centre de la ligne intermalleolaire et aux centres des articulations tibiotarsiennes ainsi que l’inclinaison de la ligne bi-scapulaire par rapport a l’horizontale etaient analyses. Resultats Parmi les 99 patients etudies (62 scolioses, 7 attitudes scoliotiques), le centre intermalleolaire etait aligne verticalement avec l’œil droit ( n = 57) ou l’œil gauche ( n = 42) et les appuis bipodaux etaient symetriques pour ces 2 groupes. Lors de l’alignement du centre intermalleolaire avec l’œil droit, l’œil gauche s’alignait par rapport a la tibiotarsienne gauche pour 88 % des cas associes a une inclinaison bi-scapulaire moyenne marquee. Lors de l’alignement du centre intermalleolaire avec l’œil gauche, l’œil droit s’alignait par rapport a la tibiotarsienne droite dans 79 % des cas associes a une inclinaison bi-scapulaire moyenne moderee. Discussion–conclusion De facon remarquable, le centre intermalleolaire s’aligne constamment verticalement avec un œil, avec un alignement frequent du 2 e œil avec le centre de l’articulation tibiotarsienne homolaterale, chez des personnes ayant des troubles orthopediques touchant le tronc et/ou les membres inferieurs. Cette asymetrie posturale est cependant associee a une symetrie des appuis bipodaux. Le choix d’un œil directeur pour organiser la posture est discute.

Introduction La deficience visuelle est un facteur predictif important de chute chez les personnes âgees et pourrait alterer le comportement postural lors d’une tâche visuelle en position debout. Quel est donc l’effet d’une acuite visuelle et d’un contraste faibles sur le mouvement de prehension et la cinetique posturale lors de la saisie d’un objet ? Materiel et methodes Trente et un jeunes adultes droitiers debout sur 2 plateformes de force devaient saisir avec leur main droite 2 cubes (un bleu a fort contraste et un jaune a faible contraste) parmi des objets distracteurs sur une table placee devant eux. Les conditions visuelles etaient normales (10/10 e ) ou modifiees grâce a une paire de lunettes simulant une acuite visuelle de 1/10 e . Les mouvements 3D de la main droite etaient analyses ainsi que la composante sagittale des forces de reaction du sol (FRSsag) et la position de leur origine (centre de pression, CP) par rapport aux pieds. Resultats La main droite mettait significativement plus de temps pour demarrer le mouvement, s’approcher du cube et toucher le cube en condition de faible acuite visuelle par rapport a celle d’acuite normale pour les 2 cubes, et, en faible acuite, pour le cube jaune par rapport au cube bleu. Au contact du cube, la position anterieure du CP ne differait pas pour les 4 conditions alors que la FRSsag etait significativement plus vers la gauche par rapport au depart dans les 4 conditions et de facon plus importante, en faible acuite, pour le cube jaune que le cube bleu. Discussion – conclusion Le temps passe pres de l’objet avant de le toucher et l’asymetrie concomitante d’appui des pieds, augmentes par une faible acuite visuelle et un faible contraste de l’objet, pourraient etre des facteurs d’instabilite posturale, potentiellement deleteres s’ils etaient mis en evidence chez la personne âgee deficiente visuelle.

Resume La reflexion ethique des equipes soignantes francaises peut etre enrichie par l'analyse des modalites de deces et de leurs causes dans un service de reanimation pediatrique. Population et methodes. — Une etude retrospective a partir d'une base de donnees informatisee et par lecture des dossiers par deux reaninecteurs pediatres, a ete menee a propos des 259 enfants decedes entre 1987 et 1993 dans un service ne recevant pas de nouveau-nes. Les modes de deces ont ete classes en trois groupes: echec de reanimation cardiopulmonaire (ER), coma depasse (CD), et deces apres decision de ⪡ ne pas reanimer ⪢ ou arret de reanimation (AR). Resultats. — La proportion de CD (38%) est restee stable au cours des sept annees; les AR ont represente 28% des deces et les ER 34%. Âge et sexe n'etaient pas differents selon le mode de deces. La principale defaillance viscerale a l'admission etait neurologique (52%) dans le groupe des AR et cardiocirculatoire (54%) dans le groupe des ER. L'existence d'une affection chronique severe (37%) ou d'une immune-suppression (19%) etait plus frequente dans le groupe AR que dans le groupe CD. Le deces etait plus tardif dans le groupe AR (mediane = 119 heures) que dans les groupes ER (10 heures) et CD (54 heures). Dix pour cent des enfans en CD ont fait l'objet d'un prelevement d'organes; 68% des CD presentaient une contre-indication medicale au prelevement et pour les 28 enfants sans contre-indication, celui-ci a ete refuse par les parents dans 61% des cas. Trente deces (12%) ont ete consideres comme surement evitables. La principale cause de deces evitables a ete une deshydratation par gastroenterite aigue (sept cas). Conclusions. — La repartition des modes de deces a ete comparable a celle de deux etudes nord-americaines alors que la frequence des AR etait plus elevee dans deux autres etudes nord-americaines mais les recrutements ont ete tres differents (presence de nouveau-nes et de nombreux enfants operes de chirurgie cardiovasculaire). De telles etudes, incluant de plus un score de gravite et une evaluation de la morbidite chez les survivants, devraient aider les equipes soignantes dans leur reflexion et leurs decisions.

Resume La consommation d'O2 et la quantite totale d'O2 consommee ont ete mesurees en continu au cours d'une epreuve eprouvante de marche en pente chez quatre sujets jeunes amputes de jambe d'origine traumatique. Le test consistait en une epreuve de 18 minutes de marche en imposant a deux reprises une pente de 12 a 15%, selon le niveau de performance du sujet. Un pied prothetique classique Sach a ete compare a une prothese Copy III. La quantite d'O2 consommee etait systematiquement plus faible avec le pied Copy III. Les differences etaient d'autant plus nettes que la consommation d'O2 etait elevee. Ces resultats suggerent la necessite d'utiliser des tests de marche relativement intense pour evaluer le benefice d'un nouveau type de prothese puis l'interet des pieds a restitution d'energie chez les sujets jeunes ayant des activites physiques regulieres.

Les techniques de reeducation et de readaptation a la marche beneficient de l’avancee des connaissances dans les domaines de la plasticite de la fonction motrice et aussi des explorations de la posture et du mouvement. L’objectif principal est d’apporter le maximum d’informations sensorimotrices necessaires au schema locomoteur et d’assurer une capacite d’adaptation de marche pour des projets dans des environnements varies. L’amelioration des performances locomotrices s’appuie sur les techniques recentes associant marche avec allegement du poids du corps, marche par mouvements induits par la contrainte, mobilites passive et active aidee motorisees. Complementairement, l’usage d’environnements divers permet de faire emerger des coordinations naturelles plus efficientes et economiques energetiquement. Les techniques d’apprentissage, essentielles en medecine de readaptation, doivent s’appliquer sur les deux agents principaux de la plasticite de la fonction motrice que sont l’activite et l’environnement. Les perspectives de realite virtuelle interactive sont particulierement interessantes en raison de la possibilite de production d’informations sensorimotrices controlees et reproductibles.

This study evaluated the asymmetry of knee kinetics during uncomfortable gait induced by prosthesis misalignment to further demonstrate the compensatory function of the knee joint of the intact limb during gait. Three-dimensional gait analysis including knee kinematics and kinetics at the beginning of stance phase was conducted in 15 healthy subjects and 17 unilateral trans-tibial amputees (TTA) walking at self-selected speed in three conditions of prosthetic alignment: initial alignment (IA); initial alignment altered either by 6 degrees of internal rotation (IR) or by 6 degrees of external rotation (ER) applied on the pylon. Patients reported best comfort of gait in IA condition and discomfort mainly in IR condition. Maximum knee flexion and knee total work at power phases K0-K2 were significantly higher in intact limbs compared to prosthetic and control limbs. In intact limbs, these variables had significantly higher values (+10-35%, p

To determine the value of ambulatory monitoring in assessing human gait. To describe the sensors, the parameters and the ambulatory devices.Literature review and practical experience about techniques, principles, objectives and limits.Accelerometry is the main technique for ambulatory monitoring because of its reliability, pertinence of signals and software developed for interpretation. Simultaneous monitoring of heart rate response is clinically relevant. Pedometers and actimeters can answer precise clinical questions about amount of walking activity.Ambulatory monitoring during long periods (one day or more) is important, especially for rehabilitation medicine because it measures the actual patient activity performed and participation. The simultaneous monitoring of environmental conditions of activity should improve the interpretation of the data collected.

Functional assessments of hand replantation after traumatic amputation are considered as good although frequent deficits of long fingers mobility and hand sensitiveness occur.To evaluate the capability of handling and the compensatory mechanisms involved in handling.Prospective study in eight right-handed males who had distal amputation of the left upper limb with hand replantation for more than two years. Eight males with paired age and handedness served as control. Skin sensitiveness (thread test), mobility (TAM), functional capability (Box and Blocks test, 400 points test) and occupational outcome were assessed. Three-dimensional analysis (opto-electronic device) of the motion of the trunk and the upper limbs (arm, forearm, hand) was made during a pointing and gripping-shifting maneuver and the time of the related phases was measured (dynamometric cube device). Correlation between clinical assessments and three-dimensional analysis were tested.Patients with replantation had a remarkable recovery of the absolute and relative times of the various phases of the handling maneuver. Only the gripping phase was significantly prolonged in patients, this result was correlated with the deficit in motor function and sensitiveness of the replanted hand. The visual control was higher because of the lack of superficial and deep sensitiveness. Compensatory mechanisms involved a lateral shift of the replanted limb segments, probably attributed to the lateral shift of the trunk.Patient with a replanted hand develops a homogenesis displacement of the trunk and the pectoral girdle to compensate the shortening and the reduction in active mobility of the hand. This compensatory mechanism, observed in a small scale in healthy too, is efficient with respect to the handling phases.

Objective. To assess the effect of internal foot progression angle (inturning) on knee dynamics in children with treated clubfeet. Design. Prospective study dividing a population of clubfeet according to the factor inturning. Background. Excessive internal or external foot progression angle increases knee flexion by a backward shift of the ground reaction force to the knee joint in children with cerebral palsy. Similarly, inturning in clubfeet was hypothesized to shift the ground reaction force backwards with reference to the knee joint, increasing the external knee flexion moment and the maximal knee flexion at stance. Methods. Three-dimensional gait analysis was performed on 20 children with surgically treated clubfeet (n=28) to assess alterations of knee dynamics related to inturning (>7°) and on 13 normal children. Results. Inturning occurred in 46% of the clubfeet and was associated during stance, at maximal knee flexion, to an increase in maximal knee flexion (+7°), external knee flexion moment (+60%) and related lever arm to the knee (+100%) and at minimal knee flexion, to a reduction in external knee extension moment (−62%) and related lever arm (−58%). Inturning was associated with a more frequent prolongation of internal knee extension moment and of rectus femoris activity exceeding 50% of stance. Conclusion. Inturning in clubfeet is associated with knee dynamics alteration, which might contribute to the long-term development of knee osteoarthritis. Relevance The therapeutic correction of inturning in clubfeet would be of importance if the consecutive knee dynamics alteration is shown by further studies to contribute to long-term degenerative knee pathology.

Foot anatomy and lower limb function were analyzed in 11 children (aged 6.5-12.5 y) 5 years after removal of one or two second toes for digital reconstruction. In addition to physical examination and x-rays, postural balance and three-dimensional measurements of gait were analyzed. Among the 15 operated feet, five had bridle scars, three had claw deformities of the third toe, five had pain in the first intermetatarsal space, and seven had overt or early-stage hallux valgus (including five after unilateral toe removal). Hallux valgus deformation was also observed in three nonoperated feet. Maintenance of balance and rate of displacement of the center of pressure when standing on one foot with eyes closed were significantly altered for operated limbs compared with nonoperated limbs. Gait was rapid because of increased step cadence. Foot progression angle and ankle and knee joint sagittal kinematics during walking were normal. Although children appeared to not be affected in their daily life by the removal of the second toe(s), related foot anatomic and functional modifications require further follow-up.

Introduction L’enfant avec paralysie cerebrale (PC) marche habituellement en posant le pied en equin avec contact au sol a plat ou par l’avant-pied. Ce comportement pourrait avoir une fonction adaptative permettant un freinage precoce de la dorsiflexion par le triceps sural plutot qu’etre impose par le dysfonctionnement de ce dernier. Dans cette hypothese, l’adaptation motrice au port de chaussures a cambrure negative de 10° (CCN) a ete etudiee. Materiel et methode Une analyse 3D de la marche (moyenne de 5 cycles) chez douze enfants avec PC (7 ± 2 ans, 8 diplegiques et 4 hemiplegiques) ayant des triceps spastiques a ete realisee (1) pieds nus et (2) avec CCN des les premiers cycles d’utilisation (CCN1) et apres 5 minutes de marche (CCN2). Resultats Le cycle de marche etait significativement raccourci en CCN1 par rapport aux conditions pieds nus et CCN2. La dorsiflexion au contact initial augmentait significativement en CCN1 (6,2° ± 5,4) et en CCN2 (4,9° ± 5,5) par rapport a la condition pieds nus (–7,3° ± 6,0). Lors du MidSwing et du TerminalSwing, l’activite integree normalisee ( % pic d’activite × % cycle de marche) du tibial anterieur etait significativement plus importante en CCN1 (332 ± 164) que pieds nus (161 ± 113) ou en CCN2 (194 ± 121) tandis que celle du soleaire ne variait pas significativement. Discussion – conclusion Aux conditions CCN1 et CCN2, la dorsiflexion au contact initial permettait une pose precoce de la chaussure a plat. Cette adaptation au port de CCN, des son debut, evoque davantage une fonction adaptative de la pose du pied en equin que la consequence d’une spasticite du triceps.

Introduction L’enfant avec paralysie cerebrale (PC) marche habituellement en posant le pied en equin. Ce comportement pourrait avoir une fonction adaptative permettant la pose rapide du pied a plat pour un freinage precoce de la dorsiflexion par le triceps sural. Dans cette hypothese, l’adaptation motrice a l’utilisation de chaussures standards a cambrure positive de 4° (CCP) et de chaussures a cambrure negative de 10° (CCN) a ete etudiee. Materiel et methode Douze enfants avec PC (7 ± 2 ans, 8 diplegiques et 4 hemiplegiques), ayant des triceps spastiques et une marche autonome, ont ete observes pieds nus, avec CCN et avec CCP, ainsi que 10 temoins (7 ± 1 ans) marchant pieds nus, a l’aide d’une analyse 3D de la marche. Resultats La dorsiflexion au contact initial etait plus importante avec CCN (4,9° ± 5,5), que pieds nus (–7,3° ± 6,0) ou avec CCP (–4,0° ± 7,0), et similaire aux temoins (3,8° ± 3,7). Lors du MidSwing et du TerminalSwing, l’activite integree normalisee ( % pic d’activite × % cycle de marche) du tibial anterieur etait plus importante avec CCN (194 ± 121) qu’avec CCP (62 ± 47), et plus faible dans ces conditions et pieds nus (161 ± 113) que chez les temoins (644 ± 213). L’activite integree du soleaire ne variait pas significativement. Discussion – conclusion La dorsiflexion au contact initial lors du port de CCN, permettant la pose rapide de la chaussure a plat, etait favorisee par une augmentation de l’activite du TA. L’adaptation de la cinematique du pied au type de chaussage evoque davantage une fonction adaptative de la pose du pied en equin que la consequence d’une dysfonction du triceps.

The upper airways may contribute to increases in airway resistance in response to a bronchial challenge, and thus decrease the specificity of such challenge tests to diagnose airway hyperresponsiveness when forced oscillation techniques are used to evaluate changes in respiratory system resistance (Rrs). A concomitent decrease in respiratory system reactance (Xrs) may indicate a change in the intrathoracic airways and/or lung parenchyma, provided that extrathoracic airway wall motion is prevented. To test the value of Xrs in the evaluation of bronchial hyperresponsiveness, we studied the respiratory impedance response to methacholine in 38 children with a history of asthma (aged 6-14.5 years), and compared the results to changes in the forced expiratory volume in one second (FEV1). Rrs and Xrs were measured by the forced oscillation technique with pseudorandom (11 subjects) or sinusoidal (27 subjects) pressure variations applied around the child's head to minimize upper airway wall motion. Changes in Rrs and in Xrs at 12 Hz (Rrs12, Xrs 12) correlated significantly with changes in FEV1 (P0.005). A decrease in FEV1or = 20% was observed in 23 subjects. When these 23 subjects were compared with the 15 children who did not show significant changes in FEV1, the responding group had larger mean +/- SEM changes in Rrs (116.0 +/- 13.2% vs 60.4 +/- 11.4%, P0.006) and in Xrs (-2.1 +/- 0.4 hPa.s/L vs -0.9 +/- 0.3 hPa.s/L, P0.03) than the nonresponders. The receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic value, i.e., specificity and sensitivity, of different levels of change in Rrs and Xrs, with reference to FEV1. The overall incidence of false results was similar for Rrs and Xrs. The optimum diagnostic value for Rrs was a 70% increase, which corresponded to a sensitivity of 87% and a specificity of 67%. For Xrs the optimum decision level was -1 hPa.s/L, corresponding to a sensitivity of 70% and a specificity of 80%. It is concluded that Xrs may improve the specificity of the forced oscillation technique in interpreting the airway response to methacholine. This may be of particular interest in young children unable to perform forced expirations.

There are few data available from European pediatric intensive care units (PICU) regarding the modes of death and their causes.Two hundred and fifty nine children, not including neonates, died in the PICU over a 7-year period (1987-1993). Data were obtained from a computerized data base and the retrospective review of medical records by two intensivists. Deaths were classified into three groups according to the terminal event: brain death (BD), unsuccessful resuscitation (UR), do-not-resuscitate order and limitation and/or withdrawal of therapy (LWT).BD was the most common mode of death (38%); UR accounted for 34% and LWT for 28% of deaths. There was no significant annual variation in the proportion of BD, UR and LWT. Age and sex were similar in the three groups. The predominant organ system failure involved upon admission was the central nervous system (52%) in the LWT group, and the cardiovascular system (54%) in the UR group. Severe chronic disease (37%) and immunosuppression (19%) were more prevalent in the LWT group than in the BD group. Time from admission to death was longer in the LWT group (median = 119 hours) as compared to the UR group (10 hours) and the BD group (54 hours). Ten percent of the BD patients became organ transplant donors. Sixty-seven per cent of BD patients had medical contraindication for organ donation: parents did not accept organ donation in 61% of potential cases. Thirty deaths (12%) seemed to be avoidable; dehydration from acute infectious gastroenteritis (n = 7) was the most common cause of avoidable death.The modes of death in our PICU were statistically not different from those seen in two of four North-American PICUs; LWT was less prevalent than in the two other PICUs, but the patient populations were very different (presence of neonates and many cardiovascular surgery patients). Assessment of the severity of illness at admission and of functional outcome in the survivors are mandatory in future studies.

Cytology and the rapid urease test on gastric biopsies may diagnose Helicobacter pylori (H. pylori) infection within an hour. We evaluated the sensitivity and reproducibility of touch cytology (imprints from biopsies). In 19 patients with duodenal ulcer, biopsies were obtained from the antrum, fundus, and bulb. H. pylori was diagnosed in 42 sites on smears: 28 by culture and 23 by histology. H. pylori was present in the antrum and fundus in 16 and in the bulb in 11. Assessment of paired antral biopsies in 29 additional patients with or without touch cytology (imprints) before specimens were sent for histology or culture revealed no difference for the presence of H. pylori. A second reading of the 58 smears by a second observer revealed agreement on the presence or absence of H. pylori in 53 (91%). In conclusion, touch cytology is a simple rapid, sensitive, and reproducible diagnostic method for H. pylori that does not alter the quality of biopsies for subsequent culture or histologic examination. For the first time, diagnostic methods have been compared on the same biopsies, eliminating sampling variation.