A standardized method for the evaluation of respiratory muscle endurance in patients with Duchenne muscular dystrophy Stefan Matecki a, * , Nathalie Topin a , Maurice Hayot a , Franc Ëois Rivier b , Bernard Echenne b , Christian Prefaut a , Michele Ramonatxo a a Laboratoire de Physiologie des Interactions, Service Central de Physiologie Clinique, Ho Ãpital Arnaud de Villeneuve, 34295 Montpellier Cedex 5, France b Service de Neurope Âdiatrie, Ho Ãpital Saint Eloi, Montpellier, France Received 30 December 1999; received in revised form 23 June 2000; accepted 26 July 2000 Abstract The aim of the study was to develop a standardized method using controlled breathing to quantify respiratory muscle endurance in children with Duchenne muscular dystrophy (DMD) and to test its reproducibility. In 10 DMD patients, all between 10 and 14 years (mean age, 11:5 ^ 1:5 years), except for two patients of 20 and 22 years, and 10 healthy children (mean age, 12 ^ 1 years), we measured the maximal time (T lim ) that a threshold load ®xed at 35% of the individual maximal inspiratory pressure (Pi max ) could be tolerated. We asked the children to maintain their rest breathing pattern until exhaustion using visual feedback and an auditory signal. The mean T lim in the DMD children was 4:45 ^ 1:45 min and values were reproducible. All healthy children were able to obtain T lim values greater than 30 min. The respiratory muscles of DMD children are more susceptible to fatigue than those of healthy subjects. This method should be satisfactory for estimating the effect of treatment and for the speci®c training of respiratory muscles in DMD patients without signi®cant learning disability. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Respiratory muscle endurance; Duchenne muscular dystrophy; Threshold valve 1. Introduction Over the past 10 years, considerable advances have been made in understanding the physiopathological mechanisms involved in Duchenne muscular dystrophy (DMD). Never- theless, the progressive weakness of the respiratory muscles remains a major problem in the management of DMD patients. The decreasing pulmonary and chest wall compli- ance observed in neuromuscular diseases [1] increases the mechanical load sustained at each breath by the impaired respiratory muscles. This increased load leads to fatigue and eventual respiratory failure [2], which is the leading cause of death in these patients [3]. In order to prevent the decline in respiratory muscle func- tion, techniques using resistive loads have been developed to train the inspiratory muscles, with the speci®c goal being to stabilize or improve maximal inspiratory pressure (Pi max ) and respiratory muscle endurance. In all these studies, Pi max has been measured with the method established by Black and Hyatt [4], which includes reproducibility testing. Respiratory endurance has been assessed with numerous different methods [5±9]. The training studies have shown contradictory results. Some investigators have shown a bene®cial effect on endur- ance, which was evaluated by the maximal time the subject was able to sustain a predetermined percentage of the maxi- mal minute ventilation [5] or the maximal time the subject was able to sustain a high predetermined percentage of the maximal transdiaphragmatic pressure [6]. Others have eval- uated endurance by the maximal ventilation produced during a predetermined period [7] or the maximal pressure sustained by the respiratory muscles at each breath for a 10- min period [9]. These last two groups did not ®nd any endurance improvement after inspiratory muscle training. Throughout the endurance measurements, the patients in all these studies were allowed to modify freely their tidal volume (V t ) or inspiratory and expiratory times (T i , T e ), despite the ®nding that breathing pattern may in¯uence the values of respiratory muscle endurance [10,11]. More- over, in these studies the methods used to evaluate endur- ance were different from the methods used in the inspiratory training protocol [5±9]. We hypothesized that the contradictory data concerning the impact of inspiratory muscle training on respiratory Neuromuscular Disorders 11 (2001) 171±177 0960-8966/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0960-8966(00)00179-6 www.elsevier.com/locate/nmd * Corresponding author. Tel.: 133-467-335-908; fax: 133-467-335-923. E-mail address: smatecki@aol.com (S. Matecki).