[Methacholine challenge in young children: measurement of resistance by interruption]

The aims of this study were 1. To evaluate the measurement of resistance by interruption (Rint) of bronchoconstriction induced by inhalation of methacholine and 2. To determine a threshold of increase of resistance in young children to differentiate responders from non-responders. Forty-six children (mean age 5 [4.3-6.1] years) referred for methacholine challenge were tested by measurement of Rint and transcutaneous oxygen tension. A fall of 20% or more in oxygen tension from the baseline was used to define the responders. The children studied had a baseline Rint significantly higher than normal (0.84 [0.68-1.01] vs. 0.76 [0.60-0.90] kPa L(-1)s; p < 0.03). Forty-one children were responders and had an increase in Rint significantly different from the non-responders (p < 0/04). An increase in Rint of 35% distinguished responders from non-responders in young children with chronic cough. Interrupter resistance increases significantly during bronchial provocation in responding young children and may be used to measure the degree of bronchoconstriction.

Pressions respiratoires maximales chez l’enfant : les exigences méthodologiques

INTRODUCTION

Measurement of maximal respiratory pressures against an occlusion has been used for a long time to assess respiratory muscle strength in the follow up of children with respiratory disease. In the early stage of disease this is the main test for diagnosing respiratory muscle involvement and the degree of that involvement. STATE OF KNOWLEDGES: The interpretation of the results is difficult on account of variability of the measurements and of the reference values. The aim of this article is to present, in the form of a literature review, the normal values available and the different determining factors as well as the advantages and limitations of these measurements.

PERSPECTIVES

The use by all the centres undertaking maximal respiratory pressure measurements in children of methodological techniques similar to those presented in this revue could be the starting point for obtaining an identical range of reference values for all.

CONCLUSION

Age, sex and the level of physical aptitude seem to be the most important determinants of maximal respiratory pressures. However, other methodological factors such as co-operation, training of the child in the performance of the manoeuvres and the type of device and protocol used, will all influence the results. These factors must be taken into consideration in order to diminish, as much as possible, the variability of the maximal pressures obtained.

[Ventilatory response to maximal exercise in healthy children]

INTRODUCTION

The evaluation of the ventilatory response of children during exercise is essential to determine its role in impaired exercise tolerance. The aim of this review is to describe the variables and the values of maximal ventilatory parameters observed in healthy children in the published literature.

STATE OF ART

The maximal ventilation (VEmax) and the tidal volume (VTmax) increase in a linear fashion with age and plateau in boys at 15 years, and in girls at 13 years. The main variables for the parameters connected to volume--VEmax and VTmax--are anthropometric characteristics, in particular, the lean body mass. Most studies show a value of 30 ml.kg(-1) for a VTmax on the total body mass in pre-puberty and a slight increase thereafter. The ventilatory reserves and the VTmax on vital capacity increase with age until respective values of 30% and 50% are reached at 17 years. The maximal parameters connected to time are independent of anthropometric characteristics. The TI/TTOT ratio (inspiratory time to total time of the respiratory cycle) is stable with a value of 0.5. The maximal respiratory frequency decreases slightly with age without differences between the genders.

PERSPECTIVES AND CONCLUSION

Only studies of larger numbers of children, proposing relationships derived from allometric equations, will be able to provide real reference values.

[Maximal oxygen uptake in healthy children: factors of variation and available standards]

Aerobic physical fitness, in children, is assessed by measurement of the maximal oxygen consumption during exercise testing. Representative norms of the studied population are required for interpretation. The aim of this article is to specify and review the available VO2max norms and factors of variation, including: sex, anthropometric characteristics (height, lean body mass and weight) and physical activity level. Ideally, VO2max norms should include lean body mass and physical activity with an allometric equation. Since such norms do not exist today, interpretation remains difficult. In France, the must satisfactory norms for non trained children include body mass without an allometric equation (boys: 47 +/- 2 ml.mn.-1 kg-1, girls: 40 +/- 3 ml.mn.-1 kg-1 with a post puberty decrease). Further studies on VO2max norms that include lean body mass and a physical activity questionnaire are required to improve exercise test interpretation in children.

[Bronchiolitis in infants. Respiratory functional exploration in the acute phase]

Respiratory function tests were performed in infants hospitalized for bronchiolitis immediately after the acute stage, in order to appreciate the function of the respiratory muscles. A study of the ventilatory mechanics, of the transdiaphragmatic pressure, of the ventilatory rate and of the blood gases was performed. Results were compared with those obtained in 10 "healthy" infants. They showed: a decrease in the dynamic compliance (DYN.C) (p less than 0.001) and an increase in the total pulmonary resistances (TPR) (p less than 0.05) providing evidence for the intensity of bronchial and bronchiolar obstruction; an increase in the abdominal and intrathoracic pressures difference (Pdi) (p less than 0.01) which may reach 3 times the normal value and which is proportional to the decrease in DYN.C. (r = 0.74; p less than 0.001), providing evidence for the intensification of the inspiratory diaphragmatic effort and of its adjustment to the degree of obstruction; a reverse of the abdominal pressure curve with respect to that in normal subjects, with an increased pressure level, providing evidence for abdominal distension and increased pressure during all the expiration, suggesting the active participation of the abdominal muscle to expiration; a change in the ventilatory rate, characterized by a high respiratory frequency, a decreased tidal volume, a shortened inspiratory time and a normal inspiratory time/total time ratio. this rate is opposed to that observed in older children with bronchial obstruction. It might optimize the respiratory muscles output, as at this age, they have not yet reached all their contractile capacity.

[Oral occlusion pressure in scoliosis and neuromuscular syndromes]

Oral occlusion pressure, a neuro-muscular index of the activity of the respiratory centers, was measured in 2 groups of children: one of 43 "healthy" children, in order to establish a predictive equation according to age (Y = 1.23 + 8.30 X A-1) and another of children presenting with respiratory failure, either due to an impairment of the thoracic cavity (10 dorsal scoliosis) or to an impairment of the respiratory muscles (29 children with muscular dystrophy or spinal muscular atrophy). The occlusion pressure increases with the degree of the ventilation deficiency in children with scoliosis. It remains paradoxically normal in children with neuro-muscular disease, irrespective of the ventilation deficiency. In the latter, the respiratory centers activity being considered as normal, this situation would indicate their muscular incapacity to correctly express this activity. It would show a severe muscular deficiency with a high risk of occurrence of respiratory distress accidents.

[Alveolar microlithiasis in children. Contribution of bronchoalveolar lavage]

This case of pulmonary alveolar microlithiasis emphasizes the rarity of the disease and its exceptional diagnosis in infants which relies on the pulmonary pathologic study. Besides allowing for diagnosis, the study of the alveolar brushing fluid permitted to describe for the first time pictures of post-necrotic cellular calcification which is probably responsible for the disease.