Valores de referência de parâmetros espirométricos em crianças e adolescentes com diferentes índices de massa corporal

Abstract

Spirometry is held as a golden standard for the diagnosis and follow-up of patients with lung diseases. It is a technique for measuring pulmonary function largely used in studies on respiratory physiology. For analysis purposes, it is recommended the comparison of spirometric measures obtained with the reference values. However, choosing a certain reference equation may frequently result in failures and characterize or not a certain ventilatory disturbance in some subjects, due to inadequacy of the equation applied to the studied population. The nutritional state plays a fundamental role in the integrity of the respiratory system. Obesity and undernutrition may affect the thoracic wall (thorax, abdomen and respiratory muscles) leading to alterations in the pulmonary function. Thus, the reference equations to spirometry use anthropometric variables to explain the pulmonary function. Due to impossibility of measuring weight and height in some groups of patients, theanalysis of pulmonary function is affected since the existing reference equations use these anthropometric measures as explanatory variables to the pulmonary function. Given that the use of arm circumference, which reflects the nutritional state, is an alternative measure in cases in which it is not possible to obtain the weight, height and skeletal size, we decided to suggest a reference equation which used arm circumference as an explanatory variable in the reference equations for FVC and FEV1. Two final reference equations were suggested for FVC and FEV1,the first using age and arm circumference, and the other using height and weight as dependent variables, in children and adolescents with different body mass indexes (BMI). These equations were compared to those used by POLGAR & PROMADHAT, HSU et al and MALLOZI using the data collected from 122 healthy children and adolescents. The sample consisted of children and adolescents, 61 females (10.54 ± 2.26 yo) and 61 males (10.26 ± 2.26 yo), classified according to BMI into Low Weight (LWG, BMI /age Percentile < 5, n=20); Eutrophic (EG, BMI /age Percentile = 5 to < 85, n=52); Overweight (OWG, BMI/age Percentile =85 to <95, n=27) and Obese group (OG, Percentile = 95, n=23). The volunteers were non-smokers and had no respiratory disease.The spirometer VITATRACE VT 130 was used in order to obtain the spirometric measures FVC and FEV1. The anthropometric measures registered were weight, height, arm circumference and tricipital cutaneous fold. The descriptive analysis was carried out by using measures of central tendency (mean and median) and of variability (standard deviation) for all the variables considered. In order to assessthe association between spirometric performance and the anthropometric measures, the Pearsons linear correlation coefficient was applied. In order to determinate the predictive models, a combination of anthropometric measures which better explain spirometric performance was attempted. The selection of an appropriate regression model was made based on the highest coefficient of determination (R2) of the dependent variable. The varianceanalysis (ANOVA) was applied for comparing mean spirometric values among the equations. The comparison of values for FEV1 and FVC, calculated by equations suggested by the present study, with the values predicted by HSU et al, and POLGAR & PROMADHAT, showed significant differences for eutrophic and low weight children and adolescents, evidencing that these equations are of limited use when appliedto the sample of this study. The values of FVC and FEV1 predicted by MALLOZI and by equations suggested by this study did not differ from the values obtained for children with different body mass indexes. This study is in accordance with results of previous works which advocate the useof standardized equations for each population. It also presents an alternative equation which uses the arm circumference as a dependent variable, allowing for the assessment of pulmonary function, when weight and height cannot be assessed.