Measurement of total lung capacity: plethysmography versus single breath helium method after treatment with bronchodilator ; Determinação da capacidade pulmonar total: pletismografia versus método de diluição do hélio em respiração única após teste broncodilatador

OBJECTIVE: Total lung capacity (TLC) can be measured using body plethysmography,single-breath helium or RX planimetry. Body plethysmography is the goldstandard test,allowing comparison with other methods. The single breath helium method (SBHe),when used in association with CO2diffusing capacity, can estimate lung volumes inpatients with airway flow obstruction. The aim of the present study is to evaluate if TLCmeasured with SBHe after treatment with bronchodilator is similar to that obtained frombody plethysmography.MATERIALS AND METHODS: The sample included 155 adult patients submitted topulmonary function testing including lung volumes at the Pulmonary Physiology Unit,Pulmonary Department at Hospital de Clínicas de Porto Alegre. The patients were placedin two groups: one group underwent SBHe with bronchodilator, and the other group wassubmitted to SBHe without bronchodilator. Afterwards, each group was subdivided intotwo subgroups: normal patients and patients with airway obstruction.RESULTS: The TLC results obtained with the body plethysmography technique weregreater than the alternative methods for all groups. In the group without bronchodilatortreatment, there was a median difference of 934 ml (CI 95% = 657 ml – 1210 ml;P<0.001) for normal patients, and a median difference of 1679 ml (95% Cl = 1289ml –2069 ml; P<0.001) for patients with airway obstruction. While bronchodilator treatmentwas used, the median difference for normal patients with airway obstruction was 1751ml (95% Cl 1516 – 1985 ml; P<0.001).CONCLUSIONS: The results showed that treatment with bronchodilator did not makeTLC measurements similar when SBHe was compared to body plethysmography, neitherfor normal patients nor for patients with airway obstruction; this leads to the conclusionthat SBHe is not a reliable test for TLC measurements. ; OBJETIVO: A capacidade pulmonar total (CPT) pode ser medida através dapletismografia, de testes de diluição de gases e por planimetria radiográfica. Apletismografia constitui-se no padrão aúreo, ...