Measurement of total lung capacity

plethysmography versus single breath helium method after treatment with bronchodilator

Abstract

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 CO2
diffusing capacity, can estimate lung volumes in
patients with airway flow obstruction. The aim of the present study is to evaluate if TLC
measured with SBHe after treatment with bronchodilator is similar to that obtained from
body plethysmography.
MATERIALS AND METHODS: The sample included 155 adult patients submitted to
pulmonary function testing including lung volumes at the Pulmonary Physiology Unit,
Pulmonary Department at Hospital de Clínicas de Porto Alegre. The patients were placed
in two groups: one group underwent SBHe with bronchodilator, and the other group was
submitted to SBHe without bronchodilator. Afterwards, each group was subdivided into
two subgroups: normal patients and patients with airway obstruction.
RESULTS: The TLC results obtained with the body plethysmography technique were
greater than the alternative methods for all groups. In the group without bronchodilator
treatment, 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 treatment
was used, the median difference for normal patients with airway obstruction was 1751
ml (95% Cl 1516 – 1985 ml; P<0.001).
CONCLUSIONS: The results showed that treatment with bronchodilator did not make
TLC measurements similar when SBHe was compared to body plethysmography, neither
for normal patients nor for patients with airway obstruction; this leads to the conclusion
that SBHe is not a reliable test for TLC measurements.