Can the single-breath helium dilution method predict lung volumes as measured by whole-body plethysmography?
OBJECTIVE
To compare TLC and RV values obtained by the single-breath helium dilution (SBHD) method with those obtained by whole-body plethysmography (WBP) in patients with normal lung function, patients with obstructive lung disease (OLD), and patients with restrictive lung disease (RLD), varying in severity, and to devise equations to estimate the SBHD results.


METHODS
This was a retrospective cross-sectional study involving 169 individuals, of whom 93 and 49 presented with OLD and RLD, respectively, the remaining 27 having normal lung function. All patients underwent spirometry and lung volume measurement by both methods.


RESULTS
TLC and RV were higher by WBP than by SBHD. The discrepancy between the methods was more pronounced in the OLD group, correlating with the severity of airflow obstruction. In the OLD group, the correlation coefficient of the comparison between the two methods was 0.57 and 0.56 for TLC and RV, respectively (p < 0.001 for both). We used regression equations, adjusted for the groups studied, in order to predict the WBP values of TLC and RV, using the corresponding SBHD values. It was possible to create regression equations to predict differences in TLC and RV between the two methods only for the OLD group. The TLC and RV equations were, respectively, ∆TLCWBP-SBHD in L = 5.264 - 0.060 × FEV1/FVC (r2 = 0.33; adjusted r2 = 0.32) and ∆RVWBP-SBHD in L = 4.862 - 0.055 × FEV1/FVC (r2 = 0.31; adjusted r2 = 0.30).


CONCLUSIONS
The correction of TLC and RV results obtained by SBHD can improve the accuracy of this method for assessing lung volumes in patients with OLD. However, additional studies are needed in order to validate these equations.
Federal University of Piauí, Parnaíba, Brazil.
Patrícia Chaves
PC
Coertjens
Federal University of Rio Grande do Sul, School of Medicine, Porto Alegre, Brazil.
Marli Maria
MM
Knorst
Federal University of the Pampa, Department of Physiotherapy, Uruguaiana, Brazil.
Anelise
A
Dumke
Federal University of Santa Maria, Santa Maria, Brazil.
Adriane Schmidt
AS
Pasqualoto
Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
João
J
Riboldi
Federal University of Rio Grande do Sul, School of Medicine, Department of Internal Medicine, Porto Alegre, Brazil.
Sérgio Saldanha Menna
SS
Barreto
D000328:Adult; D000368:Aged; D015992:Body Mass Index; D001944:Breath Tests / Q000379:methods; D003430:Cross-Sectional Studies; D005260:Female; D006371:Helium; D006801:Humans; D016014:Linear Models; D008173:Lung Diseases, Obstructive / Q000175:diagnosis* / Q000503:physiopathology; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008875:Middle Aged; D010993:Plethysmography, Whole Body; D012115:Residual Volume / Q000502:physiology; D012189:Retrospective Studies; D012720:Severity of Illness Index; D013147:Spirometry
D006371:Helium