Abstract
Background: Whole-body plethysmography (WBP) is the gold standard for measuring lung volume, but its clinical application is limited as it requires expensive equipment and is not simple to use. Studies have shown that the single-breath helium dilution (SBHD) method, which is commonly used in clinical practice, significantly underestimates lung volume in patients with obstructive lung disease (OLD). By comparing the differences in lung volume measured using SBHD and WBP, we aimed to establish a correction equation for the SBHD method to determine the total lung volume in patients with OLD of different severities.Methods: From 628 patients with OLD simultaneously subjected to SBHD and WBP, 407 patients enrolled between January 2018 and November 2019 were in the training group and 221 enrolled between December 2019 and December 2020 were in the prospective verification cohort. The multiple linear regression equation was used for data in the training group to establish a correction equation for SBHD to determine the total lung volume, and this was validated in the prospective validation cohort.Results: There was a moderate positive correlation between total lung capacity (TLC) determined using the SBHD [TLC (SBHD)] and WBP methods [TLC (WBP)] (r = 0.701; P < 0.05), and the differences between TLC (SBHD) and TLC (WBP) (ΔTLC) were related to the severity of obstruction. As the severity of obstruction increased, the TLC was underestimated by the SBHD method. We established the following correction equation: TLC (adjusted SBHD) (L) = −0.669 + 0.756*TLC(SBHD)(L) – 0.047*+0.039*height (cm)–0.009*weight(kg)(r2 = 0.753 and adjusted r2 = 0.751). Next, we validated this equation in the validation cohort. With the correction equation, no statistical difference was observed between TLC (adjusted SBHD) and TLC (WBP) among the obstruction degree groups (P > 0.05).Conclusions: The SBHD method is correlated with WBP to measure the total lung volume, but the SBHD method presents limitations in determining the total lung volume in patients with obstructive lung disease. Here, we established an effective and reliable correction equation in order to accurately assess the total lung volume of patients with OLD using the SBHD method.
Highlights
The American Thoracic Society/European Respiratory Society (ATS/ERS) has proposed the following definitions of various lung disease patterns [1]: (i) obstructive lung disease is defined as the forced expiratory volume in 1 s (FEV1)/vital capacity (VC) ratio below the fifth percentile of the predicted value; (ii) restrictive lung disease is described as a reduction in the total lung capacity (TLC) below the fifth percentile of the predicted value and a normal FEV1/VC ratio; and (iii) mixed lung disease was characterized by FEV1/VC and TLC below the fifth percentile of the predicted value
We found that underestimation of TLC by the single-breath helium dilution (SBHD) method caused misjudgment of lung disease patterns
The results showed that TLC (SBHD) and TLC (WBP) were moderately positively correlated (r = 0.701; P =0.000) (Figure 2A), the correlation coefficient between TLC and FEV1%pred was r = −0.618 (P =0.000) (Figure 2B), and the correlation coefficient between TLC and FEV1/forced vital capacity (FVC) was r = −0.685 (P =0.000) (Figure 2C)
Summary
The American Thoracic Society/European Respiratory Society (ATS/ERS) has proposed the following definitions of various lung disease patterns [1]: (i) obstructive lung disease is defined as the forced expiratory volume in 1 s (FEV1)/vital capacity (VC) ratio below the fifth percentile of the predicted value; (ii) restrictive lung disease is described as a reduction in the total lung capacity (TLC) below the fifth percentile of the predicted value and a normal FEV1/VC ratio; and (iii) mixed lung disease was characterized by FEV1/VC and TLC below the fifth percentile of the predicted value. The single-breath helium dilution (SBHD) method is convenient, rapid, inexpensive, and widely used. This method assumes that the gas is evenly distributed in the lungs [4, 7,8,9], and the reliability of the test results is low in patients with a significantly uneven ventilation distribution. Studies have shown that the single-breath helium dilution (SBHD) method, which is commonly used in clinical practice, significantly underestimates lung volume in patients with obstructive lung disease (OLD). By comparing the differences in lung volume measured using SBHD and WBP, we aimed to establish a correction equation for the SBHD method to determine the total lung volume in patients with OLD of different severities
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