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Purpose <p>The expiratory time constant (TC), reflecting the rate of lung emptying, has emerged as a marker of early small airway disease. Although TC is traditionally used in mechanical ventilation, several calculation methods are also applicable to spirometry. This study aimed to evaluate the feasibility of four spirometry-based approaches for determining TC and to compare their sensitivity to detect airway obstruction.</p> Methods <p>In this multicenter, cross-sectional study of 17,988 adult flow/volume curves, the TC was directly measured (TC<sub>M</sub>: time to exhale 63% of forced vital capacity), calculated as proposed by Ikeda (TC<sub>I</sub>) and Brunner (TC<sub>B</sub>), or derived using the slicing method (TC<sub>S</sub>). Stability was assessed by the 5th (lower limit of normal, LLN) and 95th (upper limit of normal, ULN) percentile ranges. Diagnostic performance to detect obstruction was quantified by the area under the receiver operating characteristic curve (AUC).</p> Results <p>All four TC methods were feasible but not interchangeable across spirometric categories. In the normal group, TC<sub>I</sub> (ULN at 0.7s) and TC<sub>B</sub> (ULN at 0.76) were most stable and had values below or at the 0.76s obstruction threshold. In the obstruction group, only TC<sub>M</sub> was most closely aligned with the obstruction cutoff (TC<sub>M</sub> LLN 0.75s). AUC analysis showed the TC<sub>M</sub> was most sensitive (AUC = 0.977) for detecting obstruction, outperforming TC<sub>I</sub> (AUC = 0.965), TC<sub>S</sub> (AUC = 0.890), and TC<sub>B</sub> (AUC = 0.822) (DeLong’s test, <i>p</i> &lt; 0.001 for all comparisons). This finding was most pronounced in younger individuals.</p> Conclusions <p>TC<sub>M</sub> demonstrated the highest overall accuracy for detecting obstruction.</p>

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Four Methods to Determine Expiratory Time Constants from Spirometry and Their Sensitivity to Detect Airway Obstruction

  • 期刊论文

  • 发表日期：

    2026年1月3日

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  • Filip Depta,
  • Andreas Hoheisel,
  • Surya P. Bhatt,
  • Vladimír Koblížek,
  • Sandeep Bodduluri,
  • Daiana Stolz,
  • Martin Zakucia,
  • Mária Drugdová,
  • Viktor Kašák,
  • Pavol Pobeha

摘要

Purpose

The expiratory time constant (TC), reflecting the rate of lung emptying, has emerged as a marker of early small airway disease. Although TC is traditionally used in mechanical ventilation, several calculation methods are also applicable to spirometry. This study aimed to evaluate the feasibility of four spirometry-based approaches for determining TC and to compare their sensitivity to detect airway obstruction.

Methods

In this multicenter, cross-sectional study of 17,988 adult flow/volume curves, the TC was directly measured (TCM: time to exhale 63% of forced vital capacity), calculated as proposed by Ikeda (TCI) and Brunner (TCB), or derived using the slicing method (TCS). Stability was assessed by the 5th (lower limit of normal, LLN) and 95th (upper limit of normal, ULN) percentile ranges. Diagnostic performance to detect obstruction was quantified by the area under the receiver operating characteristic curve (AUC).

Results

All four TC methods were feasible but not interchangeable across spirometric categories. In the normal group, TCI (ULN at 0.7s) and TCB (ULN at 0.76) were most stable and had values below or at the 0.76s obstruction threshold. In the obstruction group, only TCM was most closely aligned with the obstruction cutoff (TCM LLN 0.75s). AUC analysis showed the TCM was most sensitive (AUC = 0.977) for detecting obstruction, outperforming TCI (AUC = 0.965), TCS (AUC = 0.890), and TCB (AUC = 0.822) (DeLong’s test, p < 0.001 for all comparisons). This finding was most pronounced in younger individuals.

Conclusions

TCM demonstrated the highest overall accuracy for detecting obstruction.