Dataset Information

Reference value for expiratory time constant calculated from the maximal expiratory flow-volume curve.

ABSTRACT:

Background

The expiratory time constant (RC_EXP), which is defined as the product of airway resistance and lung compliance, enable us to assess the mechanical properties of the respiratory system in mechanically ventilated patients. Although RC_EXP could also be applied to spontaneously breathing patients, little is known about RC_EXP calculated from the maximal expiratory flow-volume (MEFV) curve. The aim of our study was to determine the reference value for RC_EXP, as well as to investigate the association between RC_EXP and other respiratory function parameters, including the forced expiratory volume in 1?s (FEV₁)/ forced vital capacity (FVC) ratio, maximal mid-expiratory flow rate (MMF), maximal expiratory flow at 50 and 25% of FVC (MEF₅₀ and MEF₂₅, respectively), ratio of MEF₅₀ to MEF₂₅ (MEF₅₀/MEF₂₅).

Methods

Spirometric parameters were extracted from the records of patients aged 15?years or older who underwent pulmonary function testing as a routine preoperative examination before non-cardiac surgery at the University of Tokyo Hospital. RC_EXP was calculated in each patient from the slope of the descending limb of the MEFV curve using two points corresponding to MEF₅₀ and MEF₂₅. Airway obstruction was defined as an FEV₁/FVC and FEV₁ below the statistically lower limit of normal.

Results

We retrospectively analyzed 777 spirometry records, and 62 patients were deemed to have airway obstruction according to Japanese spirometric reference values. The cut-off value for RC_EXP was 0.601?s with an area under the receiver operating characteristic curve of 0.934 (95% confidence interval?=?0.898-0.970). RC_EXP was strongly associated with FEV₁/FVC, and was moderately associated with MMF and MEF₅₀. However, RC_EXP was less associated with MEF₂₅ and MEF₅₀/MEF₂₅.

Conclusions

Our findings suggest that an RC_EXP of longer than approximately 0.6?s can be linked to the presence of airway obstruction. Application of the concept of RC_EXP to spontaneously breathing subjects was feasible, using our simple calculation method.

SUBMITTER: Ikeda T

PROVIDER: S-EPMC6849182 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Reference value for expiratory time constant calculated from the maximal expiratory flow-volume curve.

Ikeda Takamitsu T Yamauchi Yasuhiro Y Uchida Kanji K Oba Koji K Nagase Takahide T Yamada Yoshitsugu Y

BMC pulmonary medicine 20191111 1

<h4>Background</h4>The expiratory time constant (RC<sub>EXP</sub>), which is defined as the product of airway resistance and lung compliance, enable us to assess the mechanical properties of the respiratory system in mechanically ventilated patients. Although RC<sub>EXP</sub> could also be applied to spontaneously breathing patients, little is known about RC<sub>EXP</sub> calculated from the maximal expiratory flow-volume (MEFV) curve. The aim of our study was to determine the reference value fo ...[more]

PMID: 31711456

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Project description:IntroductionWe hypothesized the expiratory time constant (?E) may be used to provide real time determinations of inspiratory plateau pressure (Pplt), respiratory system compliance (Crs), and total resistance (respiratory system resistance plus series resistance of endotracheal tube) (Rtot) of patients with respiratory failure using various modes of ventilatory support.MethodsAdults (n = 92) with acute respiratory failure were categorized into four groups depending on the mode of ventilatory support ordered by attending physicians, i.e., volume controlled-continuous mandatory ventilation (VC-CMV), volume controlled-synchronized intermittent mandatory ventilation (VC-SIMV), volume control plus (VC+), and pressure support ventilation (PSV). Positive end expiratory pressure as ordered was combined with all aforementioned modes. Pplt, determined by the traditional end inspiratory pause (EIP) method, was combined in equations to determine Crs and Rtot. Following that, the ?E method was employed, ?E was estimated from point-by-point measurements of exhaled tidal volume and flow rate, it was then combined in equations to determine Pplt, Crs, and Rtot. Both methods were compared using regression analysis.Results?E, ranging from mean values of 0.54 sec to 0.66 sec, was not significantly different among ventilatory modes. The ?E method was an excellent predictor of Pplt, Crs, and Rtot for various ventilatory modes; r2 values for the relationships of ?E and EIP methods ranged from 0.94 to 0.99 for Pplt, 0.90 to 0.99 for Crs, and 0.88 to 0.94 for Rtot (P <0.001). Bias and precision values were negligible.ConclusionsWe found the ?E method was just as good as the EIP method for determining Pplt, Crs, and Rtot for various modes of ventilatory support for patients with acute respiratory failure. It is unclear if the ?E method can be generalized to patients with chronic obstructive lung disease. ?E is determined during passive deflation of the lungs without the need for changing the ventilatory mode and disrupting a patient's breathing. The ?E method obviates the need to apply an EIP, allows for continuous and automatic surveillance of inspiratory Pplt so it can be maintained ? 30 cm H?O for lung protection and patient safety, and permits real time assessments of pulmonary mechanics.

Dataset Information

Reference value for expiratory time constant calculated from the maximal expiratory flow-volume curve.

Background

Methods

Results

Conclusions

Publications

Reference value for expiratory time constant calculated from the maximal expiratory flow-volume curve.

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