Glottis Closure Influences Tracheal Size Changes in Inspiratory and Expiratory CT in Patients with COPD

Rationale and Objectives

The opened or closed status of the glottis might influence tracheal size changes in inspiratory and expiratory computed tomography (CT) scans. We investigated if the glottis status makes the tracheal collapse differently correlate with lung volume difference between inspiratory and expiratory CT scans.

Materials and Methods

Forty patients with chronic obstructive pulmonary disease whose glottis was included in the acquired scanned volume for lung CT were divided into two groups: 16 patients with the glottis closed in both inspiratory and expiratory CT, and 24 patients with the glottis open in at least one CT acquisition. Lung inspiratory (Vinsp) and expiratory (Vexp) volumes were automatically computed and lung ΔV was calculated using the following formula: (Vinsp − Vexp)/Vinsp × 100. Two radiologists manually measured the anteroposterior diameter and cross-sectional area of the trachea 1 cm above the aortic arch and 1 cm above the carina. Tracheal collapse was then calculated and correlated with lung ΔV.

Results

In the 40 patients, the correlations between tracheal Δanteroposterior diameter and Δcross-sectional area at each level and lung ΔV ranged between 0.68 and 0.74 (ρ) at Spearman rank correlation test. However, in the closed glottis group, the correlations were higher for all measures at the two levels (ρ range: 0.84–0.90), whereas in the open glottis group, correlations were low and not statistically significant (ρ range: 0.29–0.34) at the upper level, and moderate at the lower level (ρ range: 0.51–0.55).

Conclusions

A closed or open glottis influences the tracheal size change in inspiratory and expiratory CT scans. With closed glottis, the tracheal collapse shows a stronger correlation with the lung volume difference between inspiratory and expiratory CT scans.

Introduction

Computed tomography (CT) is a valuable technique for imaging the tracheobronchial tree . However, its role in the analysis of tracheal collapsibility in normal or abnormal conditions, including tracheomalacia (TM) and tracheobronchomalacia, is still controversial .

Few studies analyzed the correlation between the degree of tracheal collapse and the lung volume difference betweeninspiration and expiration. Ederle et al. did not observe a relevant correlation between inspiration or expiration changes in the trachea and lung cross-sectional areas in patients with chronic obstructive pulmonary disease (COPD). On the other hand, two studies found substantial correlations between the difference of tracheal volumes and that of inspiratory and expiratory lung volumes in smokers and patients with COPD .

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Material and Methods

Subjects

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Pulmonary Function Tests

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CT Acquisition

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Measurements of Lung Volumes on CT

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Measurement of Tracheal Size

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Statistical Analysis

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Results

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Table 1

Clinical and Pulmonary Function Tests (PFT) Characteristics (Mean ± Standard Deviation) of the Patients with COPD

All Patients ( n = 40) Closed Glottis Group ( n = 16) Open Glottis Group ( n = 24) Open Glottis Group \* ( n = 21) Age (y) 70 ± 6.9 70 ± 7.8 69 ± 6.5 69 ± 6.3 BMI 26 ± 3.4 25 ± 2.9 27 ± 3.7 26 ± 3.8 Pack-years 42 ± 21.9 40 ± 40.7 44 ± 24.9 45 ± 22.9 FEV1 (% of predicted) 77 ± 25.7 78 ± 24.7 75 ± 26.9 77 ± 26.8 FVC (% of predicted) 104 ± 20.8 104 ± 24.7 104 ± 18.8 104 ± 18.2 PEF (% of predicted) 82 ± 27.9 82 ± 21.3 81 ± 31.5 81 ± 32.1 IC (% of predicted) 94 ± 19.7 95 ± 24.8 94 ± 16.0 95 ± 16.3 VC (% of predicted) 106 ± 21.9 107 ± 27.9 104 ± 17.4 107 ± 17.6 FRC (% of predicted) 121 ± 30.7 119 ± 30.5 122 ± 31.5 121 ± 30.9 RV (% of predicted) 119 ± 45.7 116 ± 49.9 121 ± 43.3 119 ± 44.6 TLC (% of predicted) 106 ± 15.9 104 ± 16.4 106 ± 15.9 107 ± 15.8 DLCO (% of predicted) 80 ± 21.5 76 ± 19.7 83 ± 22.6 84 ± 23.2

BMI, body mass index; DLCO, lung diffusing capacity for carbon monoxide; FEV1, forced expiratory volume in the first second; FRC, functional residual capacity; FVC, forced vital capacity; IC, inspiratory capacity; PEF, peak of expiratory flow; RV, residual volume; TLC, total lung capacity; VC, vital capacity.

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Table 2

Results of Bland-Altman Analysis on Intra- and Interoperator Measurements

Intraoperator Interoperator Mean Difference 95% Limits of Agreement Mean Difference 95% Limits of Agreement Aortic arch level ΔAPD 1.7% from −8.5% to 11.9% −0.4% from −7.4% to 6.6% ΔCSA 0.7% from −9.5% to 10.8% 0.8% from −7.9% to 9.6% Carina level ΔAPD 0.2% from −10.1% to 10.6% −0.8% from −12.3% to 10.7% ΔCSA −0.6% from −13.4% to 12.2% 1.3% from −11.1% to 13.7%

APD, anteroposterior diameter; CSA, cross-sectional area.

Aortic arch level, 1 cm above the aortic arch; Carina level, 1 cm above the carina.

All Kendall τ tests applied to difference, and Δvolume were not significant ( P > .05).

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Table 3

Spearman Correlation Coefficients ρ (P Value) Between Measurements of the Tracheal Collapse and ΔVolumes

All Patients ( n = 40) Closed Glottis Group ( n = 16) Open Glottis Group ( n = 24) Open Glottis Group \* ( n = 21) Aortic level ΔAPD ρ = 0.746 ( P < .001) ρ = 0.900 ( P < .001) ρ = 0.347 ( P < .1) ρ = 0.516 ( P < .02) ΔCSA ρ = 0.708 ( P < .001) ρ = 0.847 ( P < .001) ρ = −0.294 ( P < .1) ρ = 0.473 ( P < .05) Carina level ΔAPD ρ = 0.686 ( P < .001) ρ = 0.844 ( P < .001) ρ = 0.510 ( P < .02) ρ = 0.704 ( P < .001) ΔCSA ρ = 0.705 ( P < .001) ρ = 0.850 ( P < .001) ρ = 0.554 ( P < .01) ρ = 0.774 ( P < .001)

APD, anteroposterior diameter; CSA, cross-sectional area.

Aortic level, 1 cm above the aortic arch; Carina level, 1 cm above the carina.

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Discussion

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Conclusion

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References

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Glottis Closure Influences Tracheal Size Changes in Inspiratory and Expiratory CT in Patients with COPD

Rationale and Objectives

Materials and Methods

Results

Conclusions

Introduction

Material and Methods

Subjects

Pulmonary Function Tests

CT Acquisition

Measurements of Lung Volumes on CT

Measurement of Tracheal Size

Statistical Analysis

Results

Discussion

Conclusion

References

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