3D-measurement of tracheobronchial angles on inspiratory and expiratory chest CT in COPD: respiratory changes and correlation with airflow limitation

Figures & data

Table 1 Clinical characteristics and spirometric values

Patient characteristics (n=80)	Mean ± SD	Range
Sex (male:female)	(70:10)
Age (years)	73±8	(41–87)
Height (cm)	163±7	(144–177)
Weight (kg)	60±10	(31–91)
BSA (m^2)	1.65±0.15	(1.15–2.05)
Brinkman index (n=74)	1,257±642	(200–2,800)
Spirometric values (n=65)
FVC (L)	3.13±0.87	(1.37–6.32)
FEV1 (L)	1.75±0.67	(0.54–4.33)
FEV1/FVC (%)	56.5±16.0	(22.5–98.5)
FEV1 (% predicted)	66.5±20.0	(24.1–112.0)

Abbreviations: BSA, body surface area; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; SD, standard deviation.

Figure 1 A flowchart for patient selection.

Abbreviations: COPD, chronic obstructive pulmonary disease; CT, computed tomography.

Figure 2 An example of tracheobronchial angle measurements by the research software.

Notes: On the yellow-colored airway center lines, 4 points were automatically identified: trachea (red), bifurcation (black), RMB (blue) and LMB (green). The tracheal point was set 40 mm above the bifurcation point. In this case, 3D-measurements of the 3 angles formed by the 4 points were as follows: trachea–RMB, 142.9°; trachea–LMB, 137.8°; RMB–LMB, 79.4°.
Abbreviations: LMB, left main bronchus; RMB, right main bronchus.

Table 2 Tracheobronchial angles and LV measurements

CT measurement	Inspiration	Expiration	P-valuea
Angle
Trachea–RMB (°)	142.9±10.1 (106.6–170.0)	144.7±9.3 (110.7–167.0)	<0.01
Trachea–LMB (°)	141.5±6.6 (129.9–163.1)	136.6±7.4 (117.0–157.5)	<0.0001
RMB–LMB (°)	74.4±9.7 (41.2–98.1)	77.0±9.5 (45.8–100.8)	<0.0001
LV
Whole lung (L)	5.1±1.1 (2.7–7.9)	3.1±0.7 (1.6–6.2)	<0.0001
Right lung (L)	2.7±0.6 (1.6–4.2)	1.7±0.4 (1.0–3.4)	<0.0001
Left lung (L)	2.3±0.6 (1.1–3.7)	1.4±0.4 (0.6–3.1)	<0.0001

Note:

a Comparisons between inspiratory and expiratory values were made using the Wilcoxon matched-pairs test.

Abbreviations: CT, computed tomography; LMB, left main bronchus; LV, lung volume; RMB, right main bronchus.

Figure 3 Reconstructed coronal CT images of a 72-year-old male smoker with mild COPD (FEV₁/FVC=66%, LAV%=13%).

Notes: At expiration (right), the diaphragm moves upward and the tracheobronchial angles change from those at inspiration (left). Angle measurements were as follows: trachea–RMB, 144.8° (inspiration), 140.7° (expiration); trachea–LMB, 143.9° (inspiration), 129.2° (expiration); RMB–LMB, 71.2° (inspiration), 83.0° (expiration).
Abbreviations: COPD, chronic obstructive pulmonary disease; CT, computed tomography; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LAV, low attenuation volume; LMB, left main bronchus; RMB, right main bronchus.

Table 3 Correlations between tracheobronchial angles and LV measurements

Angle measurement	LV/BSA
	Whole lung	Right lung	Left lung
Inspiration
Angle
Trachea–RMB	0.09 (NS)	0.05 (NS)	0.11 (NS)
Trachea–LMB	0.25 (P<0.05)	0.28 (P<0.05)	0.21 (NS)
RMB–LMB	−0.26 (P<0.05)	−0.22 (P<0.05)	−0.26 (P<0.05)
Expiration
Angle
Trachea–RMB	−0.06 (NS)	−0.07 (NS)	−0.04 (NS)
Trachea–LMB	0.60 (P<0.0001)	0.57 (P<0.0001)	0.61 (P<0.0001)
RMB–LMB	−0.33 (P<0.01)	−0.29 (P<0.01)	−0.37 (P<0.001)

Abbreviations: BSA, body surface area; LMB, left main bronchus; LV, lung volume; NS, not significant; RMB, right main bronchus.

Table 4 Correlations between tracheobronchial angles and COPD indices

Angle measurement	Spirometry		Emphysema index
	FEV1/FVC (n=65)	FEV1 (%predicted) (n=65)	LAV% (whole lung) (n=80)
Inspiration
Angle
Trachea–RMB	−0.24 (NS)	−0.25 (P<0.05)	0.10 (NS)
Trachea–LMB	−0.14 (NS)	−0.12 (NS)	0.18 (NS)
RMB–LMB	0.42 (P<0.001)	0.39 (P<0.001)	−0.29 (P<0.05)
Expiration
Angle
Trachea–RMB	−0.16 (NS)	−0.2 (NS)	0.11 (NS)
Trachea–LMB	−0.38 (P<0.01)	−0.38 (P<0.01)	0.34 (P<0.01)
RMB–LMB	0.38 (P<0.01)	0.38 (P<0.01)	−0.27 (P<0.05)

Abbreviations: COPD, chronic obstructive pulmonary disease; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LAV%, low attenuation volume percent (<−950 HU); LMB, left main bronchus; NS, not significant; RMB, right main bronchus.

Figure 4 Correlations between tracheobronchial angles and spirometric values.

Notes: The angles formed by the right and left main bronchi (RMB–LMB) at inspiration and expiration significantly correlate with spirometric values (FEV₁/FVC).

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LMB, left main bronchus; RMB, right main bronchus.

Figure 5 Reconstructed coronal CT images of a 54-year-old male with severe COPD (FEV₁/FVC=42%, LAV%=43%).

Notes: Compared with a mild COPD patient (shown in Figure 2), lung size and location of the diaphragm are not largely changed from inspiration (left) to expiration (right), suggesting the presence of severe air-trapping and airflow limitation. Tracheobronchial angles are similar on inspiratory and expiratory images. Angle measurements: trachea–RMB, 165.9° (inspiration), 163.9° (expiration); trachea–LMB, 141.0° (inspiration), 141.5° (expiration); RMB–LMB, 50.9° (inspiration), 53.9° (expiration).
Abbreviations: COPD, chronic obstructive pulmonary disease; CT, computed tomography; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; LAV, low attenuation volume; LMB, left main bronchus; RMB, right main bronchus.