Tracheal collapsibility in healthy volunteers during forced expiration: assessment with multidetector CT

Abstract

Purpose: To assess forced expiratory tracheal collapsibility in healthy volunteers by using multidetector computed tomography and to compare the results with the current diagnostic criterion for tracheomalacia.

Materials and methods: An institutional review board approved this HIPAA-compliant study. After informed consent was obtained, 51 healthy volunteers (age range, 25-75 years) with normal spirometry results and no history of smoking or risk factors for tracheomalacia were prospectively studied. Volunteers were imaged with a 64-detector row scanner, with spirometric monitoring at total lung capacity and during forced exhalation, with 40 mAs, 120 kVp, and 0.625-mm detector collimation. Cross-sectional area and sagittal and coronal diameters of the trachea were measured 1 cm above the aortic arch and 1 cm above the carina. The percentage of expiratory collapse, the reduction in sagittal and coronal diameters, and the number of participants exceeding the current diagnostic criterion (>50% expiratory reduction in cross-sectional area) for tracheomalacia were calculated.

Results: The final study population included 25 men and 26 women (mean age, 50 years). The mean percentage of expiratory reduction in tracheal lumen cross-sectional area was 54.34% +/- 18.6 (standard deviation) in the upper trachea and 56.14% +/- 19.3 in the lower trachea. Forty (78%) participants exceeded the current diagnostic criterion for tracheomalacia in the upper and/or lower trachea. Decreases in cross-sectional area of the upper and lower trachea correlated well with decreases in sagittal (r = 0.807 and 0.688, respectively) and coronal (r = 0.779 and 0.751, respectively) diameters (P < .001 for each correlation).

Conclusion: Healthy volunteers demonstrate a wide range of forced expiratory tracheal collapse, frequently exceeding the current diagnostic criterion for tracheomalacia.

Figure 1:

Axial CT image in 49-year-old woman obtained at end inspiration shows electronic tracing line outlining the tracheal lumen, corresponding to a cross-sectional area of 227 mm². To enhance visibility for photographic reproduction, image is shown in a bone window setting, and tracing line has been electronically thickened.

Figure 2a:

Expiratory-1 configuration in 60-year-old woman. (a) End-inspiratory CT image of upper trachea demonstrates round shape of the trachea, with cross-sectional area of 169 mm². (b) Dynamic expiratory CT image at similar level demonstrates relative flattening of posterior membranous wall with slight anterior bowing of this structure. Cross-sectional area decreased to 46 mm², a 72.8% reduction. Note reduction in size of anteroposterior dimension of chest, resulting in visualization of anterior chest wall within the field of view.

Figure 2b:

Expiratory-1 configuration in 60-year-old woman. (a) End-inspiratory CT image of upper trachea demonstrates round shape of the trachea, with cross-sectional area of 169 mm². (b) Dynamic expiratory CT image at similar level demonstrates relative flattening of posterior membranous wall with slight anterior bowing of this structure. Cross-sectional area decreased to 46 mm², a 72.8% reduction. Note reduction in size of anteroposterior dimension of chest, resulting in visualization of anterior chest wall within the field of view.

Figure 3a:

Expiratory-2 configuration in 61-year-old woman. (a) End-inspiratory CT image of upper trachea demonstrates round shape of the trachea. Cross-sectional area measured 249 mm². (b) Dynamic expiratory CT image at similar level demonstrates moderate anterior bowing of posterior membranous wall with broad convexity anteriorly. Cross-sectional area decreased to 86 mm², a 65.5% reduction.

Figure 3b:

Expiratory-2 configuration in 61-year-old woman. (a) End-inspiratory CT image of upper trachea demonstrates round shape of the trachea. Cross-sectional area measured 249 mm². (b) Dynamic expiratory CT image at similar level demonstrates moderate anterior bowing of posterior membranous wall with broad convexity anteriorly. Cross-sectional area decreased to 86 mm², a 65.5% reduction.

Figure 4a:

Expiratory-3 configuration in 71-year-old man. (a) End-inspiratory CT image of upper trachea demonstrates oval shape of the trachea. Cross-sectional area measured 257 mm². (b) Dynamic expiratory CT image at similar level demonstrates moderate bowing of posterior membranous wall with a narrow convexity anteriorly. Cross-sectional area decreased to 170 mm², a 33.9% reduction.

Figure 4b:

Expiratory-3 configuration in 71-year-old man. (a) End-inspiratory CT image of upper trachea demonstrates oval shape of the trachea. Cross-sectional area measured 257 mm². (b) Dynamic expiratory CT image at similar level demonstrates moderate bowing of posterior membranous wall with a narrow convexity anteriorly. Cross-sectional area decreased to 170 mm², a 33.9% reduction.

Figure 5:

Graph shows comparison of normative data against current and experimental thresholds for diagnosing tracheomalacia. Expiratory collapsibility of upper and lower trachea in individual healthy volunteers and percentages of total participants exceeding the current diagnostic threshold for tracheomalacia of more than 50% (dashed line and arrow) and the experimental thresholds of more than 60%, more than 70%, and more than 80% (dotted lines) are displayed. Means for collapsibility in the upper (54.34%) and lower (56.14%) trachea are above the current diagnostic threshold. FP = false-positive finding.

Figure 6:

Relationship between inspiratory (left) and expiratory (right) shapes. Numbers on diagonal lines connecting inspiratory and expiratory shapes correspond to number of healthy volunteers who showed a particular inspiratory-to-expiratory shape transformation (eg, top diagonal green line shows that, in two participants with tracheae with a round inspiratory shape, the tracheae transformed to an expiratory-1 [Exp-1] shape). Frequency of specific shapes in the study population (n = 51) is listed beside each CT image representing shape. Exp-2 = expiratory-2, Exp-3 = expiratory-3.