HSC Section 6 Nov2016 Green Book

TABLE IV. Linear Regression Results.

CT AP, mm

CT Width, mm

Variable

Estimate (SE)

P Value

Estimate (SE)

P Value

Male

3.34 (0.78)

< .0001

2.59 (0.61)

< .0001

2 0.02 (0.03)

2 0.05 (0.025) 2 0.002 (0.019)

BMI

.5040

.0389

Age

0.03 (0.02)

.2208

.9359

Estimate is the score on change in millimeters for a given variable based on the linear regression best fit line from the scatter plot. AP 5 anterior-posterior diameter; BMI 5 body mass index; SE 5 standard error; CT 5 computed tomography.

AP diameter and CT width for males of 3.34 and 2.59 mm, respectively (Table IV). We compared each anthropomorphic variable for the strongest effect by using standardized regression coeffi- cients. These were estimated from a linear regression model after the risk factors had been rescaled. Among males, the strongest predictor of CT AP diameter and air- way area was height, and for CT width it was BMI. Among females, the strongest predictor of CT AP diame- ter and airway area was BMI, and for tracheal width it was height. However, none of the variables was signifi- cant. Therefore, no further modeling was performed. Among both males and females, airway area corre- lated directly with height. Those findings are shown in Figure 3. DISCUSSION Our results support BMI to be inversely related to tracheal width on CT imaging. As shown in Figure 1, for every 1 kg/m 2 increase in BMI, the CT width decreased by 0.05 mm ( P 5 .0389). All anthropomorphic measure- ments showed a trend for decreased airway dimensions (area, AP diameter, width) with increasing BMI based on linear regression of scatter plots. This would suggest consistency with the trend we have clinically observed in smaller tracheal airway sizes in patients noted to have much larger body habitus. We speculate that this could be a secondary effect from numerous factors, one being increased pressure on the trachea due to increased adiposity in these patients. Animal studies have revealed a relationship between the natural caudal traction of the trachea by the thoracic contents and airway patency. Prior research has shown there is an influence of thoracic volumes on upper airway obstruction and compression. 11–13 Studies have shown that obese patients have problems with lower and upper airway compression due to increased weight and adiposity. 14,15 Specifically, abdominal obesity is suggested to negatively influence upper airway func- tion during sleep. 14 It is believed that increased abdomi- nal adiposity causes diaphragmatic compression of intrathoracic contents, which results in their cephalic deviation. As a result, the natural caudal traction of intrathoracic contents via the trachea is reduced and thus increases the distensibility of the airway. This is

Figures 1 and 2 provide graphical representations of the linear regression analyses. Linear regression models also yielded significant associations for gender, with males having increased size on both tracheal CT AP diameter and width measure- ments on CT imaging compared to females. After con- trolling for BMI and age, there was an increase in CT Fig. 1. Airway computed tomography (CT) width (mm) versus body mass index (BMI). The CT width on the y-axis is measured in millimeters. BMI on the x-axis is measured using weight in kilo- grams and height in meters and is calculated by dividing the sub- ject’s weight by the square of his/her height (kg/m 2 ). The white circle represents one individual male subject. The solid square represents one individual female subject. The solid line represents the linear regression analysis for all male subjects. The dotted line represents the linear regression analysis for all female subjects. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

Fig. 2. Airway area (mm 2 ) versus body mass index (BMI). The air- way area on the y-axis is measured in mm 2 . BMI on the x-axis is measured using weight in kilograms and height in meters and is calculated by dividing the subject’s weight by the square of his/ her height (kg/m 2 ). The white circle represents one individual male subject. The solid square represents one individual female subject. The solid line represents the linear regression analysis for all male subjects. The dotted line represents the linear regression analysis for all female subjects. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

Laryngoscope 125: May 2015

D’Anza et al.: BMI and Tracheal Airway Size

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