Respiratory function in 105 monotonic dystrophy type 1 (DM1) patients, normal weight (body mass index [BMI] < 25 kg/m²) and overweight (BMI ≥ 25 kg/m²).

<p>Respiratory function in 105 monotonic dystrophy type 1 (DM1) patients, normal weight (body mass index [BMI] < 25 kg/m²) and overweight (BMI ≥ 25 kg/m²).</p

Pearson’s correlation coefficients for the relation between total lung capacity (TLC) and parameters of body composition and inspiratory muscle strength.

<p>Pearson’s correlation coefficients for the relation between total lung capacity (TLC) and parameters of body composition and inspiratory muscle strength.</p

Overweight Is an Independent Risk Factor for Reduced Lung Volumes in Myotonic Dystrophy Type 1

<div><p>Background</p><p>In this large observational study population of 105 myotonic dystrophy type 1 (DM1) patients, we investigate whether bodyweight is a contributor of total lung capacity (TLC) independent of the impaired inspiratory muscle strength.</p><p>Methods</p><p>Body composition was assessed using the combination of body mass index (BMI) and fat-free mass index. Pulmonary function tests and respiratory muscle strength measurements were performed on the same day. Patients were stratified into normal (BMI < 25 kg/m²) and overweight (BMI ≥ 25 kg/m²) groups. Multiple linear regression was used to find significant contributors for TLC.</p><p>Results</p><p>Overweight was present in 59% of patients, and body composition was abnormal in almost all patients. In overweight patients, TLC was significantly (<i>p</i> = 2.40×10⁻³) decreased, compared with normal-weight patients, while inspiratory muscle strength was similar in both groups. The decrease in TLC in overweight patients was mainly due to a decrease in expiratory reserve volume (ERV) further illustrated by a highly significant (<i>p</i> = 1.33×10⁻¹⁰) correlation between BMI and ERV. Multiple linear regression showed that TLC can be predicted using only BMI and the forced inspiratory volume in 1 second, as these were the only significant contributors.</p><p>Conclusions</p><p>This study shows that, in DM1 patients, overweight further reduces lung volumes, as does impaired inspiratory muscle strength. Additionally, body composition is abnormal in almost all DM1 patients.</p></div

Multiple linear regression model for predicting total lung capacity (TLC) with the significant contributors forced inspiratory volume in 1 second (FIV1) and body mass index (BMI).

<p>Patients in the model and validation set are represented by gray circles and black crosses, respectively. The x-axis denotes the TLC expressed as percentage of the predicted value for each individual and the y-axis denotes the calculated predicted TLC (% pred.), based on FIV1 and BMI.</p

Stacked-bar histogram of total lung capacity (TLC) (% of predicted) in patients with normal weight (body mass index [BMI] < 25 kg/m², n = 43) and overweight (BMI ≥ 25 kg/m², n = 62), compared with their predicted values.

<p>The black section of the stacked-bar indicates the residual volume (RV), the gray section the expiratory reserve volume (ERV) and the white section the inspiratory capacity (IC). The RV and ERV combined (black plus grey) is the functional reserve capacity (FRC). A restrictive pattern of pulmonary function is shown for both groups, and the TLC is further decreased in overweight compared with normal-weight patients, mainly due to the decreased ERV.</p

Scatter plot of fat-free mass index (FFMI) and body mass index (BMI) in DM1, n = 71.

<p>The x-axis denotes the FFMI, expressed as percentage of gender-specific cut-off points, where 100% indicates FFMI of 16 kg/m² for men and 15 kg/m² for women. The y-axis denotes the BMI, with horizontal lines at 21 and 25 kg/m². The different body compositions are defined as cachexia (BMI < 21 kg/m² and FFMI < 100%), normal weight with muscle atrophy (21 kg/m² ≤ BMI < 25 kg/m² and FFMI < 100%), normal weight with muscle atrophy (BMI ≥ 25 kg/m² and FFMI < 100%), no impairment (21 kg/m² ≤ BMI < 25 kg/m² and FFMI ≥ 100%) and overweight (BMI ≥ 25 kg/m² and FFMI ≥ 100%).</p