Expiratory Airflow Limitation in Subjects With Obesity

Study Overview
=================
Brief Summary
-----------------
The purpose of this study is to investigate posture dependent small airway obstruction in subjects with obesity, and to study the capacity of FOT as a measurement tool for small airways obstruction.

Detailed Description
-----------------
Obesity is a cause of dyspnea due to mechanical impairment of pulmonary ventilation. One of the causes of this impairment is expiratory flow limitation, which is related to decreased lung volume. As a result, obesity can cause an asthma-like symptoms. Therefore, some patients with obesity are misdiagnosed as asthma-patients, and treated with asthma medication. The effects of bronchodilators on the mechanical airway obstruction in obese subjects have not been well established. Posture also has effect on lung volumes: they are decreased in supine position. Therefore, the interaction of obesity and supine posture might result in a larger decrease in lung volumes, and thereby a more increased airflow limitation. It has been suggested that both obesity and supine posture result in an obstruction of peripheral airways. Such an obstruction can be measured by spirometry, using the ratio of forced expiratory flow between 25 and 75% and vital capacity. This measure is highly variable, however. The forced oscillation technique (FOT) is a non-invasive method to measure the resistance and reactant of the respiratory system. Particularly the reactance has been shown useful in the measurement of airflow limitations. The investigators hypothesize that obesity causes a posture dependent end- expiratory airflow limitation due to a mechanical compression of lung tissue, resulting in increased resistance and reactance in the airways. Therefore, the investigators expect no protective effect of bronchodilation by salbutamol. The investigators expect that reactance measured by FOT detects differences in airflow limitation and correlates with airflow limitation as measured by spirometry.

Official Title
-----------------
Obesity and Expiratory Flow Limitation (EFL)

Conditions
-----------------
Obesity

Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria obese population: Male/female, age 25-60 BMI (body mass index) 30-40 kg/m2 Non or ex smokers with < 10 packyears Inclusion Criteria control population: Male/female, age 25-60 BMI (body mass index) 18.5-25 kg/m2 Non or ex smokers with <10 packyears Exclusion Criteria obese population: Asthma COPD (FEV1/FVC<0.70) Reversibility >9% in FEV1 (400 microgram salbutamol) Other significant neuromuscular, cardiac or lung disease Exclusion Criteria control population: Asthma COPD (FEV1/FVC<0.70) Other significant neuromuscular, cardiac or lung disease Reversibility >9% in FEV1 (400 microgram salbutamol)

Ages Eligible for Study
-----------------
Minimum Age: 25 Years
Maximum Age: 60 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
Accepts Healthy Volunteers

Study Plan
=================
How is the study designed?
-----------------

Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Obesity<br>Subjects with obesity, defined as BMI > 30, aged 25-60 | |
| Control<br>Subjects with a BMI 18,5-25, aged 25-60 | |

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The difference in mean values of FEF25-75/FVC between subjects with obesity and controls in supine position |  | 6 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The capacity of FOT as a measurement tool for small airways obstruction. The effects of posture and obesity on lung volumes, diffusion capacity, air flow limitation. The effect of bronchodilation by salbutamol on posture dependent flow limitation. |  | 6 months | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Obesity, expiratory flow limitation, EFL, posture, small airways obstruction, FOT