Introduction Forced oscillation technique has been used to demonstrate expiratory flow limitation (EFL, by measurement of DXrs,5Hz) in chronic obstructive pulmonary disease, however, this technique has not been widely used in the obese population. Obese individuals breathe at lower lung volumes and are therefore likely to develop EFL. We have previously demonstrated EFL occurs in individuals with obesity hypoventilation syndrome (OHS) but wished to determine if this also occurred in those with obstructive sleep apnoea (OSA) and compare differences between these groups.
Method Subjects with established OSA, OHS and healthy volunteers were recruited from the Lane Fox Respiratory Unit and Sleep Disorders Centre, St Thomas’ Hospital. Subjects underwent measurements of height, weight, spirometry and EFL (ResmonPro, ResTech, Milan, Italy).
Results Eleven healthy (HC), 8 OSA and 9 OHS subjects were recruited, age 23.6 ± 4.2, 31.4 ± 8.0 and 58.9 ± 10.4 years respectively. Body mass index (BMI): healthy subjects 17.9 ± 2.9; OSA group 41.4 ± 8.0; OHS group; 46.8 ± 9.3 kg/m2, there were significant differences in BMI between the HC and OSA and OHS groups (p < 0.001) but no difference between OSA and OHS. Spirometry (FEV1, FVC): HC 3.54 ± 1.15, 4.35 ± 1.47, OSA 2.55 ± 0.85, 3.27 ± 1.03 OHS 2.04 ± 0.74, 2.58 ± 0.85. In both the OSA and OHS groups DXrs increased with recumbency, as did the percentage of flow limited breaths (Table 1). Each group significantly increased their inspiratory resistance with the supine position compared to the upright seated position. There was a significant difference in DXrs between HC and OHS only in upright, 45° and supine positions (p < 0.05). There was also a difference in the percentage of EFL breaths between HC and OHS in the 45° and supine positions and between OSA and OHS in the 45° position (p < 0.05).
Conclusion Patients with obesity and sleep disordered breathing experience EFL, which was more evident in the OHS group compared to the OSA group. This may be a consequence of their higher BMI impacting their lung volumes to a greater extent. Furthermore, the impact of position was greater in the OHS group suggesting that EFL may be a contributing factor in the development of hypercapnic respiratory failure in these individuals.