Effects of the supine position on respiratory mechanics assessed by the forced oscillation technique in chronic obstructive pulmonary disease (COPD) and normal subjects

  • Miguel Zambrano Braun

Student thesis: Master typesMaster in Biomedicine Professional focus


Chronic Obstructive Pulmonary Disease (COPD) is due to chronic inflammation of the airways and lung parenchyma leading to either chronic airway obstruction, emphysema or both. It is mostly seen in smokers or former smokers but exposition to occupational or domestic noxious gases can also be a cause. It is treatable but not curable and currently is the fourth leading cause of death worldwide. The most disabling symptom is dyspnea, occurring at exercise or even at rest in severe disease. Some patients also complain of orthopnea, the occurrence or increase of breathlessness in the supine posture. Although it is a common symptom, the cause of orthopnea in COPD remains elusive and is poorly describe in literature. This study aims to assess the changes in respiratory mechanics occurring when switching from the sitting to the supine posture. Two techniques were used: the forced oscillation technique (FOT) and spirometry. Spirometry is the most commonly used technique in the clinic to measure lung function. The FOT consists in sinusoidal soundwaves sent by a loudspeaker into the airways in order to measure the respiratory system resistance and reactance. FOT was used to measure parameters related to respiratory resistance (R5, R20 and R5-20) and reactance (ΔX5, X5, X5in, X5ex and AX) and spirometry for the assessment of mobilized lung volumes and flows. These tests were performed in both position in 20 normal subjects (control group), and 45 stable COPD subjects with variable disease severity, of whom 25 reported orthopnea. This study showed significant differences between the COPD and control groups for both FOT and spirometry parameters in both the sitting and the supine postures with more significant increase in small airways related parameters when adopting the supine position. FOT suggests the occurrence or increase in expiratory flow limitation since ΔX5 and X5ex were increased in the supine posture, particularly in the orthopneic group. Importantly, we observed a significant decrease in inspiratory capacity (IC) in COPD subjects while it increased in supine position in the control group, suggesting an increased functional residual capacity (FRC) in the COPD group as opposed to a decrease in the control group. In the COPD group, these changes were more pronounced in orthopneic patients. We also observed a correlation between changes in dyspnea and changes in AX, ΔX5, X5 and X5ex between sitting and supine. In conclusion, this study showed that the adoption of the supine position is associated with profound changes in small airway function in patients with COPD. These changes are more pronounced in orthopneic subjects and suggest that they are responsible for the occurrence or increase in expiratory flow limitation and dynamic lung hyperinflation which play a critical role in the genesis of dyspnea in COPD.
Date of Award23 Jan 2019
Original languageEnglish
Awarding Institution
  • University of Namur
SupervisorERIC MARCHAND (Supervisor)


  • Chronic Obstructive Pulmonary Disease
  • Forced Oscillation
  • Spirometry
  • Supine position
  • Orthopnea

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