Effect of body posture on spirometric values and upper airway obstruction indices derived from the flow-volume loop in young nonobese subjects

Study objective: To define the effect of changes in body posture on flow-volume loops (FVLs) and four commonly used indices of upper airway obstruction (UAO) in young, nonobese normal subjects. Design: Prospective comparative study, Setting: Pulmonary function laboratory at an academic hospital. Participants: Thirty-one normal volunteers. Intervention: At least three FVLs per posture were obtained in the sifting, supine, and left and right lateral recumbent postures while maintaining a constant position of the head and neck in relation to the trunk. In each body posture, the largest observed flow rates were used to calculate the UAO indices. Results: When subjects changed from the sitting to each of the three recumbent postures, all spirometric values decreased significantly (p<0.0001). However, among the four UAO indices, only the FEV1/peak expiratory flow ratio increased significantly (although only slightly, by 2.9 and 4.4%, respectively) in both the right and left lateral recumbent postures (p<0.0001), but not in the supine posture. None of the subjects developed an inspiratory or expiratory plateau on the FVL in any of the three recumbent postures. Conclusions: In young, nonobese normal subjects, recumbency does not induce UAO, at least not delectable by changes in the FVL configuration or in UAO indices derived from the FVL. Furthermore, the study provides the upper limits of recumbency-related changes in the various UAO indices for young, nonobese normal subjects.