Spirometric Values in Sitting, Standing and Supine Position

Background: Spirometry may be done either in sitting or standing position. The effect of sitting, standing and supine position on ventilatory functions has not been well studied in healthy subjects. Objective: The objectives of this study were to compare the spirometric values between sitting position and supine/standing position and to find magnitude of change when going from sitting to supine position. Methods: Forty five healthy subjects (30 male and 15 female) with a median age of 21 (range 19-23 years) were asked to perform spirometry in sitting upright position. They were asked to repeat the tests in the standing and supine position after adequate rest and the means of the spirometric tests in the three positions were compared using paired t-tests. Differences declared statistically significant when p-values were less than 0.05. Result: Measurements of FVC, FEV 1 and PEFR was significantly higher in the sitting position compared to standing while there was no significant change in FEF 25-75% . Around 10% of decrease in above spirometric value was found in supine position as compared to sitting position. Conclusion: Spirometry should be done in a position in which the reference values which we are using have been derived. In patients who are not able to sit in order to complete spirometry, the supine position may be preferred but the interpretation would have to be made carefully.