Determination of functional residual capacity with 133-xenon radiospirometry. Comparison with body plethysmography and helium spirometry. Effect of body position

Abstract

This study was undertaken to estimate the accuracy of 133-xenon radiospirometry for determination of FRC in healthy subjects. Forty healthy volunteers, both smokers and non-smokers, were examined. The FRC of each subject was concurrently determined with radiospirometric, He-dilution in closed circuit, and body plethysmographic methods. The radiospirometric and He-dilution measurements were done in supine and in sitting positions, the body plethysmography on sitting subjects, only. The mean FRC measured by radiospirometry (FRC_RS) was 0.721 larger than that measured by helium spirometry (FRC_He) in sitting position (P<0.01). In supine position the FRC_RS was 0.65 I larger than the FRC_He (p<0.01). The body plethysmography gave FRC (TGV) 0.35 I larger than the FRC_He sitting (P<0.01). The FRC_He and the FRCR≥ in the sitting position were 0.48 and 0.55 I larger than in the supine position (P<0.01), respectively. Trapped air correlated significantly (P<0.01) with the difference FRC_RS-FRC_He, when sitting. The results indicate that the FRC determined radiospirometrically is significantly larger than the FRC determined with He-spirometry. The difference is systematic, suggesting that it is caused by 133-xenon dissolved in blood and accumulated in tissues of the thoracic cage and by dissimilar representation of trapped air in FRC_RS and FRC_He. With eventual correction of the systematic error, the FRC obtained as a by-product of radiospirometry may be used, e.g. for clinical purposes.

Key Words:

• age
• healthy subjects
• lung volumes
• sex