Introduction:

the variability between measurements of inspiratory capacity (IC) by spirometry or plethysmography have not been completely described. The objective of this study was to describe the repeatability between the different IC maneuvers measured by slow spirometry and its reproducibility compared with body plethysmography.

Material and methods:

this is a descriptive, cross-sectional and prospective study of a sample of healthy adults who completed IC measurements by slow spirometry by two different maneuvers and by body plethysmography.

Results:

a total of 49 participants (27 men and 22 women) with a mean age of 33.2 ± 8.3 years (26 to 65 years) were included. The repeatability of the IC was ≤ 150 mL in 96% of the subjects for spirometry maneuvers while for plethysmography it was 78% of the participants. The correlation (Pearson’s r) was 0.95 between slow spirometry maneuvers and 0.87 and 0.88 compared with plethysmography. The agreement between measurements showed potential errors of up to 576 mL between spirometry and up to 936 mL with plethysmography.

Conclusions:

the IC measurement by slow spirometry reached a repeatability of 150 mL or less in 96% of the participants, while by plethysmography it was only in 78% with potential errors close to one liter compared to plethysmography. This study supports the current recommendation of repeatability of 150 mL for the IC measurement by spirometry.