Accuracy of Balloons and Handheld Spirometers as Low-Cost Tools for Measuring Vital Capacity and Air Volume: A Laboratory-Based Validation Study.

INTRODUCTION

Vital capacity and air volume are key physiological substrates important for voice, speech, cough, and swallowing. The current gold standard equipment to assess vital capacity and air volume is a pneumotachograph. The aim of this study was to characterize the validity of four low-cost, clinically accessible tools as potential alternative methods to accurately assess vital capacity and air volume.

METHODS

This laboratory-based study examined the accuracy of four low-cost tools to assess vital capacity and air volume: two balloon-based circumference methods (<USD 1), one analogue spirometer (∼USD 100), and one consumer-grade digital spirometer (∼USD 150). In experiment 1, known volumes of air (ground truth) were injected into each low-cost tool using a 3-L calibration syringe. In experiment 2, the same tools were tested against gold standard pneumotachography equipment. Agreement was assessed using descriptive statistics, Lin's concordance correlation coefficient (ρc), Bland-Altman plots, and linear regression models. Concordance was interpreted as "moderate" if ρc = 0.90 to <0.95, "substantial" if ρc = 0.95 to <0.999, and "excellent" if ρc ≥ 0.999.

RESULTS

All four tools showed substantial agreement with the ground truth and gold standard measurements. Median absolute differences ranged from 0.07 to 0.29 L across tools. The digital spirometer demonstrated the highest agreement, with ρc ≥ 0.994 and the lowest absolute error. While balloon-based methods showed greater variability due to geometric deviations, accuracy improved significantly when correction factors from regression models were applied.

CONCLUSION

The findings support the use of balloon-based circumference techniques, analogue spirometry, and digital spirometry as low-cost alternatives for measuring vital capacity. Each tool demonstrated predictable error patterns that could be corrected to yield highly accurate estimates. These results may expand access to vital capacity measurement in outpatient, home health, and resource-limited settings.