Objective: Voice disorders affect an estimated 20% of Americans, significantly impacting health and quality of life. These disorders often involve changes to phonatory airflow, highlighting the need for accurate airflow assessment for comprehensive voice evaluations and management planning. The Phonation Quotient, one validated measure of phonatory airflow, requires precise measurement of vital capacity. However, current methods for evaluating vital capacity often rely on costly pneumotachography equipment, ranging from $2,500 to $10,000, which is inaccessible for many clinicians. Therefore, this study aimed to evaluate the validity of low-cost tools for measuring vital capacity, offering potential alternatives to traditional gold standard equipment.

Methods: In this prospective, laboratory-based study, we assessed four low-cost tools for measuring vital capacity: two circumference measurements obtained from a plastic balloon ($0.01), an analogue spirometer ($100), and a digital spirometer ($150). Each tool was tested with a 3-liter calibration syringe delivering air volumes ranging from 0 to 3 liters (L) in 0.1-L increments. Air volumes for the balloons were estimated using a spherical equation with a known circumference. Accuracy was assessed by comparing each tools’ air volumes to the syringe’s ground truth using descriptive statistics, Lin’s Concordance Correlation Coefficient (_c), and Bland-Altman plots.

Results: This study yielded an analysis of 120 data points. Findings revealed substantial agreement between the ground truth and the balloon measured at the longest (_c = 0.965) and widest (_c = 0.966) circumferences, the analogue spirometer (_c = 0.990), and the digital spirometer (_c = 0.996). Median absolute differences ranged from 0.07 L (digital spirometer) to 0.20 L (balloon, widest measurement).

Conclusions: Plastic balloons, analogue spirometers, and digital spirometers appear to be valid, low-cost options for measuring vital capacity and air volume, with digital spirometers showing the highest accuracy and with balloon measurement demonstrating the lowest accuracy. These tools could broaden access to important aerodynamic voice assessments that require vital capacity measurement. Future studies should investigate the accuracy of these assessment tools across larger and more diverse patient populations.