Abstract
Pulmonary tuberculosis (PT) and lung cancer (LC) frequently require resection, the outcomes of which are largely determined by the functional reserve of the respiratory and cardiovascular systems. The gold standard for assessing this reserve is cardiopulmonary exercise testing (CPET) with measurement of maximal oxygen consumption; however, achieving a true maximal test is often difficult, which increases the importance of submaximal indices. The aim of this study was to evaluate the informativeness of oxygen consumption at the anaerobic threshold (VO2-AT) and the slope of the ventilation-to-carbon dioxide output relationship (VE/VCO2 slope) for assessing functional reserve and predicting maximal oxygen consumption in patients with PT and LC. A single-center comparative study was conducted, including 546 patients: 377 with surgical forms of PT and 169 with LC. All patients underwent standard pulmonary function testing and CPET using an incremental workload protocol. Peak oxygen consumption (VO2peak), VO₂-AT, and the VE/VCO2 slope were analyzed. Correlations, linear regression models, prediction errors, and correlation between the methods were assessed. Results: VO2-AT demonstrated a strong association with VO2peak and the highest predictive ability in both clinical groups, yielding moderate accuracy of quantitative prediction with minimal systematic bias. The VE/VCO2 slope showed a significant but weaker relationship with VO2peak and was inferior to VO2-AT in predictive accuracy. Errors in estimating maximal oxygen consumption from submaximal indices were greater in patients with pulmonary tuberculosis, especially at relatively high VO2peak values. Conclusion: VO2-AT can serve as the primary submaximal marker of functional reserve in PT and LC patients, particularly when a true maximal test cannot be performed, with cautious interpretation of results in functionally preserved individuals.