Estimation of anaerobic threshold and peak oxygen uptake from tracheal sound during cycle ergometer cardiopulmonary...

Cardiopulmonary exercise test (CPET) is widely used for assessing exercise capacity of individuals through ventilatory anaerobic threshold (AT) and peak oxygen uptake (VO_2peak). However, CPET requires specialized equipment, resources, time, and trained personnel. In this study, we investigated the feasibility of estimating ventilatory AT and submaximal VO_2peak using tracheal respiratory sounds recording with a wearable sensor (The Patch) during incremental cycle ergometer testing. Twenty-four healthy adults (18 females, age: 31.0 ± 9.1 years, body mass index: 23.5 ± 3.3 kg/m²) underwent CPET with simultaneous tracheal sounds recording. Acoustic features (sound energy, sound intensity, respiratory rate, and ventilation) were extracted. AT was identified from breakpoints in acoustic features and compared with reference AT from ventilatory gas analysis. VO_2peak was estimated using random forest regression models with subject-specific and subject-independent training models. Agreement with CPET was investigated using Bland-Altman analysis. Ventilatory AT was detected in 84% (sound energy) and 96% (sound intensity) of participants using The Patch. Workload stage agreement with CPET was 88% and 100% for sound energy and intensity, respectively, with AT timing within 20 s in 62% and 92% of cases. The subject specific model estimated VO_2peak with minimal bias [confidence intervals] of - 1.01 [- 3.04 to 1.02] (mL/kg/min), while the subject-independent validation model exhibited wider variability of - 1.28 [- 12.39 to 9.82] (mL/kg/min). Our results shows that tracheal sound analysis can estimate ventilatory AT and provides a promising approach for non-invasive exercise capacity assessment. On the other hand, the estimation of VO_2peak shows promise but requires further validation in maximal effort protocols.