Utility of Breathing Rate in Estimation of Ventilatory Thresholds

Ventilatory Threshold (VT1) has lately been a key parameter for traction of the respiratory physiological state of the athletes. Though conventional method like capnography provides accurate detection of VT1 episode, its utility is limited to lab settings. Thus there is a requirement to detect the same through wearable devices due to its application in real-world settings, using parameters coming out from the same such as Heart Rate (HR), Breathing Rate (BR), etc. The most popular parameter currently in use to determine VT1 threshold is HR through Detrended Fluctuation Analysis (DFA). However, HR measurements are often susceptible to motion artifacts that would bias the DFA results due to high movement activities. Thus, in this paper we have explored the utility of BR to compute VT1, due to its resistance to motion artifacts. We have used DFA to calculate the same obtained from the Gas Based Method. We further validated the model by doing a feasibility check using the Respiratory Inductance Plethysmography (RIP). We observed an increase in BR and a decrease in alpha range with successive incremental workloads. The $\alpha_{br}$ obtained using DFA marked the episode of VT1 at $\alpha=0.75$ as evidenced in HR measurements. We have presented a Bland Altman analysis, to evaluate the effectiveness of BR to determine VT1, using the reference device (based on the Gas Analysis Method) and wearable device (based on RIP). The experimental evaluation showed agreement between the reference VT1 and the estimated VT1 derived from BR with close to 100% BRVT1 point lying inside the limit of agreement.