Abstract 13134: A Novel Device for Detecting Anaerobic Threshold Using Sweat Lactate Acid During Exercise

Abstract

Background: Continuous monitoring of lactate acid (LA) levels during exercise has not been possible. We aimed to visualize real-time changes in LA levels in sweat during exercise and to investigate the relationship between the lactate threshold in sweat (sLT) and LT in blood (bLT) and the ventilatory threshold (VT). Methods: Twenty-three healthy subjects (age: median; 20 [interquartile range; 20, 21] years old) and 22 consecutive patients (age: 65 [57, 73] years old) with cardiovascular diseases (CVDs) underwent exercise tests with a RAMP protocol ergometer, simultaneously monitoring changes in the LA values in sweat using a wearable lactate sensor. The sLT was identified as the first significant increase in LA above baseline based on the graphical plots and change finder scores calculated by the Change Finder algorithm using the time-series data of the LA values during exercise. We applied the Bland-Altman method to verify similarities for each threshold. Results: During exercise, the dynamic changes in LA values in sweat were successfully visualized in real-time with a sharp continuous increase up to volitional exhaustion and a gradual decrease in the recovery period. In healthy subjects, the work rate (WR) at the sLT (WR-sLT) was substantially correlated with the WR at the bLT (r=0.90). The Bland-Altman plot described a strong agreement (the mean difference: -3.0 watt). Among 22 patients, there were 8 patients whose LA values in sweat were not measured due to a non-response in the sensor. In the remaining 13 cases, except for a patient in whom the VT could not be detected, the sLT was well correlated with bLT and VT (r=0.81 and 0.65, respectively); the mean differences were -8.3 and 3.4, and there was no bias between the mean values. Finally, the logistic regression analysis revealed that a non-response in the sensor was associated with NYHA 3/4 and low peak VO2 (Odds ratio [OR] 0.01 [95% confidence interval (CI); 0.00-0.13], OR 1.45 [95% CI; 1.09-2.20], respectively) Conclusions: Our wearable device enabled a continuous and real-time LA measurement in sweat during incremental exercise in a subset of patients with CVDs as well as healthy subjects. This can provide additional information for detecting the VT.