A Novel Wearable Chest-Strap for Non-Invasive and Non-Laboratory Identification of the Respiratory Compensation Point during Running Exercise Stress Test

Background:
The second lactate threshold (LT2), also known as the anaerobic threshold, is a fundamental physiologic attribute for assessing exercise intensity and improving cardiorespiratory (aerobic) fitness level by training/rehabilitation. Currently, the principal methods for the detection of LT2 are performed in the laboratory, and require either blood samples for lactate concentrations or detection of the respiratory compensation point (RCP) by cardiopulmonary exercise testing (CPET).

Aims:
To validate the ability of a novel, non-invasive, non-laboratory wearable chest-strap to measure pulmonary ventilation (VE) during running exercise stress test, and to develop a mathematical algorithm for detecting the RCP using the chest-strap VE equivalent data.

Methods:
An advanced chest-strap was built in our laboratory, consisting of a vertical accelerometer, a heart rate monitor and a stretch sensor for measuring breathing frequency (BF), the relative tidal volume (VT, estimated by thorax expansion), and the equivalent of pulmonary ventilation. Twenty healthy adults aged 20-35 years wore the new chest-strap during treadmill maximal exercise testing. Correlation analysis was performed to compare between the chest-strap data and ventilation measured by CPET.

Results:
A very high correlation was found between the equivalent of VE measured by the new chest-strap and VE measured by CPET (r = 0.94, p<0.001). The mean deviation between the RCPs detected by the chest-strap using the new mathematical algorithm, and that identified by an expert exercise physiologist using CPET data was only 1%, and increased to only 2% when identified by the expert on the VE equivalent curves recorded by the chest-strap.

Conclusions:
Our novel chest-strap with its mathematical algorithm can accurately measures pulmonary ventilation during running exercise. The chest strap can also accurately detect the RCP as measured by CPET. Further research will verify the feasibility and reliability of the new chest-strap for detecting RCP during exercise training and real-life settings.