How do I convert the respiration data (in arbitrary units) into volume (mL)?

You need to understand that our respiration loops calculate the movement of the rib cage during the inspiration and expiration events. Therefore, the raw respiration data is measured in arbitrary units. The conversion from arbitrary units to volume is based on the following formula:

volume difference x 13.28 x (weight / 65)

The units are in mL.

Also, a calibration step is necessary if you wish to obtain absolute values for the respiration metrics. To do the calibration step, you need a spirometer. We suggest using a spirometer to measure a forced expiration that will be measured simultaneously with the Hexoskin, then calculate the amplitude of the expiration curve from the Hexoskin respiratory raw data. The volume measured with the spirometer will correspond to the amplitude of the expiratory curve. You will then be able to calculate the factor of conversion to change in volume measured by Hexoskin into an absolute value. However, it is important to know that ventilation measurements with Hexoskin are precise but accuracy varies from one person to the other. Thus, the algorithm needs calibration to provide accuracy, a calibration step needs to be done for every user and each time the user puts on the Hexoskin Shirt.