Assessment of breathing volumes and kinematics by motion capture systems: comparison of protocols

Respiratory assessment and the biomechanical analysis of the chest during breathing can be carried out by using motion capture systems. A protocol for positioning photo-reflective markers in specific chest landmarks and a computational method are mandatory in order to compute the breathing volume as a function of time from the markers' trajectories collected. Moreover, from breathing volumes, the biomechanics of respiration in the form of biomechanical indexes (i.e., compartmental percentages) can be evaluated. In this study, the full 89 markers protocol was compared to a reduced markers protocol based on 32 markers placed on the chest. Experimental trials were carrier out in two different groups: five healthy volunteers and five athletes. Breathing data of 30 seconds were collected from each subject. When the different markers protocols were used against spirometry, results demonstrated a systematic overestimation of the total volume of at least 170 mL. The correlation between full markers and the reduced markers protocols was high in both groups, R2=0.99. Kinematics of breathing can be evaluated with 32 markers, although with an underestimation of the pulmonary contribution (-4.8% at least) and overestimation of the abdominal contribution to the total volume (3.2% at least) in both groups. The 32 markers protocols showed comparable results when the synchronisation of chest wall compartments was investigated by analysing the correlation coefficients between compartments. Our findings demonstrate that the reduced markers protocol can be used to analyse the biomechanics of breathing.