Better thoracoabdominal synchrony in abdominal breathing: Evidence from complementary ensemble empirical mode decomposition-based Lissajous figure analysis

Abdominal breathing (AB) is believed to be a healthier pattern of breathing than thoracic breathing (TB). However, the objective evidence is scanty. Thoracoabdominal synchrony could be evaluated by calculating the phase angle between rib cage and abdomen motion in the Lissajous figure. A lesser phase angle indicates a better thoracoabdominal synchrony. Complementary ensemble empirical mode decomposition (CEEMD) was recently developed to extract the main component in the nonlinear and non-stationary signals. This study was designed to compare the thoracoabdominal synchrony between AB and TB via a CEEMD-based Lissajous figure analysis. Twenty-nine healthy subjects [24 males and 5 females; age 22 (21-23) years, median (interquartile range)] were recruited to receive simultaneous respiratory inductive plethysmography recording of rib cage and abdomen motion during AB and TB respectively. The main components of rib cage and abdomen motion were extracted by CEEMD. These main components were used to plot the Lissajous figure and calculate the phase angle. Compared with TB, AB revealed a significant decrease (P < 0-001) in phase angle [AB 12.13 (8.70-15.76)° vs. TB 22.56 (17.59-26.35)° ]. In conclusion, AB assumes a better thoracoabdominal synchrony than TB. This finding might help to explain why AB is a healthier pattern of breathing. In addition, the CEEMD-based Lissajous figure analysis could be an effective method for the evaluation of thoracoabdominal synchrony.