Coordination dynamics of thoracic and abdominal movements during voluntary breathing

Abstract

Thoracic and abdominal movements can be tightly coupled during voluntary breathing, such as when singing and playing wind instruments. The present study investigated the coordination of thoracic and abdominal movements during voluntary breathing using a dynamical systems approach. We examined whether there are two stable coordination patterns, and if the coordination pattern would abruptly change when the breathing frequency increased, which is known as phase transition. The participants inhaled and exhaled repeatedly at 7.5, 15, 30, 60, or 120 breaths per minute. At the beginning and end of the experiment, the participants performed breathing at their preferred frequency. As a result, the coordination pattern at the lower and preferred frequencies exhibited an in-phase pattern. When breathing frequency increased, participants showed deviated coordination patterns from the in-phase pattern to either a thoracic-leading pattern, an abdominal-leading pattern, or an anti-phase pattern depending on the individual. These deviations occurred gradually; thus, phase transition was not observed. Our findings suggest that thoracic and abdominal movements are tightly coupled at lower frequencies, but their patterns vary depending on the breathing frequency and individuals. Therefore, the present study suggests the importance of viewing breath control in terms of coordination of thoracic and abdominal movements.

Figure 1

Subjective speed and difficulty scores. Vertical bars represent between-subject standard error.

Figure 2

Mean signed and absolute relative phase angle between thoracic and abdominal movements. Solid markers represent individual participants. Open circles indicate mean value across participants. Vertical bars represent between-subject standard error. **p < 0.01, ***p < 0.001.

Figure 3

Frequency of particular thoraco-abdominal coordination patterns identified by the phase relation analysis, and a representative example of a participant’s relative phase histogram for each pattern. IP in-phase pattern, TL thoracic-leading pattern, AL abdominal-leading pattern, AP anti-phase pattern.

Figure 4

SD of relative phase angles between thoracic and abdominal movements. Solid markers represent individual participants. Open circles indicate mean value across participants. Vertical bars represent between-subject standard error. *p < 0.05.

Figure 5

Experimental setup. Participants breathed via a harmonica while looking at a fixed point on the wall from a distance of 2 m. The thoracic and abdominal movements during breathing were measured using a Hexoskin vest equipped with two strain gauge bands around the chest and waist and an electrocardiogram sensor. The data was stored in a logger equipped with a 3-axis accelerometer. The metronome beats were presented via a speaker from a laptop. The sounds of the harmonica and metronome beats were recorded using a video camera. The Hexoskin data and video recordings were synchronized by hitting a trigger button that illuminated a light-emitting diode in the view of the video camera. The participants pressed the button on a Hexoskin logger with the accelerometer at the beginning of each trial.