Introduction: Thorax movement accompanying respiration has traditionally been analyzed by wrapping a tape measure around the thorax to measure circumferential changes (Respitrace), winding a magnetic coil around the thorax and converting circumferential changes into electric signals for measurement (respiratory inductive plethysmography), and analyzing movement based on images. However, none of these techniques is capable of analyzing the acceleration of a part of the body surface. Therefore, we directly measured thorax movement in three dimensions with a 3-axis accelerometer using a compact sensor and analyzed the characteristics of thorax movement accompanying respiration as reported here.
Subject: Subjects included 22 healthy individuals aged from 19 to 26 years (M ± SD: 20.5 ± 1.5 years; Group A) and 10 healthy individuals aged from 55 to 95 years (77.5 ± 10.5 years; Group B).
Method: During deep breathing in an upright position, a 3-axis accelerometer (MVP-A3-04bc, Microstone Inc., Nagano Japan) was used to measure thorax movement on the sagittal plane at the intersection between the front edge of the axilla and the body surface. Measurements were collected for the following three levels: the axilla (upper level), the ensisternum (medium level), and the 10th rib (lower level). The acceleration measured on each horizontal level in three dimensions was compared between individuals in Group A and Group B. The significant level was below 5%.
Result: Group A showed significant positive correlations between x-axis (thorax perimeter tangential direction) mean acceleration and y-axis (craniocaudal direction) mean acceleration and between y-axis mean acceleration and z-axis (body inward-outward direction) mean acceleration on the medium level and between x-axis mean acceleration and z-axis mean acceleration and between y-axis mean acceleration and z-axis mean acceleration on the lower level. Group B showed significant positive correlations between x-axis mean acceleration and y-axis mean acceleration, between y-axis mean acceleration and z-axis mean acceleration, and between y-axis mean acceleration and z-axis mean acceleration on the upper and lower levels and between y-axis mean acceleration and z-axis mean acceleration on the medium level.
Conclusion: The young group (Group A) showed significant positive correlations between mean acceleration for only some directions at some positions. However, the old group (Group B) showed significant positive correlations between acceleration and many directions at several positions, primarily on the upper and lower levels. These findings indicate that aging changes respiratory thorax movement to three-dimensional unified movement.