Yan, Sheng, Pawel Sliwinski, and Peter T. Macklem.Association of chest wall motion and tidal volume responses during CO2 rebreathing. J. Appl. Physiol. 81(4): 1528–1534, 1996.—The purpose of this study is to investigate the effect of chest wall configuration at end expiration on tidal volume (Vt) response during CO2 rebreathing. In a group of 11 healthy male subjects, the changes in end-expiratory and end-inspiratory volume of the rib cage (ΔVrc,e and ΔVrc,i, respectively) and abdomen (ΔVab,eand ΔVab,i, respectively) measured by linearized magnetometers were expressed as a function of end-tidal[Formula: see text]([Formula: see text]). The changes in end-expiratory and end-inspiratory volumes of the chest wall (ΔVcw,e and ΔVcw,i, respectively) were calculated as the sum of the respective rib cage and abdominal volumes. The magnetometer coils were placed at the level of the nipples and 1–2 cm above the umbilicus and calibrated during quiet breathing against the Vt measured from a pneumotachograph. The ΔVrc,e/[Formula: see text]slope was quite variable among subjects. It was significantly positive ( P < 0.05) in five subjects, significantly negative in four subjects ( P < 0.05), and not different from zero in the remaining two subjects. The ΔVab,e/[Formula: see text]slope was significantly negative in all subjects ( P < 0.05) with a much smaller intersubject variation, probably suggesting a relatively more uniform recruitment of abdominal expiratory muscles and a variable recruitment of rib cage muscles during CO2rebreathing in different subjects. As a group, the mean ΔVrc,e/[Formula: see text], ΔVab,e/[Formula: see text], and ΔVcw,e/[Formula: see text]slopes were 0.010 ± 0.034, −0.030 ± 0.007, and −0.020 ± 0.032 l / Torr, respectively; only the ΔVab,e/[Formula: see text]slope was significantly different from zero. More interestingly, the individual ΔVt/[Formula: see text]slope was negatively associated with the ΔVrc,e/[Formula: see text]( r = −0.68, P = 0.021) and ΔVcw,e/[Formula: see text]slopes ( r = −0.63, P = 0.037) but was not associated with the ΔVab,e/[Formula: see text]slope ( r = 0.40, P = 0.223). There was no correlation of the ΔVrc,e/[Formula: see text]and ΔVcw,e/[Formula: see text]slopes with age, body size, forced expiratory volume in 1 s, or expiratory time. The group ΔVab,i/[Formula: see text]slope (0.004 ± 0.014 l / Torr) was not significantly different from zero despite the Vt nearly being tripled at the end of CO2 rebreathing. In conclusion, the individual Vtresponse to CO2, although independent of ΔVab,e, is a function of ΔVrc,e to the extent that as the ΔVrc,e/[Formula: see text]slope increases (more positive) among subjects, the Vt response to CO2 decreases. These results may be explained on the basis of the respiratory muscle actions and interactions on the rib cage.