Association of chest wall motion and tidal volume responses during
co2 rebreathing.
Yan, Sheng, Pawel Sliwinski, and Peter T. Macklem.
Montreal Chest Institute Research Centre and Meakins-Christie
Laboratories, McGill University, Montreal, Quebec, Canada
APStracts 3:0217A, 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 (_VRC,E
and _VRC,I) and abdomen (_VAB,E and _VAB,I) measured by linearized
magnetometers were expressed as a function of end tidal CO2 partial
pressure (PETCO2). The changes in end-expiratory and end-inspiratory
volume of the chest wall (VCW,E and VCW,I) were calculated as the sum
of the respective rib cage and abdominal volume. The magnetometer
coils were placed at the level of nipples and 1-2 cm above umbilicus,
and calibrated during quiet breathing against the VT measured from a
pneumotachograph. The _VRC,E/_PETCO2 slope was quite variable among
subjects. It was significantly positive (p < 0.05) in 5
subjects, significantly negative in 4 subjects (P < 0.05), and
not different from zero in the remaining 2 subjects. The
_VAB,E/_PETCO2 slope was significantly negative in all subjects (p
< 0.05) with much smaller inter-subject variation, likely
suggesting a relatively more uniform recruitment of abdominal
expiratory muscles and a variable recruitment of rib cage muscles
during CO2 rebreathing in different subjects. As a group, the mean
_VRC,E/_PETCO2, _VAB,E/_PETCO2, and _VCW,E/_PETCO2 slopes were 0.010
+/- 0.034, -0.030 +/- 0.007, and -0.020 +/- 0.032 litres/mmHg, only
the _VAB,E/_PETCO2 slope was significantly different from zero. More
interestingly, the individual _VT/_PETCO2 slope was negatively
associated with _VRC,E/_PETCO2 (r = -0.68, p = 0.021) and
_VCW,E/_PETCO2 slopes (r = -0.63, p = 0.037), but not associated with
_VAB,E/_PETCO2 slopes (r = 0.40, p = 0.223). There was no any
correlation of _VRC,E/_PETCO2 and _VCW,E/_PETCO2 slopes to age, body
size, FEV1.0, or expiratory time. The group _VAB,I/_PETCO2 slope
(0.004 +/- 0.014 litres/mmHg) was not significantly different from
zero in spite of the VT nearly being tripled at the end of CO2
rebreathing. In conclusion, the individual VT response to CO2, while
independent of changes in VAB,E, is a function of the changes in
VRC,E, to the extent that as _VRC,E/_PETCO2 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.
Received 7 June 1995; accepted in final form 1 April 1996.
APS Manuscript Number A605-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96