Journal of Applied Physiology, Vol 73, Issue 3 825-831, Copyright © 1992 by American Physiological Society
Oxygen cost of resistive-loaded breathing in quadriplegia
H. Manning, F. D. McCool, S. M. Scharf, E. Garshick and R. Brown
Department of Medicine, Brockton-West Roxbury Veterans Affairs Medical Center, Massachusetts 02132.
We hypothesized that, in quadriplegia, chest wall distortion would increase
the energy cost of ventilation. To assess this, we measured the oxygen cost
of breathing (VO2 resp) and changes in chest wall configuration during
inspiratory resistive-loaded breathing tasks in five quadriplegic and five
normal subjects. Each subject performed three breathing tasks that spanned
a range of work rates (Wtot). Configurational changes of the abdomen and
upper, lower, and transverse rib cage were assessed with magnetometers. We
found that 1) in both groups, VO2resp increased linearly with Wtot over the
range of tasks performed, 2) the mean slope of the regression line of
VO2resp vs. Wtot was greater for quadriplegic than for normal subjects (3.7
+/- 0.8 vs. 2.0 +/- 0.7 ml O2/J, P less than 0.01), 3) efficiency of
breathing (Wtot/VO2resp) was less for quadriplegic than for normal subjects
(1.9 +/- 0.6 vs. 3.5 +/- 1.4%, P less than 0.001), 4) during inhalation,
upper and lower rib cages behaved similarly in the two groups, but the
quadriplegic subjects had a decrease in transverse rib cage and a much
greater increase in abdomen than normal subjects, and 5) functional
residual capacity decreased in normal but not in quadriplegic subjects
during the breathing tasks. We conclude that the lesser efficiency of
breathing in quadriplegia may be related to the elastic work of chest wall
distortion, shorter mean operational diaphragm length, and possibly
differences between normal and quadriplegic subjects in mechanical
advantage of available inspiratory muscles.
