Journal of Applied Physiology, Vol 65, Issue 3 1444-1448, Copyright © 1988 by American Physiological Society
Thoracic gas volume in rabbits by low-frequency ambient pressure changes
B. D. Lyttle, C. Duvivier, G. M. Glass, M. E. Wohl and J. J. Fredberg
Childrens Hospital, Boston, Massachusetts.
R. Peslin et al. measured thoracic gas volume (TGV) in adults using a new
method employing low-frequency ambient pressure changes (APC) (J. Appl.
Physiol. 62: 359-363, 1987). We extended that methodology and then tested
the hypothesis that this technique was applicable to small mammals. TGV [at
functional residual capacity (FRC)] by APC and by conventional Boyle's law
was compared in 12 rabbits. The rabbits were anesthetized, tracheostomized,
intubated, and placed in a pressure plethysmograph. Although in the method
of Peslin et al. box pressure was oscillated at a single frequency, in our
extension box pressure was oscillated simultaneously at two frequencies
(0.1 and 0.2 Hz). Flow at the airway opening consisted of rapid events due
to spontaneous breathing, superposed on slower events due to the alveolar
gas compression. The slower events were analyzed to yield alveolar gas
compliance and, by Boyle's law, FRC. FRC by APC was highly correlated to
FRC by conventional plethysmography (r = 0.85). Compared with the
methodology of Peslin et al., our extension relaxes a key limitation and
yields systematically higher estimates of FRC. We conclude that this method
is applicable to small mammals, despite an inherently more compliant chest
wall, and that the methodological extension improves the estimate of FRC.
