Journal of Applied Physiology, Vol 58, Issue 3 1034-1039, Copyright © 1985 by American Physiological Society
Error due to dead-space admixture in single-breath method for estimation of pulmonary blood flow
J. Gronlund and P. Christensen
The single-breath method of Kim et al. (J. Appl. Physiol. 21: 1338-1344,
1966) for the estimation of pulmonary blood flow is based on a
single-alveolus lung model for which an analytical relationship has been
established between the kinetic behavior of the alveolar O2 and CO2
tensions and the pulmonary blood flow. The analysis is based on the
assumption that the dead-space contribution to the expirate is negligible
after expiration of a predefined volume. We have examined the influence of
this assumption on the estimation of pulmonary blood flow by computer
simulation in a lung model that incorporates deadspace contribution to the
expirate. Data on the fractional contribution of the dead space to the
expired gas were obtained from Tsunoda et al.'s study (J. Appl. Physiol.
32: 644-649, 1972) on the emptying pattern of normal adult lungs. The
results show that failure to take account of the dead-space contribution
can cause an underestimation in the pulmonary blood flow of greater than
30%. The error can be reduced by ignoring the first part of the expiration
but only at the cost of an increase in the sensitivity of the single-breath
method to measurement noise. This property of the system is demonstrated
experimentally. The error due to dead-space admixture depends on the total
volume of dead-space gas, the measurement noise, the pulmonary blood flow,
and the emptying characteristics of the dead-space compartment during
expiration. In normal subjects it is possible to optimize the experimental
design so that the systematic error is less than 5% and the coefficient of
variation is less than 10%.(ABSTRACT TRUNCATED AT 250 WORDS)
