Journal of Applied Physiology, Vol 61, Issue 5 1724-1731, Copyright © 1986 by American Physiological Society
Ventilatory changes of pulmonary capillary blood volume assessed by arterial density
J. S. Lee and L. P. Lee
By use of an improved density measuring system, we found that the
gravimetric density of arterial blood of dogs fluctuates at the same
frequency as the spontaneous or mechanical ventilation. Similar density
fluctuations were observed in the blood leaving isolated, perfused lobes of
dogs that were ventilated cyclicly. Employing an analysis that balanced the
erythrocyte and plasma flows through distensible capillaries containing
blood with a tube hematocrit lower than the hematocrit in large blood
vessels, we derived a relationship to estimate from the density fluctuation
the change in pulmonary capillary blood volume (Vc). For mechanical
ventilation, the maximum change in density over one ventilation cycle
increased from 0.084 +/- 0.01 to 0.47 +/- 0.05 (SE) g/l as the frequency
decreased from 29 to 6 cycles/min. These density changes were estimated to
be the result of an 1-16% change in Vc. A larger tidal volume for the
mechanical ventilation led to a larger density fluctuation. The maximum
density change of spontaneous respiration of 6 cycles/min was one-sixth of
the mechanical case, indicating a much smaller change in Vc during
spontaneous respiration. When the airway flow resistance was increased for
spontaneous respiration, larger density fluctuations were observed.
