Journal of Applied Physiology, Vol 57, Issue 5 1306-1311, Copyright © 1984 by American Physiological Society
Isoproterenol infusion promotes nitrogen washout in rats under normobaric conditions
G. W. Mack and Y. C. Lin
Cardiac output and the rate of N2 elimination were measured simultaneously
in unanesthetized rats during isobaric desaturation with 100% O2.
Whole-body N2-washout curves for the rat are characterized by three
compartment half times derived by exponential stripping, representing the
slow, intermediate, and fast components of the system. During saline
infusion (control) the respective half times for these compartments were
120, 15, and 2 min. Isoproterenol infusion increased cardiac output by 40%
and the volume of N2 eliminated by 10% over a 2-h washout. More
importantly, the half time of the slowest compartment decreased from 120 to
70 min. The intermediate compartment half time shortened from 15 to 13 min,
while the fast compartment was unaffected. The decrease in slow compartment
half time will contribute significantly to the shortening of the duration
of stay during decompression. A plot of slow compartment rate constants vs.
measured cardiac output (range 280-690 ml X min-1 X kg-1) demonstrated a
linear relationship between perfusion and the tissue-blood gas exchange
rate. The results indicate that enhanced cardiac output and generalized
vasodilation shorten the time required to desaturate the slower body
tissues. Various maneuvers or drugs that demonstrate similar cardiovascular
responses should be beneficial during prolonged decompression procedures
involved in saturation diving.
