Isoproterenol infusion promotes nitrogen washout in rats under normobaric conditions

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.