Fig. 2

Interaction of sympathetic activation with hypoxemia to precipitate VF. HR at increasing doses of isoproterenol after vagotomy is shown in (a). There were significant changes in HR over baseline (vagotomy, no isoproterenol; p = 0.02). Animals thus reached maximal HR at the lower doses. b shows the percent change in HR from baseline. The last three doses were found to yield changes similar to each other but distinct from baseline. The nonselective beta agonist also produced a decrease in mean BP (c, p < 0.001), and there were differences among the doses in post hoc tests (significantly different groups distinguished by *, **). In (d), a 3-dimensional graph of the success rates of achieving VF is shown. The graph shows an abrupt change in VF successes for both isoproterenol and dead space amounts