Johnson, Christopher P

The ganglionic blocker trimethaphan (TMP) is no longer produced; alternatives are needed to inhibit baroreflex control of the circulation during systemic hemodynamic studies. We tested the hypothesis that combination anti‐cholinergic glycopyrrolate (Gly) and α2 receptor agonist dexmedetomidine (Dex) would inhibit baroreflex buffering in response to vasodilation to a similar degree as ganglionic blockade with TMP. In 2 separate trials, 5 males received an I.V. bolus and infusion of Gly‐Dex, and 11 males received TMP infusion. To offset the fall in blood pressure with TMP, phenylephrine (PE) was used to raise pressure to pre‐TMP baseline. Terbutaline was then infused for 15 minutes at 2 doses (33 and 67 ng/kg/min). Heart rate (HR), blood pressure (BP, oscillometric cuff for Gly‐Dex, brachial arterial line for TMP+PE), and cardiac output (CO, acetylene breathing) were recorded. Resting HR was higher with Gly‐Dex (mean ± SEM: 93±7mmHg) than TMP+PE (74±3mmHg, p<0.001) but resting BP, CO, stroke volume (SV), and total peripheral resistance (TPR) were similar between Gly‐Dex and TMP+PE. The cardiovascular responses to terbutaline were similar between Gly‐Dex and TMP+PE, except for the increase in CO which was significantly greater in the TMP + PE group. We conclude that Gly‐Dex is a viable pharmacologic alternative to TMP in physiologic measures of BP and TPR during vasodilator infusions.