Spontaneous baroreflex sensitivity as a dynamic measure of cardiac anticholinergic drug effect

1 In this study, the analysis of spontaneous baroreflex sensitivity (BRS) w as applied to the dynamic assessment of cardiac anticholinergic drug effect in healthy male volunteers. 2 The anticholinergic effects of single intravenous (i.v.) injections of at ropine (10 mug kg(-1)), glycopyrrolate (5 mug kg(-1)) and scopolamine (5 mu g kg(-1)), as well as a 2-h infusion of glycopyrrolate (5 mug kg(-1) h(-1)) were investigated. Baroreflex sensitivity, a validated measure of cardiac parasympathetic reflex regulation, was repeatedly measured from 5-min recor dings of electrocardiogram (ECG) and continuous blood pressure by using the sequence technique, a method based on detection of spontaneous fluctuation s in blood pressure and heart rate. 3 Single injections of atropine, glycopyrrolate and scopolamine decreased t he mean BRS by 71 +/- 32, 68 +/- 23 and 27 +/- 45%, respectively, whereas t he slow glycopyrrolate infusion gradually decreased BRS (up to 83 +/- 11% r eduction) and increased both systolic (SAP) and diastolic arterial pressure s (DAP) (on an average, by 9 mmHg). 4 During the withdrawal of the parasympathetic blockade (indicated by incre asing BRS), the proportion of baroreflex sequences in the recordings increa sed transiently from 10 up to 20-25%, probably reflecting the restoration o f the baroreflex integrity and the baroreflex-induced attempt to counteract the blood pressure increase. 5 The sequence method to study BRS seems to be feasible in the assessment o f cardiac anticholinergic drug effects, and it also provides good time reso lution for the dynamic measurements.