Acta Anaesthesiol &and 1991: 35: 436-441

Effects of glycopyrrolate and atropine on heart rate variability T. ALI-MELKKILA, T. KAILA,K. ANTILA,L. HALKOLA and E. IISALO Departments of Anaesthesiology and Clinical Pharmacology, Turku University Central Hospital, and Cardiorespiratory Research Unit, University of Turku, Turku, Finland

Analysis of heart rate variability, combined with physiological tests (deep breathing and tilt tests) was used to characterise the effects of atropine and glycopyrrolate on the parasympathetic nervous tone of the heart in healthy male volunteers. The low dose of atropine (120 pg) administered as a continuous infusion in 15 min was associated with parasympatomimetic effects estimated by the slowing of the heart rate and an increase of the mean and beat-to-beat heart rate variability. The bradycardia and increase of heart ratc variability following infusion of glycopyrrolate (50 pg) was less marked and did not differ significantly from that of placebo. The higher doses of atropine (720 pg) and glycopyrrolate (300 pg) administered as a continuous infusion in 15 min produced an equal vagal cardiac blockade characterised by significant tachycardia and a decrease in overall and beat-to-beat heart rate variability. It is coricluded that at low doses the parasympatomimetic action of glycopyrrolate is less marked than that of atropine; and at higher doses only small differences exist between these two muscarinic antagonists in their effects on cardiac vagal outflow, assessed by heart rate and heart rate variability. Received 2 August, accepled for publication 26 November 1990

Kcy words: Atropine; autonomic nervous system; glycopyrrolate; heart rate; heart rate variability.

It is well known that atropine exerts a biphasic action The spectral analysis of HRV can be used as a noninon the heart: low doses produce a slowing of the heart vasive indicator of the vagal cardiac control in pharmrate, whereas tachycardia is observed only at higher acologic studies (9, 12-14). I n the present study we have compared the effects doses ( 1-3). Traditionally, the initial bradycardia of atropine has been explained by the central vagal of continuous infusions of atropine and glycopyrrolate stimulatory effect of anticholinergic drugs (3). Re- on heart and salivary secretion. The parasympathetic cently, a blockade at the peripheral MI-cholinoceptors tone of the heart was assessed by determining the in sympathetic ganglia or the inhibitory MI-autorecep- HRV by computing the indices of the HRV from the tors modulating the acetylcholine release has been sug- successive R-R intervals of the ECG and by determingested as the explanation of cardiac slowing following ing the respiratory variability from the successive R-R intervals of the ECG. Stimulus-related heart rate varithe low doses of atropine (4, 5). Although the pharmacodynamics of glycopyrrolate ability was determined by using the power spectrum has been extensively studied during the past few years, analysis of heart rate variability. The doses of glycopyrthere have been very few controlled studies concerning rolate and atropine were based on the potency ratio of its possible bradycardic effect (6, 7 ) . The interval be- 1:2.4, which was established in several previous dosetween the consecutive heart beats is the result of bal- response studies (7, 15). ance in the tone of two antagonistic divisions of the We were specially interested in comparing the effects autonomic nervous system: the fast reacting vagal (pa- of atropine and glycopyrrolate associated with low rasympathetic) division and the slower sympathetic plasma concentrations, since these effects may have division. The dynamic fluctuations of the heart rate clinical importance when atropine and glycopyrrolate are defined as heart rate variability (HRV) (8, 9). It are used in connection with neostigmine at the reversal has been demonstrated in many studies that HRV of neuromuscular blockade. follows the changes of cardiac vagal efferent activity and can be used as an indicator of the parasympathetic nervous control of heart rate ( 1 0 , l l ) . A comprehensive analysis of the main components of the HRV provides SUBJECTS AND METHODS much more accurate and detailed information about Subjects and sludy design the vagal cardiac control than the H R signal alone. Six healthy male volunteers, mean age 28.8 years (range 21-37),

EFFECTS O F GLYCOPYRROLATE AND ATROPINE mean w i g h t 73.5 kg (range 8L?-68) and mean height 179.7 cm (range 174-190). participated in the study after their informed consent had been obtained. The study protocol was approved by the Ethical Committee ofTurku University. Before entering the study the subjects werr rrquested to abstain from strenuous exercise, alcohol and cigarette smoking for at least 24 h and from drugs for at least 2 weeks beforr the trial. The study was carried out using a double-blind, placelici-controlled cross-over design with at least 2 weeks’ interval betwren the drugs (or placebo). The trial sessions were performed in a quirt laboratory room designed for drug studies at the Department of Clinical Pharmacology, University of Turku. Physioloyiral tesfs and electrocardiographic anahJes The drep breathing test at the frrquency of 0.1 Hz and tilting the subject hetween a horizontal position and 70” head-up tilt at the same frequrncy were used as physiological tests to provoke a standardised stimulus lor the heart rate variability analysis. Each provocation was ccintinued for 3 min. A continuous bipolar ECG recording was obtainrd from the subjects on a 4-channel instrument tape recorder (Store 4 DS, Racal Recorders Ltd., Southhampton, UK). T h r ECG from each physiological provocation test was replayed at 8 timrs real-time into a mini-computer (Eclipse S/100, Data General Corporation, CA, USA). The ECG was preprocessed by an analogue band-pass filter and a voltage threshold trigger, which produced a pulse fiJr each R wave. The trigger pulses from the ECG signal were used 10 measure each R-R interval with a resolution of 2 ms of the ciriginal recording time. The indices used to characterise the long-term (total or overall) heart rate variability (root mean square value of the differences from thr R-R interval=RMSM), and the short-term beat-to-beat variability (root mean square value ofthe differences between successive R R interval = RMSSD) were computed (Eclipse Mv4000 minicomputrr, Data General Corporation, CA, USA) as follows (16):

and RMSSD=

!. 1

-

fN

1

(RR,-RR,,,)’,

wherr KRi is the ilh R-R interval, RR,, is the mean R-R interval and N I s the number of R-R intervals. The corresponding coefficients of variation, CV and CVS, were computrd as follows:

C:\‘ = 100 RMSM/RR,,,

and

CVS = 100 RMSSDIRR,,,

For thr spectral analysis of HRV, the R-R interval series was lowpass filtered by using the SIN (X),’Xalgorithm at the frequency of one hdlf of the lowest instantaneous heart rate in the series and samplcd at a sampling rate of 2.2 times the low pass cutoff frequency. ‘The fiist Fourier transformation algorithm was then applied to the signal dnd the power spectrum of HRV was computed. In cirdrr to quantify the stimulated HRV (modulation of the heart rate bv cach respiratory event or change of posture), the magnitude of thr power spectrum peak at the stimulus frequency (breathing or tilting Irequency, 0.10 Hz) was measured and the figure was used to represent the magnitude of the stimulated component of the HRV (quantitative measure of the stimulated HRV) (17). AsseJimrrit of salivary function A visual analogue scale (VAS. numbered from 0-10: mouth normal to exrrrmely dry, respectively) was used to assess the subjective sensation o f a dry mouth. T h r salivary llow was measured according to Dollrry ct al. (18) and Wellstein & Pitschner (5): three dental cotton rolls wrre placed at the orifices of the parotid ducts and under the tongut. lor 2 min and thrn discarded. Thereafter three preweighed

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rolls were put into position for 2 min, removed and placed in sealrd tubes. The net weight increase of the second set of cotton rolls was recorded. Drug determination The plasma concentrations of atropine and glycopyrrolate werc examined using a sensitive radioreceptor assay ( R R A I modified froin the radioreceptor assays described by Aaltoncn et al. ( 19) and Ensinger et al. (20). The sensitivity of the modification for atropine and glycopyrrolate was 70 pg/ml and the interassay and intra-assay variations measured at 1.0 ng/ml standard were within 1204. Protocol After an overnight fast, thr subjects arrived at thr lahoratiiry at 9.00 a.m. An intravenous cannula was inserted into the liirearm vein fur infusions and a second cannula for blood sampling was inserted into the anterior cubital vein on the contralateral arm. The ECG leads were connected to an ECG monitor (Nihon Kohden, Lifescope 6 . Tokyo, Japan) and the ECG was continuously recorded on a frequency modulated tape recorder (Racal Store 4 DS, Southhampton. U K ) . Before the baseline recordings the volunteers rested supine for 30 min. The HRV was measured at rest and during the deep breathing and tilt tests to obtain the baseline values hefore the infusions; thereafter the salivary secretion was assessed. The same pattern of tests was performed after slow (24 ml/h, 15 min) and fast (144 ml/ h, 15 min) infusions and during the recovery phase. The drugs 0 1 placebo were administered as continuous infusions (2 mg atropine ill 100 ml of 0.9Yi, saline or glycopyrrolate 0.8 mg in 100 ml of 0.9?,, saline, 100 ml 0.9°/o saline served as placebo) according to the following scheme: 1. Infusions were started with an infusion rate of 24 ml/h for 15 min. which corresponds to approximately 120 pg of atropine and 50 pg of glycopyrrolate. 2. The infusion rate of 1 ml/h for 10 min was used during the deep breathing and tilt tests, blood sampling and assessment of salivary function. 3. The infusion rate of 144 ml/h (fast infusion) for 15 min was used to achieve a cardiac vagal blockade. l’his corresponds to approximately 720 pg of atropine and 300 pg of glycopyrrolate. 4. The infusion rate of 5 ml/h for 10 min was used during the deep breathing and tilt test, blood sampling and assessment of salivary function. Thereafter the infusion was stopped. 5. Blood samples were collected every 30 min after the end ofinfusion up to 2 h. The deep breathing and tilt tests and the assessment of salivation were performed 170 min after the start of infusion. Statistical analJlsis The variance of the heart rate and the indices of the hrart ratr variability, including the differences between the groups, were analysed using the univariate and nlultivariate analysis of variance and covariance, including repeated measures (URWAS) using BMDOVG program (2I ) . The parameters concerning the antisialogogue effects were analysed using Friedman’s analysis of variance (ANOVA), and further analyses were made using the Wilcoxon signed rank tests. The values are expressed as mean f s.d.; a P-value < 0.05 was considered significant.

RESULTS The heart rate variability values during the tilt and deep breathing tests with saline, atropine and glycopyrrolate infusions are given in Tables l and 2. Fig. 1-3 show the mean plasma concentrations of atropine and

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T. ALI-MELKKILA ET AL.

'Iablr I Heart ratr variability values for the tilt test with saline, atropine and glycopyrrolate infusions. The asterisk ( * ) indicates a statistically significant change (P