British Journal of Anaesthesia, Vol 84, Issue 3 316-322, Copyright © 2000 by Oxford University Press
H Schachinger, BU Muller, W Strobel, J Drewe and R Ritz
Arterial pressure (AP) and inter-beat interval (IBI) length are under
autonomic nervous system control. The control mechanisms can be
investigated by transfer function analysis. It is not known if this type of
analysis may be helpful in monitoring depth of sedation. In an open-label,
uncontrolled investigation, the effect of midazolam on the transfer
function between AP and IBI, and on spectral indices of AP and heart rate
(HR) variability (APV, HRV) were assessed in the absence and presence of
the benzodiazepine antagonist flumazenil. We studied 11 healthy male
volunteers. After an initial control period of 60 min, we studied three
consecutive periods, each of 60 min duration, with progressively increasing
concentrations of midazolam (0.02, 0.06, 0.14 mg kg-1 h-1). A final 60-min
period during administration of flumazenil 0.004 mg kg-1 h-1 and while the
agonist was still present was also studied. To confirm midazolam-induced
central nervous system effects, electroencephalography was performed and
Ramsay sedation scores were determined. With increasing dose of midazolam,
the high frequency (0.15- 0.4 Hz) component of the transfer function
between AP and IBI decreased progressively (mean 26.5 (SEM 3.7), 19.2
(2.9), 12.8 (1.7), 8.4 (1.6) ms mm Hg-1). This effect was antagonized by
flumazenil (21.5 (3.2) ms mm Hg-1). Other indices (e.g. HRV, APV) did not
reveal such a clear response to midazolam dose and flumazenil application.
Thus in healthy male volunteers, the transfer function between AP and IBI
in the parasympathetically dominated high frequency range varies according
to benzodiazepine agonism and antagonism. This finding has potential
implications for monitoring the effects of benzodiazepines.
ARTICLES
Effect of midazolam on transfer function between beat-to-beat arterial pressure and inter-beat interval length
Department of Internal Medicine, University Hospital Basel, Switzerland.
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