Abstract
Study ObjectivesTo determine the combined effects of aging and propofol on autonomic nervous system activity using heart rate variability (HRV) analysis. DesignProspective, two-parallel group, repeated-measures study. SettingOperating room of an academic hospital. PatientsASA physical status 1, 2, and 3 patients, including 14 young (< 65 yrs) and 14 elderly (> 65 yrs) patients. All patients were scheduled for general surgical procedures with general anesthesia. InterventionsEach patient received two successive propofol doses during induction (0.5 mg/kg and 1.5 mg/kg) with a time interval allowing the return of Bispectral Index (BIS) to awake values. MeasurementsPrimary outcomes were HRV parameters, which included normalized power spectral density at low frequency (LFnorm) and high frequency (HFnorm) bands and the ratio LF/HF. Secondary outcomes were BIS values, blood pressure, heart rate, respiratory rate, and body temperature. Main ResultsThe interaction of age and propofol dose level was significant [multivariate analysis of variance, F (3,74) = 4.72, P = 0.005], representing a combined effect of age and propofol dose level on the mean HRV parameters. Propofol induction decreased the HFnorm component and enhanced LFnorm and LF/HF in the younger group, but had no significant effect in the older group. Such an effect was not associated with a significant difference in systolic blood pressure (SBP) decrements between the younger and older groups. Within each group, propofol caused significant decreases in SBP compared with preinduction values. Heart rate did not change significantly during propofol administration between groups or within groups. ConclusionsPropofol and aging act in synergy to depress the activity of the cardiovascular component of the autonomic nervous system. However, a compensatory increase in sympathetic outflow was seen in young patients. Such counterbalance was not observed in the older group.
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