Telomeres are protein-bound DNA repeat structures at the end of eukaryotic chromosomes that are made up of a simple repetitive sequence (in humans, TTAGGG) and regulate cellular replicative capacity and cellular proliferation, protect chromosomes from fusing together during mitosis and maintain genomic stability, and prevent the loss of genetic data. Telomeres are specialized repetitive DNA sequences, typically ranging from 5,000 to 15,000 bp in humans, which are the critical chromosome capping DNA sequences. The loss of telomere repeats diminishes telomeric functional capacity.Telomere length(TL) is important in determining telomere function.This is known as the end replication problem and results in a gradual decline in TL over time. Consequently,leukocyte TL shortens in a predictable way with age by roughly 20-40 base pairs per year. Cellular senescence and subsequent cell death often occur when the mean telomere length reaches a critical value.Shortened telomeres and lower telomerase are linked to age-related risk factors and disease.Peripheral blood leukocyte express telomerase at low levels, which can be measured over a short duration (hours) to demonstrate immediate, short-term changes. Shorter mean leukocyte telomere length has been shown to be associated with risk of several age-related diseases.The dosage of propofol gradually reduced with the aging process. However,it is not known whether the telomere length and variation of telomerase in PBL relate to the dosage of propofol and time of consciousness disappearance in anesthesia induction. In this exploratory study, the investigators examined that the changes of peripheral blood leukocyte telomere length was associated with the dosage of propofol and time of consciousness disappearance in anesthesia induction.

Given the importance of telomeres in nuclear and cellular function, the central role of telomere length in determining telomere function,the investigator study that the changes of telomere length in peripheral blood leukocyte of patients are associated with the dosage of propofol in anesthesia induction.

A hundred patients with the American Society of Anesthesiologists (ASA) physical status I-II, aged from 18 to 80 years, gave an informed-written consent to participate.Testing took place in the morning after an overnight fast. Patients were scheduled for elective surgical procedures. After arrival to the operating theater, the peripheral venous line for fluid and drug administration was inserted. The electrocardiogram, heart rate, a noninvasive blood pressure, a pulse oximeter and bispectral (BIS) Index were monitored continuously. 100% oxygen was given for 3 min by face mask. Anesthesia was induced by intravenous infusion of propofol via the syringe pump at a rate of 30 mg/kg/h. Recordings began before propofol induction started. After the start of the propofol infusion and BIS Index at 80, patients were asked loudly "open eyes" and examined eyelash reflex at 15-s intervals until loss of consciousness (unresponsiveness to the verbal command, no spontaneous movements and loss of eyelash reflex); and recordings of the heart rate, a noninvasive blood pressure and BIS Index were obtained during awake baseline and unconsciousness induced by propofol. Propofol dosage and consciousness disappearance time were recorded after propofol-induced loss of consciousness. The commands were spoken in a loud voice by the investigator and were repeated up to three times, if the subject failed to respond. A subject who obeyed command was considered conscious. The BIS index is useful, and a reliable and sensitive indicator for assessing the level of consciousness during sedation and hypnosis with propofol so that the investigators recorded BIS index to evaluate level of consciousness. To minimize artifacts, patients were instructed not to open their eyes, talk, or move during the heart rate, a noninvasive blood pressure and BIS Index recordings before the propofol infusion and the sedation level was assessed until the patient's unconsciousness.

Inclusion Criteria:

• Patients were scheduled for elective surgical procedures

Exclusion Criteria:

• patients with known cardiac, pulmonary, renal disease, hearing disorders or neurological diseases, diabetes, and patients taking drugs affecting to the central nervous system or consuming more than 20 g alcohol daily, a body mass index>30