ANALYSIS OF HEART-RATE-VARIABILITY - BACK GROUND, METHODS, AND POSSIBLE USE IN ANESTHESIA

Background and methods. Small, periodic fluctuations in heart rate are well known to physicians, the respiratory sinus arrhythmia (RSA) bein g the most easily detectable form of this heart rate variability (HRV) . Since it is caused by changing activity of the autonomic nervous sys tem (ANS) controlling heart rate, HRV is investigated to gain informat ion on the functional states of the ANS. Recent developments have led to computer-aided processing of EKG signals based on time and frequenc y domain methods - the latter using power spectral analysis by fast Fo urier or autoregressive algorithms - to exactly describe and quantify HRV. Three major regions in the frequency spectrum between 0.03 and 0. 5 Hz (the suitable range for short-term recordings) have been establis hed: (1) a region around the respiratory rate, usually between 0.2 and 0.35 Hz, called high frequency (HF), (2) a region around 0.1 Hz attri buted to vasomotor activity feedback, called low (or mid-) frequency ( LF), (3) a peak around 0.04-0.05 Hz correlated to thermoregulation, ca lled very low (or low)frequency (VLF). Power spectral density of HRV i s now commonly accetped as a measure of autonomic cardiovascular contr ol activity. By studies on vagal or sympathetic blockade, the HF (or R SA) region has been attributed solely to vagal activity, while both pa rts of the ANS may contribute to the other two, with, however: the vag al part predominating the resting, healthy individuals. Clinical appli cations/anaesthesia. Thus, spectral analysis of HRV provides a measure for quantifying sympatho-vagal balance in its physiological range. Ad ditionally, reduction of HRV along with cardiovascular disease, includ ing hypertension, myocardial infarction, heart failure and sudden card iac death, as well as with autonomic dysregulation, has been reported. Since is also a striking reduction produced by most anaesthetic agent s, RSA and HRV are investigated as measures of anaesthetic depth. Ther e are contradictory data on the influence of ventilation, medication, and co-existing disease on the spectrum, and thus validation of the me thod is still to be achieved. It has, however, been proven useful in s ome studies as a parameter for risk assessment of perioperative or pos t-infarction cardiovascular complications.