Biomedical applications of time-frequency analysis

Spectral analysis of heart rate variability (HRV) provides an estimate of sympathetic and parasympathetic influences on heart rate without drugs or other invasive procedures. However, there are many situations where heart rate changes rapidly over time and the control of those changes is of considerable interest. Time-frequency analysis was utilized to expand the concept of spectral analysis of HRV to describe changes in vagal tone and sympatho-vagal balance as a function of time. There were two major advantages in using time-frequency analysis. First, vagal tone and sympatho-vagal balance were described as functions of time. Hence, a better understanding was attained about autonomic control of rapidly changing signals. Second, the rate of increase or decrease of vagal tone and sympatho-vagal balance was quantified. As a result of this methodology, pathophysiological conditions of paramount importance, such as arterial hypertension, myocardial ischemia, sudden cardiac death, and heart failure might soon undergo a novel scrutiny with practical implications.>