Smoothed pseudo Wigner-Ville distribution as an alternative to Fourier transform in rats

Techniques for examining signals in the time and frequency domains are well -established tools. These tools have their limitations; they tell us in a b road sense where the signal component exists in the frequency domain, but t hey do not tell us how its frequency characteristics change over time. The time-frequency has become a powerful alternative for the analysis of signal s. Among various time-frequency distribution methods, one of the most studi ed is the Wigner-Ville distribution. The aim of this study was to evaluate in conscious rats smoothed pseudo Wigner-Ville distribution (SPWVD) as an a lternative to the fast Fourier transform (FFT) in RR intervals and in systo lic blood pressure (SBP), before and after adrenergic and cholinergic recep tor blockade. Fourteen Wistar rats equipped with telemetry probe were evalu ated: (1) under control conditions; (2) after injection of saline 1100 mul kg(-1) i.v.); (3) after atenolol (1 mg kg(-1) i.v.); (4) after atropine met hyl nitrate (0.5 mg kg(-1) i.v.); and (5) after phentolamine (5 mg kg(-1) i .v.). FFT and SPWVD were applied to RR intervals and SEP time series. Six-m inute time series of RR intervals, systolic and diastolic pressures were an alysed. The bias and distribution of differences between FFT and SPWVD meth ods in RR intervals under base conditions were 1.4+/-0.4% (r(2)=0.94; P<0.0 1) in LF/LF+HF; 1.5+/-0.5% (r(2)=0.92; P<0.01) in HF/LF+HF and 4.8+/-1.9% ( r(2)=0.92; P<0.01) in LF/HF. In SEP the bias and distribution were 1.5+/-0. 8% (r(2)=0.90; P<0.05) in LF/LF+HF and 1.7+/-0.6% (r(2)=0.92; P<0.01) in HF /LF+HF. In the frequency domain analysis of RR intervals and SEP there was no difference between FFT and SPWVD. The agreement between the methods demo nstrates that in stationary signals both methods can be used interchangeabl y. SPWVD may be an interesting tool to analyse biomedical signals; it provi des a good resolution at high frequency and a good frequency resolution at low frequencies independently if signals remain stationary. (C) 2001 Elsevi er Science B.V. All rights reserved.