An adaptive approach to computing the spectrum and mean frequency of Doppler signals

Obesity Paradox and Recurrent Coronary Heart Disease in a Population-Based Study: Tehran Lipid and Glucose Study

BACKGROUND

Although current data shows a positive association between obesity and development of coronary heart disease (CHD) in general population, there is limited data on the important protective role of central or general obesity in patients with prevalent CHD or the "obesity paradox", from this region.

OBJECTIVES

The objective of the present investigation was to describe the relationship between BMI categories and the recurrence of CHD in patients with a history of CHD using data from a large population-based study, the Tehran lipid and glucose study (TLGS).

PATIENTS AND METHODS

The study was conducted on 440 adults, aged ≥ 30 years, with a history of CHD at baseline who attended the first (1999 - 2001) or second (2001 - 2003) phases of the Tehran Lipid and Glucose Study and had at least one year of follow-up until March 31, 2010. Cox proportional hazard models were used to evaluate the association among various BMI groups and recurrent CHD incidence.

RESULTS

During a median follow-up of 8.44 years, 169 new cases of CHD occurred (incidence density of: 54.53 per 1000 person-years). The incidence of recurrent CHD was higher in the normal BMI compared with overweight and obese categories (68.71, 47.56 and 54.46 per 1000 person-years, respectively). In multivariable models, using the forward stepwise selection approach, compared to the overweight group (0.48 95% CI, 0.30-0.80), the obese group (0.55 95% CI, 0.28-1.06) lost its significant protective effect.

CONCLUSIONS

Results of this study demonstrated an apparently protective effect for overweight in comparison with normal weight against long-term recurrent CHD in patients with history of CHD.

ANALYSIS OF THE DOPPLER ULTRASOUND SIGNAL BY WAVELET PACKET TRANSFORM

The study presented in this paper is concerned with the analysis of the ultrasound Doppler signal of the arteries in the spectro-temporal domain using the wavelet packet transform. The spectro-temporal representation is obtained by the decomposition of the Doppler signal in frequency sub-band, using filter banks associated with a well chosen wavelet. It is shown that the decomposition level depends on the stationarity of the Doppler signal, and the best profile of blood flow velocity in arteries is obtained according to an appropriate choice of wavelet type.

Three types of wavelets have been tested on two Doppler signals previously recorded from the carotid and femoral arteries. The best representation is obtained when the frequency sub-bands of the filter bank associated with chosen wavelet are regularly distributed in the frequency domain and the level of decomposition is 7.

Developments in cardiovascular ultrasound: Part 1: Signal processing and instrumentation

One of the major contributions to the improvement of spectral Doppler and colour flow imaging instruments has been the development of advanced signal-processing techniques made possible by increasing computing power. Model-based or parametric spectral estimators, time-frequency transforms, station-arising algorithms and spectral width correction techniques have been investigated as possible improvements on the FFT-based estimators currently used for real-time spectral estimation of Doppler signals. In colour flow imaging some improvement on velocity estimation accuracy has been achieved by the use of new algorithms but at the expense of increased computational complexity compared with the conventional autocorrelation method. Polynomial filters have been demonstrated to have some advantages over IIR filters for stationary echo cancellation. Several methods of velocity vector estimation to overcome the problem of angle dependence have been studied, including 2D feature tracking, two and three beam approaches and the use of spectral width in addition to mean frequency. 3D data acquisition and display and Doppler power imaging have also been investigated. The use of harmonic imaging, using the second harmonic generated by encapsulated bubble contrast media, seems promising particularly for imaging slow flow. Parallel image data acquisition using non-sequential scanning or broad beam transmission, followed by simultaneous reception along a number of beams, has been studied to speed up 'real-time' imaging.