Computerized Determination Of Velocity Time Integral In Normal Subjects.

Background:Velocity time integral (VTI) of the blood flow wave is derived from the analysis of the image of the Doppler wave. VTI can be utilized to determine hemodynamic


Introduction
In the main Doppler modalities (continuous and pulsed Doppler), the velocity information is derived from the frequency shift that occurs between transmitted and reflected ultrasound.By convention, a velocity towards the transducer is displayed above the base line of Doppler wave, and away from it bellows the base line.To record a Doppler spectrum across aortic valve, the sample volume is positioned in the aorta directly behind the valve (1) .VTI is the integral of the spectral trace or the area under the Doppler waveform (it can be determined by planimetric analysis) (1,2) .
VTI is utilized in the calculation of stroke volume, assessment of aortic valve diseases (aortic valve stenosis and regurgitation) (3,4,5), and in the predict of cardiac output (6) .
In the present study new visual basic form was established using suitable computer programe for the analysis of the images of the aortic Doppler waves to determine VTI .

Discussion
VTI is utilized in the determination of cardiac output and stroke volume (6) .Cardiac output has been measured from the pulmonary artery (9,10) and left outflow tract (11) with the use VTI obtained by pulsed -wave Doppler and continuos -wave Doppler (12) .Doppler stroke volume determination is based on the principle (stroke volume equal to VTI multiplied by the cross-sectional area of the aortic valve) (2) .
Generally Doppler echocardiography provides accurate hemodynamic information for the diagnosis, assessment of severity and follow -up of patients with aortic stenosis and aortic regurgitation (3,13) .Also Doppler echocardiography may provide a reliable noninvasive method to determine pulmonary vascular resistance depending on the peak tricuspid regurgitant velocity and VTI of the right ventricular outflow tract (14) .
In the present studies VTI is determined (computerized calculations) using personal computer and visual basic form.The method used is better than manual calculations using planimeter (which is time consuming).Also the present study can be applied to analyze the images of the Doppler waves of the patients that were previously studied (off-line method), while the Doppler wave analysis is on-line using the new echocardiography system.VTI determined of the normal subjects studied in the present study is (18.54 ± 4.4 cm for the aorta), which is comparable with the VTI that previously determined by another investigators (18 to 20 cm for the aorta) (15,16) .
In conclusion the clinical application of the present method is to determine VTI of the Doppler waves of the blood velocity across aortic valve, which can be used as reference in the evaluation of the blood flow across aortic valve.VTI is a convenient guide to determine the severity of aortic valve diseases, stroke volume, cardiac output and vascular resistance in certain cardiac disorders.
Doppler waves were analyzed to determine the derived Doppler parameters in twenty normal subjects who underwent echocardiography and Doppler study (across aortic valve in the apical five chamber view), their average values of some physical parameters and left ventricular dimensions at end systole and end diastole (LVESD and LVEDD) are shown in

1 .
The analysis of the Doppler wave is done according to the following steps: Establishment of visual basic form to analyze the Doppler waves in apical five-chamber view of the subjects studied (Fig.1), to determine the derived Doppler parameters (ET, Vm) of the blood flow across aortic valve of the patients studied.

Figure- 1 :Figure- 2 :
Figure-1: The image of the Doppler wave of the blood flow across aortic valve in apical five-chamber view.

3 :
Analysis of the Doppler wave to obtain data "required" to compute VTI Determination of X-Y coordinates of the outline of the Doppler wave Determination of ETd ( in cm) Determination of ET (in sec) ET= ETd / R R= 10 cm/ sec (the rate of the sweeping of the Doppler wave on the screen) Determination of Ad of the Doppler wave (Doppler -derived parameters of the subjects studied.