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Effect of non-linearity in predicting Doppler waveforms through a novel model.

Gayasen A, Dua SK, Sengupta A, Nagchoudhuri D - Biomed Eng Online (2003)

Bottom Line: Normal pregnancy has been successfully modeled and the doppler output waveforms are simulated for different gestation time using the model.Both these results are established clinical facts.Total harmonic distortion (THD) is found to be informative in determining the Feto-maternal health.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, Indian Institute of Technology, New Delhi, India. gayasen@cse.psu.edu

ABSTRACT

Background: In pregnancy, the uteroplacental vascular system develops de novo locally in utero and a systemic haemodynamic & bio-rheological alteration accompany it. Any abnormality in the non-linear vascular system is believed to trigger the onset of serious morbid conditions like pre-eclampsia and/or intrauterine growth restriction (IUGR). Exact Aetiopathogenesis is unknown. Advancement in the field of non-invasive doppler image analysis and simulation incorporating non-linearities may unfold the complexities associated with the inaccessible uteroplacental vessels. Earlier modeling approaches approximate it as a linear system.

Method: We proposed a novel electrical model for the uteroplacental system that uses MOSFETs as non-linear elements in place of traditional linear transmission line (TL) model. The model to simulate doppler FVW's was designed by including the inputs from our non-linear mathematical model. While using the MOSFETs as voltage-controlled switches, a fair degree of controlled-non-linearity has been introduced in the model. Comparative analysis was done between the simulated data and the actual doppler FVW's waveforms.

Results & discussion: Normal pregnancy has been successfully modeled and the doppler output waveforms are simulated for different gestation time using the model. It is observed that the dicrotic notch disappears and the S/D ratio decreases as the pregnancy matures. Both these results are established clinical facts. Effects of blood density, viscosity and the arterial wall elasticity on the blood flow velocity profile were also studied. Spectral analysis on the output of the model (blood flow velocity) indicated that the Total Harmonic Distortion (THD) falls during the mid-gestation.

Conclusion: Total harmonic distortion (THD) is found to be informative in determining the Feto-maternal health. Effects of the blood density, the viscosity and the elasticity changes on the blood FVW are simulated. Future works are expected to concentrate mainly on improving the load with respect to varying non-linear parameters in the model. Heart rate variability, which accounts for the vascular tone, should also be included. We also expect the model to initiate extensive clinical or experimental studies in the near future.

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A frame extracted from doppler FVW
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Figure 3: A frame extracted from doppler FVW

Mentions: The video recording of Doppler FVW's measured at the level of the uterine or the arcuate artery were digitized and the frames were taken out using a tool available with the special workstation provided by the silicon graphics (SGI). The application is known as "Camera" (Fig. 3). To analyze the FVW, an envelope was extracted for one period and around 75 samples were taken from it. Software was developed in C++ to approximately determine the magnitude of Fourier Series coefficients. We mapped all the periods on a fixed time of 0.83 seconds, which is a normal heart beat period and took frequency domain average of all such periods. We considered FVW's of equal time frame for purpose of analysis, in order to remove the time variations, which is to the order of ± 10% analyzed for a single patient. The problem was tackled by mapping all the periods on a fixed time of 0.83 seconds, which is a normal standard heart beat period. We took frequency domain average of all such periods analyzed for a single patient. Three patients representing three different conditions and gestation period were analyzed and the following results obtained. In abnormal pre-Eclamptic condition (patient 3), lower harmonic magnitude is lesser compared to the normal pregnancy (Fig. 4). The actual Doppler FVW's used for the analysis are collected from the records of the mothers undergoing routine diagnostic Doppler and sonography tests in our hospital clinic for the various pregnancy disorders as well as the established data from the published literature. The analysis was done primarily to validate the model, secondly to understand the total harmonic distortion and thirdly to propose different Doppler FVW's pattern that may emerge for various non-linear inputs which can be used to initiate further comparative and experimental studies in future.


Effect of non-linearity in predicting Doppler waveforms through a novel model.

Gayasen A, Dua SK, Sengupta A, Nagchoudhuri D - Biomed Eng Online (2003)

A frame extracted from doppler FVW
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC222923&req=5

Figure 3: A frame extracted from doppler FVW
Mentions: The video recording of Doppler FVW's measured at the level of the uterine or the arcuate artery were digitized and the frames were taken out using a tool available with the special workstation provided by the silicon graphics (SGI). The application is known as "Camera" (Fig. 3). To analyze the FVW, an envelope was extracted for one period and around 75 samples were taken from it. Software was developed in C++ to approximately determine the magnitude of Fourier Series coefficients. We mapped all the periods on a fixed time of 0.83 seconds, which is a normal heart beat period and took frequency domain average of all such periods. We considered FVW's of equal time frame for purpose of analysis, in order to remove the time variations, which is to the order of ± 10% analyzed for a single patient. The problem was tackled by mapping all the periods on a fixed time of 0.83 seconds, which is a normal standard heart beat period. We took frequency domain average of all such periods analyzed for a single patient. Three patients representing three different conditions and gestation period were analyzed and the following results obtained. In abnormal pre-Eclamptic condition (patient 3), lower harmonic magnitude is lesser compared to the normal pregnancy (Fig. 4). The actual Doppler FVW's used for the analysis are collected from the records of the mothers undergoing routine diagnostic Doppler and sonography tests in our hospital clinic for the various pregnancy disorders as well as the established data from the published literature. The analysis was done primarily to validate the model, secondly to understand the total harmonic distortion and thirdly to propose different Doppler FVW's pattern that may emerge for various non-linear inputs which can be used to initiate further comparative and experimental studies in future.

Bottom Line: Normal pregnancy has been successfully modeled and the doppler output waveforms are simulated for different gestation time using the model.Both these results are established clinical facts.Total harmonic distortion (THD) is found to be informative in determining the Feto-maternal health.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, Indian Institute of Technology, New Delhi, India. gayasen@cse.psu.edu

ABSTRACT

Background: In pregnancy, the uteroplacental vascular system develops de novo locally in utero and a systemic haemodynamic & bio-rheological alteration accompany it. Any abnormality in the non-linear vascular system is believed to trigger the onset of serious morbid conditions like pre-eclampsia and/or intrauterine growth restriction (IUGR). Exact Aetiopathogenesis is unknown. Advancement in the field of non-invasive doppler image analysis and simulation incorporating non-linearities may unfold the complexities associated with the inaccessible uteroplacental vessels. Earlier modeling approaches approximate it as a linear system.

Method: We proposed a novel electrical model for the uteroplacental system that uses MOSFETs as non-linear elements in place of traditional linear transmission line (TL) model. The model to simulate doppler FVW's was designed by including the inputs from our non-linear mathematical model. While using the MOSFETs as voltage-controlled switches, a fair degree of controlled-non-linearity has been introduced in the model. Comparative analysis was done between the simulated data and the actual doppler FVW's waveforms.

Results & discussion: Normal pregnancy has been successfully modeled and the doppler output waveforms are simulated for different gestation time using the model. It is observed that the dicrotic notch disappears and the S/D ratio decreases as the pregnancy matures. Both these results are established clinical facts. Effects of blood density, viscosity and the arterial wall elasticity on the blood flow velocity profile were also studied. Spectral analysis on the output of the model (blood flow velocity) indicated that the Total Harmonic Distortion (THD) falls during the mid-gestation.

Conclusion: Total harmonic distortion (THD) is found to be informative in determining the Feto-maternal health. Effects of the blood density, the viscosity and the elasticity changes on the blood FVW are simulated. Future works are expected to concentrate mainly on improving the load with respect to varying non-linear parameters in the model. Heart rate variability, which accounts for the vascular tone, should also be included. We also expect the model to initiate extensive clinical or experimental studies in the near future.

Show MeSH
Related in: MedlinePlus