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To investigate the effect of pulsatility of venous flow waveform in the inferior and superior caval vessels on the performance of functional and “failing” Fontan patients based on two primary performance measures – the conduit power loss and the distribution of inferior caval flow (hepatic factors) to the lungs.
Doppler angiography flows were acquired from two typical extra-cardiac conduit “failing” Fontan patients, aged 13 and 25 years, with ventricle dysfunction. Using computational fluid dynamics, haemodynamic efficiencies of “failing”, functional, and in vitro-generated mechanically assisted venous flow waveforms were evaluated inside an idealised total cavopulmonary connection with a caval offset. To investigate the effect of venous pulsatility alone, cardiac output was normalised to 3 litres per minute in all cases. To quantify the pulsatile behaviour of venous flows, two new performance indices were suggested.
Variations in the pulsatile content of venous waveforms altered the conduit efficiency notably. High-frequency and low-amplitude oscillations lowered the pulsatile component of the power losses in “failing” Fontan flow waveforms. Owing to the offset geometry, hepatic flow distribution depended strongly on the ratio of time-dependent caval flows and the pulsatility content rather than mixing at the junction. “Failing” Fontan flow waveforms exhibited less balanced hepatic flow distribution to lungs.
The haemodynamic efficiency of single-ventricle circulation depends strongly on the pulsatility of venous flow waveforms. The proposed performance indices can be calculated easily in the clinical setting in efforts to better quantify the energy efficiency of Fontan venous waveforms in pulsatile settings.
This chapter presents a study which recognized that the resistance index (RI) of the uterine arteries was around 0.88 until day 13 of a 28-day cycle. The researchers measured the pulsatility index (PI) in 8 women with spontaneous cycles, 20 women undergoing induction of ovulation with clomiphene citrate, and 11 women undergoing controlled ovarian stimulation for in-vitro fertilization with gonadotropin-releasing hormone agonists (GnRH-a), human menopausal gonadotropin (hMG), and human chorionic gonadotropin (hCG). The intraovarian PI showed a gradual decrease from the early follicular (1.05) through the periovulatory (0.99) to the mid-luteal phase (0.85). The detection and quantification of follicular vascularity with pulsed color Doppler is used to predict oocyte recovery rate and hence may be useful in determining the most appropriate time to administer hCG. Oocyte/embryo selection for transfer may benefit from a brief color Doppler examination of each follicle at aspiration and pooling of oocytes with respect to follicles.
Transcranial Doppler (TCD) utilizes the Doppler principle to determine the direction and velocity of blood flow. Most TCDs use long sample volumes in order to improve the signal-to-noise ratio and ease the detection of the basal cerebral arteries. Most TCDs use the fast Fourier transform (FFT) method of spectral analysis which produces the typical visual representation of blood flow velocity. The FFT method of spectral analysis is used in most TCD systems because it allows almost instantaneous detection and display of information in a form which is understandable to most observers. Pulsatility and resistance indices reflect characteristics of the Doppler shift velocity waveforms, and indicate the degree of pulsatility of the waveform. TCD is able to detect two of the major causes of neurological deficits that are abnormalities in blood flow and cerebral embolization. These have made it a valuable practical tool for treating patients in diverse clinical disciplines.
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