Pulsatile flow

About: Pulsatile flow is a research topic. Over the lifetime, 6278 publications have been published within this topic receiving 149638 citations.

Hormone ontogeny in the ovine fetus. XVII. Demonstration of pulsatile luteinizing hormone secretion by the fetal pituitary gland

Abstract: To determine whether pulsatile gonadotropin secretion occurs in the fetus, plasma immunoreactive ovine LH (oLH) concentrations were determined by homologous RIA in serial samples obtained in 51 chronically catheterized fetuses between 79 and 140 days gestation. Pulsatile secretion of LH was detected in 39 fetuses, with a peak amplitude ranging from 1.2-11.5 ng/ml (mean +/- SD, 4.5 +/- 2.3 ng/ml). The mean plasma oLH concentration between pulses was 0.4 +/- 0.23 ng/ml. The mean amplitudes of the LH pulses were similar in the age range studied, and a sex difference was not detected. The estimated interpulse interval (determined by dividing the total number of hours during which blood samples were obtained by the number of pulses demonstrated) was 2.4 h between 91 and 110 days gestation. The pattern of plasma oFSH concentration was examined in 20 fetuses between 98 and 123 days gestation. Six fetuses with gestational ages between 106 and 115 days had FSH pulses that were equal or more than 2 times the sensitivity of the RIA. This study demonstrates a pulsatile mode of LH secretion by the ovine fetal pituitary as early as 81 days gestation and provides indirect evidence for pulsatile LRF secretion by the fetal hypothalamus and an operative LRF pulse generator by midgestation, the earliest stage in gestation studied.

Neuroendocrine control of pulsatile GnRH secretion during the ovarian cycle

Abstract: This article reviews the neuroendocrine control of episodic GnRH secretion during the ovine oestrous cycle. There is general agreement that endogenous opioid peptides (EOPs) mediate the negative feedback action of progesterone on GnRH pulse frequency during the luteal phase of the ovarian cycle and recent preliminary data have implicated the dynorphin-kappa-receptor system in this effect of progesterone. Progesterone also acutely inhibits GnRH pulse frequency via a non-EOP mechanism, as naloxone does not block the rapid effects of this steroid. The effects of bicuculline, 3alpha-hydroxy-5alpha-pregnan-20-one and RU486 consistently indicated that the gamma-aminobutyric acid A (GABA-A) receptor is also not involved in the acute actions of progesterone. Thus, the neural system mediating this effect remains to be determined. Oestradiol has several actions on episodic GnRH secretion. The most well characterized action is inhibition of GnRH pulse amplitude, which is probably mediated by noradrenergic neurones. Oestradiol also increases the response to progesterone negative feedback, alters GnRH pulse shape and increases GnRH pulse frequency. The first two of these actions may involve EOPs, whereas the mechanisms underlying GnRH pulse frequency are currently unknown. Finally, there is also evidence that EOPs play a physiological role in synchronizing the firing of the GnRH neurones responsible for episodic release. Specifically, the effects of naloxone on the GnRH pulse shape lead to the hypothesis that EOP tone contributes to the termination of each GnRH pulse and prevents random firing of these GnRH neurones between pulses. Thus, it appears that EOPs play an important role in controlling several different aspects of pulsatile GnRH release during the ovine oestrous cycle.

Two-phase non-linear model for the flow through stenosed blood vessels

Abstract: Pulsatile flow of a two-phase model for blood flow through arterial stenosis is analyzed through a mathematical analysis. The effects of pulsatility, stenosis, peripheral layer and non-Newtonian behavior of blood, assuming the blood in the core region as a Herschel-Bulkley fluid and the plasma in the peripheral layer as a Newtonian fluid, are discussed. A perturbation method is used to solve the resulting system of non-linear quasi-steady differential equations. The expressions for velocity, wall shear stress, plug core radius, flow rate and resistance to flow are obtained. It is noticed that the plug core radius and resistance to flow increase as the stenosis size increases while all other parameters held constant The wall shear stress increases with the increase of yield stress while keeping other parameters as invariables. It is observed that the velocity increases with the axial distance in the stenosed region of the tube upto the maximum projection of the stenosis.

A new algorithm for deriving pulsatile blood flow waveforms tested using simulated dynamic angiographic data

Abstract: In vascular pathology the assessment of disease severity and monitoring of treatment requires quantitative and reproducible measurements of arterial blood flow. We have developed a new technique for processing sequences of dynamic digital X-ray angiographic images. We have tested it using computer simulated angiographic data which includes the effect of pulsatile blood flow and X-ray quantum noise. A parametric image was formed in which the image grey-level represents dye concentration as a function of time and distance along a vessel segment. Adjacent concentration — distance profiles in the parametric image were re-registered along the vessel axis until a match occurred. A match was defined as the point where the sum of squares of the differences in the two profiles was a minimum. The distance translated per frame interval is equal to the bolus velocity. We have tested several contrast medium injection methods including constant flow and a range of discrete pulses per second. The technique proved to be robust and independent of injection technique. Average blood flow was measured for simulated pulsatile waveforms with mean flows of up to 650 ml/min (peak velocities up to 186 cm/s) in a range of diameters from 2 mm to 6 mm. The standard deviation of the error in the mean flow estimates over the whole range of velocities and vessel sizes was ±1.4 cm/s.

Vasodilatory Effect of Pulsatile Pressure on Coronary Resistance Vessels

Abstract: Intramyocardial pressure becomes high in systole and decreases in diastole. Therefore, the transmural pressure of the intramyocardial vessels is pulsatile, resulting in the cyclic distension of these vessels. However, the effect of pulsatility on the behavior of the coronary resistance vessels has not been evaluated. To assess the influence of pulsatile pressure on the behavior of the coronary arterioles, we measured the luminal cross-sectional area (CSA) of coronary arterioles under cyclically changing transmural pressure. Isolated porcine coronary arterioles (internal diameter, 100 to 150 microns) were cannulated with two micropipettes and pressurized with square waves (1 Hz) through both pipettes so as not to induce flow-dependent vasodilation. During the presence (active, induced by acetylcholine; n = 7) or absence (passive, abolished by bradykinin; n = 7) of vascular tone, the CSA was measured under the following conditions: (1) The amplitude of the pressure pulse was changed at a fixed mean pressure. (2) The mean pressure was changed at a fixed pressure pulse. With increasing pulse pressure, the mean CSA at steady state increased under active conditions, whereas it decreased under passive conditions (P < .0001). This vasodilatory effect of pulse pressure remained present after endothelial denudation (P < .0001; n = 6 vessels with basal tone, n = 9 vessels with U46619-induced tone). The mean steady state CSA under passive conditions increased with the mean pressure (P < .05), whereas under active conditions it remained constant in the range of mean pressures between 50 and 100 mm Hg, reflecting myogenic responsiveness. These results indicate that an increase in amplitude of the pressure pulse dilates coronary arterioles. The vasodilating effect of the pulsation may compensate partly for the extra compressing effect of cardiac contraction on the intramyocardial vessels.