Electrophysiological correlates of pulsatile and surge gonadotrophin secretion.
(17/1458)
The hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator governs intermittent discharges of GnRH into the pituitary portal circulation and, consequently, modulates the pulsatile pattern of gonadotrophin secretion. Electrophysiological correlates of pulsatile gonadotrophin secretion have been demonstrated in the mediobasal hypothalamus of monkeys, rats and goats by recording multiple unit activity. A temporal coincidence between characteristic increases in multiple unit activity and gonadotrophin pulses in the circulation is seen under a variety of physiological and experimental conditions in all three species examined, providing evidence that hypothalamic multiple unit activity originates in the GnRH pulse generator. During a preovulatory gonadotrophin surge induced by oestrogen in ovariectomized animals or occurring spontaneously in intact animals, GnRH pulse generator activity is decelerated, suggesting that it is not involved in generating the gonadotrophin surge. The gonadotrophin surge may be generated by an oestrogen-responsive neuronal complex intrinsically different from the GnRH pulse generator, the electrical operation of which remains unknown. (+info)
High-resolution ultrasonic imaging of blood flow in the anterior segment of the eye.
(18/1458)
PURPOSE: To develop a noninvasive technique to visualize and measure blood flow in the iris and ciliary body. METHODS: Echo data from 50-MHz ultrasound scans of the iris and ciliary body of rabbits were digitized using a new "swept scan" modality. The method makes use of spatial oversampling to identify regions with scatterers whose range changes with time. The data allowed construction of high-resolution B-mode images with embedded flow information. Pulsatility over the cardiac cycle was evaluated by sending a series of pulses along a single line of sight containing a vessel of interest. Local blood flow and changes over the cardiac cycle before and after application of atropine were quantified. RESULTS: Flow was identified in the radial vessels and major arterial circle of the iris. Vessels with lumens as small as 40 microm in diameter and flow velocities as low as 0.6 mm/sec were measured. Change in blood velocity over the cardiac cycle was determined to be approximately 27%. Peak systolic velocity after administration of topical atropine increased by 72%. CONCLUSIONS: This technique allowed visualization of flow using the same type of very-high-frequency transducer now widely used for imaging the anterior segment. The technique can also be used at lower frequencies for more posterior tissues with similar improvement of resolution over Doppler. The ability to examine flow in the anterior segment of the eye offers a new tool for study of glaucoma, hypotony, tumors, and other disorders. (+info)
Hemodynamic model for analysis of Doppler ultrasound indexes of umbilical blood flow.
(19/1458)
A hemodynamic model for pulsatile fluid flow in a pressurized thin-walled elastic tube was applied for the computation of volumetric blood flow and velocity profiles for a given set of system parameters at any selected location along the umbilical artery. The velocity profiles over one heart cycle provide the fetal blood flow velocity waveforms (FVW) from which the usual Doppler indexes (DI) can be derived. The model was used for a comprehensive investigation of the correlation between DI and system parameters that reflect the anatomy and physiology of umbilical blood flow. The simulations showed that the radial location of the Doppler measurement is insignificant for the calculated DI, whereas the axial site is important. The analysis showed that decreasing the diameter or increasing the length of the umbilical artery reduces fetal mean blood flow rate and increases the DI. Increasing blood viscosity tends to induce similar patterns, whereas decreasing arterial compliance or increasing blood density decreases the DI with little effect on blood flow rate. Fetal heart rate has a minor effect on both DI and fetal blood flow rate. This study provides insight into the dependence of DI on the anatomic and physiological characteristics of umbilical blood flow. (+info)
Menorrhagia and uterine artery blood flow.
(20/1458)
Menorrhagia is a significant problem in women of reproductive age. In half of the cases no specific aetiology is known. Vascular factors play a role but remain poorly understood. We chose to study whether any association exists between the flow impedance of uterine arteries and the amount of menstrual blood loss. The study population consisted of 60 spontaneously menstruating 35- to 49-year-old women without endometrial hyperplasia, polyps, or submucous fibroids. The pulsatility index (PI) from uterine arteries, arcuate arteries, and radial arteries was measured by transvaginal colour Doppler. Menstrual blood loss was measured by the alkaline haematin method. A significant inverse correlation was found between uterine artery PI and the amount of menstrual blood loss, suggesting that women with lower uterine flow impedance bleed more. A regression model confirmed that this association was specific and not explained by uterine size, fibroids or any other of the 11 potential confounders included in the model. The correlation between uterine artery PI and amount of menstrual blood loss suggests that vascular factors may be involved in the pathogenesis of menorrhagia. (+info)
In vivo human brachial artery elastic mechanics: effects of smooth muscle relaxation.
(21/1458)
BACKGROUND: The effects of smooth muscle relaxation on arterial wall mechanics are controversial. We used a new, in vivo, noninvasive technique to measure brachial artery wall mechanics under baseline conditions and following smooth muscle relaxation with nitroglycerin (NTG). METHODS AND RESULTS: Eight healthy, normal subjects (6 male, 2 female; age 30+/-3.1 years) participated in the study. The nondominant brachial artery was imaged through a water-filled blood pressure cuff using an external ultrasound wall-tracking system at baseline and following 0.4 mg sublingual NTG. Simultaneous radial artery pressure waveforms were recorded by tonometry. Transmural pressure (TP) was reduced by increasing water pressure in the cuff. Brachial artery area, unstressed area, compliance, stress, strain, incremental elastic modulus (Einc), and pulse wave velocity (PWV) were measured over a TP range from 0 to 100 mm Hg. Baseline area versus TP curves generated 30 minutes apart were not significantly different. NTG significantly shifted area versus TP (P<0.0001) and compliance versus TP (P<0.001) curves upward, whereas the Einc versus TP (P<0.05) and PWV versus TP (P<0. 01) curves were shifted downward. NTG also significantly shifted stress versus strain (P<0.01) and Einc versus strain (P<0.01) curves to the right. CONCLUSIONS: We conclude that brachial artery elastic mechanics can be reproducibly measured over a wide range of TP and smooth muscle tone using a new noninvasive ultrasound technique. Smooth muscle relaxation with NTG increases isobaric compliance and decreases isobaric Einc and PWV in the human brachial artery. (+info)
Pulsatile secretion of atrial natriuretic peptide and brain natriuretic peptide in healthy humans.
(22/1458)
Both atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are involved in sodium and water homoeostasis in healthy humans. The plasma concentrations of the natriuretic peptides can be used to differentiate between dyspnoea of cardiac and pulmonary origin, and the degree of elevation of the peptide levels in the plasma in heart failure is a measure of the severity of the disease. However, the patterns of secretion of ANP and BNP are not clear either in healthy humans or in patients. The purpose of the present study was to test the hypotheses that both ANP and BNP are secreted in pulses in healthy humans, and that this phenomenon can be revealed by determination of ANP and BNP in peripheral venous blood samples. In 12 healthy subjects, blood samples were drawn every 2 min through an intravenously inserted plastic needle over a period of 2 h. Plasma concentrations of ANP and BNP were determined by RIAs, and the results were analysed for pulsatile behaviour by Fourier transformation. Pulsatile secretion of ANP was seen in 10 out of 12 subjects [nu=0.028 min(-1) (median; range 0.013-0.047 min(-1)), i.e. a pulse of ANP with an interval of 36 min (range 21-77 min)]. Pulsatile secretion of BNP was seen in nine out of 12 patients [nu=0. 021 min(-1) (range 0.013-0.042 min(-1)), i.e. a pulse of BNP with an interval of 48 min (range 24-77 min)]. The main conclusion is that the secretion patterns of both ANP and BNP are pulsatile in most healthy humans. Consequently, it is important to study whether pulsatile secretion also occurs in heart failure in order to obtain the most informative predictive values both in the differential diagnosis of dyspnoea and in the evaluation of the severity of the disease. (+info)
Pulsatile output of prostaglandin F(2alpha) does not increase around the time of luteolysis in the pregnant goat.
(23/1458)
Prostaglandin (PG) F(2alpha) secreted from the uterus is the luteolysin of the estrous cycle and is also believed to be responsible for luteolysis in the pregnant doe at term. We have reported that basal progesterone concentrations decrease before basal PGF(2alpha) concentrations increase, which is inconsistent with this view. In this study we investigated whether luteolysis is associated with increased frequency or amplitude of pulsatile PGF(2alpha) secretion in does over the last 2 wk of gestation. Progesterone concentrations decreased approximately 1 wk before parturition. There was no accompanying increase in PGF(2alpha) concentrations or pulse frequency, and those pulses that were observed were of lesser amplitude and duration than those that have been associated with luteolysis in cycling ewes. A small increase in PGF(2alpha) pulse frequency was identified during the 3 days before parturition, but this was not associated with any change in progesterone concentrations. The biological significance of these small changes in PGF(2alpha) pulse frequency is obscure, although the high concentration of this eicosanoid at labor may have been related to the final, precipitous decline in plasma progesterone concentrations. These findings do not support the notion that PGF(2alpha) is the principal luteolysin in the pregnant doe at term. (+info)
Single and serial estimates of amniotic fluid volume and umbilical artery resistance in the prediction of intrauterine growth restriction.
(24/1458)
OBJECTIVES: To determine whether single or serial estimates of both the amniotic fluid index (AFI) or pulsatility index (PI) of the umbilical artery Doppler waveform can usefully identify infants with anthropometric features of intrauterine growth restriction (IUGR). METHODS: A total of 274 women underwent serial antenatal ultrasound examinations at predetermined intervals. Four biophysical parameters were considered: AFI and PI prior to delivery and change in AFI and PI over a 28-day period in the third trimester. All values were expressed as standard deviation scores. IUGR was diagnosed if the neonate demonstrated skinfold thickness < 10th centile, ponderal index < 25th centile or mid-arm circumference to occipitofrontal circumference (MAC:OFC) < -1 SD. Receiver operator characteristic curves were used to determine an optimal cut-off point, and test performance of the biophysical parameters were expressed as likelihood ratios (LR). RESULTS: The test performances of all four ultrasound parameters for any of the three diagnostic criteria for IUGR was poor. The highest positive LR was only 2.5 (95% CI 1.5-4.1) for PI prior to delivery in the prediction of ponderal index < 25th centile. CONCLUSION: Despite positive associations between single and serial estimates of AFI and PI with abnormal neonatal morphometry, the likelihood ratios remained low. The results of this study do not support the use of single or serial estimates of AFI or umbilical artery PI in the prediction of IUGR. (+info)