Showing papers on "Pulsatile flow published in 1984"
TL;DR: It is inferred that P secretion by the ovary mediates the change in the LH secretory pattern during the luteal phase of the normal menstrual cycle, and that at least part of this effect is mediated by the central nervous system.
Abstract: Recent studies show that the frequency and amplitude of pulsatile LH secretion change during the normal human menstrual cycle; however, the neuroendocrine mechanisms underlying these changes are poorly understood. To assess the role of progesterone (P) in regulating LH secretion patterns, we treated normal women (n = 5) with im P in oil during the follicular phase of their cycle and compared LH pulse frequency, amplitude, and mean plasma level during treatment to those in normal cycling women. Normal women were studied five times in five menstrual cycles. Each study lasted 24 h, with a sampling interval of 20 min. The cycle phases studied were early follicular (twice), late follicular (LF), midluteal, and LF with P therapy to simulate luteal phase plasma P levels. LH pulse frequency was slower (P less than or equal to 0.001) in the midluteal phase than in either the early follicular phase or LF, and furthermore, P, administered in the normal follicular phase, slowed LH pulse frequency, augmented pulse amplitude, and reduced mean plasma LH levels compared to those in untreated women studied at the same cycle phase (P less than or equal to 0.02). We infer that P secretion by the ovary mediates the change in the LH secretory pattern during the luteal phase of the normal menstrual cycle, and that at least part of this effect is mediated by the central nervous system.
303 citations
TL;DR: The experiments indicate that a permanent region of poststenotic flow separation does not exist even for the severest constriction, in contrast to results for steady flow, implying that identification of flow disturbances of an organized nature may be more fundamental in recognizing mild to moderate disease.
224 citations
TL;DR: A method was developed for non-invasive measurement of human fetal blood flow that proved to possess a good accuracy and reproducibility when tested in vitro experiments and in a comparison with electromagnetic flow measurements in animals.
Abstract: A method was developed for non-invasive measurement of human fetal blood flow. The method combines real-time ultrasonography with 2 MHz pulsed Doppler technique. The blood flow is calculated from the blood velocity, estimated from the Doppler spectrum, and the vessel diameter, measured in the real-time image. Time-distance recording was applied for measurements of the pulsatile diameter changes in the fetal aorta. The method proved to possess a good accuracy and reproducibility when tested in vitro experiments and in a comparison with electromagnetic flow measurements in animals. Possible sources of error were analysed and recommendations for minimizing the risk of errors are presented.
209 citations
TL;DR: Emphasis is placed on the difference between rigid and elastic models and also Newtonian and non Newtonian flow behavior after branches where the flow has local strong convective elements such as in reverse zones and flow separation points.
161 citations
TL;DR: The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma.
73 citations
TL;DR: The relationship between blood flow and the localization of thrombosis and atherosclerosis in vivo was investigated using the approach and techniques of microrheology and it was shown that stagnation points are found in regions of disturbed flow at various sites in the arterial and venous circulations.
73 citations
TL;DR: Two individuals with apparently normal ovulation and once daily plasma P concentrations within the normal range demonstrated a nonpulsatile P profile, and these findings encourage clinical investigations to characterize pulsatile P secretion in normal women and patients in whom corpus luteum dysfunction is suspected.
69 citations
TL;DR: A new method for magnetic resonance (MR) imaging of flowing protons which can illustrate relative blood velocity in the arteries supplying the brain is described.
Abstract: The authors describe a new method for magnetic resonance (MR) imaging of flowing protons which can illustrate relative blood velocity in the arteries supplying the brain. The magnetic gradient pulse sequence was synchronized to the cardiac cycle at 100-msec. increments to track pulsatile blood flow perpendicular to the image plane. The magnitude of the signal increased with the velocity of blood in major arteries flowing in the direction of the spatially offset refocusing plane. The blood velocity in the vertebral and internal carotid arteries varied as a function of the phase of the cardiac cycle, and the velocity profiles across the vascular lumina were compatible with laminar flow.
67 citations
TL;DR: An in-vitro flow study was conducted in a mildly atherosclerotic main coronary artery casting of man using sugar-water solutions simulating blood viscosity, finding both pulsatile and steady flow data from the casting to be nearly equal to those from a straight, axisymmetric model.
Abstract: An in-vitro flow study was conducted in a mildly atherosclerotic main coronary artery casting of man using sugar-water solutions simulating blood viscosity. Steady flow results indicated substantial increases in pressure drop, and thus flow resistance at the same Reynolds number, above those for Poiseuille flow by 30 to 100 percent in the physiological Reynolds number range from about 100 to 400. Time-averaged pulsatile flow data showed additional 5 percent increases in flow resistance above the steady flow results. Both pulsatile and steady flow data from the casting were found to be nearly equal to those from a straight, axisymmetric model of the casting up to a Reynolds number of about 200, above which the flow resistance of the casting became gradually larger than the corresponding values from the axisymmetric model.
66 citations
TL;DR: Pulse-wave velocity was measured in isolated canine common carotid arteries using sinusoidal frequency pulses and it was found that the pulse- wave velocity was independent of frequency and dependent on pressure.
Abstract: Pulse-wave velocity was measured in isolated canine common carotid arteries using sinusoidal frequency pulses of 1, 2, 5, 10, 15 and 20 Hz at 50,100 and 150 mmHg. It was found that the pulse-wave velocity was independent of frequency and dependent on pressure. Using the Moens-Korteweg equation, the predicted pulse-wave velocity (y) was compared with measured pulse-wave velocity (x). A good correspondence was found (y = 1.063x — 0.337, with a correlation coefficient of 0.963). The propagation velocity of the significant harmonic components of the pulsatile pressure waveform is the same for heart rates up to 120 beats/min.
65 citations
TL;DR: If hemodynamic factors play an important role in the problems of atherosclerosis, then, for macrocirculation studies, it is necessary to take into account unsteadiness and, in particular, the actual shape of the flow-time forcing function.
TL;DR: A significant seven-fold brain flow increase followed the period of circulatory arrest in Group III and Microscopic cellular damage appeared in all groups with an equal degree of severity, regardless of the method of hypothermia and perfusion implemented.
TL;DR: Results show that the changes in impedance curves in patients with heart failure are due to greater peripheral resistance and wave reflection.
Abstract: This study was aimed at the evaluation of aortic impedance in patients with congestive heart failure. Aortic impedance (simultaneous measurements of aortic pressure and blood flow), mean (Wm) and pulsatile (Wp) powers were compared in 11 normal subjects and in 12 patients with heart failure. Pulse wave velocity (C: modified Moens-Korteweg equation, simultaneous measurements of aortic pressure and radius) was determined under control conditions in all normal subjects and in 7 patients with heart failure. Impedance curves in patients with heart failure were characterized by increased values of the impedance modulus at 0 Hz (peripheral resistance) and at low frequencies. The characteristic impedance, C, and phase were not different from normal subjects. In six patients with heart failure, impedance curves were studied during nitroprusside infusion. During the infusion of the vasodilator, the impedance modulus at 0 Hz and at low frequencies decreased. The characteristic impedance was unchanged. The zero intercept of the phase was shifted towards lower frequencies. These results show that the changes in impedance curves in patients with heart failure are due to greater peripheral resistance and wave reflection. During nitroprusside infusion the stroke volume increased and the aortic blood flow became more pulsatile (greater values of low frequency components). This modification accounts for the increased values ofWm and Wp, and is related to decreased peripheral resistance and wave reflection.
Patent•
17 Feb 1984
TL;DR: In this paper, a continuous long-term non-invasive measurement of the pressure of a pulsatile fluid flowing through a flexible tube, particularly human arterial blood flow, is disclosed.
Abstract: Apparatus and related methods for continuous long-term non-invasive measurement of the pressure of a pulsatile fluid flowing through a flexible tube, particularly human arterial blood flow, is disclosed. Specifically, the apparatus provides a continuous calibrated pressure measurement by first undertaking a "calibration" phase comprised of determining the pressure at various pre-defined conditions of flow and, in reponse thereto, ascertaining the values of a plurality of coefficients each of which is associated with a corresponding term in a pre-defined function that characterizes fluid pressure in relation to pulsatile displacement of the wall of the tube; and second, undertaking a "continuous monitoring" phase comprised of determining each subsequently occurring pressure value as the pre-defined function of each corresponding pulsatile wall displacement value, and re-initiating the calibration phase at the expiration of pre-defined time intervals which adaptively change based upon current and prior results. Methods, which are particularly useful in conjunction with the disclosed apparatus, for ascertaining systolic and diastolic arterial blood pressure values are also disclosed.
TL;DR: This study suggests that the pericardial valves with turbulent stresses comparable to those of caged ball and tilting disc valves are preferable from a hemodynamic point of view.
TL;DR: Previous steady state flow studies with magnetic resonance (MR) are extended to pulsatile flow measurements obtained with gated cardiac techniques in man with a pulsatile artificial heart device and MR signals from flowing fluids represent velocity distribution as shown in a velocity profile.
Abstract: The purpose of this investigation was to extend previous steady state flow studies with magnetic resonance (MR) to pulsatile flow measurements obtained with gated cardiac techniques in man with a pulsatile artificial heart device. Bovine blood and a solution of MnCl2 were studied. Correlation was made with complex and time-varying MR signals observed in the descending aorta on cardiac gated images obtained through the midthorax. MR signals from flowing fluids represent velocity distribution as shown in a velocity profile, and laminar flow is distinguished from nonlaminar. At very slow flow rates, signal intensity is lower than background. As the rate is increased, paradoxical enhancement occurs followed by loss of signal, which is complete at 7 liters per minute with fluid and 15 liters per minute with blood. These areas correspond to maximum fluid velocities of 41 and 88 cm/sec, respectively.
TL;DR: A pulsatile mode of LH secretion by the ovine fetal pituitary as early as 81 days gestation is demonstrated and indirect evidence for pulsatile LRF secretion byThe fetal hypothalamus and an operative LRF pulse generator by midgestation is provided, the earliest stage in gestation studied.
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.
TL;DR: It is tested the hypothesis that sustained, strenuous physical training alters the neuroendocrine regulation of pulsatile gonadotropin and/or prolactin secretion in men by administering the potent opiate-receptor antagonist, naltrexone.
Abstract: We tested the hypothesis that sustained, strenuous physical training alters the neuroendocrine regulation of pulsatile gonadotropin and/or prolactin secretion in men. Blood was sampled at 20-minute intervals over 8 hours in five endurance-trained men after a 10-15 mile run in the middle of the active training season, and in 11 nonendurance trained normal controls. In these two groups, basal patterns of physiologically pulsatile secretion of LH, FSH, and prolactin (PRL) were not significantly different in relation to the following parameters: mean serum concentration of each of the three hormones (N = 25 samples); areas under the hormone concentration vs. time curves; fractional, incremental, and absolute pulse amplitudes; and pulse frequency, or periodicity. To test for enhanced suppressive effects of endogenous opiates in trained male marathon runners, subjects were administered the potent opiate-receptor antagonist, naltrexone (1 mg/kg). This antagonist significantly stimulated pulsatile LH secretion by increasing mean serum LH values from 10.94 to 13.58 mIU/ml (P = 0.007); area under the LH concentration vs. time curve increased from 5370 to 6510 mIU/ml X 8 hours (P = 0.05) and, pulse frequency rose from 2.8 to 4.9 pulses/8 hours (P = 0.006). Naltrexone also enhanced pulse frequency of FSH secretion from 3.4 to 5.4 pulses/8 hours (P = 0.009), but did not alter serum prolactin concentrations. None of these responses differed significantly from those in normal sedentary controls.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The velocity field and the wall shear stress have been calculated numerically by the finite element method to the time-dependent Navier-Stokes equations for pulsatile flow in a model of an aneurysm and show a complex flow field with two eddies growing and disappearing during the cardiac cycle.
Abstract: The velocity field and the wall shear stress have been calculated numerically by the finite element method to the time-dependent Navier-Stokes equations for pulsatile flow in a model of an aneurysm. The results show a complex flow field with two eddies growing and disappearing during the cardiac cycle. Downstream at the outlet vessel high wall shear stress occurs, which may lead to a downstream-growing of the aneurysm. With the knowledge of a sufficiently accurate flow field, the calculation of several particle paths has been carried out. Starting points and starting time are varied. The paths demonstrate the time-dependent development, shift and disappearance of vortices during the pulsatile cycle and provide hints on zones of stasis. These are significant factors in thrombogenesis.
TL;DR: Pulsatile secretion is the more efficient means for islet A cells to stimulate hepatic glucose production and, in the dose range equivalent to concentrations in portal plasma, pulsed glucagon enhanced glucose production twofold.
Abstract: We have compared the effects of pulsatile and continuous glucagon administration on hepatocyte glucose production in order to clarify the physiological role of pulsatile hormone secretion. Two identical columns containing freshly isolated rat hepatocytes mixed with polyacrylamide gel beads were perifused with oxygenated tissue culture medium. A fixed total amount of glucagon was delivered to one column as a continuous 90-min infusion and to the other column as a series of six 3-min pulses. A 15-min interpulse interval was chosen in order to approximate the 10- to 12-min interval observed in primates while permitting the resolution of individual hepatocyte responses. With this protocol, the EC50 values for pulsatile and continuous glucagon administration were 186 +/- 41 and 884 +/- 190 (SD) pg/ml, respectively. For glucagon concentrations less than 1,000 pg/ml, pulsatile administration always led to greater hepatocyte glucose production than continuous administration (P = 0.008) and, in the dose range equivalent to concentrations in portal plasma, pulsed glucagon enhanced glucose production twofold. The data suggest that pulsatile secretion is the more efficient means for islet A cells to stimulate hepatic glucose production.
TL;DR: Pulsatile changes in the volume of an arm segment were recorded with an air-filled plethysmograph and related to intra-arterial blood pressure and arterial compliance values.
Abstract: Pulsatile changes in the volume of an arm segment were recorded with an air-filled plethysmograph and related to intra-arterial blood pressure. Alterations in transmural arterial pressure were obtained by changing the pressure in a large chamber surrounding the entire arm. Arterial compliance values were calculated in late diastole when pressure and volume changes were slow. Compliance varied with transmural arterial pressure in a hyperbolic manner, rising steeply at low pressure.
Noradrenaline and hypertensin did not change the arterial compliance values, while dihydroergotamine reduced them. Nitroglycerine caused a pronounced increase in compliance values in doses that did not change cardiac output and arterial pressure.
TL;DR: The results support the view that brain GABA exerts an inhibitory action on LH release in the rat.
Abstract: The effects of increasing brain GABA levels by administration of aminooxyacetic acid (AOAA), a GABA-transaminase inhibitor, on tonic and induced LH release were evaluated in ovariectomized rats. Pulsatile LH release was clearly inhibited by AOAA. Mean plasma LH levels fell, the frequently of pulses decreased, and the intervals between pulses increased. An absence of LH pulses was seen in some animals. Administration of the GABA antagonist, bicuculline, prevented these modifications. In addition, it enhanced mean plasma LH levels. AOAA blunted the rise of plasma LH levels produced by either oestradiol or progesterone in oestradiol-primed ovariectomized rats. In contrast, the AOAA treatment apparently facilitated the inhibitory feedback of oestradiol on LH release. The acute release of LH produced by LRH injection was not altered by AOAA. The results support the view that brain GABA exerts an inhibitory action on LH release in the rat.
TL;DR: Observations suggest that helical flows may be characteristic features of flow in the left coronary artery; whereas turbulence may not be a feature of this flow field.
Abstract: The purpose of this investigation is to describe our preliminary observations of the overall pattern of flow in a mold of the left coronary artery of a pig. Flow in the coronary mold was visualized by the injection of dye into the sinus of Valsalva. Studies were performed during steady flow at rates of 100, 200, 300, 400, and 500 mL/min. Studies were also performed during pulsatile flow, using a pulse duplicator that simulated the magnitude and phasic pattern of coronary flow at rest and during reactive hyperemia. At conditions that simulated rest, mean coronary flow was adjusted to 121 mL/min of which 24 mL/min (20 percent) was systolic. During simulated reactive hyperemia, mean flow was 440 mL/min. Visualization of flow revealed the absence of disturbances of turbulence during both steady and pulsatile flow in the left anterior descending (LAD) and left circumflex (CIRC) coronary arteries throughout the entire range of flow studied. Prominent spiraling of flow occurred during steady and pulsatile flow. Spiraling of flow was not observed in the LAD at rest during pulsatile flow, but developed during simulated reactive hyperemia. Helical flows were observed in the CIRC both during simulated rest and reactive hyperemia. These observations suggest that helical flows may be characteristic features of flow in the left coronary artery; whereas turbulence may not be a feature of this flow field. Whether the spiraling of flow that we observed related to the spiral distribution of early atheroma reported by others, is undetermined.
TL;DR: The valved right atrial-pulmonary arterial bypass pump increased cardiac index 70.9 ml/min/kg (228%) above passive pulmonary artery flow to a satisfactory level and is the recommended method of pulmonary circulatory support in profound right ventricular failure.
TL;DR: The instantaneous relationship between thevolume pulse and arterial pressure (forearm compliance) showed that nitroglycerin increased the volume pulse in association with a reduction in pulse pressure, consistent with an arterial origin of the forearm volume pulse.
Abstract: This study has investigated the origin of the pulsatile expansion of the forearm recorded by the amplification of the pulsatile signal derived from a mercury in rubber plethysmograph. Venous occlusion to pressures of 40 mmHg had no effect on the amplitude of the volume pulse, suggesting that the volume pulse originates in vessels distended by pressures above this level. Nitroglycerin in small doses (0.15 mg sublingual) increased the amplitude of the volume pulse without changing forearm vascular resistance, consistent with an arterial origin of the forearm volume pulse. The instantaneous relationship between the volume pulse and arterial pressure (forearm compliance) showed that nitroglycerin increased the volume pulse in association with a reduction in pulse pressure. As the volume pulse probably originates in the arterial system, the increase in forearm compliance is a measure of the increase in arterial compliance induced by nitroglycerin. Both the volume pulse and forearm compliance may be useful indicators of the effect of physiological and pharmacological interventions on the distensile properties of arteries.
TL;DR: Desensitization to the stimulatory effects of NE on LH release in ovariectomized, steroid-primed rats had been observed to occur rapidly within 90 min after the onset of infusion, but this did not occur even after continuous infusion of NE for periods up to 20 h.
Abstract: T he present study examined three aspects of the inhibitory effects of continuous intraventricular infusion of norepinephrine (NE) on pulsatile luteinizing hormone (LH) release in ov
TL;DR: Exposure to high shear stress did not degrade the nonthrombogenic nature of the endothelium because subsequent platelet adhesion was poorly and negatively correlated with shear Stress.
TL;DR: A significant number of saphenous vein femoral-popliteal bypass graft failures have been attributed to flow abnormalities caused by venous valves, but flaps of valve cusps were observed to disturb flow and place potentially thrombogenic surfaces within the vein lumen.
TL;DR: It is concluded that estrogen is the principal ovarian hormone restraining LH secretion in the long-term OVX rat and that progesterone has only a modest effect, even in the presence of estrogen.
Abstract: Recent reports on the effects of progesterone on the frequency of pulsatile LH release in several species have compelled a reevaluation of the regulation of pulsatile LH secretion by gonadal steroids
Journal Article•
TL;DR: The effect of pulsatile flow during cardiopulmonary bypass was studied on two groups of 11 patients each (aged between 18 and 48 years) undergoing open valvular and congenital heart surgery, and mean blood pressure and systemic vascular resistance index increased steadily during CPB; while in the pulsatile group, both BP and SVRI remained stationary.
Abstract: The effect of pulsatile flow during cardiopulmonary bypass (CPB) was studied on two groups of 11 patients each (aged between 18 and 48 years) undergoing open valvular and congenital heart surgery. In the nonpulsatile group, mean blood pressure (BP) and systemic vascular resistance index (SVRI) increased steadily during CPB; while in the pulsatile group, both BP and SVRI remained stationary. The difference of SVRI between the two groups was not significant within 30 minutes after initiation of CPB (3136 +/- 882 to 2536 +/- 530 dynes X sec X cm-5 X m2). Contrarily, it was significantly higher in the nonpulsatile group after 40 minutes of CPB (3748 +/- 562 to 2612 +/- 609 dynes X sec X cm-5 X m2, p less than 0.02) and thereafter. Oxygen consumption index (59.6 +/- 12.9 to 77.8 +/- 32.6 ml X min-1 X m-2) and carbon dioxide production index (41.1 +/- 16.0 to 59.3 +/- 28.1 ml X min-1 X m-2) measured 20 minutes after institution of CPB seemed lower in the nonpulsatile group than in the pulsatile group, but the differences were not statistically significant. Increased urine flow during CPB (1.8 +/- 1.1 to 6.3 +/- 3.8 ml X min-1 X m-2, p less than 0.001) with less variability indicated better reserve of renal function in the pulsatile group; and less percent change of postoperative sGOT from preoperative level (529.8 +/- 129.8 to 310.0 +/- 175.2%, p less than 0.005) also showed better hepatic function in the pulsatile group.(ABSTRACT TRUNCATED AT 250 WORDS)