Showing papers on "Pulsatile flow published in 1983"
Patent•
29 Jun 1983
TL;DR: In this paper, the pulsatile thoracic impedance signal is processed to produce signals indicative of the ventricular ejection time and the maximum rate of change of pulsatile impedance which are used in a microprocessor to calculate the volume of blood pumped per stroke according to an improved systolic upstroke equation.
Abstract: The invention provides apparatus and methods for using the electrical bioimpedance measurements to monitor parameters associated with blood flow in a segment of body tissue. The invention eliminates the effect of respiration from the thoracic impedance as a function of time to provide a signal indicative of pulsatile thoracic impedance changes continuously. The pulsatile thoracic impedance signal is processed to produce signals indicative of the ventricular ejection time and the maximum rate of change of pulsatile thoracic impedance which are used in a microprocessor to calculate the volume of blood pumped per stroke according to an improved systolic upstroke equation.
282 citations
TL;DR: The location of low wall shear stresses, directionally varying stresses, and longer residence times for fluid elements appears to coincide with the localization of early atheromatous plaques in human carotid specimens.
Abstract: Pulsatile flow in an in vitro model of the human carotid bifurcation was studied by flow visualization using hydrogen bubble techniques. A glass model was constructed after determining an average geometry from 57 biplanar angiograms of 22 subjects ranging from 34 to 77 years of age. The flow pulse used was a half-sine wave superimposed upon a mean flow. Maximum and minimum values of the instantaneous Reynolds number were 1200 and 400, respectively, based upon conditions in the common carotid model artery; the frequency parameter was 6.0. The division of flow into the internal external branches was 70:30. Visualization by hydrogen bubbles demonstrated significant deviations from steady flow behavior. Flow separated in the carotid sinus over the entire cycle, but the location and extent of separation varied strongly. The direction of flow near the walls of the model changed sharply during the cycle except for the region near the apex of the bifurcation where the orientation of streaklines was more nearly unidirectional at all times. Bubbles entering the separated flow region tended to remain entrapped there for several cycles. Rapid dispersion of bubbles occurred in the internal branch near the end of systole, suggesting the presence of flow disorder. The location of low wall shear stresses, directionally varying stresses, and longer residence times for fluid elements appears to coincide with the localization of early atheromatous plaques in human carotid specimens.
242 citations
TL;DR: Failure to quantitate adequately the pulsatile components of flow in these studies prevents differentiation between effective and ineffective forms of pulsatile flow and makes comparison of studies difficult.
155 citations
TL;DR: If an adequate dose of Gn-RH is provided, which takes into account the degree of impairment of hypothalamic function in the individual case, follicular maturation, ovulation and corpus luteum formation are achieved in nearly every treatment cycle, and a high conception rate is achieved.
Abstract: Summary. The physiological and pathophysiological basis of hypothalamic amenorrhoea are reviewed as well as the clinical results of chronic intermittent (pulsatile) administration of Gn-RH in the treatment of infertility. Hypothalamic amenorrhoea is considered to be the result of a deficient hypothalamic secretion of Gn-RH. By pulsatile administration of Gn-RH, which is a pre-requisite of normal pituitary gonadotrophic function, deficient endogenous Gn-RH is replaced. If an adequate dose of Gn-RH is provided, which takes into account the degree of impairment of hypothalamic function in the individual case, follicular maturation, ovulation and corpus luteum formation are achieved in nearly every treatment cycle. Although dependent also on factors other than the treated dysfunction, a high conception rate is achieved.
100 citations
TL;DR: Systolic and diastolic flow rates in aortocoronary bypass grafts and coronary arteries determined from biplane cineangiograms in 34 patients generally revealed the typical pulsatile flow pattern familiar from electromagnetic and ultrasonic flow measurements.
Abstract: The reliability of a modified videodensitometric and photodensitometric sampling technique for measuring phasic flow rates in the coronary artery system was examined. Electromagnetic flow measurements were performed in a circulatory model with continuous and pulsatile flow and intraoperatively in aortocoronary bypass grafts; cineangiograms were made simultaneously. Based on the front velocities of injected boluses of contrast medium, the densitometric measurement overestimated the electromagnetically measured flow systematically by about 20%. Systolic and diastolic flow rates in aortocoronary bypass grafts and coronary arteries determined from biplane cineangiograms in 34 patients generally revealed the typical pulsatile flow pattern familiar from electromagnetic and ultrasonic flow measurements. Flow velocities in unstenosed coronary arteries were nearly identical before and after branchings of the vessels, whereas the corresponding flow rates were higher in proximal than in distal segments. The identical flow velocities in different branches of the same vessel and the low variability of this parameter in different patients may be a suitable index of the effect of stenoses on coronary arterial blood flow.
98 citations
TL;DR: The results show that with increased angle of opening for the tilting disc valves, a large but locally confined vortex is observed along the wall in the minor flow region throughout most of the cardiac cycle.
79 citations
TL;DR: It is suggested that the classifications employed by Smith to describe the different regimes of fully-developed pulsatile flow in curved pipes may also be useful to distinguish between different entry-flow regimes.
Abstract: An experimental investitition was made of the entry flow in a curved pipe under conditions wherein a pulsatile component of flow was superimposed on a steady mean flow. Two experiments were conducted, one in a pipe of curvature ratio for αw = 12·5 and κ = 372. Laser-velocimetry measurements of the axial and secondary velocities were made throughout the cross-section at different instants of time within the cycle and at several axial locations downstream from the pipe entrance.The flow in the first experiment was found to be quasisteady, with axial and secondary velocities varying in time at the several axial stations proportionally to the instantaneous mean velocity, but essentially the same in character as low-Dean-number steady entry flow. The flow in the second experiment was more complex, with separation of the axial flow appearing at the inner bend during deceleration, starting downstream and propagating upstream toward the pipe entrance. Helical motions imbedded within the Dean circulation were also observed, and during certain portions of the cycle the secondary motions within the central core took on a jet-like structure.It suggested that the classifications employed by Smith to describe the different regimes of fully-developed pulsatile flow in curved pipes may also be useful to distinguish between different entry-flow regimes.
73 citations
TL;DR: Pulsatile tinnitus disappeared with ipsilateral jugular compression suggesting flow rather than pressure to be responsible for abnormal auditory symptoms, and formed the basis of the treatment recommendations.
Abstract: Pulsatile tinnitus is a rare presenting symptom in patients with enlarged jugular bulbs. We will describe three young women presenting with right pulsatile tinnitus associated with a megabulb deformity of the temporal bone. After extensive radiologic and audiologic evaluation, no vascular or bony abnormalities could be identified. All three patients demonstrated pulsatile bruits over the right temple. Pulsatile tinnitus disappeared with ipsilateral jugular compression suggesting flow rather than pressure to be responsible for abnormal auditory symptoms. This observation formed the basis of our treatment recommendations. Because of progressively debilitating pulsatile tinnitus, two patients elected right internal jugular vein ligations under local anesthesia. Both patients were relieved of tinnitus. We conclude that jugular vein ligation can be a safe and effective surgical treatment for pulsatile tinnitus resulting from a jugular megabulb deformity, provided two criteria are met: 1. The presence of an expanding tumor is ruled out. 2. The presence of contralateral venous drainage is established by angiography or brain scan. Anatomic and functional hemodynamic considerations of brain circulation will be emphasized in the discussion of our treatment rationale.
62 citations
TL;DR: A particle fluid suspension model is applied to the problem of pulsatile blood flow through a rigid circular tube with entrance effects, and steady pulsatile velocities for both cases are deduced by taking time t -greater than .
57 citations
TL;DR: In vitro investigation of pulsatile and steady flows through a smooth, straight circular tube and a diseased human coronary artery cast was conducted with sugar-water solutions simulating the viscosity of blood, finding pressure drops for steady flows were greater than Poiseuille flow predictions.
52 citations
TL;DR: Together with biochemical factors, fluid mechanical factors play a role in atherogenesis and the deposition of blood platelets at bends and bifurcations in human arteries and flow patterns were investigated in a simplified 3-dimensional model using Newtonian and non-Newtonian fluids.
TL;DR: The findings illustrate that circulating gonadotropin and testosterone pulses change in amplitude but not necessarily frequency during pubertal development, and primate models are a useful paradym for the longitudinal study of human male sexual development.
Abstract: Pulsatile secretion of serum gonadotropins and testosterone was studied in 46 monkeys of varying ages from 9 days of age through adult life. Although some of the hormonal analysis was longitudinal in nature, most comparisons were cross-sectional. On the basis of pulsatile secretory patterns, hCG and GnRH stimulation, skeletal age, testicular volume, and histology, we have arbitrarily defined four developmental age groups: postnatal (<7 months), prepubertal or juvenile (7–27 months), pubertal (28–59 months), and adult (≥60 months). In accomplishing the pulsatile studies, blood was withdrawn at 15-min intervals over 24 h without anesthesia using a mobile vest and tether assembly to support an indwelling cannula. GnRH and hCG challenge tests were done on one or more occasions on all animals. Plasma samples were analyzed for concentrations of FSH, LH, testosterone, dihydrotestosterone and δ4-androstenedione by established RIAs and an in vitro bioassay for LH.During the frequent sampling period of 24-h duratio...
TL;DR: It is suggested that neither corticosteroids nor pulsatile flow affect complement activation, but caution should be exercised in women receiving methylprednisolone, however, women showed significantly more complement activation than men.
Abstract: Forty four patients undergoing open heart surgery were divided into three groups. Group 1 (17 patients) underwent routine anaesthesia and surgery; group 2 (17 patients) received two doses of methylprednisolone (30 mg/kg), one during induction of anaesthesia and the other immediately before induction of cardiopulmonary bypass; and group 3 (10 patients) received pulsatile flow while undergoing pulsatile perfusion by the heart-lung machine. A modification of the previously described technique was used to detect and measure complement activation in plasma before and during the bypass period using crossed immunoelectrophoresis. About 45% of all patients showed measurable complement activation (greater than 4.5%) during cardiopulmonary bypass and the mean activation in this group was 6.4%. There was no significant difference between the three groups in complement activation. In group 2, however, women showed significantly more complement activation than men (p less than 0.05). It is suggested that neither corticosteroids nor pulsatile flow affect complement activation, but caution should be exercised in women receiving methylprednisolone.
TL;DR: The frequency of pulsatile LH release was maximal within 8 days, with no further increases occurring over the next 2 weeks, and the long-term increase seen at 8 days or 3 weeks was not only due to increases in LH pulse frequency and amplitude, but also to dramatic increases in basal LH secretion.
Abstract: These experiments examined the time course of changes in the characteristics of pulsatile luteinizing hormone (LH) secretion that occur after ovariectomy (OVX) in the rat, and compared the response of the brain and pituitary to the absence of ovarian steroid negative feedback. The literature indicates that the brain could respond to OVX by altering the frequency and/or amplitude of the pulsatile luteinizing hormone releasing hormone (LH-RH) release which triggers pulsatile LH secretion, while the pituitary could respond by altering basal LH output and/or its response to LH-RH. In vivo experiments examined changes in mean blood LH levels, LH pulse amplitudes and pulse frequencies in control rats on diestrus 1 (Dl) and at 7 h, 14 h, 1, 2 or 8 days, or 3 weeks following OVX. In addition, anterior pituitaries from rats on Dl or rats ovariectomized for 1, 2 or 8 days, or 3 weeks, were incubated in vitro with or without LH-RH to examine changes in both basal and LH-RH-induced LH release.
TL;DR: Comparing fluid flow parameters for steady flow with those for time-varying flow in a simplified two branch model which simulates the region of the abdominal aorta near the celiac and superior mesenteric branches of the dog shows many similarities to previous steady flow studies in a canine aortic cast.
Journal Article•
TL;DR: Subcutaneous administration of luteinizing hormone-releasing hormone is effective without the inherent risks or discomfort of intravenous catheters and the physiologic levels of gonadotropins resulting from ovulation induction with lute inizing hormones may increase the chances that only a single preovulatory follicle will develop.
TL;DR: Routine CPB demonstrates no evidence of adrenocortical hypofunction and the addition of pulsatile flow produces little improvement, and there was no correlation between urinary Na+/K+ ratios and either plasma cortisol or aldosterone levels.
TL;DR: D danazol in premenopausal women lowers serum E2 concentrations by decreasing the frequency and increment of E2 pulses, prevents compensatory gonadotropin rise, and lowers the frequency but increases the amplitude and increments of LH pulses.
TL;DR: Both LA-FA and P-LA-FA bypasses limited infarct extension and reduced mortality after acute coronary occlusion through effective unloading of the left ventricle and the addition of diastolic counterpulsation led to further significantinfarct reduction, when compared with LA- FA bypass alone.
Abstract: • A left atrial—femoral artery (LA-FA) bypass system was designed to deliver synchronous pulsatile blood flow. We compared it with nonpulsatile LA-FA bypass in its effectiveness to limit infarct extension after ligation of the left anterior descending coronary artery at its origin in 35 dogs. Nonpulsatile LA-FA bypass resulted in a 70% reduction in the size of infarct. The addition of synchronous diastolic counterpulsation (P—LA-FA) further reduced the size of infarct, when compared with that in controls (95%) or animals that underwent LA-FA bypass (83%). Both LA-FA and P—LA-FA bypasses limited infarct extension and reduced mortality after acute coronary occlusion through effective unloading of the left ventricle. The addition of diastolic counterpulsation to LA-FA bypass led to further significant infarct reduction, when compared with LA-FA bypass alone. These effects were most likely secondary to improvements in myocardial blood flow distribution. ( Arch Surg 1983;118:965-969)
TL;DR: Hollow-fiber device has been used to investigate the effect of ultrafiltration swing on the performance of membrane-enzyme reactor and experiments with β-galactosidase and ONPG have shown that bidirectional ultra filtration induced by pulsatile flow gives rise to an increase in conversion.
Abstract: Hollow-fiber device has been used to investigate the effect of ultrafiltration swing on the performance of membrane-enzyme reactor. Experiments with β-galactosidase and ONPG have shown that bidirectional ultrafiltration induced by pulsatile flow gives rise to an increase in conversion relative to that obtained at steady operation without ultrafiltration swing. This increase apparently comes from the enhanced mass transfer due to ultrafiltration.
TL;DR: Tissue-cultured bovine aortic endothelial cells were subjected to flow in an in vitro circulatory loop designed to simulate the flow and pressure conditions in the aorta and showed that the cells not only remained adherent for up to 2 weeks under flow conditions, but also underwent hypertrophy and proliferation in response to the flow regimen.
Abstract: Tissue-cultured bovine aortic endothelial cells were subjected to flow in an in vitro circulatory loop designed to simulate the flow and pressure conditions in the aorta. The cells were cultured under stationary conditions on tubes of fibronectin-coated Silastic or of Dacron velour. The tubes were then added to the flow loop, which circulated complete tissue culture medium in a pulsatile mode. Light microscopy and cell counts showed that the cells not only remained adherent for up to 2 weeks under flow conditions, but also underwent hypertrophy and proliferation in response to the flow regimen.
TL;DR: Data indicate that NE is an excitatory neurotransmitter in the regulation of pulsatile LH release on D1, and acting through an alpha-adrenergic receptor, this neurotransmitter presumably influences both the frequency of the L HRH pulse generator and the amount of LHRH released per pulse.
Abstract: This study examined (1) the possible involvement of catecholamines in the regulation of pulsatile LH release on diestrus 1 (Dl) in the rat estrous cycle, and (2) the possible importance of pulsatile LH release on Dl to ovarian estradiol and progesterone secretion on this day of the cycle. Blockade of dopamine receptors on Dl had no effect on LH secretion. However, inhibition of norepinephrine (NE) synthesis or blockade of α- but not β-adrenergic receptors decreased mean blood LH levels, and greatly suppressed pulsatile LH secretion by decreasing both LH pulse frequency and amplitude. In contrast, in the same rats, interference with brain NE function had no effect on plasma FSH levels. These data indicate that NE is an excitatory neurotransmitter in the regulation of pulsatile LH release on Dl. Acting through an α-adrenergic receptor, this neurotransmitter presumably influences both the frequency of the LHRH pulse generator and the amount of LHRH released per pulse. Moreover, the release of LH and FSH on Dl can be separated, suggesting possible differences in the mechanisms regulating secretion of these two gonadotropins. Regardless of whether pulsatile LH release had been greatly suppressed or not altered, no change occurred in plasma progesterone levels, indicating pulsatile LH release on Dl is not important for the release of progesterone that occurs on this day of the cycle. With respect to estradiol, no consistent pattern emerged between changes in pulsatile LH release induced by interference with brain NE function and plasma estradiol levels. Thus, no definitive conclusion was possible on the potential importance of pulsatile LH release to estradiol secretion on Dl.
TL;DR: The flow visualization study in the model human aorta suggests that, from a fluid dynamic point of view, orientation of the major flow orifice of the tilting disc valve toward the wall of lesser curvature is not advisable.
TL;DR: In vitro fluid dynamic characteristics of aortic valve prostheses were experimentally measured for physiological relevant pulsatile flows using hot-film velocimetry and showed that peak turbulent normal stresses were obtained at 108 ms after the opening of the valves.
Abstract: In vitro fluid dynamic characteristics of aortic valve prostheses were experimentally measured for physiological relevant pulsatile flows using hot-film velocimetry. The prostheses studied were (i) centrally occluding ball-in-cage and (ii) tilting disc valves. The valves sewn to a plexiglass ring were placed in a specially designed valve chamber. The valve chamber was mounted in a mock circulatory system in which glycerol solution was used as the blood analogue fluid. Physiological pulsatile flow experiments were conducted at a time-averaged flow rate of 86·7 cm3s−1, (mean Reynolds number of 1320 based on the cross-sectional averaged velocity with a tissue annulus, diameter, of 27 mm). With the aid of a three-sensor probe, the instantaneous values of the three velocity components (component along the axis, as well as radial and tangential velocity, components in a cross-section) were measured and used to compute the mean velocity profiles as well as turbulent normal stresses. The results showed that peak turbulent normal stresses were obtained at 108 ms after the opening of the valves with maximum magnitudes of 110 Pa, 45 mm downstream from the silastic ball valves, compared to about 35 Pa for the stellite ball valve. The largest turbulent normal stresses of about 150 Pa were obtained behind tilting disc valves in the minor flow region parallel to the tilt axis.
TL;DR: In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use.
Abstract: The need for better and longer lasting trileaflet valves has led to the design and development of the Abiomed polymeric trileaflet valve prosthesis. In-vitro fluid dynamic studies on sizes 25 and 21 mm valves in the aortic position indicate an overall improvement in performance compared to the Carpentier-Edwards and Ionescu-Shiley tissue valves in current clinical use. The pressure drop studies yielded effective orifice areas of 1.99 and 1.54 cm2, and performance indices of 0.41 and 0.45 for the Nos. 25 and 21 valves, respectively. Leaflet photography studies indicated that the two valve sizes had maximum opening areas of 225 and 145 mm2, respectively, at a normal resting cardiac output. Steady and pulsatile flow velocity measurements with a laser-Doppler anemometer (LDA) system indicate that the flow field downstream of the Abiomed valve is jetlike and turbulent. Maximum mean square axial velocity fluctuations of 55 and 83 cm/s, and turbulent shear stresses of 220 and 450 N/m2 were measured in the immediate vicinity of the nos. 25 and 21 valves, respectively. The Abiomed valves studied had been originally configured for use in valved conduits, and it is therefore our opinion that further improvements can be made to the valve and stent design, which would enhance its fluid dynamic performance.
TL;DR: The arteries-arterioles seemed to be collapsed with blood flow cessation, when the diastolic portion of a pulsatile inflow pressure was reduced to zero, and Vascular distension seemed to reopen the arterial-arteriolaar collapse, and during these conditions the vascular bed offered only little resistance to the systolic peak injection.
Abstract: The effect of local arterial hypotension upon blood flow was studied in 13 healthy humans. Blood flow was measured by the local 133Xe washout technique in the calf or foot region. Changes in arterial pressure was achieved by elevation of the leg above heart level, while the subject rested in supine position. In papaverine-infiltrated subcutaneous tissue, local arterial pressure and blood flow was linearly related. In subcutaneous and skeletal muscle tissue with normal vasomotor tone, blood flow remained constant during a decrease in regional arterial pressure of 30 mmHg--autoregulation of blood flow. Blood flow ceased in vasoparalysed tissue as well as in tissue with normal vasomotor tone, when the local diastolic arterial pressure was reduced to zero. The elevated foot showed signs of vascular ischaemia during these conditions. When the vessels in the ischaemic foot were distended by inflating a femur cuff to a pressure level above the diastolic blood pressure beneath the cuff, the colour of the foot changed into bluish-red and a substantial blood flow was recorded. It is concluded, that the arteries-arterioles seemed to be collapsed with blood flow cessation, when the diastolic portion of a pulsatile inflow pressure was reduced to zero. Vascular distension seemed to reopen the arterial-arteriolar collapse, and during these conditions the vascular bed offered only little resistance to the systolic peak injection.
TL;DR: The oestrogen and progesterone feedback control of the mid-cycle gonadotrophin surge and the site of action (hypothalamic or hypophysial) of these steroids are contrasted in the monkey and rat.
Abstract: This article reviews the neuroendocrine factors which control the menstrual cycle in the macaque monkey. It describes the pulsatile characteristics of gonadotrophin secretion, the control of LH pulses by an arcuate neural Gn-RH oscillator and the significance of pulsatile Gn-RH secretion. The factors which may modulate the activity of the Gn-RH arcuate neural oscillator are anaesthesia, ovarian hormones and endogenous opiates, as well as the possible significance of changes in Gn-RH pulsatile characteristics. Finally, the oestrogen and progesterone feedback control of the mid-cycle gonadotrophin surge and the site of action (hypothalamic or hypophysial) of these steroids are contrasted in the monkey and rat.
TL;DR: Vasoactive intestinal polypeptide (VIP) has powerful vasodilating effects, shown by a striking conductance increase especially in the vertebral artery, the left descending coronary artery, and the left gastric artery.
Abstract: Vasoactive intestinal polypeptide (VIP) has powerful vasodilating effects, shown by a striking conductance increase especially in the vertebral artery (+100%), the left descending coronary artery (+200%), the left gastric artery (+550%), the superior pancreaticoduodenal artery (+200%), and the gastroduodenal artery (+220%). The conductance increase was also significant in the common and the proper hepatic artery (+60% and 50%, respectively). Total peripheral conductance was progressively increased by 45%; arterial pressure was reduced by 20%. Blood flow was assessed with non-cannulating electromagnetic flow sensors in anesthetized dogs. VIP was injected in a brachial vein at intervals of 1 min in amounts of 1–1024 ng·kg-1, following a logarithmic scale. The pulsatile flow and pressure signals were analog–digital-converted and processed simultaneously by a computer program to obtain mean flow (ml·min-1) and mean pressure (mmHg) values for every 3 sec. The hemodynamic data were presented as conductances. No...
TL;DR: The hydraulic waterfall model, consisting of a narrow thinwalled collapsible tube contained in a pressurised box to mimic intramyocardial pressure, is concluded that the hydraulic waterfall is a valuable model of the coronary bed.
Abstract: A model based on the waterfall mechanism has been suggested to explain the relationship between pressure and flow in the non-autoregulating coronary arterial bed.1 We used the hydraulic waterfall model to study both the mean and the oscillatory pressure-flow relations. The hydraulic model consisted of a narrow thinwalled collapsible tube (diameter 1.4 mm) contained in a pressurised box (external pressure) to mimic intramyocardial pressure. The mean perfusion pressure-mean flow relation for a constant external pressure was straight with a slope equal to the (Poiseuille) resistance of the tube and an intercept determined by the external pressure (zero flow pressure). For oscillatory external pressure the mean pressure-mean flow relation was convex to the pressure axis at low flows and straight for high flows. The slope of the straight section was again equal to the tube's Poiseuille resistance. When perfusion pressure was sufficiently low and external pressure oscillated "systolic coronary flow" reversed in systole; when flow was stopped pressure remained oscillatory and above zero. The relationship between pulsatile perfusion pressure and pulsatile flow amplitudes was also described by the (Poiseuille) resistance of the collapsible tube. It is thus concluded that the hydraulic waterfall is a valuable model of the coronary bed.
The electrical analogue of the waterfall introduced by Downey and Kirk1 does not describe the experimental observations on oscillatory phenomena as pointed out by Spaan et al. 2 These investigators therefore suggested an electrical analogue that predicts these observations correctly. However, this model does not exhibit a zero flow pressure. One of the model's components arises from neglecting this intercept, and should be replaced by a resistor that varies such that an intercept pressure results. Both electrical models thus seem to be of limited use and a new model is suggested.