Showing papers on "Pulsatile flow published in 1986"

Flow-induced release of endothelium-derived relaxing factor

Abstract: To analyze the potential mediator(s) involved in flow-induced endothelium-dependent vasodilation, we measured the wall tension of intraluminally perfused canine femoral artery segments and compared the content of 6-ketoprostaglandin F1 alpha (determined by radioimmunoassay) and the relaxing activity of the effluent (determined by bioassay on canine coronary artery rings). During perfusion at a steady flow of 2 ml/min the effluent contained 6-keto-prostaglandin F1 alpha and relaxed the bioassay rings. Sudden increase in steady flow rate to 4 ml/min, or the introduction of pulsatile flow, increased the release of 6-keto-prostaglandin F1 alpha and induced further relaxations of the bioassay ring. No relaxations were observed with the effluent passing through a femoral artery segment without endothelium. Indomethacin significantly depressed the release of 6-keto-prostaglandin F1 alpha during increases in flow but had no significant effect on the relaxing activity of the effluent. In the presence of indomethacin, increases in flow produced significant relaxation in the perfused femoral artery segments with endothelium. Superoxide dismutase restored the relaxing activity of the effluent during increases in flow at a transit time of 30 seconds. These data demonstrate that in addition to prostacyclin, flow triggers the release of another relaxing substance (or substances) from vascular endothelial cells that has characteristics similar to the endothelium-derived relaxing factor released by acetylcholine.

Efficacy of pulsatile versus continuous insulin administration on hepatic glucose production and glucose utilization in type I diabetic humans.

Abstract: To evaluate the role of pulsatile insulin administration, hepatic glucose production (HGP) and utilization were studied in type I diabetic patients in the fasting state and during a euglycemic insulin (1 mU · kg −1 · min −1 i.v.) clamp with continuous and pulsatile insulin administration. In the latter study, insulin was infused at twice the continuous rate with 3-min-on/7-min-off intervals, thereby reducing total insulin delivery by 40%. The restraining effect of pulsatile insulin on basal HGP (1.91 ± 0.35 mg · kg −1 · min −1 ) was equipotent to continuous insulin exposure (1.80 ± 0.17 mg · kg −1 min −1 ). During the insulin-clamp studies, HGP was equally suppressed by pulsed (0.62 ± 0.12 mg · kg −1 min −1 ) as by continuous insulin infusion (0.63 ± 0.12 mg · kg −1 · min −1 ). Insulin-stimulated glucose utilization was not significantly altered in either study (2.55 ± 0.27 vs. 2.92 ± 0.23 mg · kg −1 min −1 ). When in further studies the total insulin dose given during the pulsatile study was infused continuously (0.6 mU · kg −1 · min −1 ), HGP in the basal state and residual HGP during the insulin-clamp study were 25–30% higher than in the pulsatile experiments, whereas glucose utilization was not significantly different. In conclusion, by reducing total hormone delivery by up to 40%, but given in a pulsatile fashion, insulin is equally potent in controlling HGP as continuous insulin administration. This greater efficacy of pulsatile exposure in suppressing HGP is accompanied by an equipotent effect on glucose utilization. Application of pulsatile insulin substitution in intravenous-pump users may reduce systemic hyperinsulinemia and, in the long run, insulin resistance by reversing downregulation of insulin receptors.

Evidence that pulsatile follicle-stimulating hormone secretion is independent of endogenous luteinizing hormone-releasing hormone.

Abstract: Although LHRH can stimulate the release of both LH and FSH from the pituitary, there are a number of instances in which the secretion of LH and FSH are divergent. Previous studies from our laboratory have indicated that pulsatile LH and FSH secretion are independently regulated by gonadal factors. We have, therefore, reexamined the role of LHRH in regulating pulsatile gonadotropin secretion by evaluating the effect of passive LHRH immunoneutralization on LH and FSH secretion in castrate adult male rats. Injection of 500 μl ovine anti-LHRH serum no. 772 (LHRH-AS) into 2-week-castrate rats caused an 85% suppression of mean plasma LH levels by 2 h, which lasted through 48 h. Mean plasma FSH, however, was reduced by only 19% after 2 h and by only 59% after 48 h. When cannulated 2-week-castrate rats were bled every 10 min, both LH and FSH were secreted in a pulsatile manner. Injection of 500 μl LHRH-AS caused an immediate abolishment of LH pulses and a rapid reduction in mean plasma LH through 24 h. Pulsatile ...

Electrochemically-driven pulsatile drug dispenser

Abstract: An improved drug dispenser for the pulsatile or peristaltic delivery of drugs. The drug dispenser includes a fluid reservoir for storing the drug to be dispensed, an electrochemical pump for pumping the drug from the fluid reservoir, and a pump valve responsive to the pump pressure such that when the pump pressure reaches some predetermined value, the pump valve releases the pressure exerted upon the drug. The result is a low cost, low weight ad efficient drug dispenser for the pulsatile delivery of drugs.

Method of assessing the reproducibility of blood flow measurement: factors influencing the performance of thermodilution cardiac output computers.

Abstract: Measurements of blood flow by three different makes of thermodilution cardiac output computer in an artificial circulation were analysed by linear regression against absolute flow measured by timed blood volume collection. For each computer the horizontal distance between the 95% confidence limits for a single prediction was calculated at a standard flow rate of 5 litres per minute. This measurement represents the range of flow rates that could give rise to an identical measurement and provides a summary of the reproducibility of the computer's results and its ability to detect a change of flow rate. This measurement was used to evaluate the effect on each computer's performance of pulsatile or continuous flow, injectate volume, and injectate temperature. With continuous flow the optimum results were 1.8, 0.85, and 0.85 litres per minute and with pulsatile flow they were 1.3, 1.05, and 1.65 litres per minute. There was generally a deterioration in performance when pulsatile flow was evaluated. Under the conditions of the experiment optimum performance in both flow modes was obtained with 5 ml of ice cold injectate, but these findings cannot necessarily be extrapolated to the clinical situation. With pulsatile flow the overall range of blood flows that could give rise to identical measurements were for each computer 2.0, 1.5, and 3.1 litres per minute, corresponding to 40, 30, and 62% changes of the standard flow rate of 5 litres per minute.

Clinical observations on the relationship between cerebrospinal fluid pulse pressure and intracranial pressure.

Abstract: A method is described for monitoring the relationship between CSF pulse pressure and ICP in clinical patients. Highly significant linear relationships were found during 65 continuous ICP recordings in 58 patients. The slope value of this relationship showed a positive correlation with the elastance coefficient, a volume-pressure parameter assessed by bolus injection. However, the correlation was too weak to allow for a confident prediction of the elastance coefficient on the basis of CSF pulse pressure in the individual patient. This was attributed to the variable magnitude of the volume change underlying the CSF pulse pressure: the pulsatile variation in cerebral blood volume. This quantity was calculated on the basis of a mathematical model from the slope value and the elastance coefficient and was found to vary between 0.36 and 4.38ml. During plateau waves a disproportionate increase in pulse pressure with the ICP was observed in contrast with a relative decrease in intracranial elastance. This phenomenon was ascribed to an increase in the pulsatile variation in cerebral blood volume. It is concluded that, under certain conditions, the intracranial volume-pressure relationship can be continuously monitored by means of CSF pulse pressure analysis. The findings during plateau waves suggest that the pulse pressure also reflects the state of the cerebral vasomotor tone.

A direct growth effect of growth hormone in rat hindlimb shown by arterial infusion.

Abstract: We have developed a method for infusing substances into one hindlimb of the rat via the arterial supply. A catheter attached to an osmotic minipump is inserted into the right superior vesical artery and advanced to the junction of the right common iliac artery. This arrangement permits either constant or pulsatile infusion for 7 days. We employed this method to study the direct action of rat growth hormone (rGH) on the proximal tibial epiphysial plate in hypophysectomized rats. Infusion of neither the solvent nor ovine prolactin (2 micrograms X rat-1 X day -1) affected epiphysial plate width compared with control (uninfused) legs. The rGH infused at 0.4 and 2.0 micrograms X rat-1 X day-1 produced dose-related local growth effects that were of similar magnitude with either constant or pulsatile (eight 1-h pulses/day) infusion. However, the higher dose of rGH also resulted in a systemic effect (i.e., epiphysial plate growth in the uninfused limb), and the pulsatile mode produced a greater systemic effect than that produced by constant infusion. Our results indicate that GH can act directly on cartilage in vivo to maintain growth and that its effectiveness is not enhanced by pulsatile delivery. In contrast, the indirect (i.e., systemic) growth effects of the hormone may be enhanced by intermittent infusion. Our infusion system is well suited for studying the direct effect of substances on hindlimb tissues in conscious, unrestrained rats over extended periods.

Pulsatile versus nonpulsatile blood flow in the treatment of acute cerebral ischemia.

Abstract: The effects of pulsatile and nonpulsatile perfusion on local cerebral blood flow (CBF) and on computerized mapping (CME) of electroencephalograms (EEG) in nonischemic and ischemic brain were studied using a canine stroke model. Nine anesthetized mongrel dogs were placed on normothermic right atrial-femoral artery cardiopulmonary bypass at a flow of 100 ml/kg/minute. Local CBF measurements and CME data were collected during nonpulsatile perfusion and maximal pulsatile perfusion. The stroke model was then produced, and local CBF measurements and CME data were again collected during nonpulsatile and pulsatile perfusion. In the nonischemic brain, local CBF increased 19%, from 32 +/- 10 to 38 +/- 11 ml/100 g/minute (P less than 0.01), when perfusion was changed from nonpulsatile flow (pulse pressure less than 4mm Hg) to pulsatile flow (pulse pressure 39 +/- 11 mm Hg). In the ischemic brain, local CBF increased 55%, from 11 +/- 5 to 17 +/- 7 ml/100 g/minute (P less than 0.01), when perfusion was changed from nonpulsatile (pulse pressure less than 3 mm Hg) to pulsatile (pulse pressure 36 +/- 7) flow. EEG power data, expressed as a power ratio index (PRI = low frequency power/high frequency power), improved significantly, from 110 +/- 33 to 101 +/- 41 (P less than 0.01) with pulsatile perfusion. These data demonstrate the importance of pulsatile blood flow in ischemic brain.

Ventricular/vascular interaction in patients with mild systemic hypertension and normal peripheral resistance.

Abstract: Total left ventricular external power and aortic input impedance spectra were calculated from recordings of pulsatile pressure and flow in the ascending aorta of 22 human subjects undergoing cardiac catheterization. Eleven subjects had increased aortic pressure (systolic 153 +/- 3.8[SEM] mm Hg, p less than .001; diastolic 91 +/- 2.4 mm Hg, p less than .03; mean 118 +/- 2.4 mm Hg, p less than .001) and constituted the group with mild hypertension (average age 50 +/- 1.9 years). The other 11 (age-matched) subjects had normal arterial pressures and constituted the control group. Cardiac output in the hypertensive group was abnormally high (6.9 +/- 0.3 liters/min, p less than .04) compared with that in control subjects (6.1 +/- 0.2 liters/min), so that peripheral resistance was similar. Characteristic aortic impedance (index of aortic elastance) was increased in the hypertensive group (142 +/- 19 vs 72 +/- 4.5 dyne-sec-cm-5, p less than .002), as was the fluctuation of impedance moduli and phase. These elevated pulsatile components of arterial load were associated with a significant (p less than .002) increase in pulsatile left ventricular external power (89%), and the increased cardiac output was associated with a significant (p less than .001) increase in steady flow power (31%). The ratio of pulsatile to total power was also increased (38%) in the hypertensive group (p less than .001). Increased characteristic aortic impedance in the hypertensive group suggests that the human aorta is stiffer, and fluctuations in the impedance spectra suggest increased or less dispersed wave reflections.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulsatile versus nonpulsatile blood flow in the treatment of acute cerebral ischemia

Abstract: The effects of pulsatile and nonpulsatile perfusion on local cerebral blood flow (CBF) and on computerized mapping (CME) of electroencephalograms (EEG) in nonischemic and ischemic brain were studied using a canine stroke model. Nine anesthetized mongrel dogs were placed on normothermic right atrial-femoral artery cardiopulmonary bypass at a flow of 100 ml/kg/minute. Local CBF measurements and CME data were collected during nonpulsatile perfusion and maximal pulsatile perfusion. The stroke model was then produced, and local CBF measurements and CME data were again collected during nonpulsatile and pulsatile perfusion. In the nonischemic brain, local CBF increased 19%, from 32 +/- 10 to 38 +/- 11 ml/100 g/minute (P less than 0.01), when perfusion was changed from nonpulsatile flow (pulse pressure less than 4mm Hg) to pulsatile flow (pulse pressure 39 +/- 11 mm Hg). In the ischemic brain, local CBF increased 55%, from 11 +/- 5 to 17 +/- 7 ml/100 g/minute (P less than 0.01), when perfusion was changed from nonpulsatile (pulse pressure less than 3 mm Hg) to pulsatile (pulse pressure 36 +/- 7) flow. EEG power data, expressed as a power ratio index (PRI = low frequency power/high frequency power), improved significantly, from 110 +/- 33 to 101 +/- 41 (P less than 0.01) with pulsatile perfusion. These data demonstrate the importance of pulsatile blood flow in ischemic brain.

MR gated subtraction angiography: evaluation of lower extremities.

Abstract: We report the first clinical experience with a new method for projective imaging of blood vessels (angiography) using magnetic resonance. Vascular contrast is produced noninvasively by the phase response of moving protons. Diastolic and systolic gated images produce, respectively, flow signal and flow void; the difference image is a map of the pulsatile flow: an arteriogram. Preliminary studies are presented of the lower extremities of one healthy volunteer and four patients (one each with occlusive disease, soft-tissue tumor, arteriovenous malformation, and venous femoral-popliteal graft). Patient data are compared with accompanying conventional arteriograms, and the new method is discussed.

The role of the pulsatile pressure variations in intracranial pressure monitoring.

Abstract: The magnitude of the pulsatile intracranial pressure variations (CSF pulse pressure) is determined by the elastance of the craniospinal system and by the magnitude of the pulsatile variations in cerebral blood volume (CBV). The pulsatile change in CBV is, among other factors, determined by the compliance of the cerebral vascular bed which, in its turn, is dependent on the cerebral vasomotor tone. This concept has led the authors to devise a method for the assessment of both the elastance and the state of the cerebral vasomotor tone based on the relationship between CSF pulse pressure and intracranial pressure. This relationship was found to be of a linear nature both in clinical patients and in experimental animals. A significant, positive correlation was found between the slope of this relationship and the value of the craniospinal volume-pressure relationship: the elastance coefficient. During elevation of the intracranial pressure a breakpoint was observed in the relationship between CSF pulse pressure and the intracranial pressure above which the pulse pressure increased more rapidly. The elastance remained constant above this breakpoint. The same phenomenon was observed during plateau waves in clinical patients. Induced changes in systemic arterial pressure produced opposite effects on CSF pulse pressure and elastance coefficient. In these cases the discrepancy between pulse pressure and elastance was attributed to the pulsatile changes in CBV and this could be verified by means of electromagnetic flowmetry. The advantage of this method is that all the information is contained within the intracranial pressure signal itself, from which it can be extracted by simple means without the use of invasive tests.

Visualization of moving fluid: quantitative analysis of blood flow velocity using MR imaging.

Abstract: A new method for the measurement of blood flow using magnetic resonance imaging has been developed. The flow velocities are calculated from the distances that the fluid has moved. The distances are directly visualized by a new pulse sequence. In a phantom study, the measured flow rates showed very good correlation with actual flow rates of up to 20 l/min (3 m/sec). In a volunteer study, pulsatile flow velocities of a large artery were measured with electrocardiographic gating. The flow pattern of a cardiac cycle at the abdominal aorta is similar to that revealed by other methods of measurement, such as Doppler ultrasound. This method allows reasonably accurate quantitative analysis of blood flow in the large arteries.

Artifacts from pulsatile flow in MR imaging.

Abstract: Previous investigators have examined the effect of blood flow on the apparent blood vessel signal intensity These studies reported flow brightening and darkening effects within vessels In this paper we have investigated another type of flow artifact, which originates from the pulsatile nature of blood flow These flow artifacts have characteristic bright and dark "ghosting" patterns which appear close to small vessels, usually arteries, which are bright in slow flow Similar to the amplitude-of-motion artifacts caused by patient motion (eg, breathing and cardiac motion) the ghosting artifacts due to pulsatile flow are best characterized as frequency modulated spectral sidebands The pulsatile artifacts can have both dark and bright structures and usually appear close to the "moving" vessel that generates the artifact In this paper we present a study of the chief features of these pulsatile flow artifacts, and we develop a theoretical description of their origins in terms of "accidental" velocity-encodings that occur strongly in most magnetic resonance imaging sequences

Relationship between human chorionic gonadotrophin-induced changes in testicular microcirculation and the formation of testicular interstitial fluid.

Abstract: The relationship between testicular vascular permeability and testicular microcirculation as measured by laser Doppler flowmetry was studied in adult rats. In untreated control animals there was an oscillatory testicular blood-flow pattern with a frequency of 10.6 +/- 0.8 pulses/min and the amount of testicular interstitial fluid (IF) collected was 61.5 +/- 2.2 microliter/g testis. Treatment of the rats with 25-200 i.u. human chorionic gonadotrophin (hCG) s.c. 8 h before the experiment resulted in a change in the testicular flow pattern from pulsatile to continuous and an increase in IF volume. Treatment with hCG (50 i.u., s.c.) changed the testicular blood-flow pattern from oscillatory to continuous 4, 8 and 16 h after treatment. The flow pattern returned to being pulsatile 32 h after treatment with hCG. The IF information was increased at those times when the blood-flow pattern was continuous. No effects on blood flow or IF formation were observed with 12.5 i.u. hCG s.c. The present study shows a dose- and time-dependent covariation between the increase in testicular IF volume and the disappearance of the pulsatile flow in testicular microcirculation. It appears that a continuous flow pattern favours the transport of fluid from blood vessels to the interstitium.

Multiphasic MR imaging: a new method for direct imaging of pulsatile CSF flow.

Abstract: A new technique is described that allows for the creation of pure pulsatile flow magnetic resonance (MR) images in a single acquisition. Five to 16 electrocardiographically gated images spanning the entire cardiac cycle are obtained with use of a gradient-echo pulse sequence. The section can be varied from 4 mm thick to full thickness projection. Taken singly, each image provides direct assessment of flow direction and velocity. Subtraction of image pairs eliminates signal detected from stationary protons, producing images of pulsatile flow. In this study the technique was used to image the flow of cerebrospinal fluid (CSF) in healthy subjects and in one patient with syringohydromyelia. The data suggest that multiphasic MR imaging provides a powerful means for the noninvasive assessment of CSF pulsatile flow dynamics and may have potential clinical application for the investigation of a variety of abnormalities such as normal pressure hydrocephalus, syrinx, and spinal block.

Temporal relationship of the pulsatile fluctuation of luteinizing hormone and progesterone in cattle: a time series cross-correlation analysis.

Abstract: The temporal relationship between the pulsatile patterns of plasma luteinizing hormone (LH) and progesterone (P4) was studied in mid-luteal (ML) and early-pregnant (EP) dairy cows. Blood samples were collected (via external jugular vein cannulae) at 10-min intervals for 16 h in 5 ML cows (d 10 to 12 of the cycle) and for 10 h in 5 EP cows (d 52 to 56 of gestation). Concentrations of LH and P4 were determined by radioimmunoassays and a time series cross-correlation analysis was utilized to evaluate the temporal relationship between them. A pulsatile pattern was found for both hormones in both groups, and in all animals LH peaks were uniformly followed by P4 peaks. In 80% of the cows in both groups the highest cross-correlation occurred between samples LH(n) and P4 (n + 1) (n = sample number), suggesting that a lag time of about 10 min is necessary for luteal stimulation. Results from both groups demonstrate that P4 is released from the corpus luteum in a pulsatile manner and that its release is at least partially dependent upon the pulsatile pattern of plasma LH. Correlation coefficients between LH and P4 mean level, basal levels, peak frequencies and peak amplitudes obtained in both groups indicate that the conceptus alters the hypothalamic-pituitary-ovarian relationship found in the ML cows, suggesting the existence of another factor(s) acting along with LH to release P4 in EP cows.

Blood flow conduit

Abstract: A improved blood flow conduit provided with external inflatable balloons and having rigid end portions for facilitating insertion into blood vessels and means for detecting pulsatile flow in the conduit and excessive pressure in the balloons.

Evidence for the pulsatile release of PGF-2α inducing the release of ovarian oxytocin during luteolysis in the ewe

Abstract: Frequent blood samples were removed from a utero-ovarian vein, a jugular vein and a femoral artery of 5 ewes during luteolysis. Analysis of these samples for oxytocin-associated neurophysin revealed a significant venous-arterial difference across the ovary and uterus but not across the head. This occurred during the pulsatile surges as well as when levels were basal and confirms the corpus luteum as a major source of the pulsatile surges of oxytocin-associated neurophysin and oxytocin that occur during CL regression and also of the elevated luteal phase concentrations of both hormones. The pulsatile surges of oxytocin-associated neurophysin measured in the utero-ovarian vein were accompanied by the release of an approximately equimolar amount of oxytocin. The concentration of PGF-2 alpha in the utero-ovarian vein samples began to increase before the levels of oxytocin and oxytocin-associated neurophysin started to increase. This suggests that uterine PGF-2 alpha initiates the release of ovarian oxytocin and oxytocin-associated neurophysin during luteolysis in the ewe.

Design of a function test apparatus for prosthetic heart valves. Initial results in the mitral position

Abstract: A test rig has been developed to investigate the function of prosthetic heart values under pulsatile flow conditions. The rig uses a servo-controlled pump to produce a physiological flow waveform through the valve. The pressure difference across the valve and flow through the valves are measured to assess the valve function. The mean pressure difference, root mean square (RMS) forward flow and regurgitant volumes are calculated on a computer. In the initial study, seven popular mechanical prostheses (sizes 29 and 27 mm) were evaluated in the mitral position under five different flow conditions. The mean pressure difference was dependent on the position of the downstream pressure tapping, the orientation of the valve and the time interval used to average the signals. The orientation of some valves also affected the regurgitant volumes. These variations (10-25%) were similar in size to the differences measured between individual valves. Test conditions have to be specified very carefully for accurate comparison of valve function to be made.

In vitro evaluation of six mechanical and six bioprosthetic valves.

Abstract: The in vitro function of 6 tissue valves and 6 mechanical valves (all size 29) was assessed in a purpose-built pulse duplicator under different pulsatile flow conditions. Valve function was analyzed by measuring the mean pressure difference across each valve during forward flow, and the reverse flow through each valve during valve closure (dynamic regurgitation) and in the fully closed position (static regurgitation). Although valves of the same type showed similar characteristics, there were significant differences in function between different types of valves. Porcine valves showed much higher forward flow pressure gradients than pericardial, tilting disc, or bileaflet mechanical valves. However, the porcine valves showed least regurgitation, with pericardial valves having less regurgitation than mechanical valves.