Showing papers on "Pulsatile flow published in 1981"

Combined doppler and phased-array echocardiographic estimation of cardiac output.

Abstract: The capability of a pulsed Doppler flowmeter combined with a phased-array imaging system to measure volume flow was tested in vitro and in patients undergoing cardiac catheterization. The Doppler-phased-array system (DPA) was used to determine vessel diameter and a superimposed cursor was used to locate the range and angle of the Doppler sample volume. DPA estimates of continuous flow through tubing in a water tank correlated strongly (r = 0.99) with measured flow corresponding to physiologic ranges from 3-12 l/min. For pulsatile flow in a water tank, a correlation of r = 0.86 with measured flow was obtained, whereas DPA estimates of cardiac outputs compared with Fick estimates in the 11 patients produced a correlation of r = 0.83. These data indicate that estimates of cardiac output are possible using the DPA approach.

Manipulation of ascending aortic pressure and flow wave reflections with the Valsalva maneuver: relationship to input impedance.

Abstract: Dramatic changes in the shape of pulsatile ascending aortic pressure and flow wave forms occur during the Valsalva maneuver in man. To study these changes, aortic pressure and flow signals were recorded in eight patients using a multisensor catheter. Aortic input impedance was derived during the control, strain and postrelease phases of the Valsalva maneuver. During control, well-defined minima and maxima occurred in the spectral plots of impedance moduli. This pattern was accentuated during the postrelease phase. In contrast, input impedance during strain was almost equal to the characteristic impedance for all harmonics. These results imply that during the control and postrelease phases, strong reflections return to the ascending aorta, but during the strain phase, reflections are minimal, absent or more diffuse. From wave transmission theory, it also follows that pulsatile pressure and flow wave forms should be similar in shape in the absence of reflections and dissimilar in the presence of reflections. This was observed in all eight patients. By provoking changes in the arterial tree during the Valsalva maneuver, the magnitude and timing of wave reflections were significantly altered, resulting in marked changes in the shape of pulsatile aortic pressure and flow wave forms. This study demonstrates the importance of reflections in determining the shape of the arterial pulse.

Laser-Doppler Continuous Real-Time Monitor of Pulsatile and Mean Blood Flow in Tissue Microcirculation

Abstract: A noninvasive instrument capable of instantaneous (~ 30 msec resolution) and continous evaluation of local flow in tissue microcirculation has been developed based on laser Doppler velocimetry. Laser light is delivered to and detected from the region to be studied by flexible, graded-index fiber optic light guides. The Doppler-broadening of laser light scattered by moving red blood cells within the tissue is analyzed in real-time by an analogue processor which provides a continuous output of the instantaneous mean Doppler frequency in the photocurrent detected by a square-law detector. The mean Doppler frequency is predicted by theory to be linearly correlated with microcirculatory blood flow in a variety of tissues, and the Laser-Doppler signal has been correlated with measurements of average tissue blood flow by other techniques. The local spatial ensemble of moving red blood cells within lmm3 of the microcirculation allows an instantaneous assessment of flow pulsations during the cardiac cycle as well as slower changes in average flow. The instrument has been designed to facilitate simple rapid clinical measurements of local spatial and temporal variations in microcirculatory flow. Measurement of local tissue blood flow in normal volunteers and patients has demonstrated the ease of accurately measuring basal and perturbed flow (reactive hyperemia, thermal hyperemia, position changes).

Role of aortic input impedance in the decreased cardiovascular response to exercise with aging in dogs.

Abstract: The diminished cardiac output response to exercise with advancing age may be attributable to intrinsic inability of the old ventricle to respond appropriately and/or to an additional loading imposed upon the ventricle by the aged vascular system. The steady (resistance) and pulsatile (characteristic impedance) load components together comprise the vascular load faced by the ejecting ventricle. To study the effect of exercise on both vascular components of load, the aortic input impedance was measured in chronically instrumented young and old beagle dogs during graded treadmill exercise before and after beta blockade. Ascending aortic flow was measured by a cuff electromagnetic flow probe, and pressure was measured by a high-fidelity semiconductor transducer. At low levels of exercise the old animals demonstrated a striking 20% increase in characteristic impedance and a 28% decrease in peripheral resistance with no increase in stroke volume. This vascular loading and limitation in stroke volume persisted across the higher exercise levels. In contrast, the young group demonstrated no increase in characteristic impedence, a progressive decrease in peripheral resistance, and a progressive increase in stroke volume across the same exercise levels. These age differences in vascular response and ventricular output were abolished by beta blockade. The groups did not demonstrate a difference in heart rate response, but the young had a greater increase in external left ventricular power than the old across exercise. These data demonstrated a profound difference in the response of young and old vasculature to exercise. At low and intermediate exercise levels the pulsatile vascular load appeared to be a major factor in the limitation of stroke volume in old dogs. At high levels of exercise, the limited exercise response in the old dog may be caused in part by a diminished inotropic responsiveness as well as by the vascular loading.

Experimental study of physiological pulsatile flow in a curved tube

Abstract: In this paper, an experimental determination of the three-dimensional velocity distribution due to the physiological pulsatile flow of a Newtonian, incompressible fluid at various locations in a curved tube of circular cross-section is presented. Our results show four interesting features of the pulsatile flow development in the curved tube. First is the presence of a reversed flow along the inner wall of the tube during the diastolic (deceleration) phase of the pulsatile flow cycle. Second is that the flow does not appear to be fully developed in the curved tube through the cross-section whose L/a ratio is equal to 16·9, the final location at which measurements were made in this study, where L is the axial length and a is the radius of the curved tube. A third feature observed is the vacillation of the peak axial velocity across the horizontal diameter of the tube from the upstream to the downstream region in the curved tube. In the upstream region (L/a = 3·4), the maximum axial velocity measured occurred nearest to the outer wall. The maximum axial velocity shifted towards the inner wall in the middle of the tube (L/a = 10·2), while in the downstream region (L/a = 16·9), the maximum axial velocity measured was again near the outer wall. Finally, trapped vortical motions are observed to occur at the inner wall of the tube in the downstream region.

Attenuation of the stress response to cardiopulmonary bypass by the addition of pulsatile flow.

Abstract: The effect of pulsatile flow during cardiopulmonary bypass on the hormonal stress response was studied in 26 patients. Thirteen had routine and 13 had pulsatile bypass with an average pulse pressure of 30 mm Hg. Plasma vasopressin levels were significantly elevated during bypass in both groups, but were lower with pulsation (66 +/- 11 vs 36.3 pg/ml, p less than 0.05). Epinephrine levels increased in both groups during bypass, but were higher after bypass (1179 +/- 448 vs 713 +/- 140 pg/ml, p less than 0.05) and in the recovery room (1428 +/- 428 vs 699 +/- 155 pg/ml, p less than 0.05) in the nonpulsatile group. The same response was noted in the norepinephrine levels (924 +/- 225 vs 465 +/- 90 pg/ml, p less than 0.05; 1015 +/- 491 vs 717 +/- 112 pg/ml, p less than 0.05). There were no significant changes in renin activity in either group, but the increase after cardiopulmonary bypass was greater in the nonpulsatile group (2.0 +/- 0.7 vs 1.36 +/- 0.4 ng/ml/hr, NS). These data suggest that pulsatile flow significantly attenuates the vasopressin and catecholamine stress response to cardiopulmonary bypass. This may explain the increased flow requirements and better tissue perfusion and organ function and the decreased incidence of postoperative hypertension after bypass using pulsatile flow.

The effect of naloxone on pulsatile gonadotrophin release in normal subjects

Abstract: SUMMARY The gonadotrophin response to naloxone infusion has been investigated in three adult males, and three adult females in the early follicular phase. The frequency of LH secretory episodes and the mean LH levels increased in both sexes. The data suggest that the pulsatile release of LH is under inhibitory opiate control.

Flow studies in a model carotid bifurcation.

Abstract: Boundary layer separation in a plexiglass model carotid bifurcation was investigated in relation to the origin of atherosclerotic plaque clinically found in this region. Our model was comparable to a human carotid in both dimensions and geometry. Water flowed through the model at Reynolds numbers from 200 to 1200 under steady and pulsatile flow conditions, with outflow through the external and internal branches varied. The near-wall flow was visualized by slow injection of dye through ports machined in the model. Under steady flow at a physiological Reynolds number of 500 and a flow split at the bifurcation similar to that of a human carotid at rest, boundary layer separation was found to occur in a carotid sinus across from the external carotid origin, forming a shell of slowly moving fluid around the bifurcation. The rapidly moving mainstream impinged directly on the flow divider. The location of atherosclerotic plaque correlates best with the low shear region of separation and not with the region of high shear at the flow divider. Preliminary studies with pulsatile flow demonstrated little change from the steady flow results.

Determination of volume of arterial blood flow by an ultrasonic device.

Abstract: This paper describes the results of a reevaluation of the reliability of a newly developed ultrasonic volume flow meter which was developed by Yoshimura and his co-workers (1978). Measurements of volume blood flow (cc/sec) by this new technique were compared with measurement by the electromagnet flow meter. Experiments were performed with an in vitro model as well as with physiological pulsatile flow in an animal model. Results of the study indicated a high degree of correlation between values measured by both techniques with a correlation coefficient of 0.99 I believe that this is an important technical development in the field of noninvasive quantitative determination of blood flow.

Pressure operated pulsatile fluid flow device

Abstract: Pulsations are created in a fluid flow stream by a pulsatile device. The device includes a flexible, resilient element which oscillates under the influence of a pressure differential to interrupt the fluid flow at regular intervals, thereby causing the outlet flow to pulsate. The device may be connected directly to a supply of fluid under pressure.

Further Studies on Dopamine-Induced Suppression of Pulsatile LH Release in Ovariectomized Rats

Abstract: Third ventricular administration of dopamine (DA) in ovariectomized rats suppresses pulsatile LH secretion in a dose-dependent manner (Neuroendocrinology 29: 149, 1979). Since infusion of norepinephrine (NE) also produces a similar response, and DA can be taken up by noradrenergic fibers and converted to NE, an experiment was carried out to determine whether DA acted by directly activating DA receptors. This study also examined which parameters of pulsatile LH secretion were affected during DA-induced suppression of this release process, i.e., the LH interpulse interval and/or the magnitude of increase in blood LH levels produced by LH pulses. Infusion of DA in control rats pretreated with tartaric acid or /-butaclamol decreased mean blood LH levels. This effect is due entirely to a marked increase in the LH interpulse interval, since no change was seen in the magnitude of increase in blood LH levels produced by those LH pulses that did occur during DA infusion. Blockade of DA receptors with pimozide prevented the decrease in blood LH levels in response to DA and significantly reduced the change in the LH interpulse interval. These data indicate that DA suppresses pulsatile LH release solely by affecting the periodicity of this rhythm, and that this effect is mediated primarily through an activation of DA receptors. Pretreatment with d-butaclamol, another DA receptor antagonist, had no effect on the response to DA. As in control rats, DA-induced suppression of pulsatile LH release was again due entirely to a lengthening of the LH interpulse interval. d-Butaclamol does block the inhibition of pulsatile LH release due to peripheral administration of the DA receptor agonist, apomorphine (Endocrinology 100: 796, 1977). However, when concentrations of apomorphine equimolar to DA were infused into the third ventricle in d- or l-butaclamol-treated rats, comparable suppressions of pulsatile LH release occurred. This suggests that the failure of d-butaclamol to prevent the suppression of pulsatile LH release by intraventricular DA administration was apparently due to an ineffective level of DA receptor blockade.

A servo‐controlled roller pump for constant flow or constant pressure blood perfusion under normal pulsatile or non‐pulsatile conditions

Abstract: This paper describes the design of a servo-controlled precision roller pump applicable for constant blood flow or constant blood pressure perfusion in research on the peripheral circulation. The pump, and its feed-back control, can simulate normal cardiac induced autoperfusion by reproducing the arterial pulse pressure configuration with high fidelity. Its design is such as to minimize damage of the red blood cells and consequent release of vasoactive substances, a problem encountered with most conventional pumps. The present pump principle may also find a use in heart-lung machines and dialysis equipment and can be used as a precision infusion pump.

The effect of pulsatile perfusion on preservation of left ventricular function after aortocoronary bypass grafting.

Abstract: Pulsatile perfusion has been reported to be of value in intraoperative myocardial protection. To evaluate this technique, we studied 26 patients undergoing aortocoronary bypass grafting. Ejection fraction determinations from multigated cardiac blood pool scans, serial hemodynamic monitoring, and total CPK and MB-CPK sampling were performed early (4, 6 and 8 hours after bypass) and 10 days after operation. In 12 patients, pulsatile perfusion was started immediately after aortic cannulation and continued until 10 minutes after cessation of bypass; 14 patients had standard nonpulsatile perfusion. All patients had a single aortic cross-clamping and potassium cardioplegia. Cross-clamp time (46 +/- 3 and 46 +/- 3 minutes [+/- SEM]), total bypass time (94 +/- 4 and 89 +/- 6 minutes), and mean perfusion pressure (82 +/- 5 and 83 +/- 3 mm Hg) were comparable in the pulsatile and nonpulsatile groups, respectively, as were extent of coronary disease and number of bypass grafts. Preoperative and postoperative ejection fractions for pulsatile and nonpulsatile groups, respectively, were 0.57 +/- 0.03 and 0.55 +/- 0.04 before operation, 0.37 +/- 0.03 and 0.40 +/- 0.04 4 hours after bypass, 0.40 +/- 0.03 and 0.46 +/- 0.04 at 6 hours, 0.51 +/- 0.05 and 0.52 +/- 0.07 at 8 hours and 0.56 +/- 0.05 and 0.53 +/- 0.04) 10 days after operation. Mean arterial pressure, left atrial pressure and serial cardiac indexes were similar in both groups. There were no perioperative myocardial infarctions by ECG in either group. Total CPK (586 +/- 78 and 617 +/- 140 IU/l) and peak MB-CPK (73 +/0 14 and 61 +/- 11 IU/l) were comparable in the pulsatile and nonpulsatile groups, respectively. Pulsatile perfusion offers no advantage in myocardial preservation after aortocoronary bypass grafting in patients with normal left ventricular function.

Growth of loudness for sinusoidal and pulsatile electrical stimulation.

Abstract: The perception of loudness produced by elec­ trically stimulating a cochlear prosthesis is different for different electrical waveforms. The two wave­ forms studied in the present experiment were bi­ phasic pulses and sinusoids. In general, the growth of loudness curves are steeper for biphasic pulses than for sinusoids, when the two waveforms are equated for equal charge per unit time. The growth of loudness curves are steeper for low frequencies than for high frequencies, for both pulsatile and sinusoidal stimulation.

Effect of partial deafferentation of the hypothalamus on stress-induced LH suppression and prolactin release.

Abstract: Stress of immobilization suppressed pulsatile LH release and decreased mean serum LH levels within 10 min, lasting at least for 2 h in ovariectomized rats. Anterior cuts (radius, 2 mm) at the level of

Flow visualization in a mold of an atherosclerotic human abdominal aorta.

Abstract: Flow in a mold of an atherosclerotic human abdominal aorta and common iliac arteries was studied by flow visualization at a mean Reynolds number of 500 during both pulsatile and steady flow. Flow separation and transient flow reversals were found distal to atherosclerotic plaques during pulsatile flow; whereas flow separation resulting in regions of permanent eddies were observed distal to plaques only during steady flow.

Effect of electrical stimulation of the dorsomedial hypothalamic nucleus on pulsatile LH release in ovariectomized rats.

Abstract: The present experiments were carried out to examine the influence of electrical stimulation of the dorsomedial hypothalamic nucleus (DMH) on pulsatile LH release in ovariectomized rats, and the possible involvement of serotonin (5HT) in mediating any observed effects. Unanesthetized animals were bled continuously through jugular vein cannulae for an initial 1½ h control period. Rats were then stimulated for two 1-hour periods, separated by a 45-min nonstimulation period. DMH stimulation suppressed pulsatile LH release and decreased mean blood LH levels during both stimulation periods in control rats as well as animals in which 5HT synthesis was inhibited by p-chlorophenylalanine or 5HT receptors were blocked by metergoline. The decrease in mean blood LH levels in all groups was due solely to an increase in the LH interpulse interval. Those LH pulses that did occur during the stimulation-induced suppression did not show a decreased LH pulse amplitude. Rather, in control and metergoline-treated animals this parameter increased during stimulation, suggesting a buildup of readily releasable LHRH and/or pituitary LH. Lastly, estradiol benzoate suppressed pulsatile LH secretion but did not reverse the inhibitory LH response to DMH stimulation. These experiments indicate that the DMH, because of neurons originating within this nucleus and/or fibers passing through, may be a brain region that influences pulsatile LH release in a suppressive manner. This effect is exerted solely on the periodicity of the process and not through a 5HT-mediated mechanism.

Application of pulsatile cardiopulmonary bypass for profound hypothermia in cardiac surgery.

Abstract: Profound hypothermia with core cooling has been considered unsafe as compared with surface cooling because of the induced metabolic acidosis. We carried out studies on mongrel dogs to determine whether or not conventional cardiopulmonary bypass with pulsatile blood flow for core cooling could replace the bypass with non-pulsatile flow. The recovery time from anoxic damage of the brain due to circulatory arrest was also studied. Cerebral excess lactate (ΔXL) (Huckabee) was determined throughout the course of hypothermia. During the cooling period from 30°C down to 20°C, the mean value of ΔXL in the pulsatile group was significantly lower than that in the non-pulsatile group (p < 0.01). After forty minutes of the first total arrest at 20°C, thirty minutes of pulsatile perfusion tended to eliminate the anaerobic metabolism of the brain caused by the first total circulatory arrest (p < 0.1). Thus, the anaerobic metabolism in the brain appears to be highly suppressed with pulsatile cardiopulmonary bypass during the cooling period. Correction of congenital heart disease in infancy can probably be more safely performed if pulsatile cardiopulmonary bypass for cooling and rewarming is employed instead of the non-pulsatile bypass.

The NMR blood flowmeter--applications.

Abstract: Nuclear Magnetic Resonance(NMR) permits the noninvasive measurement of blood flow signals unimpaired by clothes, bandages, casts, etc. The cylindrical crossed‐coil NMR blood flowmeter was used to measureblood flow through a cross‐section of the human forearm. Two calibration procedures are described: one for pulsatile flows and the other for flows with a high non‐pulsatile component. Flow measurements from normal arms, from limbs with arterial obstruction, arteriovenous hemodialysis fistulas or other conditions are reported. An application of the flow scanning technique for separation of flow signals from individual arteries (e.g., ulnar and radial) is described. The flat crossed‐coil NMR flowmeter was applied to detect blood flow from individual arteries (e.g., brachial, popliteal, etc.). Applications of a ranging technique developed to detect signals at predetermined depths are described.

Why pulsatile flow during cardiopulmonary bypass

Abstract: The use of pulsatile perfusion during cardiopulmonary bypass is not a new concept. Early studies by Parsons and by McMaster1,2 had indicated the physiological importance of arterial pulsatility many years before the introduction of clinical perfusion. Some pioneer workers in the field of perfusion attempted to develop pulsatile bypass pumps, but were hampered by inadequate technology and fears of increased haemolysis with pulsatile perfusion. Over the past two decades, non-pulsatile perfusion has become accepted as the conventional, if fundamentally unphysiological, mode of total-body perfusion during open heart surgical procedures.