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PubMed1983

Laser anemometry measurements of pulsatile flow past aortic valve prostheses.

Experimental results are presented on physiological pulsatile flow past caged ball and tilting disc aortic valve prostheses mounted in an axisymmetric chamber incorporated in a mock circulatory system. The measurements of velocity profiles and turbulent normal stresses during several times in a cardiac cycle were obtained using laser-Doppler anemometry. Our 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. The turbulent normal stresses measured downstream to the tilting disc in the minor flow region parallel to the tilt axis were found to be larger than those measured downstream to the caged ball valves. Comparison of measurements with steady flow at flow rates comparable to peak pulsatile flow rate show that the turbulent normal stresses are larger by a factor of two in pulsatile flow with a frequency of 1.2 Hz.

Aortic Valve↗
PubMed1999

Implementation of spectral width Doppler in pulsatile flow measurements.

In this paper, we present an automatic beam-vector (Doppler) angle and flow velocity measurement method and implement it in pulsatile flow measurements using a clinical Doppler ultrasound system. In current clinical Doppler ultrasound flow velocity measurements, the axis of the blood vessel needs to be set manually on the B-scan image to enable the estimation of the beam-vector angle and the beam-vector angle corrected flow velocity (the actual flow velocity). In this study, an annular array transducer was used to generate a conical-shaped and symmetrically focused ultrasound beam to measure the flow velocity vectors parallel and perpendicular to the ultrasound beam axis. The beam-vector angle and flow velocity is calculated from the mode frequency (f(d)) and the maximum Doppler frequency (f(max)) of the Doppler spectrum. We develop a spectrum normalization algorithm to enable the Doppler spectrum averaging using the spectra obtained within a single cardiac cycle. The Doppler spectrum averaging process reduces the noise level in the Doppler spectrum and also enables the calculation of the beam-vector angle and flow velocity for pulsatile flows to be measured. We have verified the measurement method in vivo over a wide range of angles, from 52 degrees to 80 degrees, and the standard deviations of the measured beam-vector angles and flow velocities in the carotid artery are lower than 2.2 degrees and 12 cm/s (about 13.3%), respectively.

Blood Flow Velocity↗
PubMed1995

Pulsatile flow during cardiopulmonary bypass speeds thermal energy transfer: a possible explanation for the reduced afterdrop.

The instantaneous thermal energy balance and rates of thermal energy transfer during hypothermic cardiopulmonary bypass were measured for a group of patients receiving continuous flow and compared with a group receiving pulsatile flow. Cooling was more rapid and the rate of thermal energy delivery during rewarming significantly greater in the pulsatile flow group despite similar rewarming times. The final thermal energy balance at the end of cardiopulmonary bypass was larger and the period of postoperative hypothermia shorter in those receiving pulsatile flow. The greater rate of thermal energy transfer may explain the reduced afterdrop.

Body Temperature Regulation↗
PubMed1993

Retrograde cerebral perfusion using pulsatile flow under conditions of profound hypothermia.

We investigated the effects of pulsatile flow for retrograde cerebral perfusion under profound hypothermia. Total cardiopulmonary bypass was carried out in adult mongrel dogs to induce hypothermia. One hour of total circulatory arrest was then performed at 20 degrees C in the control group of 6 dogs. In another group of 6 dogs, after cardiac arrest was obtained at 20 degrees C, retrograde cerebral perfusion with nonpulsatile flow was performed through both sides of the internal maxillary vein for 60 minutes; in a third group of 6 dogs, retrograde pulsatile perfusion was continued for 60 minutes. At the end of either retrograde perfusion or total circulatory arrest for 60 minutes, cerebrospinal fluid pressure and blood flow in the cerebral tissues were measured, and cerebral tissues were collected to measure water and adenosine triphosphate content. A significant difference was found for water content between the group undergoing retrograde perfusion with pulsatile flow as opposed to nonpulsatile flow. Cerebral tissues in the group perfused retrogradely with nonpulsatile flow contained more water than in the group perfused with pulsatile flow. Cerebrospinal fluid pressure was lower in the group perfused retrogradely with pulsatile flow when compared with nonpulsatile flow, but no significant difference could be found. As for cerebral flow and adenosine triphosphate content, no significant differences could be found between the groups perfused retrogradely with pulsatile or with non-pulsatile flow. Values were always higher, nonetheless, in the groups perfused with pulsatile flow. We conclude that retrograde cerebral perfusion with pulsatile flow, when used under conditions of profound hypothermia, possesses more cerebroprotective effects than does non-pulsatile perfusion or circulatory arrest.

Adenosine Triphosphate↗
PubMed1992

Effect of pulsatile flow on microvascular resistance in adult rabbit lungs.

We have determined the effect of pulsatile flow on segmental vascular resistance in lungs from 29 adult rabbits. In group I (n = 4), II (n = 8), and III (n = 8) lungs were isolated. In group IV (n = 9) rabbits were anesthetized, their chests were opened, and lungs were studied in vivo. Group I and II lungs had steady-flow perfusion: group I with intact vasotonus and group II with papaverine treatment. Group III lungs (papaverine treated) were perfused for two consecutive 45-min periods with steady and pulsatile flow. In all isolated lungs and in lungs of five anesthetized rabbits, we measured pressures in subpleural 20- to 50-microns-diam arterioles and venules by use of the micropipette servo-nulling method. Measurement of distribution of blood flow in lungs of four anesthetized rabbits by use of radiolabeled microspheres revealed no abnormality of blood flow to the micropunctured lobe. We found that total and segmental vascular resistances were similar in group I and II lungs, with microvessels representing 55% of total resistance. In group III lungs, total resistance was 30% lower during pulsatile flow than during steady flow because of a lower microvascular resistance. Lungs in vivo (group IV) had a significantly lower total vascular resistance than isolated lungs and had a low fractional resistance in microvessels (approximately 28%). We conclude that, in isolated perfused adult rabbit lungs, vascular resistance is very high, particularly in the microvascular segment, and that pulsatile flow decreases microvascular resistance.

Animals↗
PubMedDate not supplied

Does pulsatile flow improve glucose tolerance during extracorporeal circulation.

The present study was designed to determine the effect of pulsatile glow on glucose tolerance during cardiac surgery. Twenty patients were divided into two equal groups; ten patients receiving non-pulsatile bypass and the remaining patients receiving pulsatile flow. Patients receiving pulsatile flow had significantly lower systemic resistance in the intensive care unit. Glucose tolerance, however, was similar in both patient groups. Insulin secretion was impaired and serum glucose remained elevated throughout the period of extracorporeal circulation. We conclude from this study that glucose tolerance is unaffected by pulsatile flow.

Blood Glucose↗
PubMed1992

Pulsatile flow visualization in the abdominal aorta under differing physiologic conditions: implications for increased susceptibility to atherosclerosis.

The infrarenal abdominal aorta is a common site for clinically significant atherosclerosis. As has been shown in other susceptible locations, vessel geometry, flow division rates, and pulsatility may result in hemodynamic conditions which influence the preferential localization of disease in the abdominal aorta segment. Pulsatile flow visualization was performed in a glass model of the aorta constructed from measurements of angiograms and cadaver aortas. Flow rates and pulsatile waveforms were varied to reflect typical physiological conditions. Under normal resting conditions, the flow patterns in the infrarenal aorta were more complex than those in the suprarenal location. Time varying vortex patterns appeared at the level of the renal arteries and propagated through the infrarenal aorta into the common iliac arteries. A region of oscillating velocity direction extended from the renal arteries to the aortic bifurcation along the posterior wall. Dye became trapped along the posterior wall, requiring several cardiac cycles for clearance. In contrast, there was rapid clearance of the dye in the anterior aorta. Under postprandial conditions, the flow patterns in the aorta were basically unchanged. Simulated exercise conditions created laminar hemodynamic features very different from the resting conditions, including a decrease in dye residence time. This study reveals significant time-dependent variations in the hemodynamics of the abdominal aorta under differing physiologic conditions. Hemodynamic factors such as low wall shear stress, oscillating shear direction, and high particle residence time may be related to the clinically seen preferential plaque localization in the infrarenal aorta.

Angiography↗
PubMed2001

Postoperative course of S-100B protein and neuron-specific enolase in patients after implantation of continuous and pulsatile flow LVADs.

BACKGROUND: In the early post-operative period after implantation of a continuous flow left ventricular assist device (LVAD) a non-pulsatile flow occurs. We compared the post-operative time-courses of protein S-100B (S100B) and neuron-specific enolase (NSE) as biochemical markers of brain injury in patients after implantation of a continuous flow LVAD and patients receiving a pulsatile flow LVAD. METHODS: Since 1998 the continuous flow DeBakey VAD has been implanted in 8 patients at our institution. For comparison purposes, a group of 7 consecutive patients in whom a pulsatile Novacor N100 LVAD was implanted were investigated. In both groups cardiopulmonary bypass (CPB) with cardiotomy suction was used. S100B and NSE were measured in serum pre-operatively, 4 hours after CPB, and on days 1, 3, 7, and 14 after implantation of the LVAD. A neurologic examination was performed pre-operatively and post-operatively on days 3 and 14. RESULTS: No differences were found between groups in pre-operative characteristics. The analysis of variance with repeated measurements for S-100B and NSE showed significant time effects (p = 0.004, p = 0.009, respectively) but no group effects (p = 0.06, p = 0.26, respectively) and no interaction between groups and time (p = 0.12, p = 0.48, respectively). The pre-operative serum level of S100B was significantly higher (p = 0.03) in the DeBakey VAD group. The pre-operative serum level of NSE was similar in the 2 groups (p = 0.7). In both groups there was a significant increase of S100B and NSE immediately after surgery (S100B: p = 0.006, p = 0.019; NSE: p = 0.01, p = 0.001). The values returned to pre-operative levels in the DeBakey VAD group on day 1 after implantation and in the Novacor group for S100B on day 3 and NSE on day 1. Post-operatively the mean values of S100B and NSE in the DeBakey VAD group compared with the Novacor group were significantly elevated only on day 3 (p = 0.005, p = 0.023).No neurologic complications were noted in patients with a continuous flow LVAD, whereas in the pulsatile LVAD group 2 patients presented neurologic abnormalities during the study period. CONCLUSIONS: The similar course of biochemical markers of brain damage in both groups may indicate that the non-pulsatile flow in the early post-operative period does not lead to increased brain injury or permeability of the brain blood barrier.Elevated levels of S100B and NSE in the post-operative period can be used as diagnostic markers of brain injury in patients after implantation of both types of LVAD.

Adult↗
PubMed1992

Short-term effects of levobunolol on ocular pulsatile flow.

In a randomized, double-masked, placebo-controlled study, we evaluated the effect of levobunolol 0.5%, a nonselective beta-blocker, on intraocular pressure, volume amplitude, and ocular pulsatile flow in healthy individuals and patients with glaucoma. Volume amplitude and ocular pulsatile flow were derived from measurements of pulse amplitude with a pneumatonometer. Two hours after instillation of levobunolol, intraocular pressure decreased from 26.0 +/- 5.1 mm Hg to 17.8 +/- 3.9 mm Hg (28.3%) (P less than .001) in glaucomatous eyes and 20.2 +/- 3.6 mm Hg to 14.5 +/- 4.2 mm Hg (29.6%) (P less than .001) in healthy eyes. Ocular pulsatile flow was increased after treatment with levobunolol from 482.1 +/- 133.3 microliter/minute to 548.5 +/- 180.3 microliter/minute (13.3%) (P less than .006) in glaucomatous eyes and 457.6 +/- 178.2 microliter/minute to 528 +/- 223.8 microliter/minute (12.3%) (P greater than .05) in healthy eyes. There was no significant change in intraocular pressure, volume amplitude, or ocular pulsatile flow in placebo-treated eyes. The implication of these data for glaucoma therapy is not clear. Although we used an instrument that supposedly measures total pulsatile flow, it may be that optic nerve blood flow is dependent on total, both pulsatile and nonpulsatile, flow. Further, even though retinal blood flow is a small component of total ocular blood flow, it may be equally or more important than choroidal flow because of the necessity to maintain the perfusion of the retinal ganglion cells.

Adult↗
PubMed1987

Anesthetic and supportive management during experimental pulsatile flow perfusion studies in calves.

The purpose of this study was to determine the factors influencing successful experimental cardiopulmonary bypass studies using pulsatile flow perfusion and the medications and methodology necessary to produce successful bypass in calves. In six calves showing no cardiopulmonary pathology prior to bypass procedures, successful anesthesia and surgical intervention was accomplished. Animals were maintained on 5 hours of pulsatile flow bypass perfusion. Successful recovery from the procedures was accomplished. In two calves with pre-existing pulmonary pathology, anesthetic and surgical intervention was accomplished with the utilization of extensive anesthetic management and cardiac supportive medications until the animals could be initiated into 5 hours of pulsatile flow bypass perfusion, in spite of major pulmonary dysfunction. In these two animals, attempts to resuscitate upon termination of pulsatile flow perfusion were unsuccessful due to pre-existing excessive lesions in the lungs. This study shows a contrast between complete success of a pulsatile flow system in normal subjects versus the ultimate failure in experimental animals with pre-existing pulmonary pathology. The inability of experimental calves with a diseased lung to resume spontaneous cardiopulmonary function after the challenges of thoracic intervention indicates the unsuitability of animals with marked pre-existing pulmonary disease status for use in cardiopulmonary bypass studies.

Anesthesia, General↗
PubMed1989

Visualization and finite element analysis of pulsatile flow in models of the abdominal aortic aneurysm.

Pulsatile flows in glass models simulating fusiform and lateral saccular aneurysms were investigated by a flow visualization method. When resting fluid starts to flow, the initial fluid motion is practically irrotational. After a short period of time, the flow began to separate from the proximal wall of the aneurysm. Then the separation bubble or vortex grew rapidly in size and filled the whole area of the aneurysm circumferentially. During this period of time, the center of the vortex moved from the proximal end to the distal point of the aneurysm. The transient reversal flow, for instance, which may occur at the end of the ejection period, passed between the wall of the aneurysm and the centrally located vortex. When the rate and pulsatile frequency of flow were high, the vortex broke down into highly disturbed flow (or turbulence) at the distal portion of the aneurysm. The same effect was observed when the length of the aneurysm was increased. A reduction in pulsatile amplitude made the flow pattern close to that in steady flow. A finite element analysis was made to obtain velocity and pressure fields in pulsatile flow through a tube with an axisymmetric expansion. Calculations were performed with the pulsatile flows used in the visualization experiment in order to study the effects of change in the pulsatile wave form by keeping the time-mean Reynolds number and Womersley's parameter unchanged. Calculated instantaneous patterns of velocity field and stream lines agreed well with the experimental results. The appearance and disappearance of the vortex in the dilated portion and its development resulted in complex distributions of pressure and shear fields. Locally minimum and maximum values of wall shear stress occurred at points just upstream and downstream of the distal end of the expansion when the flow rate reached its peak.

Aorta, Abdominal↗
PubMed1993

Determination of principal reynolds stresses in pulsatile flows after elliptical filtering of discrete velocity measurements.

The purpose of this study was to develop a method to accurately determine mean velocities and Reynolds stresses in pulsatile flows. The pulsatile flow used to develop this method was produced within a transparent model of a left ventricular assist device (LVAD). Velocity measurements were taken at locations within the LVAD using a two-component laser Doppler anemometry (LDA) system. At each measurement location, as many as 4096 realizations of two coincident orthogonal velocity components were collected during preselected time windows over the pump cycle. The number of realizations was varied to determine how the number of data points collected affects the accuracy of the results. The duration of the time windows was varied to determine the maximum window size consistent with an assumption of pseudostationary flow. Erroneous velocity realizations were discarded from individual data sets by implementing successive elliptical filters on the velocity components. The mean velocities and principal Reynolds stresses were determined for each of the filtered data sets. The filtering technique, while eliminating less than 5 percent of the original data points, significantly reduced the computed Reynolds stresses. The results indicate that, with proper filtering, reasonable accuracy can be achieved using a velocity data set of 250 points, provided the time window is small enough to ensure pseudostationary flow (typically 20 to 40 ms). The results also reveal that the time window which is required to assume pseudostationary flow varies with location and cycle time and can range from 100 ms to less than 20 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed2000

Effects of artificial circulation by pulsatile and non-pulsatile flow on brain tissues.

We examined the effects of artificial circulation by pulsatile and non-pulsatile flow on microcirculation in the brain from the viewpoints of circulation and metabolism in the brain. A centrifugal pump was fixed in the bypass in the right heart of 10 pigs. In 5 of the 10 pigs, a pulsatile flow pump was fixed in the bypass in the left heart (P group), and in the remaining 5 pigs, a centrifugal pump was fixed in the bypass in the left heart (NP group). Hemodynamics were periodically monitored for 3 hours while maintaining about 100 mmHg of the mean aortic pressure. Intracranial pressure (ICP), cerebral tissue blood flow and cerebral blood flow (CBF) were measured and compared with the initial values. As the parameters of metabolism in the brain, the cerebral oxygen consumption and lactic acid - pyruvic acid ratio were evaluated. If the cerebral blood flow was reduced by cardiogenetic shock, we suggest that blood circulation and metabolism in the brain were maintained by artificial circulation. It also indicated that there was no significant difference in blood circulation and metabolism in the brain between artificial pulsatile and non-pulsatile flow circulation.

Animals↗
PubMed1996

The calibration of gas volume measuring devices at continuous and pulsatile flows.

A gas circuit that was capable of passing continuous or pulsatile flows via a 350 L Collins chain-compensated gasometer was built and evaluated. Various turbine volume transducers and dry gas meters were tested with gas compositions and flows that mimicked: a) inspired pulsatile flow over the physiological range and, b) mixed expirate being withdrawn from a Douglas bag. We found the Collins gasometer to be very accurate throughout its elevation, but its mixing fan is not required and atmospheric air should be left to saturate and the added water vapour calculated. Dry gas meters can be accurate to within 1% when calibrated (60 to 150 L/min), but require at least 25 L to be passed through them. The Morgan Ventilometer is an extremely reproducible device (coefficient of variation 0-0.2%, n = 60), but an increase in calibration syringe rate will elevate the calibration factor and reduce the percentage accuracy (one unit increase in calibration factor reduces accuracy by 0.6 - 1.0%). The optimal calibration syringe rate appears to be 30 - 45 b/min. Entrainment through the attached respiratory tubing can also alter the validity of the Ventilometer's calibration procedure.

Equipment Design↗
PubMed1984

Comparison of steady and pulsatile flow near the ventral and dorsal walls of casts of human aortic bifurcations.

Steady and pulsatile flows were passed through casts of human aortic bifurcations and, by means of a laser Doppler anemometer, fluid velocities were measured at selected sites near the ventral and dorsal walls. At these sites, in the vicinity of the bifurcation, the influence of secondary flow is significant and therefore an appreciation of the phasic variation of secondary flow patterns is important. Results are presented comparing the flow direction in both steady and pulsatile flow at sites in three casts. The common features of the flow at these sites were the persistence of the flow direction during the accelerating and decelerating phases of the pulsatile cycle, and the consistently smaller angle (measured from the inlet centerline) of the pulsatile flow direction as compared to the angle of the flow direction in steady flow.

Aorta↗
PubMed1998

A continuous and pulsatile flow circulation system for evaluation of cardiovascular devices.

The design of a nonpulsatile and pulsatile system using a centrifugal pump is presented. To induce a pulsatile flow with a centrifugal pump, an independent pneumatically driven unit provided flow patterns over a wide range of frequencies and amplitudes. The pulsatile flow was generated by the axial displacement of a cylinder that periodically compressed the flexible conduit that is connected to the pump. The system can accommodate flow rates up to 6,000 ml/min and transmural pressures up to 500 mm Hg and is capable of maintaining the pressure at a constant value. This circuit produced reproducible pressure waves having a frequency up to 4 Hz. The periodicity of the transmural pressure between 80 and 180 mm Hg was similar to the pressure wave propagation observed in peripheral circulation. Capable of adequately reproducing continuous and pulsatile flow, the apparatus is therefore versatile to allow in vitro evaluation of cardiovascular devices.

Centrifugation↗
PubMed1998

Color Doppler ultrasound pulsatile flow signals of thoracic lesions: comparison of lung cancers and benign lesions.

Color Doppler ultrasound (US) was performed in 153 patients (including 102 with lung cancer and 51 with benign lesions) to assess pulsatile flow signals in thoracic lesions. The values of resistive index (RI) and pulsatility index (PI) of color Doppler US pulsatile flow signals in lung cancers and benign lesions were measured, analyzed, and compared. In the enrolled 153 patients with thoracic lesions, 61 lung cancers and 34 benign lesions had detectable color Doppler US pulsatile flow signals, and lung cancers had lower RI and PI values than benign lesions (RI: 0.70+/-0.03 vs. 0.79+/-0.04, p < 0.05; PI: 1.61+/-0.15 vs. 2.44+/-0.25, p < 0.005). However, overlapping RI and PI values in lung cancers and benign lesions somewhat limited color Doppler US pulsatile flow signals to differentiate lung cancers from benign lesions. Further analysis of RI and PI values in subgroups of lung cancers [squamous cell carcinoma (SCC, n = 34), adenocarcinoma (AC, n = 18), and small-cell lung cancer (SCLC, n = 6)] and benign lesions [cavitary benign lesions (CBL, n = 8), and noncavitary benign lesions (NCBL, n = 26)] revealed that all different cell types of lung cancers (SCC, AC, and SCLC), indeed, had lower RI and PI values than NCBL (for RI, all p < 0.01; for PI, all p< or =0.001). Moreover, the mean RI and PI values showed a significant incremental decrease from NCBL (mean RI, PI = 0.88, 2.94) toward SCC and AC (for SCC, mean RI, PI = 0.71, 1.68; for AC, mean RI, PI = 0.68, 1.67) and, finally, to SCLC (mean RI, PI = 0.62, 1.05). In contrast, CBL had relatively lower RI and PI values than AC and SCLC (for CBL, mean RI, PI = 0.53, 0.80; both p > 0.05 for RI and PI), and even a significant difference from SCC (p < 0.05 for RI and PI). We conclude that color Doppler US pulsatile flow signal is somewhat limited to differentiate lung cancers from benign lesions, but provides a noninvasive in vivo model to assess the neovascularity intensity of lung cancers.

Adenocarcinoma↗
PubMed1982

Steady and pulsatile flow distribution in a multiple branching network with physiological applications.

Flow rate of distribution in steady and pulsatile flow is investigated in a multiple branching network including six successive generations in the same plane. In this model, the geometry dependence of flow rate distribution has already been pointed out in steady flow (previous study) by observing the occurrence of non-uniform flow rate distribution at terminal orifices despite the symmetrical dichotomy, identical distance and cross-sectional profile of the 64 parallel pathways. In the present study, we point out two additional properties of the steady flow rate distribution. (i) The flow rate distribution is not markedly sensitive to a change in viscosity and therefore Reynolds number does not appear to be a determinant factor to modify the flow distribution. (ii) The effect of a branch obstruction on flow rate distribution is limited in space and its extension remains the same for the different Reynolds numbers tested. These properties also characterize the interdependence between the model geometry and the flow distribution in steady state. The results obtained in pulsatile flow show that the flow distribution remains similar to steady state as long as the parameter lambda = Qp/Qs (Qp = amplitude of flow oscillation, Qs = steady component of the total flow) is less than 1. When lambda is greater than 1, the flow distribution may become uniform, which means that contrary to the steady flow case, the velocity profiles become rapidly symmetrical downstream from the bifurcations. Physical explanations for this are proposed after considering the theoretical problem of pulsatile developed flow in a straight tube. In this case, the parameter lambda again plays a crucial role in the velocity distribution.

Arteries↗