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PubMedDate not supplied

Precise quantification of pulsatility is a necessity for direct comparisons of six different pediatric heart-lung machines in a neonatal CPB model.

Generation of pulsatile flow depends on an energy gradient. Surplus hemodynamic energy (SHE) is the extra hemodynamic energy generated by a pulsatile device when the adequate pulsatility is achieved. The objective of this study was to precisely quantify and compare pressure-flow waveforms in terms of surplus hemodynamic energy levels of six different pediatric heart-lung machines in a neonatal piglet model during cardiopulmonary bypass (CPB) procedures with deep hypothermic circulatory arrest (DHCA). Thirty-nine piglets (average weight, 3 kg) were subjected to CPB with a hydraulically driven physiologic pulsatile pump (PPP; n=7), Jostra-HL 20 pulsatile roller pump (Jostra-PR; n=6), Stockert Sill pulsatile roller pump (SIII-PR; n=6), Stockert Sill mast-mounted pulsatile roller pump with a miniature roller head (Mast-PR; n=7), Stockert Sill mast-mounted nonpulsatile roller pump (Mast-NP; n=7), or Stockert CAPS nonpulsatile roller pump (CAPS-NP, n=7). Once CPB was begun, each animal underwent 20 minutes of hypothermia, 60 minutes of DHCA, 10 minutes of cold reperfusion, and 40 minutes of rewarming. The pump flow rate was maintained at 150 ml x kg(-1) x min(-1) and the mean arterial pressure (MAP) at 45 mm Hg. In the pulsatile experiments, the pump rate was kept at 150 bpm and the stroke volume at 1 ml/kg. The SHE (ergs/cm3) = 1,332 ([(integral fpdt) / (integral fdt)] - MAP) was calculated at each experimental stage. During normothermic CPB (15 minutes on pump), the physiologic pulsatile pump generated the highest surplus hemodynamic energy (8563 +/- 1918 ergs/cm3, p < 0.001) compared with all other pumps. The Jostra HL-20 and Stockert Sill pulsatile roller pumps also produced adequate surplus hemodynamic energy. Nonpulsatile roller pumps and the Stockert Sill mast-mounted pulsatile roller pump did not generate any extra hemodynamic energy. During hypothermic CPB and after DHCA and rewarming, the results were extremely similar to those seen during normothermic CPB. The surplus hemodynamic energy formula is a novel method to precisely quantify different levels of pulsatility and nonpulsatility for direct and meaningful comparisons. The PPP produced the greatest surplus hemodynamic energy. Most of the pediatric pulsatile pumps (except Mast-PR) generated significant surplus hemodynamic energy. None of the nonpulsatile roller pumps generated adequate surplus hemodynamic energy.

Animals↗
PubMed2003

[Pulsatile ocular blood flow and choroidal blood flow in age-related macular degeneration].

BACKGROUND: The determination of pulsatile ocular blood flow (POBF) by measuring intraocular pressure pulse is a reliable way of evaluating choroidal blood flow. METHODS: We studied ocular haemodynamic abnormalities by examining the choroidal blood flow using POBF in patients with age-related macular degeneration (AMD). RESULTS: POBF was lower in patients with exudative AMD than in patients with non-exudative AMD and normal subjects. CONCLUSION: The decreased choroidal blood flow may induce choroidal neovascularization via angiogenic factor induced by hypoxia in patients with exudative AMD. Further studies of choroidal circulation, which may be important for the understanding the mechanism of AMD, are needed.

Choroid↗
PubMed2005

Prediction of graft flow impairment by intraoperative transit time flow measurement in off-pump coronary artery bypass using arterial grafts.

BACKGROUND: We assessed the validity of intraoperative transit time flow measurement (TTFM) in predicting graft flow abnormalities. METHODS: Intraoperative graft flow measurement using TTFM and early postoperative coronary angiography was performed in 58 patients who underwent total arterial off-pump coronary artery bypass. Five variables (flow pattern, mean flow, pulsatility index, insufficiency ratio, and fast Fourier transformation ratio) were measured and compared between 103 normal and 14 abnormal (occluded or competitive) grafts. RESULTS: The grafts anastomosed to the right coronary territories showed significantly less diastolic dominant pattern, lower mean flow and fast Fourier transformation ratio, and higher pulsatility index than grafts to the left coronary artery territories (p < 0.05). None of the abnormal grafts showed a diastolic dominant flow pattern. The abnormal grafts demonstrated significantly lower mean flow and fast Fourier transformation ratio and higher pulsatility index and insufficiency ratio than normal grafts (p < 0.05). When our criteria for detection of abnormal graft flow, [(1) systolic dominant or balanced pattern of the flow curve in the left coronary territories, systolic dominant pattern of the flow curve in the right coronary territories; (2) mean flow < 15 mL/min; (3) pulsatility index > 3 in the left coronary territories and > 5 in the right coronary territories; and (4) insufficiency ratio > 2%] were applied, the sensitivity and specificity of TTFM to detect the graft flow abnormality were 96.2% and 76.9%, respectively. CONCLUSIONS: Our data suggest that TTFM is a reliable intraoperative tool to predict graft flow impairment.

Coronary Angiography↗
PubMed1992

Pulsatile pressure-flow relations and pulse-wave propagation in the umbilical circulation of fetal sheep.

The relations between pulsatile pressures and flows in the umbilico-placental circulation have been investigated using chronically instrumented fetal sheep. Under resting conditions, mean arterial pressure fell by 30 +/- 6%, from 44 +/- 2 to 31 +/- 2 mm Hg between the aortic termination and the arteries feeding the cotyledons, and pressure waves were substantially damped during propagation between the two recording sites. This high flow resistance and wave attenuation are attributed to the very thick walls and extreme length of the umbilical arteries. Unique relations between pulsatile components of pressure and flow, characterized as vascular impedance spectra, were also observed. At rest, impedance to pulsatile flow was only slightly below resistance to steady flow, and impedance phase was positive at low frequencies. Pulse-wave reflections had more modest effects in this bed than others. Thus, oscillations in impedance spectra and percent wave transmission with increasing frequency, which are widely accepted manifestations of wave reflections, were relatively small. Positive impedance phases at low frequencies indicated that novel mechanisms influence phase relations between pressure and flow. A significant vascular compliance residing in the peripheral vascular beds could account for this findings. The vasodilator nitroprusside enhanced wave-reflection effects, whereas the vasoconstrictor angiotensin II reduced these effects. These changes were opposite to the effects of vasoactive substances in other systems, probably because these drugs act predominantly on the supply (umbilical) arteries rather than on the peripheral placental vasculature. When peripheral vascular resistance was selectively elevated by infusing 50-microns microspheres, reflection effects were enhanced: the pressure pulse in the umbilical artery was transmitted without attenuation, or was amplified, and impedance spectra more closely resembled patterns typical of other vascular beds. Specifically, impedance modulus fell sharply with increasing frequency, and impedance phase was negative at low frequency. In addition, we observed coordinated oscillations in impedance modulus and phase that are characteristic of beds that exhibit wave-reflection effects. These findings indicate that the specialized anatomy and control mechanisms observed in the umbilical circulation result in unique hemodynamic function, in which wave-propagation effects exert influences not readily predictable from studies on other systems.

Angiotensin II↗
PubMed2005

Pulsatile ocular blood flow in patients with asymmetric internal carotid artery stenosis.

BACKGROUND: The pulsatile ocular blood flow (POBF) of patients with asymmetric internal carotid artery (ICA) stenosis was measured bilaterally. The purpose of this study was to investigate the sensitivity of POBF assessments in screening for ICA stenosis. METHODS: Seventeen subjects with asymmetric ICA stenosis confirmed with carotid duplex ultrasound were recruited. The diagnoses of ICA stenosis were categorised into less than 50 per cent, 50 to 69 per cent and 70 per cent or greater. Their POBF and ocular dimensions were measured after local anaesthesia. Twenty-three normal healthy subjects were recruited as the control. All of the subjects had an inter-ocular axial length difference of less than one millimetre. RESULTS: There were 14 males and three females in the patient group with a median age of 74 years. Fourteen patients had reduced POBF to the eye ipsilateral on the side with greater ICA stenosis. The reduction in POBF ranged from 3.1 to 49.2 per cent. Two patients had reduced POBF contralateral to the side with greater ICA stenosis. One patient had similar POBF between the eyes. The control group included six males and 17 females with a median age of 65 years. The difference in their POBF between the eyes ranged from 0.3 to 13.0 per cent. CONCLUSIONS: Stenosis of the internal carotid artery was found to reduce the POBF ipsilateral to the side with greater stenosis. The overlap in the difference in inter-ocular POBF between the patient and control groups led to a low sensitivity (calculated as 41.2 per cent) for screening ICA stenosis from an assessment of POBF. Therefore, POBF assessment is not a good diagnostic tool for screening for ICA stenosis.

Aged↗
PubMed1984

A comparative flow study of the Omniscience and the Björk-Shiley cardiac valve prostheses.

The pressure-flow rate characteristics of two new convex-concave pivoting disc prosthetic heart valves are evaluated in vitro. The Omniscience and Björk-Shiley prostheses are chosen since both use curved occluders with similar dynamic function, but with different occluder curvature and eccentricity. The Omniscience prosthesis is shown to have consistently less pressure loss, and therefore less energy loss, over a range of steady state and pulsatile flow rates. The enhanced flow characteristics of the Omniscience valve are attributed to the larger opening angle of the occluder, the method of retaining the occluder, in the valve frame, the smaller curvature of the occluder, the smaller pivot-axis eccentricity, and the smaller profile thickness of the occluder. The valves are also tested in the closed position, with steady state pressure gradients causing leakage or backflow. This data is compared with the pulsatile pressure-flow rate data to gain insight into the nature of regurgitation. The total regurgitation of the pivoting disc valves are thought to be strongly dependent upon both the maximal opening angle of the occluder and the radial clearance between the disc and the valve orifice. Both the Omniscience valve and the Björk-Shiley valve are found to have nearly equal volumes of total regurgitation.

Aortic Valve↗
PubMed1973

Spectrum analysis in ultrasonic Doppler blood flow monitoring: experience in its application to deeply situated vessels.

Ultrasonic Doppler monitoring of pulsatile flow patterns in the major systemic arteries has been rendered possible by the development of intravenous and intra-esophageal probes, thereby obviating major surgery or arterial catheterization. The information provided by Doppler flow signals obtained in this way is considerably enhanced by the use of spectrum analysis. The advantages include immunity from interference from noise or extraneous signals, the separation of two or more superimposed flow signals, and superposition of pressure and flow signals for time correlation and comparison.

Abdomen↗
PubMed2003

Pulsatile ocular blood flow in primary open-angle glaucoma and ocular hypertension.

PURPOSE: To compare pulsatile ocular blood flow measurements in untreated ocular hypertensive (OHT) subjects and primary open-angle glaucoma (POAG) patients. DESIGN: A prospective observational study in an institutional setting. METHODS: A total of 97 subjects were recruited to the study (50 ocular hypertensives, 24 glaucoma patients, and 23 normal subjects). "High-risk" OHT had intraocular pressure (IOP) > 25 mm Hg; "low-risk" OHT had IOP <or= 25 mm Hg. Pulsatile ocular blood flow (POBF) measurements were made with a pneumotonometer in sitting, standing, and supine positions. Intraocular pressure was measured with Goldmann tonometry. Twenty-six patients were started on topical treatment to reduce intraocular pressure, and the measurements were repeated at a review visit. RESULTS: Untreated POAG patients and high-risk OHT had reduced POBF (P <.001) and pulse volume (P <.001) compared with both normals and low-risk OHT. Women had higher POBF than men (P =.009, two-way analysis of variance). Subjects with pharmacologically lowered IOP had a significant increase in mean POBF (+80.9 microl/min, P =.02) and a significant reduction in mean arterial blood pressure (-11.0 mm Hg, P =.003). Postural reduction in POBF (from sitting to supine) increased and became statistically significant in POAG and OHT subjects on treatment (P <.0001). CONCLUSION: High-risk ocular hypertensives have reduced POBF when compared with low-risk ocular hypertensives and normals and do not differ significantly from POAG patients. Our findings support the clinical impression that ocular hypertensive subjects with IOP of over 25 mm Hg should be monitored closely and may benefit from prophylactic treatment to lower intraocular pressure.

Aged↗
PubMedDate not supplied

Cerebrospinal fluid flow artifact. A possible pitfall on fast-spin-echo MR imaging of the spine simulating intradural pathology.

We have noted that fast-spin-echo T2-weighted images of the cervical and thoracic regions of the spine can produce low-signal artifacts in the spinal subarachnoid space which might be misinterpreted as tumor or abnormal vascular flow voids. These are possibly related to complex cerebrospinal fluid pulsatile flow and should be recognized as artifactual by the radiologist.

Arteriovenous Malformations↗
PubMed1994

A synthetic leaflet heart valve with improved opening characteristics.

A new geometry for the design of polyurethane leaflet heart valves has been investigated. The geometry termed the 'alpharabola' has a radius of curvature that increases from the centre of the leaflet at the free edge towards the base of the valve and perimeter of the leaflet. The hydrodynamic function and leaflet opening characteristics of the new valve design have been compared to a valve with a spherical leaflet geometry using the same material. The pressure and flow required to open alpharabola leaflets in steady flow tests was markedly lower than for spherical leaflets. Under pulsatile flow conditions with the valve leaflets fully open, the pressure drop across the alpharabola and spherical leaflets was similar, but much lower than in a porcine bioprosthesis. High speed photography showed that the alpharabola leaflets opened in less than 30 ms with the leaflet opening initiating in the base of the leaflet where the radius of curvature was larger. The synthetic leaflet valve has demonstrated short term durability in accelerated fatigue tests to 100 million cycles.

Biomechanical Phenomena↗
PubMed2002

Numerical simulation of steady flow fields in a model of abdominal aorta with its peripheral branches.

In the present study, a numerical calculation procedure based on a finite volume method was developed to simulate steady flow fields in a model of abdominal aorta with its peripheral branches. The study focused on the steady baseline flow fields and the wall shear stress (WSS) distribution as well as the localization of the reversed flow regions and results were compared to those obtained by other investigators. In the case of resting conditions, the existence of a region of reversed flow of about one to two diameters in size and next to the renal arteries and along the posterior wall as observed by other researchers was confirmed. However, under the exercise conditions this region could be wiped out. The flow reversal along the lateral walls proximal to the bifurcation persisted in both rest and exercise conditions. The WSS distribution and the wall shear stress gradient distribution were obtained. The lowest WSS occurred near the ostia of the renal arteries and the lateral walls of the iliac arteries. And the highest is always at the turn to the branch. The results were generally consistent with those obtained experimentally and numerically by other investigators. It was also shown that the steady flow might be used to depict the averaged behavior of pulsatile flow. The present computer code provides a platform for the future more realistic simulations.

Aorta, Abdominal↗
PubMed1986

MR gated subtraction angiography: evaluation of lower extremities.

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.

Adult↗
PubMed1981

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

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.

Adult↗
PubMed1990

Recent advances in carotid artery evaluation.

This chapter was intended to provide an overview of ultrasound duplex scanning at the human carotid bifurcation. Although results of clinical studies are useful in patient management, much remains to be learned in the area of understanding the disease process and determining what features, obtainable by ultrasound, will predict clinical outcome. Listed below are the important points covered by this chapter. 1. Ultrasound duplex scanning can detect and quantify carotid artery disease with respect to the gold standard of contrast arteriography. 2. Contrast arteriography is not the ideal gold standard for assessment of cartotid artery disease. A new standard incorporating attributes of not only anatomy but also physiology is needed. 3. Using currently available ultrasound systems it is not possible to obtain the Doppler angle (i.e., the angle formed by the transducer axis and the blood flow-velocity vector). This angle is often estimated by the angle formed by the transducer axis and the axis of the blood vessel. This assumes that the flow-velocity vectors are axial, which turns out to be a poor assumption at bifurcations, curves, and sites of intraluminal disease. Specifying the Doppler angle involves assumptions that should always be kept in mind. 4. All Doppler data should be collected at the same angle formed by the sound beam relative to the vessel axis. Whereas results of Doppler studies can be reported in units of either frequency or velocity, assumptions made about the Doppler angle and acquiring data at arbitrary angles can produce large errors when quantifying flow velocities. 5. Blood flow disturbances cannot automatically be equated with the presence of disease. Some disturbances are localized secondary blood flow patterns produced by changes in vascular geometry coupled with pulsatile flow. 6. The lack of blood flow disturbances cannot automatically be equated with a normal or disease-free artery. Accumulation of plaque within the sinus region at the minimal and moderate disease stages appears to eliminate or attenuate local flow disturbances characteristic of a normal bifurcation. 7. An understanding of the blood flow patterns at clinical sites of interest is important to the correct interpretation of data. Both the imaging and pulsed Doppler modalities are essential to this understanding: the imaging capability to place the pulsed Doppler sample volume and appreciate changes in vascular anatomy, and the pulsed Doppler to obtain the character of blood flow at specific sites within the blood vessels.

Carotid Arteries↗
PubMed2001

Acute effect of latanoprost on pulsatile ocular blood flow in normal eyes.

PURPOSE: To determine the effect of an acute dose of 0.005% latanoprost on intraocular pressure and pulsatile ocular blood flow in normal eyes. METHODS: Nineteen volunteers received a single dose (two drops) of latanoprost 0.005% in one eye and placebo in the fellow control eye, randomized and masked to the observer. Intraocular pressure, perfusion pressure, pulsatile ocular blood flow, and systemic circulatory parameters were measured before and 8 hours after dosing. RESULTS: The mean (+/- SE) intraocular pressure, perfusion pressure, and pulsatile ocular blood flow before treatment were 17 +/- 1 mm Hg, 46 +/- 3 mm Hg, and 13 +/- 1 microl per second, respectively, in both the treated and control eyes. The mean intraocular pressure reduction was 4.9 and 2.1 mm Hg (28% and 12%) in the treated and fellow eye, respectively. The mean perfusion pressure increase was 5.6 and 2.8 mm Hg (12% and 6%) in the treated and fellow eye, respectively. The mean pulsatile ocular blood flow increase was 2.7 and 0.2 microl per second (20% and 1%) in the treated and fellow eye, respectively. The treated eye change in pulsatile ocular blood flow was not correlated to the change in perfusion pressure. Simultaneous reduction of intraocular pressure and increase or no significant change in pulsatile ocular blood flow occurred in 15 of 19 (79%) of the treated eyes. The systemic blood pressure and pulse rates remained in normal ranges over the 8-hour period. CONCLUSION: In this study, topical latanoprost significantly reduces intraocular pressure and increases ocular blood flow in normal eyes 8 hours after dosing. These effects of latanoprost may be beneficial in the management of glaucoma patients.

Aged↗
PubMed1980

[Systemic vascular reactions to increases in total blood flow].

Vasomotor reactions to the increase of systemic blood flow by 100 ml/min occurred in anesthetized cats with left ventricular bypass: the increase of the pulsatile flow produced reflex vasodilatation, while its reduction to the initial value entailed vasoconstrictor reflex. In case of pulsatile perfusion responses of resistance vessels to the same change of systemic flow included opposite reflex and myogenic factors. Inhibition of the systemic myogenic vascular tone in absence of pulse alterations of pressure and flow is discussed.

Animals↗
PubMed2002

Evaluation of pulsatile choroidal blood flow in branch retinal vein occlusion.

BACKGROUND: The present study was undertaken to compare pulsatile choroidal blood flow in patients with branch retinal vein occlusion (BRVO) with the values in normal controls. METHODS: The study included male and female patients with manifest BRVO (n=16) and a healthy sex- and age-matched control group (n=36). Fundus pulsation amplitude (FPA) was measured in the fovea by laser interferometry to assess pulsatile choroidal blood flow. RESULTS: The FPA in eyes with BRVO (4.4 microm) was significantly higher than in the fellow eye (3.8 microm; P<0.0005). There was also a significant difference between the affected eye of the patients and the healthy control group (3.3 microm; P<0.0009). CONCLUSION: The increase in FPA indicates increased choroidal blood flow resulting from some local mechanisms compensating for the decrease in retinal blood flow.

Aged↗
PubMed1991

Assessment of pressure drop flowrate relationship of axillobifemoral bypass grafts.

An in vitro study was conducted to measure the pressure distributions in knitted polyester axillobifemoral bypass grafts under steady and pulsatile flow of a Newtonian fluid. The relationship between pressure drop and flowrate was determined across the outflow branches of two types of axillobifemoral grafts. Pressure losses were greater across the 90 degrees side branch of the T-type graft than in the Y-type graft at all Reynolds numbers studied. Mean pulsatile pressure drops in the T graft were greater than those measured in steady flow at the same Reynolds number. Estimates of the likely in vivo pressure drops are made under resting and exercise flow conditions. It is suggested that the Y graft is less likely to have a significant effect on blood supply to the lower limbs, even at high blood flowrates.

Biomechanical Phenomena↗