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PubMedDate not supplied

Changes in hepatic parenchymal blood flow with colorectal metastases: increase in arterial and decrease in portal blood flow.

BACKGROUND/AIMS: We investigated the changes in arterial and portal blood flow in the non-tumorous liver parenchyma in the presence of colorectal hepatic metastases using the H(2)15O dynamic positron emission tomography method. METHODOLOGY: Thirty-eight patients were classified into colorectal hepatic metastases (MET), hemangioma (HEM), and no liver tumor (NR) groups. We quantitatively measured arterial blood flow and portal blood flow in each anatomical segment of the non-tumorous liver parenchyma. RESULTS: In the MET, HEM and NR groups, the non-tumorous arterial blood flow was 39.89, 32.77 and 28.85 mL/100 g/minute. Each non-tumorous portal blood flow was 71.61, 100.39 and 94 mL/100 g/minute. We observed a significant difference in arterial blood flow between MET and NR (p = 0.0296), although there was no significant difference in total blood flow among three groups. In MET, we discovered a significant correlation between tumor and non-tumorous arterial blood flow in the liver parenchyma (r = 0.7120, p = 0.0209). Non-tumorous arterial blood flow and PBF were 39.07 and 62.74 mL/100 g/minute in the segment with metastases, and 41.95 and 66.23 mL/100 g/minute without metastases. There were no significant differences in any blood flow between those with and without metastasis. CONCLUSIONS: The presence of hepatic metastases increased arterial blood flow with a compensatory decrease in portal blood flow within the non-tumorous liver parenchyma, irrespective of the number, location and size of the metastatic lesions.

Adult↗

PubMed1989

Systemic oxygen uptake during hypothermic cardiopulmonary bypass. Effects of flow rate, flow character, and arterial pH.

A factorial experiment was undertaken to study the effects on systemic oxygen uptake of alteration in flow rate between 1.5 and 2.0 L.min-1.m-2, flow character between nonpulsatile or pulsatile perfusion, and acid-base management between attempted pH and alpha stat control during hypothermic cardiopulmonary bypass. Twenty-four patients undergoing elective coronary bypass were studied. After 10-minute periods of stability at moderate hypothermia (28 degrees +/- 1 degrees C), blood samples were aspirated from the arterial and venous lines. Samples were analyzed for oxygen content, saturation, and tension, pH, base excess, and lactate. Systemic oxygen uptake was significantly greater at 2.0 than 1.5 L.min-1 m-2 by 18 (7, 30) ml.min-1.m-2, whereas it was not significantly affected by change in flow character (-4[-16, 7] ml.min-1.min-2) or arterial pH (-2 [-12, 8] ml.min-1.m-2 per 0.1 pH unit). Venous oxygen tension, saturation, and content were significantly increased at the higher compared with the lower flow rate (p less than 0.05), whereas arterial oxygen tension and oxygen extraction were not. Increases in arterial oxygen content and saturation from low to high flow rates were marginally nonsignificant (F = 4.08, critical value = 4.17; F = 3.99 critical value = 4.21). Base excess was significantly affected by alteration in arterial pH but not flow rate, flow character, or stage (p less than 0.05). Lactate concentrations were unaffected by flow rate, flow character, or arterial pH, but there was a small but significant overall decrease during the course of cardiopulmonary bypass (p less than 0.05). Reasons why systemic oxygen uptake was affected by flow rate but not by flow character or arterial pH are discussed. A flow rate of 1.5 L.min-1.m-2 during cardiopulmonary bypass with moderate hypothermia results in a less than maximal systemic oxygen uptake.

Acid-Base Equilibrium↗

PubMed1987

In vitro calibration and surgical implantation of electromagnetic blood flow transducers for measurement of left coronary blood flow and cardiac output in the pony.

Electromagnetic flow transducers were implanted via left thoracotomy in 8 ponies (122.7 to 263.6 kg) around the main pulmonary and left main coronary arteries for continuous measurement of mean and pulsatile blood flow. Flow transducers were calibrated in vitro with a gravity flow system. The mean +/- SE pulmonary flow was 73.1 +/- 5.1 ml/kg of body weight/min. Left coronary flow was 0.95 +/- 0.07 ml/kg/min (1.3% of cardiac output) and was not believed to be an accurate measurement. This was caused by the inability to implant a zero-flow occluder, requiring the use of minimum flow during systole as zero-flow base line. However, relative changes in left coronary flow were measured. Ponies were maintained up to 5 weeks with no adverse effects. Measurement of mean pulmonary flow with chronically implanted electromagnetic flow transducers provided an accurate continuous measurement of cardiac output with a minimum of restraint.

Animals↗

PubMed1996

Doppler analysis of pulmonary venous flow profiles in orthotopic heart transplant recipients: a comparison with mitral flow profiles and atrial function.

Previous Doppler studies of transmitral flow profiles in heart transplant recipients suggested left ventricular (LV) diastolic dysfunction. The influence of left atrial filling and emptying on mitral Doppler profiles in heart transplant recipients has not been studied systematically. In the present study, pulmonary venous flow profiles, mitral flow profiles, left atrial area change and mitral annulus motion were analyzed in 20 orthotopic heart transplant recipient and 20 control subjects by transthoracic and transesophageal echocardiography and Doppler. Mitral flow profiles revealed a "restrictive" pattern with a high early-to-late diastolic flow velocity ratio in transplant patients (2.16 +/- 0.52 vs. 1.30 +/- 0.25, p < 0.0001), which was mainly due to a reduced late diastolic maximum mitral flow velocity (32.6 +/- 8.3 vs. 51.6 +/- 12.4 cm/s, p < 0.0001). Left atrial area change (35.9 +/- 13.9 vs. 58.1 +/- 17.0%, p < 0.0006) and mitral annulus motion (9.2 +/- 3.3 vs. 12.2 +/- 2.0%, p < 0.05) were reduced in transplant recipients, compared to controls. Pulmonary venous flow parameters in transplant recipients were markedly altered during systole, when pulmonary venous flow parameters are influenced primarily by atrial function rather than by diastolic LV properties: peak systolic flow velocity (45.5 +/- 8.2 vs. 62.3 +/- 14.0 cm/s, p < 0.001), maximum flow velocity ratio (0.87 +/- 0.19 vs. 1.45 +/- 0.33), time velocity integral of pulmonary venous flow during systole (9.3 +/- 2.3 vs. 17.1 +/- 4.0 cm, p < 0.001) and the systolic fraction of the time velocity integral (52.6 +/- 10.8 vs. 68.5 +/- 6.8%, p < 0.001) were lower in heart transplant recipients than in controls. These findings are compatible with atrial dysfunction and reduced mitral annulus motion. The results of this study indicate that LV diastolic dysfunction is not the only possible cause of altered transmitral Doppler profiles in heart transplant recipients. Atrial abnormalities represent a major contributing factor to altered mitral and pulmonary venous flow patterns. Analysis of transmitral Doppler profiles alone are therefore not adequate for analysis of diastolic LV function in heart transplant recipients.

Adult↗

PubMed1976

Peripheral arterial insufficiency, effect of physical training on walking tolerance, calf blood flow, and blood flow resistance.

Twenty-three patients with intermittent claudication were submitted to physical training during 4-6 months. Eleven other patients with intermittent claudication served as a control group and were given placebo tablets during the same period. The aim of the investigation was to study the influence of physical training on the blood flow conditions in the calf. The effect of treatment on walking tolerance, on calf blood flow, blood flow resistance, and systolic blood pressure graident between the systemic circulation and the vascular bed in the calf was studied. Half a year after the end of the treatment period the patients were reexamined. The walking tolerance increased in both groups but more in the trained group. The increase in walking tolerance even in the control group was caused by the fact that the control group began to train to some extent. In neither group the maximal calf blood flow changed significantly compared with the pretreatment values. The maximal blood flow showed an increasing trend in the training group after a period fo 4 months compared with the control goupr (2p greater than 0.10). The blood flow resistance at maximal dilatation did not change significantly as compared with the initial values in any of the groups, but there was a significant difference (2p greater than 0.05) between the two groups with a decrease in the training group after 4 months. The changes in maximal calf blood flow and the changes in blood flow resistance at maximal dilatation were not related to the changes in walking tolerance. Half a year after the treatment period the walking tolerance had not decreased and there was no difference between the two groups. The maximal calf blood flow, the blood flow resistance, and the systolic pressure gradient were unchanged in comparison with the pretreatment values and there were no statistically significant differences between the two groups. The small changes in blood flow conditions observed after physical training cannot be the only factor explaining the well known improvement in walking tolerance. However, training may cause a redistribution of the blood flow in the working muscle.

Aged↗

PubMed1998

Small-diameter H-graft portacaval shunt reduces portal flow yet maintains effective hepatic blood flow.

Small-diameter H-graft portacaval shunts (HGPCSs) effectively treat bleeding varices due to cirrhosis, although the effects of such shunts on hepatic blood flow are not well established. Proponents of HGPCS believe that portal flow diverted through the shunt is regained through increased hepatic arterial inflow while others argue that this flow is never recovered; resulting in compromised nutrient flow. In this study, we sought to determine the effects of HGPCS on effective hepatic and portal blood flow. Patients undergoing HGPCS had portal pressures and flow (via color-flow Doppler ultrasound) measured intraoperatively before and after placement of HGPCS. Effective hepatic blood flow was determined utilizing low-dose galactose clearance 1 day preoperatively and 5 days postoperatively. Over a 7-year period, 64 patients (42 male and 22 female), average age 54 +/- 13.6 years (SD), were studied. Cirrhosis was due to alcohol in 37 patients, hepatitis in 9, alcohol and hepatitis in 5, and assorted other causes in 13. Child's class was A in 11 patients, B in 35, and C in 18. Both portal flow and pressures decreased significantly postoperatively (15 +/- 14.2 to 10 +/- 15.1 mL/min [P < 0.05] and 29 +/- 13.0 to 18 + 6.2 mm/Hg [P < 0.05]), whereas effective hepatic blood flow decreased insignificantly (1441 +/- 1719 to 1332 +/- 863 mL/min). Small-diameter HGPCS significantly reduce portal pressures and portal blood flow while maintaining effective hepatic flow. These findings suggest that hepatic arterialization occurs as early as 5 days after shunting and thus support the application of HGPCS.

Adult↗

PubMed1987

Measurement of pulsatile limb and finger blood flow by electrical impedance plethysmography: criteria for the diagnosis of abnormal flow.

The range of pulsatile arm and finger blood flow, measured by electrical impedance plethysmography, has been investigated in a hospital ward. The range of absolute blood flows, in ml min-1, was found to be too wide to be used as a standard for identifying single blood flow readings as being abnormal. A blood flow ratio was calculated by dividing the blood flow in the right forearm or middle finger by the blood flow in the left forearm or middle finger. This ratio was found to have a clearly defined range. A blood flow in a unilaterally injured or otherwise abnormal arm or finger was considered to be significantly altered if the blood flow ratio fell outside the previously defined normal range. The diagnosis of significantly altered arm and finger blood flow from abnormalities in the blood flow ratio was tested in a series of experiments, in which artificial changes in upper limb flow were created by high elevation of the right hand. The ratio was measured in 11 patients with unilateral upper limb injuries and in 3 patients who required an urgent assessment of the upper limb circulation. Abnormalities in the ratio were identified in 12 out of 18 subjects after high elevation of the hand and in 8 out of the 14 patients.

Arm↗

PubMed1997

Interaction between haematocrit and pulmonary blood volume on pulmonary vascular flow resistance and pressure flow relationships.

OBJECTIVE: Pulmonary vascular flow resistance depends on blood viscosity, mainly due to haematocrit, and on vessel dimensions determining blood volume in this highly compliant vascular bed. We, therefore, evaluated the interaction between haematocrit, blood flow, and transpulmonary vascular pressure gradient under conditions of controlled pulmonary blood volume. DESIGN: Experimental study in isolated zone-III rabbit lungs perfused with autologous blood. SETTING: Laboratory for experimental studies. INTERVENTIONS: Stepwise and independent variation of flow (50, 100, and 200 ml/min), pulmonary blood volume (increments of 2.5 ml and 5 ml imposed by changes of left atrial pressure), and haematocrit (0-50%) varied by haemodilution (Krebs-Henseleit/albumin) or haemoconcentration (centrifugation). MEASUREMENTS: Pulmonary arterial, left atrial, and airway pressures as well as reservoir volume (reflecting reciprocal changes of lung blood volume) and lung weight. RESULTS: Haemodilution from the normal haematocrit (32%) to 10% at constant pulmonary blood volume and flow decreased flow resistance only slightly, whereas haemoconcentration (50%) increased flow resistance up to 130%. At the same time increments of in pulmonary blood volume of 2.5 and 5 ml (approx. 15 and 30% of normal pulmonary blood volume) at constant haematocrit significantly shifted downwards pressure-flow relationships for all investigated haematocrits (0-50%). CONCLUSIONS: Because of the multiple interrelationships between haematocrit, blood flow and pulmonary blood volume, haematocrit effects on pulmonary flow resistance and pressure-flow relationships in the pulmonary vasculature should be studied at controlled blood volume. While haemodilution only has minor effects, haemoconcentration changes pressure-flow relationships markedly. Pulmonary blood volume has a major impact on slope and position of pressure-flow relationships for all haematocrits investigated.

Animals↗

PubMed1993

Effect of altering pump flow rate on cerebral blood flow and metabolism in infants and children.

The effects of reduced pump flow rate (PFR) on cerebral blood flow, cerebral oxygen consumption (CMRO2), oxygen extraction, cerebral vascular resistance, and total body vascular resistance were examined in 27 pediatric patients during hypothermic cardiopulmonary bypass (hCPB). During steady state hCPB the extracorporeal flows were randomly adjusted to a conventional PFR and a reduced PFR for each patient. The reduced pump flow rates were dictated by surgical needs. Cerebral blood flow measured using Xenon 133 clearance, and CMRO2 and oxygen extraction were calculated. Our results demonstrated that cerebral blood flow and CMRO2 are unchanged if pump flow rates are reduced by 35% to 45% of conventional PFRs at moderate and deep hypothermic temperatures. Reductions in PFR of 45%-70% from conventional PFRs affect the brain differently during either moderate or deep hCPB. At moderate hCPB (26 degrees to 29 degrees C), reductions in PFRs of 45% to 70% resulted in a significant decrease in cerebral blood flow and CMRO2, whereas oxygen extraction increased in a compensatory manner. During deep hCPB (18 degrees to 22 degrees C), PFR reductions of 45% to 70% of conventional PFR significantly reduced cerebral blood flow and CMRO2 but did not increase oxygen extraction, suggesting that at deep hypothermic temperatures, cerebral blood flow and CMRO2 exceed cerebral metabolic needs. Cerebral vascular resistance increased significantly with decreasing temperature but was not affected by pump flow reductions. We have derived indices for minimal acceptable low-flow cardiopulmonary bypass based on the known effects of temperature on cerebral metabolism and have speculated on its utility based on our limited data and a literature review.

Adolescent↗

PubMed1997

Urine flow in childhood: a study of flow chart parameters based on 1,361 uroflowmetry tests.

PURPOSE: We attempted to analyze the parameters of the urine flow chart in children. MATERIAL AND METHODS: We evaluated 1,361 uroflowmetry tests of healthy boys and girls, analyzed voided volume in relation to age and body surface area, and made a descriptive study of flow chart parameters. Analysis of variance was used for comparative study of these parameters in sex, age and body surface area groups. RESULTS: Mean values of maximum and average flow increased with voided volume, patient age and body surface, and they were higher in girls. However, mean values of flow time and time to maximum flow were higher in boys. Flow time increased with volume, and decreased with age and body surface, although time to maximum flow increased slightly with volume and did not change with age in boys or girls. CONCLUSIONS: Generally, we noted significant differences in maximum and average flow, and flow time and time to maximum flow in the different age groups and in both sexes. Regarding flow curve shape, a normal flow pattern (bell-shaped curve) was noted in more than 90% of cases. The plateau curve was apparent in 5.2 and 0.7% of boys and girls, respectively.

Adolescent↗

PubMed1999

Urinary flow rate recording: the impact of a single dose of a diuretic on clinic logistics and flow rate parameters.

PURPOSE: We determine the impact of a single dose of a diuretic given to patients scheduled for flow rate recording on clinic waiting time and flow rate parameters, and whether such practice induces artifacts in recording independent of those inherent in repeat recordings. MATERIALS AND METHODS: A total of 99 volunteers with a mean age plus or minus standard deviation of 54 +/- 10.9 years with no known urological condition participated in an open label, crossover study. On 2 separate occasions they came to the clinic for a flow rate recording, and were randomized to receive 20 mg. furosemide upon arrival at the first or second visit. Clinic waiting time, pre-void bladder volume, voided volume, maximum flow rate and other parameters were captured in a database and analyzed. RESULTS: Independent of diuretic use an increase in voided volume and maximum flow rate (19.8 to 21.2 ml. per second) was noted from the first to second visit. Diuretic use independent of sequence induced an increase in voided volume and significant reduction in waiting time (155 versus 81 minutes, p <0.001) without affecting maximum flow rate (19.9 versus 21.1 ml. per second, p = 0.058). Diuretic use on the second visit enhanced the learning effect on maximum flow rate, while first visit use negated the learning effect on the second visit. Waiting time reduction was significant independent of sequence. The positive correlation between voided volume and maximum flow rate remained unchanged with or without the diuretic. CONCLUSIONS: Repeat flow rate recordings are associated with a measurable learning effect leading to an increase in maximum flow rate. The use of 20 mg. furosemide reduces waiting time without inducing additional artifacts or significant changes in flow rate parameters. This practice is recommended for busy offices or clinical research centers to enhance urine flow, patient satisfaction and ultimately compliance with care.

Adult↗

PubMed2002

Interaction between water flow and spatial distribution of microbial growth in a two-dimensional flow field in saturated porous media.

Bacterial growth and its interaction with water flow was investigated in a two-dimensional flow field in a saturated porous medium. A flow cell (56 x 44 x 1 cm) was filled with glass beads and operated under a continuous flow of a mineral medium containing nitrate as electron acceptor. A glucose solution was injected through an injection port, simulating a point source contamination. Visible light transmission was used to observe the distribution of the growing biomass and water flow during the experiment. At the end of the experiment (on day 31), porous medium samples were destructively collected and analyzed for abundance of total and active bacterial cells, bacterial cell volume and concentration of polysaccharides and proteins. Microbial growth was observed in two stripes along the length of the flow cell, starting at the glucose injection port, where highest biomass concentrations were obtained. The spatial distribution of biomass indicated that microbial activity was limited by transverse mixing between glucose and nitrate media, as only in the mixing zone between the media high biological activities were achieved. The ability of the biomass to change the flow pattern in the flow cell was observed, indicating that the biomass was locally reducing the hydraulic conductivity of the porous medium. This bioclogging effect became evident when the injection of the glucose solution was turned off and water flow still bypassed the area around the glucose injection port, preserving the flow pattern as it was during the injection of the glucose solution. As flow bypass was possible in this system, the average hydraulic properties of the flow cell were not affected by the produced biomass. Even in the vicinity of the injection port, the total volume of the bacterial cells remained below 0.01% of the pore space and was unlikely to be responsible for the bioclogging. However, the bacteria produced large amounts of extracellular polymeric substances (EPS), which likely caused the observed bioclogging effects.

Benzenesulfonates↗

PubMed2002

Pre-selection of patients for pressure-flow analysis based on the maximum flow rate.

OBJECTIVE: To study the effects of the application of flow rate prescreening to select men for invasive pressure-flow studies, notably the reduction of invasive pressure-flow measurements that can be achieved and the proportion of men in whom, on the basis of the application of a prescreening, an invasive measurement is unjustly not indicated (false negatives). In addition, the variables on which these effects depend are studied. MATERIALS AND METHODS: Two hundred and sixty-two pressure-flow measurements in 131 patients (2 measurements/patient) and 89 free-flow measurements that preceded the invasive measurements in some patients were studied. A mathematical model was developed based on the outcomes of the invasive measurements. By means of the model the effects of several flow rate prescreening scenarios were estimated. A comparison of the model predicted and actually observed effects of flow rate prescreening was made for those measurements that were preceded by a free-flow rate measurement. RESULTS: The application of a free-flow rate prescreening may result in a reduction of the number of invasive measurements of 20-30% at a 5% false negative rate. The reduction that may be achieved at an assumed constant false negative rate depends on the distribution of the maximum flow rate in the population and on the definition of bladder outlet obstruction used. When the measurement selection procedure was applied to the free-flow rate measurements that were available in 89 patients, a 21% reduction in invasive measurement indications was found (25% expected). Four patients (4.5%) would have been unjustly excluded from invasive procedures (maximally 5% expected), three of these four patients were borderline obstructed. CONCLUSION: Considering the bother and risk to the patient and the cost of invasive measurements we think that a 20-30% gain in efficiency at a 5% risk of unjustly declaring a patient unobstructed makes a flow rate prescreening procedure cost effective in the diagnosis of bladder outlet obstruction.

Algorithms↗

PubMed2001

Simultaneous observations of haemolymph flow and ventilation in marine spider crabs at different temperatures: a flow weighted MRI study.

In vivo magnetic resonance imaging (MRI) and angiography were applied to the marine spider crab Maja squinado for a study of temperature effects and thermal tolerance. Ventilation and haemolymph circulation were investigated during progressive cooling from 12 degrees C to 2 degrees C. The anatomical resolution of MR images from Maja squinado obtained with a standard spin echo sequence were suitable to resolve the structures of various internal organs. The heart of the animal could be depicted without movement artifacts. The use of a flow compensated gradient echo sequence allowed simultaneous observations of ventilation, reflected by water flow through the gill chambers as well as of haemolymph flow. Simultaneous investigation of various arteries was possible by use of flow weighted MRI. In addition to those accessible by standard invasive flow sensitive doppler sensors, flow changes in gill, leg arteries and the venous return could be observed. Both ventilation and haemolymph flow decreased during progressive cooling and changes in haemolymph flow varied between arteries. Haemolymph flow through the Arteria sternalis, some gill and leg arteries was maintained at low temperatures indicating a reduced thermal sensitivity of flow in selected vessels. In support of previous invasive studies of haemolymph flow as well as heart and ventilation rates, the results demonstrate that the operation of gills and the maintenance of locomotor activity are critical for cold tolerance. A shift in haemolymph flow between arteries likely occurs to ensure the functioning of locomotion and ventilation in the cold.

Animals↗

PubMed2003

Water flow patterns in subsurface flow constructed wetlands designed for on-site domestic wastewater treatment.

Bypass flow in subsurface flow constructed wetlands, which may be related to several wetland characteristics, reduces detention time and may result in inadequately treated wastewater. Subsurface flow constructed wetlands, 2.3 m wide by 4.8 m long and containing a gravel matrix, were used to investigate the impact of wetland depth, inlet pipe location, loading volume, and plants on water flow. Flow patterns were determined using blue dye or bromide as tracers. The blue dye adsorbed to the gravel and was not an effective tracer for following water movement. Water dispersed as it flowed through the wetland, and approximately two pore volumes of added water were required to displace approximately 99% of the bromide tracer added as a pulse. In 17 and 25 cm deep wetlands, water flow was uniform with depth, and inlet depth had little influence on water flow patterns. Water flow in a 40 cm deep wetland was not uniform with depth for either inlet pipe placement. The presence of plants caused preferential water flow around root masses, thereby, limiting their potential to interface with wastewater. Water mixing by dispersion from the surface to deeper depths may enhance aeration. Bromide was first detected in effluent after only 0.5 pore volumes of tap water had been added. This indicates that detention time for some wastewater would be less than expected, since plug flow is usually assumed in subsurface flow constructed wetlands. This occurrence should be considered for time-dependent treatments, such as fecal coliform and biological oxygen demand reduction.

Adsorption↗

PubMed1990

Interaction between tracheal sound and flow rate: a comparison of some different flow evaluations from lung sounds.

We simultaneously recorded tracheal sound and air flow from nine normal subjects (seven males and two females). Sound was picked up at the supra sternal notch with an air-coupled sensitive microphone held in a small airtight probe. Flow was measured at the mouth using a pneumotachograph Fleisch n degrees 2. Both sound and flow were directly digitized at a sampling rate of 5120 Hz and then divided in 128-sample blocks. For each sound block the frequency spectrum was computed using the fast Fourier transform. In order to evaluate instantaneous flow-rate from tracheal sounds we investigated eight methods divided in two groups of four. In the first group (i.e., reference curves methods), we assumed that a relationship existed between sound and flow and was thus reflected by the variations of certain parameters. We chose to use simple straightforward relationships, already known and published. We tested four different parameters. During a calibration phase, we built for each parameter P a reference curve representing the variations of P versus flow and being specific to each subject. Then, an unknown flow was evaluated in calculating P on a 128-sample block, and the reference curve gave the corresponding flow. In the second group, we made a hierarchial clustering analysis of sound spectra for revealing the frequency modifications, induced by the flow. We tested two kinds of spectra as well as two ways of associating a flow to a given cluster. This led us to four other methods for calculating the flow. All the eight methods but one gave a mean uncertainty in the measure of flow of about 15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1997

Quantitative Assessment of Simulated Regurgitant Flow Using Direct Digital Acquisition of Doppler Color Flow Images.

Analysis of jet momentum and proximal isovelocity surface area (PISA) have been shown to be accurate in quantitating regurgitant flow for axisymmetric free jets. However, eccentric jets directed against chamber walls are often encountered in clinical practice and could confound the assessment of regurgitant flow. Thus, we used direct digital color flow mapping to calculate flow by the momentum method and PISA in a flow model. Steady flow jets were driven through a 2-mm round orifice at flow rates of 3, 6, 9, 12, 15, and 20 mL/sec. Jets were directed centrally and against the lateral wall of a 150 mL chamber. The raw data from a 3.25/2.5 MHz transducer (Vingmed CFM 750) was digitally transferred to a Macintosh IIci computer for analysis of the velocities comprising the jets. By linear regression, PISA was accurate in assessing flow for both free jets and wall jets (r(2) = 0.98) with regression lines approximating unity. The momentum method was highly accurate for free jets (r(2) = 0.98) but systematically underestimated flow for wall jets (r(2) = 0.70, y = 0.21x + 0.88). Thus, analysis of simulated regurgitant flow using digital display of velocities encoded in the color flow jet is accurate for free jets by both the PISA and momentum techniques. In wall jets, the momentum technique underestimates flow because the requirement for jet axisymmetry is not met.

Journal Article↗

PubMed1998

Effect of the no-flow interval and hypothermia on cerebral blood flow and metabolism during cardiopulmonary resuscitation in dogs.

BACKGROUND AND PURPOSE: We sought (1) to determine the effect of brief periods of no flow on the subsequent forebrain blood flow during cardiopulmonary resuscitation (CPR) and (2) to test the hypothesis that hypothermia prevents the impact of the no-flow duration on cerebral blood flow (CBF) during CPR. METHODS: No-flow intervals of 1.5, 3, and 6 minutes before CPR at brain temperatures of 28 degreesC and 38 degreesC were compared in 6 groups of anesthetized dogs. Microsphere-determined CBF and metabolism were measured before and during vest CPR adjusted to maintain cerebral perfusion pressure at 25 mm Hg. RESULTS: Increasing the no-flow interval from 1.5 to 6 minutes at 38 degreesC decreased the CBF (18. 6+/-3.6 to 6.1+/-1.7 mL/100 g per minute) and the cerebral metabolic rate (2.1+/-0.3 to 0.7+/-0.2 mL/100 g per minute) during CPR. Cooling to 28 degreesC before and during the arrest eliminated the detrimental effects of increasing the no-flow interval on CBF (16. 8+/-1.0 to 14.8+/-1.9 mL/100 g per minute) and cerebral metabolic rate (1.1+/-0.1 to 1.3+/-0.1 mL/100 g per minute). Unlike the forebrain, 6 minutes of preceding cardiac arrest did not affect brain stem blood flow during CPR. CONCLUSIONS: Increasing the no-flow interval to 6 minutes in normothermic animals decreases the supratentorial blood flow and cerebral metabolic rate during CPR at a cerebral perfusion pressure of 25 mm Hg. Cooling to 28 degreesC eliminates the detrimental impact of the 6-minute no-flow interval on the reflow produced during CPR. The brain-protective effects of hypothermia include improving reflow during CPR after cardiac arrest. The effect of hypothermia and the impact of short durations of no flow on reperfusion indicate that increasing viscosity and reflex vasoconstriction are unlikely causes of the "no-reflow" phenomenon.

Animals↗