scholarly journals Blood Flow in Portal Systems with Special Reference to the Rat Pituitary Gland

1992 ◽  
Vol 12 (1) ◽  
pp. 128-138 ◽  
Author(s):  
P. D. Lees ◽  
D. T. Lynch ◽  
H. K. Richards ◽  
A. H. J. Lovick ◽  
S. Perry ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Median Eminence ◽  
Venous Drainage ◽  
Mean Value ◽  
Portal System ◽  
Posterior Pituitary ◽  
Flow Rates ◽  
Fischer 344 ◽  
Rat Pituitary

Regional pituitary blood flow has been studied in adult female Fischer 344 rats by [14C]iodoantipyrine autoradiography. A general mathematical solution has been derived to allow the calculation of blood flow in the second compartment of a portal system and the proportion of blood “shunted” through the first compartment without exposure to tissue uptake from a knowledge of (a) the volume ratios of the two compartments, (b) the tissue tracer uptakes of the two compartments, and (c) the arterial tracer concentration with respect to time of a freely diffusible tracer. Significant diffusion limitation and/or arteriovenous shunting has been demonstrated in the neurohypophysis, suggesting that the majority of incoming blood is “shunted” unchanged to the adenohypophysis. The mean value of the shunt is 89% (range of 84–93%) for the median eminence and lies between 72% (range of 52–82%) and 73% (range of 59–81%) for the posterior pituitary. Neurohypophysial flow rates of 1.20 (range of 0.99–1.55) ml g−1 min−1 for the median eminence and 1.68 (range of 0.83–3.53) ml g−1 min−1 for the posterior pituitary were measured. These values represent “tissue-available” (nonshunted) flow; estimated mean total (shunted plus nonshunted) neurohypophysial flow rates were 11.7 (range of 9.5–17.5) ml g−1 min−1 for the median eminence and 6.1 (range of 3.1–8.9) ml g−1 min−1 (minimum) for the posterior pituitary. Adenohypophysial blood flow is heterogeneous. In the long portal territory, the flow rate was 1.18 (range of 0.95–1.75) ml g−1 min−1 but short portal territory flow calculation is complicated by an unquantifiable nonportal venous drainage; using the natural limits of zero and 100% gives a minimum adenohypophysial flow rate of 1.42 (range of 0.76–2.07) ml g−1 min−1 and a maximum value of 1.97 (range of 1.03–2.82) ml g−1 min−1.

The Effect of Hematocrit on the Clearance of Small Molecules during Hemodialysis

1983 ◽  
Vol 6 (3) ◽  
pp. 127-130 ◽  
Author(s):  
C. Woffindin ◽  
N.A. Hoenich ◽  
D.N.S. Kerr
Keyword(s):  
Blood Flow ◽  
Regression Analysis ◽  
Small Molecules ◽  
Flat Plate ◽  
Flow Rate ◽  
Distribution Curve ◽  
Blood Flow Rate ◽  
Hollow Fibre ◽  
Urea Clearance ◽  
Flow Rates

Data collected during the evaluation of a series of hemodialysers were analysed to see the effect of hematocrit on the clearance of urea and creatinine. All evaluations were performed on patients with a range of hematocrits with a mean close to 20%. The urea clearance of those in the upper half of the distribution curve (mean hematocrit 29.4%) was not significantly different from that of patients in the lower half of the distribution curve (mean hematocrit 16.9%) whether the clearance was studied at high or low blood flow rates and with hollow fibre or flat plate disposable hemodialysers. Likewise, there was no correlation between hematocrit and urea clearance by regression analysis. In contrast, the clearance of creatinine was affected by hematocrit being greater at lower hematocrit values. This difference was independent of blood flow rate and dialyser type and was confirmed by regression analysis.

scholarly journals In vivo / in vitro Correlation of Pharmacokinetics of Gentamicin, Vancomycin, Teicoplanin and Doripenem in a Bovine Blood Hemodialysis Model

2021 ◽  
Vol 12 ◽  
Author(s):  
M G Vossen ◽  
S Pferschy ◽  
C Milacek ◽  
M Haidinger ◽  
Mario Karolyi ◽  
...  
Keyword(s):  
Blood Flow ◽  
Renal Replacement Therapy ◽  
Protein Binding ◽  
Replacement Therapy ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Bovine Blood ◽  
Flow Rates ◽  
Dialysate Flow Rate

Background: Elimination of a drug during renal replacement therapy is not only dependent on flow rates, molecular size and protein binding, but is often influenced by difficult to predict drug membrane interactions. In vitro models allow for extensive profiling of drug clearance using a wide array of hemofilters and flow rates. We present a bovine blood based in vitro pharmacokinetic model for intermittent renal replacement therapy.Methods: Four different drugs were analyzed: gentamicin, doripenem, vancomicin and teicoplanin. The investigated drug was added to a bovine blood reservoir connected to a hemodialysis circuit. In total seven hemofilter models were analyzed using commonly employed flow rates. Pre-filter, post-filter and dialysate samples were drawn, plasmaseparated and analyzed using turbidimetric assays or HPLC. Protein binding of doripenem and vancomycin was measured in bovine plasma and compared to previously published values for human plasma.Results: Clearance values were heavily impacted by choice of membrane material and surface as well as by dialysis parameters such as blood flow rate. Gentamicin clearance ranged from a minimum of 90.12 ml/min in a Baxter CAHP-170 diacetate hemofilter up to a maximum of 187.90 ml/min in a Fresenius medical company Fx80 polysulfone model (blood flow rate 400 ml/min, dialysate flow rate 800 ml/min). Clearance of Gentamicin vs Vancomicin over the F80s hemofilter model using the same flow rates was 137.62 mL vs 103.25 ml/min. Doripenem clearance with the Fx80 was 141.25 ml/min.Conclusion: Clearance values corresponded very well to previously published data from clinical pharmacokinetic trials. In conjunction with in silico pharmacometric models. This model will allow precise dosing recommendations without the need of large scale clinical trials.

scholarly journals Effects of Arterial Pco2 and Cerebrospinal Fluid Volume Flow Rate Changes on Choroid Plexus and Cerebral Blood Flow in Normal and Experimental Hydrocephalic Cats

1983 ◽  
Vol 3 (3) ◽  
pp. 369-375 ◽  
Author(s):  
S. Nakamura ◽  
G. M. Hochwald
Keyword(s):  
Blood Flow ◽  
Cerebrospinal Fluid ◽  
Cerebral Cortex ◽  
Choroid Plexus ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Brain Blood Flow ◽  
Choroidal Blood Flow ◽  
Flow Rates

The effect of changes in brain blood flow on cerebrospinal fluid (CSF) volume flow rates, and that of changes in CSF volume flow rates on brain blood flow were determined in both normal and kaolin-induced hydrocephalic cats. In both groups of cats, blood flow in grey and white matter, cerebral cortex, and choroid plexus was measured with 105Ru microspheres during normocapnia, and again with 141Ce microspheres after arterial Pco2 was either increased by 300% or decreased by 50%. Blood flow measurements were also made during perfusion of the ventricular system with mock CSF and repeated during perfusion with anisosmotic mannitol solutions to alter CSF volume flow rate. In 30 normal and 26 hydrocephalic cats, blood flow to the cerebral cortex, white matter, and choroid plexus was similar; only blood flow to the caudate nucleus was greater in normal cats. The weight of the choroid plexus from hydrocephalic cats decreased by 17%. Blood flow in the choroid plexus of all cats decreased by almost 50% following hypercapnia or hypocapnia, without a change in the CSF volume flow rate. There was no change in cerebral or choroidal blood flow when CSF volume flow rate was either increased by 170% or decreased by 80%. These results suggest that choroid plexus blood flow does not limit or affect the volume flow rate of CSF from the choroid plexus. CSF volume flow rate can be altered without corresponding blood flow changes of the brain or choroid plexus. Choroid plexus blood flow and the reactivity of both brain and choroidal blood flow to changes in arterial Pco2 were not affected by the hydrocephalus. The lower CSF formation rate of hydrocephalic cats can be attributed in part to the decrease in the mass of choroid plexus tissue.

scholarly journals The effect of reduction of perfusion rate on lactate and oxygen uptake, glucose output and energy supply in the isolated perfused liver of starved rats

1979 ◽  
Vol 184 (3) ◽  
pp. 635-642 ◽  
Author(s):  
R A Iles ◽  
P G Baron ◽  
R D Cohen
Keyword(s):  
Oxygen Uptake ◽  
Flow Rate ◽  
Mean Value ◽  
Normal Flow ◽  
Perfusion Rate ◽  
Flow Rates ◽  
Perfusate Flow ◽  
Intrinsic Capacity ◽  
Lactate Uptake ◽  
Glucose Output

1. Lactate and O2 uptake and glucose output were studied in isolated livers from starved rats at perfusate flow rates varying from 100 to 7% of “normal” (11.25-0.75 ml/min per 100 g body wt.). 2. With moderate diminution of flow rate, lactate and oxygen uptake fell more slowly than would be expected if uptake purely depended on substrate supply. 3. Use of a mathematical model suggests that the intrinsic capacity of the liver for lactate uptake is unaffected until the flow rate falls below 25% of “normal”. 4. Some lactate uptake was always observed even at 7% of the “normal” flow rate. 5. At flow rates below 33% of the “normal”, lactate was increasingly metabolized by pathways other than gluconeogenesis, which became a progressively less important consumer of available O2. 6. ATP content decreased with diminution of flow rate, but substantially less markedly than did lactate uptake and glucose output. 7. Intracellular pH fell from a mean value of 7.25 at “normal” flow rate to 7.03 at 7% of the “normal” flow rate.

Sensitivity of patient-specific numerical simulation of cerebal aneurysm hemodynamics to inflow boundary conditions

2007 ◽  
Vol 106 (6) ◽  
pp. 1051-1060 ◽  
Author(s):  
Prem Venugopal ◽  
Daniel Valentino ◽  
Holger Schmitt ◽  
J. Pablo Villablanca ◽  
Fernando Viñuela ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Artery Aneurysm ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Stress Distributions ◽  
Flow Rates

Object Due to the difficulty of obtaining patient-specific velocity measurements during imaging, many assumptions have to be made while imposing inflow boundary conditions in numerical simulations conducted using patient-specific, imaging-based cerebral aneurysm models. These assumptions can introduce errors, resulting in lack of agreement between the computed flow fields and the true blood flow in the patient. The purpose of this study is to evaluate the effect of the assumptions made while imposing inflow boundary conditions on aneurysmal hemodynamics. Methods A patient-based anterior communicating artery aneurysm model was selected for this study. The effects of various inflow parameters on numerical simulations conducted using this model were then investigated by varying these parameters over ranges reported in the literature. Specifically, we investigated the effects of heart and blood flow rates as well as the distribution of flow rates in the A1 segments of the anterior cerebral artery. The simulations revealed that the shear stress distributions on the aneurysm surface were largely unaffected by changes in heart rate except at locations where the shear stress magnitudes were small. On the other hand, the shear stress distributions were found to be sensitive to the ratio of the flow rates in the feeding arteries as well as to variations in the blood flow rate. Conclusions Measurement of the blood flow rate as well as the distribution of the flow rates in the patient's feeding arteries may be needed for numerical simulations to accurately reproduce the intraaneurysmal hemodynamics in a specific aneurysm in the clinical setting.

High Blood flow Rates with Adjustment of Needle Diameter do not Increase Hemolysis during Hemodialysis Treatment

2007 ◽  
Vol 8 (4) ◽  
pp. 252-257 ◽  
Author(s):  
F. Techert ◽  
S. Techert ◽  
L. Woo ◽  
W. Beck ◽  
H. Lebsanft ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Venous Pressure ◽  
Blood Flow Rate ◽  
Needle Size ◽  
Flow Rates ◽  
Blood Damage ◽  
Before And After ◽  
Needle Diameter ◽  
Hb Concentration

Background Higher blood flow in dialysis therapy is often avoided due to concerns about shear-induced blood damage despite the lack of reliable data. Objective This study investigated the influence of higher blood flow rates on plasma free hemoglobin (Hb) concentration after hemodialysis (HD) treatment. Methods Thirty-two chronic HD patients were treated once with a blood flow rate of 250 mL/min using a 17G needle, and once with a blood flow rate of 500 mL/min using a 14G needle. Arterial and venous pressure and blood pressure (BP) were recorded before and after treatment. Blood samples were taken before and after treatment for analysis of plasma free Hb, pH, HCO3, base excess, hematocrit value, urea, sodium, potassium and calcium. Results HD treatment at blood flow rates of 500 mL/min did not increase plasma free Hb compared to treatments at blood flow rates of 250 mL/min. Frequency of intradialytic BP drops was not different either. By adaptation of the needle size, negative arterial pressure could be kept at a similar level. Urea reduction rates were significantly higher during treatments with higher blood flow rates. Conclusion Higher blood flow rates can be applied without an increased hemolysis risk provided that needle sizes are adapted accordingly.

Effect of blood flow rate and blood flow history on newborn pulmonary microcirculation

1991 ◽  
Vol 261 (2) ◽  
pp. H271-H279 ◽  
Author(s):  
C. D. Fike ◽  
M. R. Kaplowitz
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Left Atrial ◽  
Total Pressure ◽  
Pulmonary Blood Flow ◽  
Blood Flow Rate ◽  
Atrial Pressure ◽  
Left Atrial Pressure ◽  
Flow Rates ◽  
Pulmonary Arterial

The purpose of this study was to determine whether increased pulmonary blood flow and/or the history of pulmonary blood flow alters microvascular pressures in lungs of newborns. Using the direct micropuncture technique, we measured pressures in 20- to 60-microns-diameter arterioles and venules in isolated lungs of newborn rabbits at consecutive blood flow rates of 50 (baseline), 100, and/or 200 ml.min-1.kg-1. Then in some lungs we returned blood flow rate to baseline and repeated microvascular pressure measurements. We kept left atrial pressure the same at all blood flow rates. When blood flow rate increased and left atrial pressure was maintained constant, pulmonary arterial, 20- to 60-microns-diameter arteriolar, and 20- to 60-microns-diameter venular pressures increased such that the percentage of total pressure drop that occurred across veins increased. When we returned blood flow to baseline, venular pressure returned to baseline, but arteriolar and pulmonary arterial pressures returned to values less than baseline so that the percentage of the total pressure drop that occurred across microvessels decreased. Thus both blood flow rate and blood flow history are important determinants of the longitudinal distribution of pulmonary vascular pressures across newborn lungs. These findings also suggest that in newborn lungs venules greater than 60 microns diameter are poorly distensible such that higher blood flow rates result in increased microvascular pressures. Hence, under conditions of increased pulmonary blood flow, such as occurs with left to right shunts, the tendency for edema formation will increase in newborn lungs even if left atrial pressure does not increase.

THE EFFECT OF LOCAL COOLING ON THE SENSITIVITY TO NORADRENALINE OF VESSELS IN THE FEET

1967 ◽  
Vol 45 (1) ◽  
pp. 75-82 ◽  
Author(s):  
Peter Gaskell ◽  
Garth M. Bray
Keyword(s):  
Blood Flow ◽  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Dose Rate ◽  
Flow Rate ◽  
Venous Occlusion ◽  
Local Cooling ◽  
Flow Rates ◽  
The Mean ◽  
The Right

Local cold markedly reduces the rate of blood flow in the extremities. Experiments were performed to see whether it also increased the sensitivity of vascular smooth muscle to noradrenaline in terms of a reduced threshold dose. Rate of blood flow in the feet was measured by venous occlusion plethysmography. The plethysmographs were filled with water at 21 °C for the left foot and 34 °C for the right. Noradrenaline in doses of 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, and 6.4 μg/minute were infused intravenously for periods of 5 to 7 minutes. Rate of flow during noradrenaline infusion was expressed as a percentage of the rate just before noradrenaline. Fifteen experiments on 13 subjects were performed but not all doses were administered in each experiment. The mean of the percentage flow rates for all infusions at a given dose of noradrenaline was not less than 100% for either foot until 0.8 μg/minute was administered, when flow was reduced in both warm and cool feet. Thus, cooled vessels were not shown to be more sensitive than warm vessels. Noradrenaline infused at 3.2 μg/minute caused a significantly greater reduction in flow rate in the cool than in the warm feet but this is not interpreted as a greater reactivity of the cooler vessels to the drug.

Air handling characteristics of five membrane oxygenators

Perfusion ◽  
1994 ◽  
Vol 9 (5) ◽  
pp. 357-362 ◽  
Author(s):  
AP Mehra ◽  
A. Akins ◽  
A. Maisuria ◽  
BE Glenville
Keyword(s):  
Flow Rate ◽  
Venous Drainage ◽  
Clinical Situation ◽  
Low Flow ◽  
Time Interval ◽  
Arterial Line ◽  
Flow Rates ◽  
Handling Characteristics ◽  
Wide Range ◽  
Membrane Oxygenators

This project looked at the potential of five different membrane oxygenators to allow passage of catastrophic quantities of air in a clinically simulated environment. All the oxygenators were set up in an identical circuit using heparinized human blood as the perfusate. The study was carried out at flow rates ranging from 1.0 to 6.0 I/min. The clinical situation of obstructed venous drainage was simulated by clamping the venous return line at each respective flow rate, while the initial level of blood in the open system hard shell venous reservoir was maintained at 600 ml. The time interval between the application of the clamp on the venous line and the first appearance of macroscopic air in the arterial line was recorded at each level of flow rate. A graph of time versus flow rate was plotted for each oxygenator type. At a flow rate of 6 I/min, the Safe II oxygenator took 20 seconds to allow passage of air after the venous line was clamped, while it took the Bentley Univox Oxygenator only 10 seconds. The Dideco oxygenator, which has a valve incorporated in its reservoir, did not, however, allow any air to be pumped forward at all. At low flow rates, some of the oxygenators offered protection against passage of air into the arterial line. Thus the Cobe oxygenator offered protection at flow rates of less than 2 I/min, the Safe II oxygenator at flow rates of up to 2.5 I/min and the Bard oxygenator at flow rates up to 3 I/min. This study has demonstrated the potential of membrane oxygenators to allow passage to clinical quantities of air into the arterial line. This study also has demonstrated that the top to bottom flow feature offers protection against passage of air at low flow rates only, while a simple valve is quite effective in preventing passage of air at a wide range of clinically relevant flow rates.

Respiratory responses to intravenous and intrapulmonary CO2 in awake dogs

1978 ◽  
Vol 45 (1) ◽  
pp. 109-114 ◽  
Author(s):  
E. C. Greco ◽  
W. E. Fordyce ◽  
F. Gonzalez ◽  
P. Reischl ◽  
F. S. Grodins
Keyword(s):  
Blood Flow ◽  
Venous Blood ◽  
Mean Value ◽  
Low Flow ◽  
Co2 Response ◽  
Flow Rates ◽  
Ventilatory Responses ◽  
Ventilatory Drive ◽  
Significant Difference ◽  
Co2 Response Curve

Ventilatory responses to CO2 inhalation and CO2 infusion were compared in the awake dog. The CO2 was introduced directly into the systemic venous blood via a membrane gas exchanger in a femoral arteriovenous shunt circuit, and the extracorporeal blood flow, QX, was maintained constant at one of two rates: low, 0.5 l/min; or high, 2.0 l/min. A total of 13 experiments was performed in four dogs comprising 50 control and 25 inhalation and infusion observations at each of the two flow rates. Comparison of CO2-response curve slopes, S = delta V E/delta PaCO2, between CO2 inhalation and infusion showed no significant difference either within or between flow rates. The mean value of S for all conditions was 1.88 l/min per Torr with a 95% confidence interval of 1.66 -2.14. An independent additive ventilatory drive amounting to 28% of low-flow control VE was found at the highflow rate. We conclude that at constant blood flow the responses to both CO2 inhalation and infusion are hypercapnic and not significantly different.

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