Square-wave electromagnetic flowmeter employing commercially available recorder

1963 ◽  
Vol 18 (6) ◽  
pp. 1265-1267 ◽  
Author(s):  
Allen M. Scher ◽  
Julian Zepeda ◽  
Otis F. Brown
Keyword(s):  
Blood Flow ◽  
Electromagnetic Flowmeter ◽  
Measuring System ◽  
Base Line ◽  
Square Wave ◽  
Delay Unit ◽  
Highly Sensitive ◽  
Zero Flow

The availability of a stable, highly sensitive commercial recorder led us to construct a simple delay unit and square-wave driver for the purpose of measuring blood flow electromagnetically. The construction of the flowmeter heads is described briefly, and some analysis is made of possible deficiencies in flowmeter heads employing iron cores. The flow-measuring system is sensitive and linear and, when the magnet drive is turned off, the base line is within a few microvolts of true zero flow. blood flow in intact animals; epoxyresin embedding implantation Submitted on March 4, 1963

Circuit for automatically zeroing aortic flow base line from electromagnetic flowmeter

1977 ◽  
Vol 232 (5) ◽  
pp. H534-H536
Author(s):  
D. G. Wantzelius ◽  
K. L. Goetz
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Output Voltage ◽  
Cardiac Cycle ◽  
Electromagnetic Flowmeter ◽  
Aortic Flow ◽  
Base Line ◽  
Flow Conditions ◽  
Zero Flow

We describe an inexpensive circuit designed to correct base-line drift of electromagnetic flowmeters automatically when cardiac output is being measured. The circuit measures the flowmeter output voltage during a portion of each diastole when blood flow in the aorta is assumed to be zero. Any deviation of the flowmeter output voltage from zero during this time represents either base-line offset or drift. The output voltage obtained during zero flow conditions is stored throughout the next cardiac cycle and subtracted continuously from the flowmeter output during each beat, thus giving a beat-by-beat correction of any base-line drift.

Analysis of oxygen delivery and uptake relationships in the Krogh tissue model

1989 ◽  
Vol 67 (3) ◽  
pp. 1234-1244 ◽  
Author(s):  
P. T. Schumacker ◽  
R. W. Samsel
Keyword(s):  
Blood Flow ◽  
Critical Point ◽  
Real Data ◽  
Whole Body ◽  
O2 Uptake ◽  
Highly Sensitive ◽  
O2 Extraction ◽  
O2 Supply ◽  
Experimental Findings ◽  
O2 Delivery

Normally, tissue O2 uptake (VO2) is set by metabolic activity rather than O2 delivery (QO2 = blood flow X arterial O2 content). However, when QO2 is reduced below a critical level, VO2 becomes limited by O2 supply. Experiments have shown that a similar critical QO2 exists, regardless of whether O2 supply is reduced by progressive anemia, hypoxemia, or reduction in blood flow. This appears inconsistent with the hypothesis that O2 supply limitation must occur by diffusion limitation, since very different mixed venous PO2 values have been seen at the critical point with hypoxic vs. anemic hypoxia. The present study sought to begin clarifying this paradox by studying the theoretical relationship between tissue O2 supply and uptake in the Krogh tissue cylinder model. Steady-state O2 uptake was computed as O2 delivery to tissue representative of whole body was gradually lowered by anemic, hypoxic, or stagnant hypoxia. As diffusion began to limit uptake, the fall in VO2 was computed numerically, yielding a relationship between QO2 and VO2 in both supply-independent and O2 supply-dependent regions. This analysis predicted a similar biphasic relationship between QO2 and VO2 and a linear fall in VO2 at O2 deliveries below a critical point for all three forms of hypoxia, as long as intercapillary distances were less than or equal to 80 microns. However, the analysis also predicted that O2 extraction at the critical point should exceed 90%, whereas real tissues typically extract only 65–75% at that point. When intercapillary distances were larger than approximately 80 microns, critical O2 extraction ratios in the range of 65–75% could be predicted, but the critical point became highly sensitive to the type of hypoxia imposed, contrary to experimental findings. Predicted gas exchange in accord with real data could only be simulated when a postulated 30% functional peripheral O2 shunt (arterial admixture) was combined with a tissue composed of Krogh cylinders with intercapillary distances of less than or equal to 80 microns. The unrealistic efficacy of tissue O2 extraction predicted by the Krogh model (in the absence of postulated shunt) may be a consequence of the assumed homogeneity of tissues, because real tissues exhibit many forms of heterogeneity among capillary units. Alternatively, the failure of the original Krogh model to fully predict tissue O2 supply dependency may arise from basic limitations in the assumptions of that model.

Derecruitment of filtration surface area in paraquat-injured isolated dog lungs

1990 ◽  
Vol 68 (4) ◽  
pp. 1581-1589 ◽  
Author(s):  
T. Shibamoto ◽  
J. C. Parker ◽  
A. E. Taylor ◽  
M. I. Townsley
Keyword(s):  
Blood Flow ◽  
Surface Area ◽  
Vascular Resistance ◽  
High Flow ◽  
Base Line ◽  
Flow Rates ◽  
Blood Flows ◽  
Capillary Filtration Coefficient ◽  
Specific Index ◽  
Filtration Surface

The capillary filtration coefficient (Kf,c) is a sensitive and specific index of vascular permeability if surface area remains constant, but derecruitment might affect Kf,c in severely damaged lungs with high vascular resistance. We studied the effect of high and low blood flow rates on Kf,c in papaverine-pretreated blood-perfused isolated dog lungs perfused under zone 3 conditions with and without paraquat (PQ, 10(-2) M). Three Kf,cs were measured successively at hourly intervals for 5 h. These progressed sequentially from isogravimetric blood flow with low vascular pressure (I/L) to high flow with low vascular pressure (H/L) to high flow with high vascular pressure (H/H). The blood flows of H/L and H/H were greater than or equal to 1.5 times that of I/L. There were no significant changes in Kf,c in lungs without paraquat over a 50-fold range of blood flow rates. At 3 h after PQ, I/L-Kf,c was significantly increased and both isogravimetric capillary pressure and total protein reflection coefficient were decreased from base line. At 4 and 5 h, H/L-Kf,c was significantly greater than the corresponding I/L-Kf,c (1.01 +/- 0.22 vs. 0.69 +/- 0.09 and 1.26 +/- 0.19 vs. 0.79 +/- 0.10 ml.min-1.cmH2O-1.100 g-1, respectively) and isogravimetric blood flow decreased to 32.0 and 12.0% of base line, respectively. Pulmonary vascular resistance increased to 12 times base line at 5 h after PQ. We conclude that Kf,c is independent of blood flow in uninjured lungs. However, Kf,c measured at isogravimetric blood flow underestimated the degree of increase in Kf,c in severely damaged and edematous lungs because of a high vascular resistance and derecruitment of filtering surface area.

Human renal response to meat meal

1986 ◽  
Vol 250 (4) ◽  
pp. F613-F618 ◽  
Author(s):  
T. H. Hostetter
Keyword(s):  
Blood Flow ◽  
Renal Blood Flow ◽  
Renal Plasma Flow ◽  
Statistical Significance ◽  
Prostaglandin E ◽  
Base Line ◽  
Meat Meal ◽  
Time Period ◽  
Beef Steak ◽  
Renal Vascular

Glomerular filtration rate (GFR) increases after a meat meal in several species. The mechanism of this phenomenon is unknown and the excretory and metabolic responses largely unexplored. We examined in humans the nature of the hemodynamic response to a meat meal, the role of salt and water load in this response, and the associated renal excretory responses. Ten normal volunteers were studied after eating an average of 3.5 g/kg body wt of lean cooked beef steak and, on a separate day, after ingesting an amount of sodium and water equivalent to that in the steak. Average GFR increased by 28% for the entire 3 h after the meat meal compared with the same time period after the control salt solution (90 +/- 8 vs. 114 +/- 6 ml X min-1 X 1.73 M-2, mean +/- SE, P less than 0.05) and by 15% compared with the base-line periods, although this difference was not of statistical significance. However, not all subjects demonstrated an increase, and in those eight who did the degree was variable from 5 to 46% for the 3-h mean above the basal value. During the hour of peak GFR, the increment was associated with a nearly proportional increase in renal plasma flow and renal blood flow (all P less than 0.05). The increase in renal blood flow was entirely due to a significant fall in renal vascular resistance. The vasodilation was not accompanied by any change in prostaglandin E excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern of blood flow in the pulmonary veins of the dog

1965 ◽  
Vol 20 (6) ◽  
pp. 1118-1128 ◽  
Author(s):  
Eugene Morkin ◽  
John A. Collins ◽  
Harold S. Goldman ◽  
Alfred P. Fishman
Keyword(s):  
Blood Flow ◽  
Pulmonary Circulation ◽  
Pulmonary Veins ◽  
Electromagnetic Flowmeter ◽  
Sine Wave ◽  
Left Ventricular ◽  
Mean Flow ◽  
Venous Flow ◽  
Pulmonary Venous Flow ◽  
Atrial Contraction

The pattern of blood flow in the large pulmonary veins was studied in dogs by chronic implantation of sine-wave electromagnetic flowmeters and cineangiographic observations. These revealed that: 1) pulmonary venous flow is continuous and pulsatile with peak rate of flow of approximately twice the mean flow; 2) the initial rapid increase in venous flow occurs 0.10 sec after the onset of ventricular systole, reaching a peak at the time of closure of the A-V valves; 3) left atrial contraction produces a fleeting slowing or reversal of flow; and 4) respiratory variations in pulmonary venous flow follow those in pulmonary arterial flow, beat by beat. The genesis of phasic pulmonary venous flow was investigated by analysis of pressure and flow curves from the two sides of the heart, by consideration of the energy required for left ventricular filling, and by reconstruction of the pulmonary venous flow pulse using a mathematical model of the pulmonary circulation. These three lines of evidence are consistent in indicating that the transmitted right ventricular pressure is the major determinant of the pulmonary venous flow pattern in the dog. pulsatile pulmonary venous flow; pulmonary venous flow; pulmonary circulation; ventricular suction; respiration on pulmonary circulation; pulmonary venous angiography; pulmonary veno-atrial junctions; electromagnetic flowmeter; cineangiography Submitted on November 16, 1964

Cerebral blood flow and evoked potentials during Cushing response in sheep

1989 ◽  
Vol 256 (3) ◽  
pp. H779-H788
Author(s):  
R. C. Koehler ◽  
J. E. Backofen ◽  
R. W. McPherson ◽  
M. D. Jones ◽  
M. C. Rogers ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Cerebral Blood Flow ◽  
Intracranial Pressure ◽  
Arterial Pressure ◽  
Evoked Potentials ◽  
Aortic Pressure ◽  
Base Line ◽  
Auditory Evoked Responses ◽  
Cushing Response

We determined how alterations in systemic hemodynamics, characteristic of the Cushing response, are related to changes in cerebral blood flow (CBF), cerebral metabolic rate of O2 (CMRO2), and brain electrical conductive function, as assessed by somatosensory-evoked potentials (SEP) and brain stem auditory-evoked responses (BAER). In three groups of eight pentobarbital-anesthetized sheep, intracranial pressure was gradually elevated to within 50, 25, or 0 mmHg of base-line mean arterial pressure and then held constant for 40 min by intraventricular infusion of mock cerebrospinal fluid. Microsphere-determined CBF fell when cerebral perfusion pressure was less than 50 mmHg. CMRO2 fell when CBF fell greater than 30-40%. Mean aortic pressure and cardiac output increased when CBF fell greater than 40%, i.e., at approximately the level at which CMRO2 fell. Furthermore, the magnitude of the increase in arterial pressure and cardiac output correlated with the reduction of CMRO2. SEP latency did not increase unless CBF fell greater than 55-65%, corresponding to a 20-30% reduction of CMRO2. Increased latency of BAER wave V was associated with a fall in midbrain blood flow of greater than 65-70%. Thus increase in SEP and BAER latencies required reductions of flow greater than those required to elicit a systemic response. This demonstrates that there is a range of intracranial pressure over which the increase in arterial pressure preserves sufficient CBF to sustain minimal electrical conductive function. The best predictor of the onset and magnitude of the Cushing response in adult sheep is the decrease in CMRO2.

scholarly journals Simplified measurement of intra-access pressure.

1998 ◽  
Vol 9 (2) ◽  
pp. 284-289
Author(s):  
A Besarab ◽  
S Frinak ◽  
R A Sherman ◽  
J Goldman ◽  
F Dumler ◽  
...  
Keyword(s):  
Blood Flow ◽  
Delivery Systems ◽  
Chamber Pressure ◽  
Hemodialysis Access ◽  
Fluid Density ◽  
Special Equipment ◽  
Venous Outflow ◽  
Bernoulli’S Equation ◽  
The Difference ◽  
Zero Flow

The measurement of intra-access pressure (P[IA]) normalized by mean arterial BP (MAP) helps detect venous outlet stenosis and correlates with access blood flow. However, general use of P(IA)/MAP is limited by time and special equipment costs. Bernoulli's equation relates differences between P(IA) (recorded by an external transducer as PT) and the venous drip chamber pressure, PDC; at zero flow, the difference in height (deltaH) between the measuring sites and fluid density determines the pressure deltaPH = P(IA) - P(DC) Therefore, P(DC) and PT measurements were correlated at six different dialysis units, each using one of three different dialysis delivery systems machines. Both dynamic (i.e., with blood flow) and static pressures were measured. Changes in mean BP, zero calibration errors, and hydrostatic height between the transducer and drip chamber accounted for 90% of the variance in P(DC), with deltaPH = -1.6 + 0.74 deltaH (r = 0.88, P < 0.001). The major determinants of static P(IA)/MAP were access type and venous outflow abnormalities. In grafts, flow averaged 555 +/- 45 ml/min for P(IA)/MAP > 0.5 and 1229 +/- 112 ml/min for P(IA)/MAP < 0.5. DeltaPH varied from 9.4 to 17.4 mmHg among the six centers and was related to deltaH between the drip chamber and the armrest of the dialysis chair. Concordance between values of P(IA)/MAP calculated from PT and from P(DC) + deltaPH was excellent. It is concluded that static P(DC) measurements corrected by an appropriate deltaPH can be used to prospectively monitor hemodialysis access grafts for stenosis.

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