Pressure-flow Characteristics Research Articles

Reperfusion of inflow-limited myocardium following hypothermic potassium-induced cardioplegia

Previous studies have shown that transmural reperfusion patterns may be markedly abnormal following periods of ischemia. The present study was done to elucidate the effects of hypothermic potassium cardioplegia on pressure-flow characteristics during reperfusion of myocardial regions with chronically compromised arterial inflow. Prior to cardiopulmonary bypass studies. Ameroid constrictors were placed on the circumflex coronary artery of 10 adult dogs to create a myocardial region subserved by inflow-restricting collaterals. Subsequently, during cardiopulmonary bypass at 80 mm Hg, 10 minutes of ischemic arrest was induced with hypothermic potassium cardioplegia (15 degrees C, pH 7.4, potassium chloride 25 mEq/L). Transmural myocardial flow was measured in normal and collateral-dependent regions during control conditions and at 1, 5, and 10 minutes of reperfusion. Also, retrograde circumflex pressures were monitored as an additional index of perfusion of the collateral regions. A normal endocardial/epicardial flow ratio was maintained in the normal regions at 1, 5, and 10 minutes of reperfusion. In contrast, a marked decrease in endocardial/epicardial flow ratio occurred transiently in the collateral regions at 1 minute of reperfusion (0.28 +/- 0.05). Simultaneously, retrograde circumflex pressures fell from 55 +/- 3.5 mm Hg to 42 +/- 3.0 mm Hg (p less than 0.001). By 5 minutes of reperfusion, retrograde circumflex pressure, mean flow, and transmural endocardial/epicardial ratios returned to normal in collateral regions. These data suggest that, even with optimal myocardial protection, changes in transmural flow occur very early during reperfusion and are exaggerated in inflow-restricted myocardial regions. Mechanisms responsible for these changes may include refilling of epicardial vessels emptied during the cross-clamp period or an early epicardial hyperemic response. Despite these alterations, normal transmural flow patterns are reestablished rapidly. Thus, when detailed attention is paid to adequate myocardial protection, abnormal reperfusion characteristics are obviated, and this is particularly important in myocardium supplied by inflow-compromised coronary vessels.

The effect of lung edema on pulmonary vasoactivity of furosemide

Previous data suggest that furosemide improves gas exchange in pulmonary edema by preferential perfusion of nonedematous lung units. To test whether this is a direct effect of furosemide on the pulmonary vasculature as opposed to a secondary phenomenon resulting from the known peripheral effects of this drug, the effect of furosemide on the pressure-flow characteristics of the pulmonary vasculature was studied in six isolated perfused canine lungs with different degrees of gravimetrically determined edema. Furosemide shifted the pressure-flow curve by decreasing the mean intercept or average closing pressure of the pulmonary vascular bed from 13.8 ± 5.3 to 9.5 ± 5.4 cm H 2O and the zero-flow critical closing pressure from 9.3 ± 4.3 to 4.7 ± 3.5 cm H 2O ( P < 0.05). The slopes of these curves did not change between control and furosemide treatment. The decrease in intercept and the decrease in zero-flow critical closing pressures were closely correlated with the increase in edema ( r = −0.895 for average closing pressure and r = −0.928 for critical closing pressure) ( P < 0.05). Furosemide doubled the pulmonary blood flow in the isolated lobe for the same driving pressure and the greater the amount of lobar edema the less pronounced was this furosemide-associated increase in blood flow. This direct effect of furosemide on the pulmonary vasculature could explain the improved gas exchange seen before a decrease in pulmonary edema, since this pulmonary vasoactivity would result in preferential perfusion of nonflooded alveolar units.

Transmural myocardial flow distribution during hypothermia: Effects of coronary inflow restriction

Hypothermic coronary perfusion and blood cardioplegia have been used clinically to minimize intraoperative myocardial damage. However, pressure-flow characteristics in regions supplied by inflow-limiting collateral coronary arteries have not been investigated during hypothermic conditions. In this study tracer microspheres determined transmural myocardial blood flow distribution during cardiopulmonary bypass in normothermic empty, beating dog hearts (EBH), during hypothermic sanguineous perfusion at 15 degrees C (HP), and after hemodilution of cooled (15 degrees C) hearts to a hematocrit value of 20 vol% (HDL). Animals in Group I (N = 8) had normal hearts. Group II dogs (N = 9) had one region supplied predominantly by narrow collateral vessels (CR) and another nourished by normal coronary arteries (NR). Retrograde circumflex pressures were measured continuously for Group II as an additional index of CR perfusion. Flow characteristics in Group I hearts were always similar to the NR of Group II dogs. With HP, endocardial blood flow in the NR decreased from approximately 0.80 to 0.50 ml/min/gm. Subsequently, following HDL this flow increased to approximately 1.70 ml/min/gm, or over twice control levels. In comparison, flow to CR endocardium decreased even more during HP (0.12 ml/min/gm). Even though control flow levels were reestablished in CR endocardium by adding HDL, an unfavorable endocardial/epicardial ratio persisted. With both HP and HDL, retrograde circumflex pressure never changed from EBH values. These data suggest that a significant endocardial flow defect exists during periods of hypothermic sanguineous perfusion and may become more prevalent in regions subserved by inflow-limiting coronary vessels. Similar flow maldistributions may occur in patients if blood-containing cardioplegic solutions are used and during systemic hypothermia. Significant hemodilution helps minimize these imbalances and permits salutary effects of hypothermia to be delivered more evenly across the ventricular wall.

Internal jugular catheterisation in small children. The use of a posterior approach.

Internal jugular catheterisation, using a posterior approach, was attempted in 50 infants and children aged from 1 day to 12 years, weighing 1.25 to 30 kg. Thirty-five of the patients weighed less than 10 kg. Catheterisation was successful in 49 cases. Initial catheter position was satisfactory in 48 of the 49 cases and satisfactory pressure waveform and flow characteristics were achieved in all 49 cases. There were no complications attributable to the technique. The technique proved reliable and easily learnt and is recommended as a particularly suitable approach to central venous catheterisation in small children.

Geotechnical Instrumentation Requirements for at-Depth Testing and Repository Monitoring in TUFF

This paper outlines geotechnical instrumentation requirements for the possible establishment of a nuclear waste repository in tuff on the Nevada Test Site (NTS). The Nuclear Regulatory Commission (NRC) has specified a continuing program to confirm performance during the operational period of the repository, which could last 50 years. Minimum required geotechnical measurements for confirmation of performance include thermal and thermomechanical responses; changes in stress, strain, and displacements; and pore pressure and groundwater flow characteristics. Conditions expected in tuff are: maximum rock temperatures of less than 250°C, stresses less than 100 MPa, strains between ±0.01 mm/mm, and pore pressures less than 35 KPa in the unsaturated zone where hydraulic head is not the primary contributor. The paper describes instrumentation needed to make the desired measurements. In general, the instrumentation and data system are required to be stable and reliable for tens of years. Designs must consider requirements for temperature stability, temperature expansion compensation, moisture resistance, and long-term durability in mining-type environments. Severe requirements such as these suggest consideration of techniques for in-situ replacement of instrumentation. State-of-the-art instrumentation is briefly described along with a discussion of needs for refinement, replacement/ recalibration and instrumentation development.

Experimental validation of quantitative coronary arteriography for determining pressure-flow characteristics of coronary stenosis.

SUMMARY The applicability of classic fluid dynamic equations to tapering stenoses in vasoactive, flexible coronary arteries in vivo and the validity of quantitative coronary arteriography was tested by comparing experimentally measured and x-ray-predicted pressure gradients at equal flows for left circumflex stenoses in five dogs chronically instrumented with a balloon. occluder, flow probe, and proximal and distal catheters for.injection of contrast media or recording distal coronary pressure. Arterial borders on cut-film orthogonal arteriograms were digitized and computer processed into a three-dimensional reconstruction of the stenosis. The total pressure gradient was calculated from stenosis dimensions using classic fluid dynamic equations. Over the full range of flow, the correlation of x-ray-predicted and experimentally measured pressure gradient for 51 separate stenoses was y = 1.11x ± 0.75, r = 0.95, p < 0.001, with a standard deviation about the regression line of 9.4 mm Hg and with 95% of x-ray-predicted values falling within ± 18.5 mm Hg of the experimentally measured values (95.% confidence limits). Mean experimentally measured and x-ray-predicted pressure gradients were 10.1 7.7 mm Hg (± SD) and 10.9 ± 5.6 mmn Hg at low flow and 48.2 ± 23.1 mm Hg and 55.8 ± 28.8 mm Hg at high flow, respectively. The mean difference was 3.9 ± 4.3 mm Hg at rest flow and 11.9 ± 10.5 mm Hg at high flow. For all data over the entire range of flows, the frequency distribution of differences between x-ray-predicted and experimentally measured gradients was a bell-shaped curve with a peak, or mean difference, of ± 4 mm Hg, a standard deviation of ± 9.8 mm Hg and 95% confidence limits for individual values of ± 19.6 mm Hg. These data demonstrate the validity of applying classic fluid dynamic theory to tapering stenoses in vivo. Quantitative coronary arteriography on the average or in individual instances approximately predicts the pressure gradient-flow characteristics of coronary arterial stenoses in intact animals. However, as indicated by the above measures of variability, there is considerable scatter in x-ray predictions that limits its applicability to individual clinical cases. We believe that this scatter is a result of difficulties in visually tracing arterial borders on arteriograms and can most likely be reduced by automatic border recognition techniques.

Microcirculatory model relating geometrical variation to changes in pressure and flow rate

A primary first step in defining the functional capabilities of a given microcirculatory bed is to describe the distribution of intravascular pressure and flow throughout the network using an idealized geometrical model. By applying an approach developed by the geomorphological sciences, changes in vessel lengths, numbers, and diameters were systematically related to order number by applying three mathematical relationships. From measurements of a number of vascular modules, generalized relationships were obtained which applied to the microcirculation as a whole. An idealized model was developed by the computer-generation of node-node connections based on their probabilities of occurrence, and by generation of lengths and diameters, based on equations relating diameter and length to branching order number. Networks of this type were readily analyzable in terms of pressure-flow characteristics, using linear network analysis techniques. The current study focused on two specific microvascular beds: [1] rabbit omentum, in which numerous studies have related in vivo pressures and flows to geometry, and [2] human bulbar conjunctiva, in which quantitative data is almost totally nonexistent. In view of the close correlation between measured and predicted omental pressure and flow values, it was apparent that the current modeling scheme offered a close approximation to in vivo values. A more significant application, however, is in the correlation of complex alterations in vascular geometry with the accompanying hydrodynamical changes.

The comparative effects of pulsatile and nonpulsatile myocardial perfusion during cardiopulmonary bypass

The salutary effects of pulsatile perfusion (P) during clinical cardiopulmonary bypass (CPB) remain controversial. The notion exists that coronary blood flow may be enhanced by P, especially when a significant coronary stenosis occurs. In this study pressure-flow characteristics were assessed during CPB with and without P in 13 fibrillating dog hearts (37°C). Radionuclide microspheres measured transmural blood flow in normal myocardium (NR) and in regions supplied by collateral coronary arteries (CR) which restrict blood inflow at mean pump pressures of 80 and 50 mm Hg during either P or nonpulsatile perfusion (NP). Retrograde circumflex pressure (RC P) also served as an index of CR perfusion. At both pressures, mean myocardial blood flow to both NR and CR was not augmented by P despite aortic pulse pressures of approximately 50 mm Hg. Moreover, endocardial/epicardial flow ratios were unchanged from control in both regions after beginning pulsatile flow. At the same time, the mean RCP in CR was not affected by P even though a pulsatile pattern was transmitted across the collateral bed. Thus, the most significant factors affecting transmural blood flow during pulsatile CPB appear to be the coronary perfusion pressure and degree of inflow limitation, not the perfusion wave form. Therefore, any benefits which might be associated with clinical pulsatile perfusion during CPB appear to result from factors other than coronary blood flow augmentation.

Pressure-flow characteristics of the roots ofZea mays

Root pressure is generally considered to be osmotic in origin. This explanation is not held by all workers, however. An alternative view contends that while an osmotic component certainly exists, the xylem concentrations are inadequate to account for the total pressure and that therefore the remainder must result from some form of active water pumping (see for example [2,4]). In the ideal method of testing this claim one would allow the root pressure to attain its maximum value, collect a sample of the xylem sap and compare its osmotic pressure to that developed by the root. Unfortunately, this is impossible with present techniques, since to develop maximum pressures requires zero flow, in which case no sap can be collected. One can, however, reduce the flow very nearly to zero and still obtain a small sample for comparison. Such an experiment was performed by collecting 50 µl samples of exudate from each of 22 plants under 2.7 bar pressure and pooling them for analysis. Since the exudation flowrate in this case was reduced to an average of only 7% of the unimpeded rate, the results should represent a close approximation to the ideal case. The osmotic pressure of the exudate collected in this way was found to be 3.2 bar above that of the bathing solution, well in excess of the applied pressure. Thus in the present instance, there is no need to assume that root pressure is generated by any means other than osmotic.

A new lack of twist for the Judkins left coronary catheter.

We have developed a modified Judkins left coronary arteriography catheter. The catheter is fabricated from 7 French thin-walled tubing made of extruded polyethylene. This tubing has a larger lumen diameter than either the 7 French or 8 French torque-control tubings used for standard Judkins coronary arteriography catheters. The large lumen substantially improves the pressure-flow characteristics of the catheter. Accordingly, it is considerably easier to inject contrast medium through this tubing. Although this tubing has no torsional rigidity, the lack of torque-control has proved to be an advantage rather than a detriment in the use of the catheter. Based on experience of over 2,000 studies with this catheter, we feel that it is superior to standard torque-control catheters for left coronary angiograms.

Needle tracheostomy: a laboratory study.

Percutaneous needle tracheostomy and transtracheal ventilation continues to be advocated for the management of upper airway obstruction. Recent studies recommend the use of artificial ventilation. However, as apparatus for this is not always available and because there remains some doubt regarding conditions for successful use of needle tracheostomy during spontaneous respiration, we undertook such a study in dogs. Pressure-flow characteristics of short hollow needles 18-10 SWG were first determined. The smallest of these (14 SWG Bardic Intracath) that would deliver flow sufficient (by calculation) to meet the respiratory requirement of 10-13 kg laboratory dogs was selected for further study. Respiration was possible by spontaneous or artificial methods in the presence of complete tracheal occlusion. Little or no deterioration was noted in an hour of such breathing. Artificial ventilation by machine and by hand could considerably lower PaCO2. We conclude that the technique is possible provided appropriate needles are selected and care is given to their method of use.

Flow through Successive Enlargement, Turning, and Contraction—Pressure and Fluid Flow Characteristics

Flow through Successive Enlargement, Turning, and Contraction—Pressure and Fluid Flow Characteristics

Mechanical properties of the harbor porpoise lung, Phocoena phocoena

The pressure-volume and pressure-flow characteristics of the excised lungs of 5 harbor porpoise were determined. It was found that: (1) in comparison to terrestrial mammals the lung volume relative to body weight is large, (2) the lungs are capable of emptying to <17% of total lung capacity, (3) peak expiratory flowrates of 5 to 10 vital capacities (VC) · sec −1 are relatively high for mammals, (4) isovolume pressure flow curves showed a clustering of flowrate plateaus from 40 to 80% VC, with a marked drop in the flow rate plateau at 20% VC, (5) the profile of flow-volume curves is unusually square shaped with flows remaining above 2 VC · sec −1 at a lung volume of 20% VC, (6) this feature is responsible for the short emptying time of <0.2sec. It is concluded that cartilaginous airwary reinforcement, which extends to the alveolar sac, is responsible for the unusual flow-volume properties. These porpoises have the capability of exchanging a large percent of their lung gas very rapidly during their brief pass through the air-water interface.

Techniques for arteriography and hydraulic analysis of coronary stenoses in unsedated dogs.

This report describes techniques for obtaining pressure flow characteristics and arteriograms of controlled coronary stenoses in unsedated, trained dogs. Coronary flow velocity was recorded by calibrated Doppler velocity transducers linear to three times maximum coronary flow velocity. Pressure losses across stenoses were measured by a differential pressure transducer through small catheters implanted in the distal and proximal left circumflex coronary artery or ascending aorta, a system that was linear within +/-5% to 30 Hz. Coronary stenoses were produced by saline-filled, perivascular cuff constrictors inflated to constant pressure by a pressure regulator. Catheters were implanted in the pulmonary artery for injection of intravenous drugs or diffusible radionuclides and in the left atrium for injection of radionuclide microspheres. Contrast medium was injected through the proximal coronary catheter, and high-resolution arteriograms were obtained by single-spot filming on ultra detail X-ray film and cassettes at end diastole by triggering X-ray exposures from the electrocardiogram. In 13 dogs studied consecutively, the surgical mortality was 15.4%. All implanted instruments functioned for an average of 8 wk per dog.

Pressure-flow characteristics of coronary stenoses in unsedated dogs at rest and during coronary vasodilation.

The pressure-flow characteristics of 100 left circumflex stenoses in 10 chronically instrumented unsedated dogs were studied under resting conditions and during pharmacological coronary vasodilation. At rest, the pressure loss (deltaP) due to a stenosis and arterial flow velocity (V) were related by the equation, deltaP = FV + SV2, where F is the coefficient of pressure loss due to viscous friction in the stenotic segment and S is the coefficient of pressure loss due to flow separation at the diverging end of the stenosis. The linear term due to viscous friction accounted for 65% and the nonlinear term due to flow separation accounted for 35% of the total pressure loss at resting coronary flow. At peak coronary flow after coronary vasodilation, the pressure loss due to viscous friction accounted for 33% and pressure loss due to flow separation accounted for 67% of the total pressure loss. The pressure gradient-velocity relationship at high flows was characterized by the same general equation but with proportionately larger values of the coefficient S and therefore greater pressure loss associated with flow separation than predicted by the resting gradient-velocity relationship. The pressure loss predicted for high coronary flow velocities on the basis of the gradient-velocity equation at rest was only 64% of the actual experimentally observed pressure gradient at peak coronary flow. The augmented separation loss following coronary vasodilation probably was due to dilation of the epicardial artery adjacent to the fixed stenotic segment which caused more severe relative percent narrowing and a larger divergence angle at the distal end of the stenosis, the primary geometric determinants of separation losses.

Pressure-flow characteristics of the coronary collateral circulation during cardiopulmonary bypass. Effects of ventricualr fibrillation.

Even though ventricular fibrillation is used frequently during cardiopulmonary bypass (CPB), the effects of fibrillation on myocardial regions supplied by collateral vessels have not been determined. To study these effects, nine dogs with left ventricles (ameroid model) consisting of a region of myocardium supplied by collateral vessels (CR) and a region supplied by normal coronary arteries (NR) were subjected to normothermic CPB at two perfusion pressures. In both the empty beating heart (EBH) and empty fibrillating heart (EFH) regional myocardial flow was determined by tracer microspheres. Retrograde coronary pressure was measured via cannulation of the circumflex artery distal to the ameroid induced occlusion. When perfusion pressure was maintained at 80 mm Hg, retrograde coronary pressure was similar in the EBH (46 +/- 4 mm Hg) and in the EFH (48 +/- 3 mm Hg). During fibrillation subendocardial flow in the CR was unchanged, while flow in the NR increased (P less than 0.02). In addition, the endo/epi was greater in the NR than in the CR (P less than 0.01), a difference which did not exist in the EBH. The flow response to fibrillation in the CR could be produced in the NR by reducing the perfusion pressure to 50 mm Hg. These data suggest that during CPB, fibrillation exaggerates existing subendocardial perfusion deficits in collateral regions and the impaired flow response appears to be related to a low regional intravascular pressure.

Pressure-flow characteristics of the coronary collateral circulation during cardiopulmonary bypass

Hemodilution is employed frequently during cardiopulmonary bypass (CPB). Previous investigators have shown that normal coronary arteries are capable of supplying the increase in blood flow required to maintain tissue oxygenation during moderate hemodilution. However, the effects of hemodilution on myocardial regions supplied by collateral vessels have not been determined. Thus 14 dogs were divided into two groups and were subjected to hemodilution during normothermic CPB: Group I, “normal hearts” supplied by normal coronary arteries; Group II, “collateralized” hearts (Ameroid model) having regions of myocardium supplied by collateral vessels as well as regions of myocardium supplied by normal coronary arteries. Regional myocardial blood flow was determined by tracer microspheres. Retrograde coronary pressure (RCP) was measured in the collateralized hearts by cannulation of the circumflex artery distal to the Ameroid-induced occlusion. Data were collected in the empty beating state at hematocrit values of 39 ± 1.6 and 20 ± 0.7 percent, while perfusion pressure was maintained at 80 mm. Hg. Mean heart rate was 141 ± 3 beats per minute at a hematocrit value of 40 percent and did not vary with subsequent interventions. In the collateralized hearts, the endocardial flow difference between the normal and collateral regions which existed at a hematocrit value of 40 percent was markedly exaggerated at 20 percent (p < 0.01), even though hemodilution did not result in an epicardial flow difference. With hemodilution, RCP decreased from 48 ± 4 mm. Hg (p < 0.001) as perfusion pressure was held constant. These data suggest that during CPB, hemodilution is associated with an increased perfusion defect in regions of myocardium supplied by collateral vessels. Therefore, the subendocardium of the collateral region does not receive the flow increase necessary to maintain oxygen delivery at pre-hemodilution levels. This may result in prolonged periods of impaired regional oxygen delivery in patients with known coronary artery disease subjected to hemodilution during corrective surgery.

Arterial pressure-flow relationships in the anesthetized dog.

Arterial pressure-flow (Pa-\(\dot Q\)) and closing arterial pressure-flow (Pc-\(\dot Q\)) relationships of the systemic vascular bed were determined in anesthetized dogs with the aid of a right heart bypass preparation.Pc was estimated from plateau values of arterial pressure obtained during stop-flow procedures and plotted against the flow which existed immediately prior to the procedure. Two types of arterial pressure-flow relationships were observed. With type I, thePa-\(\dot Q\) curve was steep and extrapolated to a positive arterial pressure at zero flow which was equal to the meanPc occurring over the experimental flow range. With type II, the slope of thePa-\(\dot Q\) curve was relatively shallow and extrapolated to right atrial pressure (0 mm Hg). ThePc-\(\dot Q\) relationships were identical for all dogs. These data suggest the existence of a pressure regulatory function in the downstream arterial vasculature in type-I animals which established an effective back pressure to arterial perfusion and decouples the arterial pressure-flow characteristics from the remainder of the systemic circulation.

Structure-Fluid Interaction Between a Vibrating Wall and Flow in a Channel

The effects of structural vibration on the pressure and velocity fields of a two-dimensional channel flow are examined in terms of three dimensionless parameters related to the amplitude and frequency of vibration and the frictional pressure losses in the channel. Pressure-flow characteristics for the pumping system supplying fluid to the channel are varied between the extremes of the constant flow rate and constant pressure-drop modes of operation. The constant flow rate mode exhibits a larger response to the vibrating wall motion than the constant pressure-drop mode of operation. Structural motion is shown to alter both the time-averaged and dynamic pressure and velocity fields in the channel compared to the steady flow values. Pressure eddies that scale on the order of the structural dimensions arise due to the interaction of the vibrating channel wall with the mean flow field. These eddies have dimensions in between the scales of boundary layer eddies and acoustic eddies and therefore can be significant in exciting large structural vibrations in the fundamental mode through a feedback effect. The hydrodynamic mass associated with the structural vibration will be reduced due to the leakage of fluid out the ends of the channel. The effects of the wall vibration on the mean flow field should be considered for flows in narrow passages when estimating the fluid-structure inter-action forces due to the flow of a high-density fluid past a surface.

Pressure Drop and Flow Characteristics of Packed Fluidized Systems

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPressure Drop and Flow Characteristics of Packed Fluidized SystemsB. C. Pillai and M. Raja RaoCite this: Ind. Eng. Chem. Process Des. Dev. 1976, 15, 2, 250–255Publication Date (Print):April 1, 1976Publication History Published online1 May 2002Published inissue 1 April 1976https://doi.org/10.1021/i260058a007RIGHTS & PERMISSIONSArticle Views320Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (503 KB) Get e-Alerts