Percent Change In Flow Research Articles

Non-invasive assessment of mesenteric hemodynamics in patients with suspected chronic mesenteric ischemia using 4D flow MRI.

Chronic mesenteric ischemia (CMI) is a rare disease with a particularly difficult diagnosis. In this study, 4D flow MRI is used to quantitatively evaluate mesenteric hemodynamics before and after a meal in patients suspected of having CMI and healthy individuals. Nineteen patients suspected of CMI and twenty control subjects were analyzed. Subjects were scanned using a radially undersampled 4D flow MR sequence (PC-VIPR). Flow rates were assessed in the supraceliac (SCAo) and infrarenal aorta, celiac artery, superior mesenteric artery (SMA), left and right renal arteries, superior mesenteric vein (SMV), splenic vein, and portal vein (PV) in a fasting state (preprandial) and 20min after a 700-kcal meal (postprandial). Patients were subcategorized into positive diagnosis (CMI+, N = 6) and negative diagnosis (CMI-, N = 13) groups based on imaging and clinical findings. Preprandial, postprandial, and percent change in flow rates were compared between subgroups using a Welch t test. In controls and CMI- patients, SCAo, SMA, SMV, and PV flow increased significantly after meal ingestion. No significant flow increases were observed in CMI+ patients. Percent changes in SMA, SMV, and PV flow were significantly greater in controls compared to CMI+ patients. Additionally, percent changes in flow in the SMV and PV were significantly greater in CMI- patients compared to CMI+ patients. 4D flow MRI with large volumetric coverage demonstrated significant differences in the redistribution of blood flow in SMA, SMV, and PV in CMI+ patients after a meal challenge. This approach may assist in the challenging diagnosis of CMI.

Relation Between Endothelial Microparticles and Endothelial Function Following Acute Exercise in Men with CAD

Purpose: Microparticles (MP) are small membranous vesicles shed from formed elements such as circulating platelets and vascular endothelial cells. They express surface antigens characteristic of their cell-of-origin and contain DNA, RNA, miRNA and intracellular proteins. Depending on the dynamic morphological state of the parent cell, phenotypically varied MP may be released into the circulation. MP serve not only as markers, but also potential mediators of inflammation, coagulation and endothelial dysfunction. This study examined the relation between total MP, endothelial MP (EMP), platelet MP (PMP) and endothelial function (a validated surrogate measure of early atherosclerosis) in response to acute exercise in men with coronary artery disease (CAD). Methods: Eight men with CAD (65.7 ± 4.5 yr, VO2max 18.6 ± 4.1 ml/kg/min, BMI 29.7±3.3 kg/m-2) underwent 20 min of treadmill walking at 66 % VO2max. Endothelial dependent dilation of the brachial artery was assessed before and 1 h following the acute bout of exercise. Vessel diameter was determined using high resolution vascular ultrasonography (SonoSite, MicroMaxx) from flow mediated dilation (FMD) following 5 min of forearm occlusion. Endothelial independent vasodilation (EID) was measured following the administration of glyceryl trinitrate (0.4 mg). MP counts were enumerated by flow cytometry from platelet poor plasma (PPP) stored at –80°C. MP were characterized based on size (0.5 – 1.0 μm sizing gate) and their ability to bind annexin V. MP had also to bind to CD62E or CD41 to be of endothelial or platelet origin respectively. Results: Compared to baseline, FMD was significantly increased at 60 min following the acute bout of exercise. There was no change in EID. There was significant relation between the percent change in total MP (annexin V+ events) and the percent changes in flow mediated dilation 60 min after the exercise bout and between the percent change in EMP (annexin V+/CD62E+ events) and the percent changes in flow mediated dilation 60 min after the exercise bout. Conclusion: Changes in endothelial function in response to acute exercise may be mediated by alterations in circulating levels of MP.

Flow dependence of the aortic valve area in patients with aortic stenosis: Assessment by application of the continuity equation

It has been argued that the aortic valve area (AVA) in patients with aortic stenosis increases with flow. Others, however, have attributed the apparent increase to flow dependence of the empiric constant in the Gorlin formula. We examined the changes in AVA during changes in transvalvular flow induced by dipyridamole infusion in 34 patients with aortic stenosis. Two-dimensional and Doppler echocardiography was used and AVA was calculated according to the continuity equation, which does not include empiric constants. Flow increased in 29, decreased in four, and was unchanged in one patient. There was a linear correlation between percent change in flow and percent change in AVA: δ AVA% = 1.1+δ flow% · 0.56 (r = 0.72; p < 0.001 ) In conclusion, AVA was found to be flow dependent. The magnitude of change in AVA observed by noninvasive recordings agrees with previous invasive studies according to the Gorlin formula.

An alternative to radioactive microspheres for measuring regional myocardial blood flow, part 2: Laser-doppler perfusion monitor

To compare measurements of regional myocardial blood flow volume between microsphere measurement of regional flow (0.5- to 2- g tissue sampling) and a potential alternative measure, local flow (1 mm3) in the microcirculation measured by laser-Doppler perfusion monitor. Prospective, randomized, controlled. University research laboratory. Pigs. After anesthetization, in 5 pigs (25 to 30 kg), the left anterior descending coronary artery was isolated and its resting flow measured by a perivascular-Doppler flowmeter. Left ventricular pressure and first time derivative of left ventricular pressure were measured. The laser-Doppler probe needle (type N) (Model ALF-21, Transonic Systems, Inc, Ithaca, NY) was inserted 2 to 3 mm into the wall of the left ventricle, parallel to the coronary artery. All 5 pigs were subjected to 0 (control), 50% , 75%, and 100% constriction of the left anterior coronary artery. Measurements by radio-active microspheres correlated poorly with those by laser-Doppler and extremely poorly with those by perivascular Doppler flowmeter. For percent change from baseline in the constricted arterial zone, radioactive measurements correlated well with those by laser-Doppler but not those by Doppler flowmeter. Also, radioactive measurements of percent change in flow in the circumflex (nonconstricted) zone and laser-Doppler measurements in the constricted arterial zone did not correlate well. Laser-Doppler can be recommended for experimental research to monitor local flow. These measurements may relate to change in regional flow during normal perfusion and hypoperfusion. Before the laser-Doppler perfusion monitor can be used clinically, tissue trauma from the 0.55-mm needle needs to be evaluated.

Global alteration in perfusion response to increasing oxygen consumption in patients with single-vessel coronary artery disease.

Recent evidence suggests that, in coronary artery disease (CAD), myocardial blood flow (MBF) regulation is abnormal in regions supplied by apparently normal coronary arteries. However, the relation between this alteration and MBF response to increasing metabolic demand has not been fully elucidated. MBF was assessed at baseline, during atrial pacing tachycardia, and after dipyridamole (0.56 mg/kg IV over 4 minutes) in 9 normal subjects and in 24 patients with ischemia on effort, no myocardial infarction, and isolated left anterior descending (n = 19) or left circumflex (n = 5) coronary artery stenosis (> or = 50% diameter narrowing). Perfusion of both poststenotic (S) and normally supplied (N) areas was measured off therapy by positron emission tomography and [13N]ammonia. Normal subjects and CAD patients showed similar rate-pressure products at baseline, during pacing, and after dipyridamole. In CAD patients, MBF was lower in S than in N territories at rest (0.68 +/- 0.14 versus 0.74 +/- 0.18 mL.min-1.g-1, respectively, P < .05), during pacing (0.92 +/- 0.29 versus 1.16 +/- 0.40 mL.min-1.g-1, respectively, P < .01), and after dipyridamole (1.18 +/- 0.34 versus 1.77 +/- 0.71 mL.min-1.g-1, respectively, P < .01). However, normal subjects showed significantly higher values of MBF both at rest (0.92 +/- 0.13 mL.min-1.g-1, P < .05 versus both S and N areas), during pacing tachycardia (1.95 +/- 0.64 mL.min-1.g-1, P < .01 versus both S and N areas), and after dipyridamole (3.59 +/- 0.71 mL.min-1.g-1, P < .01 versus both S and N areas). The percent change in flow was strictly correlated with the corresponding change in rate-pressure product in normal subjects (r = .85, P < .01) but not in either S (r = .04, P = NS) or N regions (r = .08, P = NS) of CAD patients. Besides epicardial stenosis, further factors may affect flow response to increasing metabolic demand and coronary reserve in patients with CAD.

Bronchial blood flow measured by video dilution technique in sheep.

Bronchial blood flow was studied with the video dilution technique (VDT) in seven sheep. All animals were anesthetized (thiamylal and halothane) and ventilated. A videodensitometer and a videotape replay of the fluoroscopic image of dye moving through the common bronchial artery were used to construct dye mass vs. time curves. The areas under the curves were inversely proportional to flow in the bronchoesophageal artery, the site of dye injection. At thoracotomy, an electromagnetic flow probe (EMFP) was placed on the common bronchial artery (the major branch of the bronchoesophageal artery) to measure blood flow changes simultaneously by EMFP and by VDT. These two methods of measurement of blood flow to the airways were compared to validate the use of VDT in this circulation. Common bronchial artery blood flow was increased by injection of radiocontrast dye into the fluoroscopically positioned bronchoesophageal artery catheter causing hyperosmotically induced hyperemia. In 160 simultaneous measurements in five sheep, the percent change in flow as measured by EMFP and VDT correlated closely (r = 0.96). When flow changed because of spontaneous aortic pressure changes or pharmacologic intervention (28 simultaneous measurements in five sheep), the percent change in flow by EMFP and VDT also correlated well (r = 0.98). Bronchial blood flow changes in sheep can be measured accurately using the video dilution technique.

Cerebrovascular carbon dioxide reactivity and conductance in patients awake and under general anesthesia.

Paired cerebral blood flow measurements at two levels of arterial carbon dioxide (CO2) tension were made in 36 awake patients and 85 patients under general anesthesia to measure the percent change in flow per mm Hg change in PaCO2 (CO2 reactivity). CO2 reactivity was significantly greater in the generally anesthetized (5.96) than in the awake group (3.65). In both groups, a linear correlation was found between mean percent CO2 reactivity and conductance (the reciprocal of resistance), up to a level of conductance of 0.85 in awake and 0.95 in unconscious patients. When the CO2 reactivity of 18 awake patients and 59 unconscious patients was compared with that of respective control groups, only 11 patients were found to have abnormal CO2 reactivities for their conductance levels.

The effect of intracoronary injection of contrast medium upon coronary blood flow.

The changes in coronary blood flow in response to intracoronary injection of 3 ml of 76% Renografin were studied in 47 patients using the thermodilution technique for continuous measurement of coronary sinus blood flow. Within seconds after left coronary injection, an increase in coronary sinus flow began which peaked at an average of 53% above control in 5-10 seconds. There was a corresponding decrease in coronary resistance. Flow returned to control level in almost all patients within one minute of injection. Twenty-four of 35 patients had no change in coronary sinus flow in response to right coronary injection. This can be explained by the fact that most of the venous flow from the right coronary artery returns in such a way that it cannot be measured by the coronary sinus catheter. Of the eleven patients who did show an increase, seven had angiographically documented right to left collaterals, suggesting that the increase in flow was the result of vasodilatation of the left coronary bed by contrast arriving via the right to left collaterals. The percent changes in flow and resistance in response to left coronary injection were isgnificantly greater in the 13 normals than in the 34 with obstructive disease of the left coronary artery (P lessthan 0.01). Flow rose 70 plus or minus 27% (mean plus or minus standard deviation) in the normals versus 46 plus or minus 25% in the patients with coronary artery disease, while resistance fell 44 plus or minus 9% versus 33 plus or minus 11%. The differences, however, were not sufficient for these changes to be of value in the assessment of the degree of impairment of the coronary arterial bed in the individual patient.

CORRECTION

An error appeared in the abstract of the article "The Relationship of Regional Cerebrovascular CO 2 Reactivity to Blood Pressure and Regional Resting Flow" by Robert H. Ackerman, M.D., which appeared in STROKE, volume 4, page 725 (September-October) 1973. The following is the corrected abstract. Cerebrovascular CO 2 reactivity (the change in cerebral blood flow per mm Hg change in Pa CO CO 2 ) is shown to be directly related to resting flow and inversely related to blood pressure for regional as well as for mean CBF data. Both regional and mean CO 2 reactivity therefore are proportional to the ratio resting flow/blood pressure. This ratio is the reciprocal of resistance and may be called conductance . When regional CO 2 reactivity for 428 cerebral areas is plotted against an approximation of regional conductance, the data describe positive linear relationships similar to those found when mean CO 2 reactivity is plotted against mean conductance. These relationships can be demonstrated whether CO 2 reactivity is calculated with specific or percent change in flow. The data suggest that under physiological conditions CO 2 reactivity is related to the basal tone of the cerebrovascular bed. The way in which CO 2 reactivity relates to conductance, therefore, may be a more reliable index of the integrity of the cerebrovascular CO 2 response than the CBF change per se. Analysis of CO 2 reactivity as a function of conductance may facilitate the interpretation of mean and regional CO 2 reactivity and may provide a more meaningful basis for comparison of the CO 2 response between individuals.

The relationship of regional cerebrovascular CO2 reactivity to blood pressure and regional resting flow.

Cerebrovascular CO 2 reactivity (the change in cerebral blood flow per mm Hg change in Pa co co 2 ) is shown to be directly related to resting flow and inversely related to blood pressure for regional as well as for mean CBF data. Both regional and mean CO 2 reactivity therefore are proportional to the ratio resting flow/blood pressure. This ratio is the reciprocal of resistance and may be called conductance . When regional CO 2 reactivity for 428 cerebral areas is plotted against an approximation of regional conductance, the data describe positive linear relationships similar to those found when mean CO 2 , reactivity is plotted against mean conductance. These relationships can be demonstrated whether CO 2 reactivity is calculated with specific or percent change in flow, the data describe positive linear lerationships similar to those found when mean CO 2 basal tone of the cerebrovascular bed. The way in which CO 2 reactivity relates to conductance, therefore, may be a more reliable index of the integrity of the cerebrovascular CO 2 response than the CBF change per se. Analysis of CO 2 reactivity as a function of conductance may facilitate the interpretation of mean and regional CO 2 reactivity and may provide a more meaningful basis for comparison of the CO 2 response between individuals.