1,720,976 research outputs found
Effects of preload on regional nonischemic end-systolic performance
No full textBACKGROUND: Nonischemic segmental performance, assessed by end-systolic measures of shortening and thickening, decreases during ischemia. These changes in performance are likely to be dependent on the size, and, possibly, the site of the ischemic zone. This study was designed to examine the effect of preload, independently from ischemic zone size, on nonischemic end-systolic performance. METHODS: Twelve beagles were instrumented with sonomicrometers and micromanometer pressure gauges. End-systolic pressure length and thickness relationship data were obtained during vena caval balloon inflation. Control data were obtained both in left anterior descending and in left circumflex regions at left ventricular end-diastolic pressures of 5, 10 and 15 mmHg. The left circumflex artery was occluded for 90 s and nonischemic end-systolic pressure length and thickness data were obtained at each diastolic pressure. A 20 min recovery period was allowed between coronary occlusions. RESULTS: The isovolumic bulge in the ischemic area was more pronounced at an end-diastolic pressure of 5 mmHg than it was at an end-diastolic pressure of 15 mmHg. The slope of the nonischemic end-systolic pressure length and thickness relationships decreased at an end-diastolic pressure of 5 mmHg, whereas at 10 and 15 mmHg the slope of these relationships did not change significantly. The shift in the nonischemic end-systolic pressure-length relationship to the right was more pronounced at a low end-diastolic pressure (5 mmHg) than it was at a high end-diastolic pressure (15 mmHg). Similarly, the extent of the shift in the end-systolic pressure-thickness relationship to the left was more marked at a low end-diastolic pressure than it was at the higher end-diastolic pressure. CONCLUSION: Regional ischemia decreases the end-systolic performance of the nonischemic region. The extent of the shift and the degree to which the slopes of the nonischemic end-systolic relations decrease are influenced by loading conditions
Nonischemic end-systolic performance. Effects of alterations in regional and global left ventricular contractility.
No full textNonischemic end-systolic performance decreases during ischemia. These changes in performance are likely to be dependent on the size and site of the ischemic zone, as well as the prevailing loading conditions. This study was designed to examine the effect of regional and generalized changes in inotropy on nonischemic end-systolic performance, independent of the ischemic zone size. Twenty dogs were instrumented with sonomicrometers and micromanometer pressure gauges. End-systolic pressure-thickness relationship data were obained during vena-caval balloon inflation. Measurements were obtained before and 90 s after left circumflex (LC) artery occlusion. Then, simultaneous with the occlusion of the LC artery, isoproterenol (0.04 microg/ml) was infused into the left anterior descending artery. After recovery, the same protocol was repeated before and after propranolol (0.5 mg/kg). In a separate set of animals, the same measurements were made following 2.5 and 5 microg/kg/min dobutamine. The effect of ischemia on the nonischemic end-systolic pressure-thickness relationship was expressed as the extent to which the relationship is shifted to the left. Infusion of intracoronary isoproterenol into the perfusion bed of the nonischemic zone produced a significant increase in the slope of the end-systolic pressure-thickness relationship. During ischemia, however, the extent of leftward shift of this relationship was less than that following beta-blockade. Intravenous dobutamine resulted in a dose-dependent increase in the slope of the nonischemic end-systolic pressure thickness relationship, but the extent of leftward displacement of the relationship in response to regional ischemia was less than that following the control occlusion. The nonischemic segment is coupled with the nonfunctioning ischemic zone in such a way that it is required of the nonischemic segment to operate at decreased end-systolic thickness for any end-systolic pressure, the extent of which is to be determined, in part, by the size of the ischemic zone and the contractile state of the nonischemic myocardium. The lower the contractile state prior to coronary occlusion the greater extent of leftward shift of the pressure-thickness relationship
Regional nonischemic performance as assessed by end-systolic measures of shortening and thickening.
No full textOBJECTIVES: Nonischemic contractile segmental performance was characterized by the end-systolic pressure-length and pressure-thickness relations during regional ischemia induced by proximal left anterior descending and left circumflex coronary artery occlusions. BACKGROUND: The increases in shortening and thickening of the nonischemic myocardium during acute ischemia have been attributed to alterations in the regional loading conditions. However, it is uncertain to what extent ischemia affects the contractile performance of the nonischemic zone. METHODS: Twenty-seven beagle dogs were instrumented with sonomicrometers and micromanometer pressure gauges. End-systolic pressure-length and pressure-thickness relation data were obtained during vena cava balloon inflation. Control data were obtained in both left anterior descending and left circumflex regions. Then, in random order, either the left anterior descending or left circumflex coronary artery was occluded for 90 s, and hemodynamic and nonischemic end-systolic pressure-length and pressure-thickness data were obtained. After a 45-min recovery period, the other artery was occluded, and the same recordings were obtained. RESULTS: The end-systolic pressure-length relation exhibited variable degrees of rightward and downward shifts and the end-systolic pressure-thickness relation variable degrees of leftward and downward shifts. Left circumflex coronary artery occlusion was associated with a greater downward displacement (decreased slope) of the nonischemic end-systolic pressure-length relation than left anterior descending coronary artery occlusion. The baseline slope was the best predictor of the change in slope of the end-systolic pressure-length and pressure-thickness relations. The left circumflex coronary artery supplied a larger proportion of left ventricular myocardial mass than the left anterior descending coronary artery. CONCLUSION: Acute ischemia profoundly affects the end-systolic performance of the nonischemic segment. Furthermore, the site, and probably size, of the ischemic zone may be important determinants of nonischemic contractile performance
Effects of preload, afterload and inotropy on dynamics of ischemic segmental wall motion.
No full textOBJECTIVES: This study sought to explore the separate and combined effects of changes in preload, afterload and contractility on the dynamics of systolic bulging. BACKGROUND: The extent of ischemic systolic bulging has been shown to be mechanically disadvantageous to left ventricular pump performance. The factors that determine ischemic segmental wall motion have not been systematically studied. METHODS: Fourteen beagles were instrumented with sonomicrometers, micromanometer pressure gauges and a balloon in the inferior vena cava. Regional function was evaluated before and after 90 s of proximal left circumflex coronary artery occlusion. Occlusions were repeated after increasing systolic pressure by 5 to 10 (afterload I) and 15 to 20 mm Hg (afterload II) with graded aortic occlusion during inotropic stimulation with dobutamine (2.5 and 5 micrograms/kg body weight per min intravenously), with simultaneous 5 micrograms/kg per min dobutamine infusion and afterload II and during 2.5% halothane (negative inotrope) concentration. A 20-min recovery period was allowed between each stage of the experiment so that regional function returned to its preocclusion level. Ischemic wall motion was characterized by percent systolic bulging and its peak positive systolic lengthening rate (+dL/dt). RESULTS: Because bulging is markedly influenced by regional preload, systolic bulging was characterized over a wide range of end-diastolic lengths of the ischemic segment during caval balloon occlusion. During each intervention, a decrease in regional preload increased the extent of percent systolic bulging. This preload dependency was more pronounced with dobutamine infusions. An increase in afterload was not associated with increased percent systolic bulging at any given preload. At a predetermined preload, bulging was not appreciably altered when an increase in left ventricular systolic pressure was not associated with a change in peak positive first derivative of left ventricular pressure (+dP/dt) but was significantly worse when peak +dP/dt increased. Dobutamine caused a dose-dependent increase in percent systolic bulging and peak +dL/dt that was positively correlated with peak +dP/dt. CONCLUSIONS: By using different loading and inotropic interventions and analyzing the regional wall motion behavior over a range of regional preloads, we can conclude that preload and rate of pressure (tension) development are the principal determinants of systolic bulging. Increases in left ventricular pressure alone had a minimal effect on systolic bulging
Assessment of regional myocardial performance with end-systolic pressure lenght and thickness relationships.
No full textAlthough end-systolic pressure length and thickness relationships (ESPLR, ESPTR) are now widely used as substitutes for the end-systolic pressure volume relationships, there are some reservations about their use as an index of left ventricular (LV) performance. This study addressed three issues, namely: (1) which loading technique (decreasing preload by inferior vena cava (IVC) balloon occlusion or increasing systolic pressure by aortic constriction) is the most likely to yield usable data; (2) reproducibility of these relationships over a 30 min period; and (3) whether by using end-ejection (zero aortic flow) as a definition of end-systole, ESPLR and ESPTR can be used to characterize myocardial performance independent of load. Thirteen anesthetized beagles, weighing 16-25 kg, were used for this study, and were instrumented with sonomicrometers. We found that when ESPLR and ESPTR were constructed from data derived during aortic constriction, the slopes of these relationships were steeper and more curvilinear than when they were constructed from data recorded during IVC occlusion. In addition, the mean between ESPLR, ESPTR obtained 30 min apart was small, although there was a fair degree of variability between the first and second measurements. Using end-ejection to define end-systole, both ESPLR and ESPTR were relatively insensitive to loading conditions (LV end-diastolic pressure of 8-12 mmHg and 14-18 mmHg, aortic systolic pressure of 7-10 mmHg and 20-25 mmHg above baseline (in terms of the slope and shift (leftward or rightward) in these relationships, but were sensitive to inotropic interventions (dobutamine 2.5 micrograms/kg per min and 5 micrograms/kg per min). We conclude that, ESPLR and ESPTR, defined from measurements at end-ejection, can be used as adequate descriptors of regional myocardial performance if they were constructed from data over a similar pressure range during IVC balloon occlusion
Durante occlusione coronarica sperimentale la dobutamina rallenta ulteriormente la costante di tempo del rilasciamento isovolumetrico.
No full textAlthough end-systolic pressure-length relationship (ESPLR) is now widely used as a regional substitute for the end-systolic pressure-volume relationship, there are some reservations about its use as an index of systolic performance. This study aimed at assessing whether by using end-ejection (zero aortic flow) as a definition of end-systole, ESPLR can be used to characterize myocardial performance independent of load, and if the choice of the region where to implant the sonomicrometers is critical. Ten anaesthetized dogs (16 +/- 2 kg) were instrumented with a left ventricular (LV) pressure micromanometer and an aortic flow probe. Sonomicrometers were implanted in the apical (L1) and the mid-ventricular (L2) regions of the anterior LV wall, and in the basal region of the lateral wall (L3). End-systolic pressure-length relationships were obtained during acute preload reduction induced by the inflation of a vena caval balloon. This evaluation was repeated after increasing end-diastolic pressure to 14-18 mmHg (delta PL), after increasing systolic pressure by 15 (delta P-I) and 25 mmHg (delta P-II) with graded descending aorta occlusion, and during dobutamine infusions at 2.5 (Db 2.5) and 5 micrograms/kg/min (Db5). End-systolic pressure-length relationships (r > 0.97; pressure range: 70-100 mmHg) were characterized by their slopes (Ees), the extrapolated intercept at zero pressure (L0) and the values of segment length at a pressure of 75 (L75) and 100 mmHg (L100). In all the myocardial regions studied by sonomicrometry, the increments in preload and afterload did not significantly shift ESPLR
Diastolic dysfunction and mortality in septic patients: a systematic review and meta-analysis (vol 41, pg 1004, 2015)
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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