A graphic orientated data analysis system for hemodynamic research.

A software program to process and to extract physiological functional hemodynamics data has been developed and reported. The purpose of this software system is to process and capture cardiovascular hemodynamics and physiological functional data after data acquisition. The system utilized an interactive graphic display and script control to extract the data. With a minimum interface, it is capable of analyzing multiple channels of data and simultaneously obtaining the results. The extracted data includes global cardiovascular functional parameters and with script process the software will calculate stroke work from the pressure length relationship. The results are stored in files for further statistical analysis. The procedures are reliable and readily applicable to examine and analyze the acquired data with minimal observer bias.

Potential clinical applications of recombinant human haemoglobin in blood conservation.

Haemoglobin solutions have been tried as blood substitutes for decades with little success. Problems with early haemoglobin solutions include instability of the haemoglobin tetramer in the plasma, resulting in dissociation of the protein into dimers, as well as excessively high oxygen affinity for clinical oxygen transport capabilities. Newer haemoglobin solutions are currently under development and may prove adequate to transport oxygen while avoiding excessive toxicity. However, these compounds pose other difficulties, including a short plasma half-life and the potential for systemic hypertension due to nitric oxide binding. Several haemoglobin solutions are now undergoing human testing for potential clinical use. Haemoglobin can be harvested from outdated packed red blood cell units and chemically altered for use in clinical scenarios. Likewise, bovine haemoglobin may be obtained and modified for use as a blood substitute. While both these approaches may yield clinically useful oxygen carrying solutions, neither is completely free from infectious risk. The use of recombinant technology to produce a genetically altered haemoglobin from Escherichia coli allows avoidance of infectious risks and a functional haemoglobin which does not need further chemical modification. Use of this first generation of recombinant human haemoglobin as a blood substitute may be limited due to its short half-life of <12 hours, but clinical uses such as replacement fluid for acute normovolaemic haemodilution during the perioperative period may allow significant blood savings for patients and the potential to avoid patient exposure to allogeneic transfusions.

The effects of mechanical cardiac stabilization on left ventricular performance.

OBJECTIVE: Mechanical cardiac stabilization is beneficial for precise coronary anastomoses on the beating heart. However, the effect of mechanical cardiac stabilization on hemodynamics, left ventricular performance, and the degree of injury to underlying tissue are uncertain. METHODS: Twelve swine (20-30 kg) underwent median sternotomy and a mechanical stabilizing device (United States Surgical, Norwalk, CT) was positioned astride a segment of left anterior descending coronary artery (LAD). Coronary blood flow was measured by Doppler. Sonomicrometry crystals were placed distal to the stabilizer in a region of myocardium subtended by the LAD, and a left ventricular micromanometer was inserted. Regional myocardial function was determined using the preload recruitable stroke work (PRSW) relationship. Data were acquired at three time points: 20 min before (PRE) and after placing the stabilizer (EXPT); and 20 min after removing the stabilizer (POST). Tissue subjacent to the stabilizer was then biopsied. Means +/- standard deviation are reported. RESULTS: The mechanical stabilizer caused a decrease in cardiac output from 4.2+/-1.5 to 3.6+/-1.3 l/min (P < 0.05), which returned to baseline values after its removal. Regional myocardial function (percent systolic shortening and MW and x-intercept of the PRSW relationship) was unchanged. Blood pressure, heart rate, and LAD blood flow remained constant. Histologic findings included a layer of myocyte necrosis less than 1 mm in depth immediately beneath the stabilizer. CONCLUSIONS: These data demonstrate that mechanical stabilization of the LAD may temporarily decrease cardiac output. This is not attributed to impaired contractility or ischemia, but is secondary to direct ventricular compression with reduced stroke volume. Injury to underlying tissue is negligible.

Effect of mild hypothermia during cardiopulmonary bypass on erythrocytic hemoglobin oxygen delivery.

OBJECTIVES: To observe and define the degree of change in hemoglobin oxygen affinity induced by hypothermic extracorporeal circulation (ECC). DESIGN: A prospective, nonrandomized, observational study. SETTING: A single university medical center. PARTICIPANTS: Seventeen patients presenting for elective cardiac surgery. INTERVENTIONS: Systemic hypothermia during ECC. MEASUREMENTS AND MAIN RESULTS: During and after ECC, simultaneous arterial and mixed-venous whole-blood samples were obtained and immediately analyzed for gas tensions and hemoglobin saturation. Samples were obtained during the following times on ECC: initially after cardiopulmonary bypass onset during normothermia (37 degrees C), after cooling to 32 degrees C, and after rewarming to 37 degrees C. A fourth sample was obtained 10 to 20 minutes after discontinuation of cardiopulmonary bypass. Extracorporeal pump flow and thermodilution-determined cardiac output were also recorded for calculation of oxygen delivery and consumption. Mixed-venous results were used to calculate in vivo the blood gas tension at which hemoglobin was 50% saturated with oxygen (P50). There were no differences in P50 for the 17 patients by analysis of variance (ANOVA) for repeated measures with paired t-test with Bonferroni correction. Furthermore, no change in P50 was observed during the course of cooling and rewarming in any individual patient's samples. Oxygen delivery decreased after hypothermia and rewarming from mild hypothermia; oxygen consumption was decreased after rewarming and markedly increased after discontinuation from ECC. CONCLUSION: Mild hypothermia to 32 degrees C during ECC does not result in in vivo alterations in oxyhemoglobin dissociation and thus does not induce changes in oxygen delivery to peripheral tissues. However, oxygen usage appears to be markedly increased after cardiopulmonary bypass.

Measurement of gastrointestinal intramucosal pH is a poor guide to tolerable levels of anemia during isovolemic hemodilution in a canine model of coronary stenosis.

OBJECTIVE: To determine the relationship between gastrointestinal intramucosal pH and myocardial oxygenation during isovolemic hemodilution in dogs with critical coronary artery stenoses. DESIGN: Prospective sequential evaluation of ileal intramucosal pH and regional myocardial function of a critically perfused area of myocardial tissue in a canine model of normovolemic hemodilution. SETTING: A research laboratory. SUBJECTS: Fifteen dogs. INTERVENTIONS: A micrometer snare was placed around a main coronary artery (8 left anterior descending artery, 7 right coronary artery). Three pairs of sonomicrometer crystals were placed in the heart to measure regional myocardial contraction. A gastrointestinal tonometer was placed in the ileum and used to measure luminal PCO2. This PCO2 value was used to calculate the ileal intramucosal pH. The animals underwent normovolemic hemodilution until myocardial ischemia occurred in the region supplied by the snared vessel. Measurements were continued for a further 40 minutes. MEASUREMENTS AND MAIN RESULTS: Following instrumentation, stabilization, and critical constriction of a coronary vessel, percentage changes in systolic shortening of myocardial tissue in the region of critical perfusion were determined every 20 minutes. Ileal intramucosal pH and commonly measured cardiovascular variables were determined at the same time points. Myocardial ischemia occurred after 80 minutes of hemodilution, when the mean (+/- SD) hemoglobin concentration had fallen from a baseline level of 123 +/- 18 g/L to 82 +/- 14 g/L (P < .01). From the start of hemodilution to 40 minutes after myocardial ischemia occurred, there were no significant changes in heart rate, cardiac output, oxygen consumption, arterial acid-base balance, or arterial PCO2. Oxygen delivery decreased by approximately 45% (5.99 +/- 1.66 to 3.41 +/- 0.90 mL/kg per minute; P < .01) but there were no changes in ileal intramucosal pH (7.31 +/- 0.08 to 7.30 +/- 0.08; P = .90). CONCLUSIONS: Myocardium compromised by coronary stenosis is more sensitive to normovolemic hemodilution-induced ischemia than the normally perfused gut mucosa. This limits the potential utilization of the measurement of gastrointestinal intramucosal pH as a guide to tolerable levels of anemia in critically ill patients.

Cost effectiveness of blood transfusions: risk and benefit.

Allogenic blood transfusion carries the remote but well-known risk of disease transmission. The advent of an all-volunteer donor pool and modern screening techniques have made the blood supply the safest it has ever been. Despite these advances, however, clerical errors are still a cause of transfusion morbidity. Less well defined are the effects of allogenic blood on immunosuppression with resultant increase in infections and tumor recurrence. Strategies to reduce the need for allogenic blood include autologous predonation, acute normovolemic hemodilution perioperatively, and the salvage of shed blood. Autologus predonation eliminates many disease risks while keeping costs at least comparable to allogenic blood. Acute normovolemic hemodilution offers the advantage of low cost and the use of autologus fresh blood at the end of the operation. In the future, artificial blood substitutes now undergoing clinical trials, may play an important role in reducing the need for allogenic transfusions. Two promising agents are hemoglobin-based oxygen carriers and perfluorocarbons. Both offer the advantage of long shelf life and eliminate the need for crossmatching, but they are limited by short half-life.

Acute regional myocardial ischemia and recovery after cardiopulmonary bypass: effects of intensity of antecedent ischemia.

Aortic cross-clamping with inadequate myocardial preservation has been shown to cause postoperative decreases in myocardial performance following coronary artery bypass graft surgery. We have demonstrated a mild decrement in myocardial beta-receptor function associated with cold cardioplegia in a normal animal model; in normal human hearts, however, response to beta-adrenergic inotropic stimulation was diminished significantly. Beta-receptor dysfunction also is associated with chronic myocardial ischemia that is associated with severe ischemic heart disease. Although the change in beta-receptor function with acute regional myocardial ischemia associated with severe ischemic heart disease is not understood fully, we found that the intensity of regional ischemia significantly affects functional recovery after cardiopulmonary bypass (CPB). Myocardial stunning does not appear to be significant in this dysfunction; however, alterations in beta-receptor density and function may play a critical role in post-CPB ventricular function.

Measurement of vertebral cortical integrity during pedicle exploration for intrapedicular fixation.

STUDY DESIGN: This study determined the predictive ability of electrical impedance measurement in detecting cortical perforation in a porcine model of pedicular exploration. OBJECTIVE: This study tested the hypothesis that a large decrease in electrical impedance would occur as a result of perforation of the vertebral cortex by the pedicle probe. SUMMARY OF BACKGROUND DATA: The resistivity of cortical bone has been reported to be 25 to 100 times greater than that of soft tissues. METHODS: A total of 42 pedicles of the lumbar spines of six swine were explored using the instrumented pedicle probes. RESULTS: Using a 1 microAmp 30-Hz current source, measurement of electrical impedance predicted cortical rupture with a sensitivity, specificity, and accuracy of 95%. Maximum applied voltages of 2.8 mV did not result in myogenic stimulus. CONCLUSIONS: Electrical impedance measurement provides an accurate real-time measurement of cortical perforation. This technique is adapted readily for use with pedicular screws and screw tape. Further investigation to determine the clinical use of this technique is recommended.

Jugular bulb saturation and cognitive dysfunction after cardiopulmonary bypass.

Inadequate cerebral oxygenation during cardiopulmonary bypass may lead to postoperative cognitive dysfunction in patients undergoing cardiac operations. A psychological test battery was administered to 255 patients before cardiac operation and just before hospital discharge. Postoperative impairment was defined as a decline of more than one standard deviation in 20% of tests. Variables significantly (p < 0.05) associated with postoperative cognitive impairment are baseline psychometric scores, largest arterial-venous oxygen difference, and years of education. Jugular bulb hemoglobin saturation is significant if it replaces arterial-venous oxygen difference in the model. Factors correlated with jugular bulb saturation at normothermia were cerebral metabolic rate of oxygen consumption (r = -0.6; p < 0.0005), cerebral blood flow (r = 0.4; p < 0.0005), oxygen delivery (r = 0.4; p < 0.0005), and mean arterial pressure (r = 0.15; p < 0.05). Three measures were significantly related to desaturation at normothermia and at hypothermia as well: greater cerebral oxygen extraction, greater arterial-venous oxygen difference, and lower ratio of cerebral blood flow to arterial-venous oxygen difference. We conclude that cerebral venous desaturation occurs during cardiopulmonary bypass in 17% to 23% of people and is associated with impaired postoperative cognitive test performance.

Importance of severity of coronary artery disease for the tolerance to normovolemic hemodilution. Comparison of single-vessel versus multivessel stenoses in a canine model.

The response of global cardiovascular and regional myocardial function (as seen with sonomicrometry) to continuous, progressive hemodilution (Dextran 70) was compared in dogs with proximal circumflex coronary artery stenosis and dogs with proximal circumflex coronary artery and proximal left anterior descending artery stenoses. Hemodilution-induced failure, defined as greater than 50% loss in function or death of the animal, was determined for systolic shortening in the circumflex coronary artery and left anterior descending artery territories, mean arterial pressure, and maximum left ventricular rate of pressure rise. Time to failure was compared between groups by log-rank tests. Systolic shortening of the circumflex coronary artery failed at a similar median time point in both groups (30 minutes in the group with single-vessel stenosis and hemodilution versus 40 minutes in the group with multivessel stenosis and hemodilution). Systolic shortening of the left anterior descending artery (80 versus 50 minutes), mean arterial pressure (70 versus 50 minutes), and maximum left ventricular rate of pressure rise (70 versus 40 minutes), however, failed significantly later (p < 0.01) in animals with single circumflex coronary artery stenosis. A marked increase (+50%) in systolic shortening of the left anterior descending artery was observed during hemodilution only in the circumflex coronary artery stenosis group. The better hemodilution tolerance in the circumflex coronary artery stenosis group may be explained by the compensatory increase in myocardial contractile function in non-coronary flow-compromised myocardium, which seems to be crucial for global cardiovascular stability during hemodilution in the presence of coronary stenoses.

Regional ischemia during hemodilution in flow compromised myocardium: evidence for incomplete metabolic recovery.

The hypothesis that mild decreases in myocardial function may occur with preservation of normal levels of intramyocardial ATP was tested. A model of single vessel coronary stenosis using eight mongrel dogs in an open chest preparation was used. Myocardial oxygen supply was altered by performing acute normovolemic hemodilution with a colloid solution. The results demonstrated significant alterations in myocardial ATP content with hemodilution-induced mild regional dysfunction, which was not in line with the hypothesized effects of ischemia on myocardial function. In addition, restoring myocardial function by minimal reinfusion of shed blood in this study did not restore myocardial energy stores, an effect that may be called metabolic stunning. The results suggest that myocardial stunning may not be an important and ubiquitous process during intraoperative myocardial ischemia. Further, myocardial function appears to be capable of quickly recovering from mild ischemia although metabolic function may be slower. Finally, the concept of decrements in myocardial function occurring in order to preserve myocardial metabolic stores does not appear to occur universally, which may be significant in the prevention or treatment of mild perioperative ischemia.

Cardiovascular and coronary physiology of acute isovolemic hemodilution: a review of nonoxygen-carrying and oxygen-carrying solutions.

Acute isovolemic hemodilution is used increasingly to avoid the potentially serious side effects of homologous blood transfusions. Cardiovascular physiology during hemodilution is characterized by a marked increase in cardiac output and organ blood flow to compensate for the decrease in arterial oxygen-carrying capacity. During advanced hemodilution an increased oxygen extraction is also observed, such that oxygen consumption generally is maintained even during advanced hemodilution. The increase in cardiac output is related mainly to a decrease in blood viscosity and an enhanced sympathetic tone resulting in stimulation of the heart. The magnitude and the mechanisms involved in the increase depend upon species, state of awareness (awake versus anesthetized), type of anesthesia, type of exchange solution, and condition of the heart prior to hemodilution. Recent laboratory findings, as well as clinical practice in cardiac surgery, suggest that moderate hemodilution to hematocrit values of approximately 25% is well tolerated in single vessel coronary artery disease which should thus not be regarded as an absolute contraindication for moderate hemodilution. An integral concept to minimize homologous blood transfusions consists of preoperative autologous blood donation, preoperative isovolemic hemodilution, meticulous (asanguineous) surgical technique, and acceptance of minimum hemoglobin levels during the entire hospitalization. The incidence of homologous blood transfusions will be reduced using acute isovolemic hemodilution. This incidence will be further reduced once hemoglobin solutions become clinically available for specific indications. At present, research activities are concentrated on defining the critical level of hemodilution in various pathologic conditions and to investigate pharmacology and physiology of the new hemoglobin solutions. Finally, several chemically modified hemoglobin-based oxygen-carrying solutions devoid of renal toxicity will be available in the future. The cardiovascular physiology and pharmacology of these hemoglobin solutions have been studied. Cardiac output is generally constant and oxygen extraction is increased to maintain oxygen consumption during hemodilution with hemoglobin solutions. In most studies, some vasoconstriction was observed also, which might result from interaction of the hemoglobin molecule with the EDRF/NO system. However, with enhanced purification, chemical modification or microencapsulation of the hemoglobin molecule, vasoconstriction can be limited.

Pressure-volume loops: a dynamic approach to the assessment of ventricular function.

Analysis of ventricular function in terms of pressure-volume or pressure-dimension relationships allows global and regional ventricular dynamics to be fully analyzed. In addition, this approach allows the relationships between muscle function (contractility, stiffness, potential energy) and pump function (stroke volume, stroke work) to be determined and predicted. Alterations in ventricular loading conditions can also be examined in terms of muscle and pump function. However, this analysis is more complex than initially thought and considerable care must be taken especially when regional ischemia is concerned. Moreover, some of the early assumptions have been disproved and conclusions can only be drawn from studies in which full assessment of changes in pressure and dimensions is available.

[Hemodilution tolerance in coronary heart disease: single vessel versus multiple vessel disease]. / Hämodilutionstoleranz bei koronarer Herzkrankheit: Eingefäss- versus Mehrgefäss-Erkrankung.

Isovolemic hemodilution is well tolerated in experimental models of single vessel coronary artery disease. Little information, however, is available on the hemodilution tolerance in presence of multivessel coronary artery disease. 42 dogs were anesthetized and instrumented to determine global cardiovascular and regional myocardial functions (systolic shortening, SS) in the anterior apical LV territory supplied by the left anterior descending coronary artery (LAD) as well as in the posterior apical LV wall supplied by the circumflex coronary artery (LC) using sonomicrometry. Critical coronary stenoses were imposed on the proximal LAD and LC according to the experimental group assignment and group 1V-HD (LC stenosis only) and group 2V-HD (LC and LAD stenoses) were then progressively hemodiluted using Dextran 70,000. 1000 ml blood per hour was thereby continuously exchanged with 900 ml Dextran until the animal expired or 120 minutes were reached. 12 dogs (LAD and LC stenoses) served as controls (2V-C). All groups started with similar hemoglobin values and these decreased similarly in both hemodiluted groups. Myocardial contractile function in the LC territory failed similarly in the 1V-HD and 2V-HD groups during progressive hemodilution. The LAD myocardium, however, responded markedly different in the 2V-HD as compared to the 1V-HD group: In the 2V-HD group, SSLAD started to decrease shortly into hemodilution, whereas SSLAD progressively increased during the first 60 min of continuous hemodilution in the 1V-HD group. The presence of non-compromised LV myocardium with the ability of a compensatory increase in contractile function thus seems to crucial for the hemodilution tolerance in the setting of coronary artery disease.

Pacing-induced left ventricular asynchronies in dogs with critical coronary stenosis: mechanisms and effect of anesthetics.

The mechanisms leading to left ventricular (LV) asynchronies are incompletely understood, and reports on the functional significance of asynchronies for the affected segments are conflicting. To characterize LV asynchronies, 16 anesthetized dogs with critical stenosis of the left anterior descending coronary artery (LAD) were instrumented to measure subendocardial contractile function (sonomicrometry) and the ECG in the LAD territory. The subendocardial ECG was also recorded from the anterior basal LV territory. Time of regional S wave arrival (TS) and time of onset of segment shortening were determined. The animals underwent atrial pacing with increasing frequencies until systolic LAD territory contractile dysfunction and eventual LV asynchronies were observed. Six animals without LAD stenosis served as controls to define the normal response (mean +/- 2.SD) to increasing pacing rates of systolic shortening and onset time of segment shortening (time difference between TS and onset of segment shortening). LAD contractile dysfunction was considered as a systolic shortening below the normal range, and LV asynchronies as an onset time of segment shortening above the normal range. When LV asynchronies occurred, onset time of segment shortening in the LAD territory was 80.1 +/- 4.9 ms versus 14.8 +/- 3.7 ms at control (P < 0.01); the time difference between S wave arrival in the LAD and circumflex territories, however, was unchanged. LV asynchronies were associated with marked LAD territory contractile dysfunction (systolic shortening of 9.6 +/- 0.8% v 21.0 +/- 1.9% at control, after systolic shortening of 31.3 +/- 3.8% v 9.0 +/- 2.6% at control; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrous oxide causes myocardial ischemia when added to propofol in the compromised canine myocardium.

We sought to determine the influence of nitrous oxide on the compromised heart during propofol anesthesia. This study investigated the cardiovascular effects of the combination propofol and nitrous oxide (N2O). Seven beagles were monitored to measure global and regional left ventricular function. Recordings both before and after critical constriction (CC) of the left anterior descending coronary artery (LAD) were performed after propofol, 300 micrograms.kg-1.min-1, and 10 min after exposure to and discontinuation of 67% N2O. Data were analyzed with ANOVA for repeated measures at 95% confidence level. In the absence of CC, N2O caused moderate, reversible hemodynamic depression (LVdP/dtmax, -13.8%; cardiac output, -17.2%; LAD coronary blood flow, -10.9%) and no regional dysfunction. After CC global hemodynamic depression was of similar magnitude (LVdP/dtmax, -19.9%; cardiac output, -9.2%; stroke volume, -9.2%) but did not recover completely. Systolic shortening in the compromised area decreased (-30.3%) and postsystolic shortening developed to represent 20.3% of total shortening. Despite only moderate hemodynamic depression, 67% N2O causes substantial regional dysfunction in compromised myocardium when added to propofol.

Hemodilution induces stable changes in global cardiovascular and regional myocardial function.

The cardiovascular responses associated with isovolemic hemodilution have been described. However, the stability of these responses over time remains controversial. We hypothesized that the hemodynamic responses to isovolemic hemodilution are stable over time. Nine fentanyl-midazolam-anesthetized dogs were monitored to follow global cardiovascular and regional myocardial function. Isovolemic hemodilution was performed to a moderate (hemoglobin = 7.5 g%) target hemodilutional state that was maintained for 4 h. Data were obtained at each hemodilutional state and each hour during the 4-h period of sustained moderate hemodilution. During acute hemodilution, cardiac output increased from 2.6 +/- 0.5 L/min to 3.0 +/- 0.5 L/min (P < 0.05) and mean coronary flow increased from 20.8 +/- 2.4 mL/min to 31.4 +/- 5.5 mL/min (P < 0.05). Cardiac output and mean coronary flow remained elevated during the extended hemodilutional period. In addition, norepinephrine increased from 586 +/- 152 pg/mL to 1135 +/- 247 pg/mL (P < 0.05) during acute isovolemic hemodilution and remained at this increased level during extended hemodilution. Epinephrine levels did not change with hemodilution. Compensatory mechanisms such as increases in cardiac output and mean coronary flow observed during acute hemodilution persist during extended periods of hemodilution.

Acute isovolemic hemodilution and blood transfusion. Effects on regional function and metabolism in myocardium with compromised coronary blood flow.

The use of isovolemic hemodilution to prevent adverse side effects of homologous blood transfusions has increased. The lowest level of hemoglobin that can be tolerated without regional myocardial dysfunction, however, had not been precisely defined for left ventricular myocardium with compromised coronary blood flow. This level was determined in our study in 19 dogs with critical stenosis of the left anterior descending coronary artery during graded isovolemic hemodilution. Regional function was assessed by sonomicrometry in the territory supplied by the left anterior descending coronary artery, as well as in two noncompromised left ventricular areas; oxygen extraction and consumption in the left anterior descending coronary artery region were assessed by analysis of anterior descending coronary venous oxygen saturation. The median lowest level of hemoglobin tolerated without contractile dysfunction of the territory supplied by the left anterior descending artery was 7.5 gm/dl, with lower and upper quartiles of 6 and 9 gm/dl. In addition to a marked increase in cardiac output and transstenotic left anterior descending flow, global cardiac and regional myocardial functions were unchanged at a hemoglobin level of 7.5 gm/dl, as compared with a control level of hemoglobin of 12.0 +/- 0.4 gm/dl. At a mean level of hemoglobin of 6.0 +/- 0.4 gm/dl, marked contractile dysfunction developed in the left anterior descending region: Systolic shortening decreased from 24.2% +/- 2.1% to 17.9% +/- 1.9% (p < 0.01); postsystolic shortening increased from 4.0% +/- 3.0% to 12.2% +/- 3.8% (p < 0.01); and in the left anterior descending region, oxygen consumption decreased. The increase of arterial level of hemoglobin by only 1.9 +/- 0.2 gm/dl restored contractile function in the left anterior descending region, regional oxygen consumption, and oxygen extraction across the left anterior descending region. Moderate isovolemic hemodilution is relatively well tolerated in left ventricular myocardium with compromised coronary blood flow, and hemodilution regional contractile dysfunction induced by hemodilution is reversible by minimal blood transfusion.

Is post cardiopulmonary bypass dysfunction a special form of stunning?

It has been suggested that cardioplegic arrest during cardiopulmonary bypass (CPB) produces global myocardial ischemia with a risk of myocardial stunning. It has also been postulated that anesthetic technique may affect the course of post-CPB myocardial stunning via exaggerated myocardial depression. However, we have previously found that global ventricular and regional myocardial responses to halothane do not differ in post-CPB and pre-CPB dogs. Our examination of the effects of CPB on the beta-adrenergic function revealed that beta-adrenergic receptor function is only slightly decreased immediately following (i.e., 1 min) and 30 minutes post-CPB. A dose-response relationship was established for dobutamine, with decreased responsiveness noted at both times. Since other data show normal inotropic stimulation of stunned myocardium, decreases in dobutamine responsiveness cannot be explained by beta-receptor desensitization. Overall, these data indicate that CPB does not result in myocardial stunning. The differences between these data and others showing myocardial stunning following CPB may be due to several factors, such as anesthetic regimen, lack of coronary blood flow abnormalities, and a reduction in sarcoplasmic reticular damage due to the hypothermic conditions used.

Is esmolol cardioprotective? Tolerance of pacing tachycardia, acute afterloading and hemodilution in dogs with coronary stenosis.

OBJECTIVES: The aim of this study was to determine whether esmolol, an ultrashort-acting beta-adrenergic antagonist, possesses cardioprotective properties unrelated to a concomitant decrease in heart rate. BACKGROUND: Previous studies have demonstrated beneficial effects of beta-adrenergic blocking agents with unchanged heart rates. METHODS: The effect of esmolol (100 micrograms/kg per min) on the response of global cardiovascular and regional myocardial contractile function (sonomicrometry) to pacing-induced tachycardia and acute left ventricular afterloading was assessed in dogs with a critical stenosis of the left anterior descending coronary artery (LAD). These responses were observed at the baseline hemoglobin level (12.5 +/- 0.3 g/100 ml) as well as after hemodilution-induced mild regional contractile dysfunction (7.4 +/- 0.4 g/100 ml) in the area supplied by this artery (LAD area). Data were analyzed by using a repeated measures multivariate analysis of variance with complete block design treating pacing rate and afterloading, respectively, as the repeated measure. RESULTS: Esmolol decreased the maximal first derivative of left ventricular pressure (dP/dtmax); global cardiovascular and regional myocardial contractile function were otherwise unchanged. Esmolol did not alter the response of global cardiovascular or regional myocardial function to pacing-induced tachycardia or to acute left ventricular afterloading, both at the baseline hemoglobin level as well as during mild hemodilution-induced LAD area contractile dysfunction. CONCLUSIONS: At an infusion rate of 100 micrograms/kg per min we were unable to demonstrate cardioprotective esmolol effects in a canine model of critical coronary stenosis with controlled heart rate and identical loading conditions.