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Biomedical subjects

G Bashein

Publications and source records attributed to G Bashein.

At least 37 records · Page 2Linked to original sources
PubMed1990

A randomized study of carbon dioxide management during hypothermic cardiopulmonary bypass.

Eighty-six patients undergoing coronary artery bypass graft (n = 63) or intracardiac (n = 23) surgery were randomly assigned with respect to the target value for PaCO2 during cardiopulmonary bypass. In 44 patients the target PaCO2 was 40 mmHg, measured at the standard electrode temperature of 37 degrees C, while in 42 patients the target PaCO2 was 40 mmHg, corrected to the patient's rectal temperature (lowest value reached: mean 30.1, SD 1.9 degrees C). Other salient features of bypass management include use of bubble oxygenators without arterial filtration, flows of 1.8-2.4 l.min-1.m-2, mean hematocrit of 23%, and mean arterial blood pressure of approximately 70 mmHg, achieved by infusion of phenylephrine or sodium nitroprusside. Neuropsychologic function was assessed with series of tests administered on the day prior to surgery, just before discharge from the hospital (mean 8.0, SD 5.8 days postoperatively, n = 82), and again 7 months later (mean 220.7, SD 54.4 days postoperatively, n = 75). The scores at 8 days showed wide variability and generalized impairment unrelated to the PaCO2 group or to hypotension during cardiopulmonary bypass. At 7 months no significant difference was observed in neuropsychologic performance between the PaCO2 groups. Regarding cardiac outcome, there were no significant differences between groups in the appearance of new Q-waves on the electrocardiogram, the postoperative creatine kinase-MB fraction, the need for inotropic or intraaortic balloon pump support, or the length of postoperative ventilation or intensive care unit stay. These findings support the hypothesis that CO2 management during cardiopulmonary bypass at moderate hypothermia has no clinically significant effect on either neurobehavioral or cardiac outcome.

Carbon Dioxide↗
PubMed1990

Ventricular volume measurement from a multiplanar transesophageal ultrasonic imaging system: an in vitro study.

We have developed a system to assess the feasibility of using multiple transesophageal ultrasonic images to measure left-ventricular volume, an important variable in patient management. The system includes a special transesophageal probe with a micromanipulator for acquiring cardiac images in multiple planes with known interplanar spatial relationship and an off-line processing system to compute the volume. In vitro studies with the probe demonstrated that the distance between two targets in space can be identified within 2 mm (SD = 0.4 mm) for points in the imaging plane 3.4 mm (SD = 0.5 mm) for points not lying in the imaging plane. This gives an average accuracy of +/- 6.5% for distances greater than 4.5 cm. Comparison of ultrasonic measurements of the volume of water-filled balloons and excised hearts to the volume required to fill them, revealed a correlation coefficient of 0.992, a regression line having a slope of 1.0 and an ordinate intercept at 0.2 mL, and a standard error of the estimate of 8 mL.

Calibration↗
PubMed1989

The quotient of mean arterial pressure and heart rate predicts hypoperfusion of collateral-dependent myocardium.

This study tested the hypothesis that the quotient of mean arterial pressure (MAP) and heart rate (HR) (pressure divided by rate = PRQ) effectively predicts myocardial hypoperfusion in regions of myocardium supplied with blood via collateral vessels. Regression analysis of data gathered in a study of the effects of halothane and atrial pacing on the distribution of myocardial blood flow has discovered a strong relationship between the PRQ and the inner-to-outer flow ratio in the collateral-dependent zone (R = 0.78). A significant relationship was also found between PRQ and the ratio of subendocardial blood flow in the ischemic zone to subendocardial flow in the normally perfused zone (R = 0.61). These ratios demonstrate that hypoperfusion of the inner layers of the collateral-dependent zone occurred during the condition of hypotension combined with tachycardia; while normal flow distribution was present if MAP exceeded HR. Halothane (1% end-tidal) did not alter the distribution of coronary flow, indicating that halothane does not cause a coronary steal in this model. The results of this study support the concept that the PRQ is an effective predictor of myocardial hypoperfusion when flow to ischemic zones is delivered by collateral vessels in nonfailing, canine hearts.

Animals↗
PubMed1989

Measurement of left ventricular ejection fraction and volumes with three-dimensional reconstructed transesophageal ultrasound scans: comparison to radionuclide and thermal dilution measurements.

A transesophageal, ultrasonic cardiac imaging probe was built that incorporated a mechanism for changing the angle of the imaging plane of a conventional phased array in a precise and known manner. This probe was used to acquire an angular spatial sequence of two-dimensional images of the left ventricular cavity over a series of cardiac cycles by sweeping the imaging plane through it stepwise. The endocardial borders of these images were manually outlined off-line and the application of a three-dimensional reconstruction algorithm was then used to compute the left ventricular end-diastolic and end-systolic volumes and ejection fraction. A study was conducted with seven anesthesized dogs to compare ultrasonic determinations by this method with determinations and measurements made using radionuclide and thermal dilution methods. Comparison of 33 ejection fractions, measured by the ultrasonic volume method and by the gated blood pool radionuclide approach, yielded a correlation coefficient of 0.87 and a standard error of the estimate of 5.7% measured over a range of 10% to 58% (average, 40%). Comparison of the ultrasonically measured volumes with those calculated from stroke volume (derived from thermal dilution cardiac output measurement) and ejection fraction (measured by radionuclide technique) produced a correlation coefficient of 0.92 and a standard error of the estimate of 10.3 mL over a range of 18 to 130 mL (average, 56 mL). The accuracy of volume and ejection fraction measurements with this new ultrasonic method seems comparable to that of other currently used clinical approaches such as radionuclide and angiography.

Animals↗
PubMed1989

Evaluation of a blood gas and chemistry monitor for use during surgery.

An observational study was performed to evaluate a new blood gas and chemistry monitor (GEM-6 Diamond Sensor Systems, Ann Arbor, Michigan) in nine patients during cardiac surgery. Paired blood samples were analyzed by the instrument under test and by standard clinical laboratory instruments. The differences between the measurements of the new and the standard instruments are summarized as follows (mean +/- standard deviation, units of measure, number of samples): pH (-0.039 +/- 0.02, 154); PCO2 (2.63 +/- 1.8 mmHg, 154); venous PO2 (-2.0 +/- 3.0 mmHg, 72), hematocrit (4.7 +/- 2.7%, 98), potassium (0.18 +/- 0.13 mmol, 100), and ionized calcium (0.195 +/- 0.11 mmol, 100). Because the differences in arterial PO2 measurements were markedly heteroscedastic, a logarithmic transformation was employed, which upon retransformation gave the test instrument's 95% confidence limits as within 5.1% below to 46% above the nominal value on 82 samples. However, on the 14 samples having nominal values below 165 mmHg (the upper limit of the calibrated range of the GEM-6) the 95% confidence limits were from 5.4% below to 23.6% above the nominal reading. No failures of the test instrument occurred during the evaluation, and quality control standards run before, midway through, and again after sampling from each patient all gave readings within the manufacturer's tolerance. For all variables except hematocrit and ionized calcium, this instrument matches the values from the laboratory well enough over the clinically important range to supplant it for intraoperative monitoring purposes.

Acid-Base Equilibrium↗
PubMed1989

Measurement of stroke volume with three-dimensional transesophageal ultrasonic scanning: comparison with thermodilution measurement.

The accuracy of measuring cardiac stroke volume with a new transesophageal phased array ultrasonic probe was investigated in 10 dogs. The method involved scanning the heart to obtain serial images covering the entire left ventricular cavity at end-expiration. An off-line computer analysis of the images was used to form three-dimensional reconstructions of the left ventricular cavity at end-diastole and end-systole, from which stroke volume was determined. Comparison with stroke volume determined by thermodilution during a wide range of hemodynamic conditions gave the following results for least-squares regression on 57 determinations (with the 95% confidence limits in parentheses): slope 0.95 (0.842-1.06), ordinate intercept 2.1 (2.0-2.2) ml, standard error of the estimate 4.1 ml, and correlation coefficient of 0.92 (0.87-0.95). Histologic examination of sections of esophagus surrounding the tip of the probe in nine dogs demonstrated minimal trauma to the esophageal wall, with eight specimens described as normal and one showing mild inflammation. The authors conclude that three-dimensional reconstruction of the left ventricular cavity from multiple transesophageal images offers a safe and accurate, although presently tedious, method for determining stroke volume.

Animals↗
PubMed1989

Neurobehavioral outcomes in cardiac operations. A prospective controlled study.

To assess the severity and duration of new organic brain dysfunction after cardiac operations, we used an extensive battery of neuropsychologic tests to evaluate 65 patients undergoing coronary artery bypass grafting and 25 patients undergoing intracardiac operations with cardiopulmonary bypass. Patients were tested the day before the operation, before discharge from the hospital, and approximately 7 months later. Compared to 47 nonsurgical control subjects tested at comparable time intervals, surgical subjects showed generalized impairment of neuropsychologic abilities near the time of discharge from the hospital. At follow-up testing, there was no evidence of residual impairment among the surgically treated patients as a whole. In fact, they showed greater improvement compared to initial test scores than did control subjects. However, performance of 10 patients (11%) declined on half of the neuropsychologic variables between preoperative and follow-up testing. Neurobehavioral outcome was not related to the type of operation (coronary bypass versus intracardiac), to factors of cardiopulmonary bypass (duration, aortic occlusion time, hypotension, arterial carbon dioxide tension, minimum hematocrit value, minimum temperature). The only predictor of negative outcome was advanced age. We conclude that, although neurobehavioral impairment is common during hospitalization after cardiac operations, the prognosis for eventual full recovery is favorable, although less so among the elderly.

Anxiety↗
PubMed1988

In vitro assessment of a flow-through fluorometric blood gas monitor.

The Gas-STAT blood gas monitor uses fluorometric techniques to continuously monitor blood gas tensions and acid-base status in the extracorporeal perfusion circuit during cardiac surgery. We evaluated the in vitro performance of this instrument by using a tonometry loop to simulate the clinical environment and to provide controlled gas tensions and pH in the circulating fluid. In this article we report the in vitro study in which 35 Gas-STAT blood gas sensors were used to assess the precision, stability, response time, and specificity of the instrument and to confirm the sterile integrity of its flow-through cells. The blood gas monitor exhibited precision values for pH, carbon dioxide tension (PCO2), and oxygen tension (PO2) of 0.1%, 1.3%, and 1.0%, respectively; stabilities were 0.002 units/h for pH, 0.5 mm Hg/h for PCO2, and 1.4 mm Hg/h for PO2; time constants (tau, a response to within 1/e of a new gas tension, approximately 63%) were 81 seconds for PCO2 and 72 seconds for PO2. No significant interference was detected in in vitro tests of 30 drugs and metabolites typically encountered during cardiac surgery. Bacterial challenge of the flow-through cell membranes showed that they provide an effective barrier isolating the sensors from contaminants in the fluid path. Our quality control consisted of measurement of a midrange gas standard as an unknown immediately following sensor calibration; this simple program is proposed as a complement to the manufacturer's operating procedures.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Gas Analysis↗
PubMed1988

Clinical assessment of a flow-through fluorometric blood gas monitor.

We performed an observational study to evaluate a flow-through fluorometric instrument (Gas-STAT) that continuously measures the carbon dioxide tension (PCO2), oxygen tension (PO2), and pH of blood in the cardiopulmonary bypass circuit. Setup and calibration of the instrument typically required 20 minutes. During bypass, 129 blood samples were drawn from 16 patients for comparison with conventional measurements obtained with a blood gas machine. Data for each variable, within each sensor, were analyzed by linear regression. The ranges of the standard errors of the estimate were 0.7 to 4.2 mm Hg for PCO2, 18.3 to 78.7 mm Hg for the high PO2 range, 1.4 to 7.1 mm Hg for the low PO2 range, and 0.008 to 0.049 for pH. The regression lines differed from the identity line (P less than 0.05) in at least one variable in most patients, and large deviations from the line of identity in both slope and intercept were common. Among 58 sensors evaluated, failures occurred in 5 (2.9%) of the 174 optodes, and minor leakage occurred in 2 (3.4%) of the flow-through cells. We conclude that although this flow-through fluorometric instrument is an adequate monitor of trends in blood gases during cardiopulmonary bypass, it is not accurate enough to supplant conventional laboratory measurements.

Blood Gas Analysis↗
PubMed1987

A data acquisition system for clinical research.

We developed a system for automatic collection and synchronization of multiple physiological variables during clinical investigations. Centered around an eight-track instrumentation tape recorder, the system solves several problems encountered in gathering this type of research data: (1) slowly changing variables are digitized and compressed onto a single track by recording them in one serial message, allowing for recording many more variables than there are tape tracks available; (2) simultaneous analog recording allows retention of original data for variables that may be processed subsequently by multiple schemes; (3) data acquisition is verified with both analog chart recording and numerical video display monitors; (4) off-line computer processing time is decreased at least twofold by using tape playback speeds faster than the recording speed; (5) cost is kept low by using an inexpensive 1/4-inch (0.64-cm) tape medium and dedicated microcomputers; and (6) the system is unobtrusive, portable, and easily reconfigured for different clinical studies. It proved to be reliable in a study of more than 80 patients undergoing cardiac surgery.

Computers↗
PubMed1986

An endoscopic micromanipulator for multiplanar transesophageal imaging.

We have developed an esophageal probe with a precision micromanipulator and a transversely oriented 32 element ultrasonic array which operates at 3.5 MHz. The probe allows us to obtain multiple two-dimensional images of the heart with known angular relationships between them over a series of cardiac cycles. Our ultimate purpose is to acquire images for left ventricular volume estimation with a three-dimensional reconstruction method. Technical details of the probe design are given. In vitro tests have shown that the imaging plane can be angulated within 1.5 degree root mean square error. In vivo results with dogs have demonstrated its ability to obtain multiplanar short axis images of the heart.

Animals↗
PubMed1985

Effect of halothane on coronary collateral circulation.

The authors studied the effect of halothane in a canine model of coronary collateral circulation secondary to chronic occlusion of a coronary artery. Two sets of experiments were performed. In the first experiments, Ameroid constrictors were placed around the left anterior descending coronary artery to produce complete occlusion in three weeks. An inflatable occluder was placed around the circumflex coronary artery in order to apply a mild stenosis to the artery supplying the collateral vessels to produce vasodilation distal to the stenosis. Regional myocardial blood flows were measured using radioactive microspheres. Blood flows to normal and collateralized myocardium were decreased significantly during halothane anesthesia, but perfusion of the subendocardium in both regions was maintained even in the presence of mild stenosis of the circumflex coronary artery supplying the collateral vessels, as indicated by unchanged endocardial/epicardial blood flow ratios. In the second experiments, chronic occlusions of both circumflex and right coronary arteries were produced using Ameroid constrictors. In these animals, sedated using xylazine, pacing-induced tachycardia produced a marked but reversible decrease in blood flow to the collateralized subendocardium. During halothane anesthesia at normal heart rate, blood flow to the collateralized subendocardium was well maintained, but tachycardia produced marked decrease in blood flow to the collateralized subendocardium, leading to the demise of four of seven dogs. The authors conclude that in this chronic canine model, in which control measurements were made during sedation using xylazine, coronary collateral blood flow is well maintained during halothane anesthesia at normal heart rate, but tachycardia during halothane anesthesia severely limits blood flow to the collateralized subendocardium.

Animals↗