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Biomedical subjects

R W Brower

Publications and source records attributed to R W Brower.

At least 55 records · Page 3Linked to original sources
PubMed1982

Do coronary collaterals influence the outcome of bypass graft surgery?

The importance of coronary collateralization on the outcome of bypass grafting was evaluated in patients recatheterized one year after surgery. Because the severity of coronary artery disease correlated with the extent of collateralization, and ventricular function with previous myocardial infarction, we performed a matched pair study where differences in these variables were eliminated between pairs which differed only with respect to the extent of collateralization visualized during angiography. From a data bank of 814 operated patients, 143 matched pairs were formed. In the matched pair series of patients collaterals appear to provide some degree of additional blood flow to ischemic areas to allay resting symptoms before surgery, but collaterals are inadequate to meet the additional requirements of pacing-induced stress. The 2 groups were indistinguishable one year after bypass surgery. As the non-collateralized group was more symptomatic before surgery, it demonstrated greater subjective benefit from the procedure, however, this would be obscured in a consecutive series where collateralization generally correlates with severity of coronary artery disease.

Adult↗
PubMed1982

Coronary artery bypass surgery; a stimulus to modify existing risk factors?

Coronary arterial atherosclerosis is known to be associated with the risk factors of a positive family history, smoking, systemic hypertension, diabetes mellitus, and elevated serum cholesterol levels. Modification of these risk factors, where possible, is prudent. The risk factor data of 226 (212 men, 14 women) subjects who underwent coronary artery bypass surgery for symptomatic obstructive coronary artery disease are presented. Prior to surgery, an attempt was made to educate the subjects in regard to the risk factors and they were urged to modify these factors. All underwent repeat evaluation one year after operation. Although over half of the subjects had had a prior myocardial infarction and all had had aortocoronary bypass surgery, strong stimuli to modify risk factors, there was little modification of the risk factors of smoking and serum cholesterol. There was some modification of the hypertension risk factor. This study documents the need for a very early approach in life to prevent acquiring risk factors and the need for more research into better methods of behavior modification in the adult population.

Adult↗
PubMed1981

Nifedipine in the treatment of unstable angina, coronary spasm and myocardial ischemia.

The effects of nifedipine, a potent calcium antagonist, were studied in patients with unstable angina, coronary spasm and myocardial ischemia. Data from two separate groups of patients studied in the cardiac catheterization laboratory indicate that intracoronary injection of nifedipine promptly reversed coronary spasm--whether provoked or spontaneous--in five of six patients. In other patients, direct intracoronary injection of the drug was compared with intravenous administration. After intracoronary injection, local mechanical cardiac action virtually ceased, and the ventricular wall became thinner during systole. Thus, a specific inhibitory action on contractile energy expenditure could be demonstrated in the presence of increased coronary flow. This "oxygen-sparing" effect was tested in a group of 31 patients with symptomatic unstable angina whose pain at rest, with ST-T changes, had not responded to 8 hours of treatment with maximal beta adrenergic blockade, nitrates and bed rest. The addition of 6 X 10 mg of nifedipine rendered 27 of these patients asymptomatic within 1.5 hours. In the four patients who did not respond, coronary arteriography demonstrated severely stenotic lesions. Two of the four patients subsequently responded to intraaortic balloon pumping and bypass surgery; one patient had a myocardial infarction and one who had a 90 percent reduction in the diameter of the left main coronary artery, died. It is concluded that nifedipine should be added to beta adrenergic blockade therapy if the latter does not appear to be immediately effective. This combination has not been shown to cause any hemodynamic deterioration, and only a minority of the patients treated sustained a myocardial infarction during the first 3 months of follow-up. The use of nifedipine in unstable angina deserves further clinical evaluation.

Adult↗
PubMed1981

Sequential versus conventional coronary artery bypass graft surgery in matched patient groups.

The relative merits of sequential bypass grafting were compared to those of conventional bypass grafting in 247 patients undergoing uncomplicated coronary artery bypass graft surgery. The duration of both ischemic arrest and cardiopulmonary bypass could be predicted on the basis of the number of end-to-side and side-to-side anastomoses. Multivariate regression showed that sequential grafting can be executed more quickly than conventional grafting because: 1. the suture time for side-to-side anastomoses is less than that for end-to-side (5 vs. 12 min) and, 2. fewer aortic anastomoses are required. The rate of perioperative myocardial infarction was similar in both groups. In 109 patients recatheterized at one year, both groups improved equally in functional class, there was no significant difference in mortality, and graft patency was similar in both groups. The principal advantage of sequential grafting therefore is a shorter duration of ischemic arrest and cardiopulmonary bypass, while graft patency and the overall benefit of surgery remains the same.

Adult↗
PubMed1980

Evaluation of pattern recognition rules for the apex of the heart.

The observer variability and accuracy of rules for the automatic recognition of the left ventricular (LV) apex are reported. To form a data base for examining this problem 18 co-workers were asked to independently identify the apex of 79 left ventriculograms (LVgrams) in the 30-degree right anterior oblique projection at end-disastole (ED) and end-systole (ES), and to assign a confidence score from 0% to 100% for each apex. The group consisted of five clinical cardiologists (G1), six trained analysts (G2), and seven other experienced observers (G3). The LVgrams were selected to include those from 31 normal individuals and those from 48 patients with mixed akinesis/dykinesis as coded by conventional scoring techniques. There was no significant difference in the confidence for the ED vs ES apices. However, confidence of G1 was significantly lower than that of G2. The standard deviation in the observer-detected apex correlated (r = -0.92) with the mean observer confidence, which suggests a basis for quantifying "confidence" in the automated apex detection. The apex determined with respect to the superior aspect of the aortic valve proved superior to all other tested methods. the concept of "peakedness index" is introduced and used to estimate observer variability.

Adult↗
PubMed1980

Interaction of left ventricular relaxation and filling during early diastole in human subjects.

Seventeen patients with coronary artery disease were studied with cineangiography and simultaneous tip manometry at resting heart rate and maximal tachycardia induced by atrial pacing. During early diastole, defined as the interval from the opening of the mitral valve to the point of minimal left ventricular pressure, 20 percent of total ventricular filling took place at resting heart rate, but 62 percent occurred during tachycardia. Minimal pressure was significantly correlated with the time constant of pressure decay during the isovolumic phase (r = 0.75 at resting heart rate and r = 0.81 during tachycardia). The measured minimal pressure could be predictd by extrapolating the exponential decay of ventricular isovolumic pressure to the time of occurence of the minimal pressure, which occurred on average 2.7 time constants from the peak negative rate of change of pressure. At resting heart rate the time constant of relaxation was inversely correlated with ventricular inflow volume (r = -0.64) and inflow rate (r = -0.72). It is concluded that left ventricular relaxatin has a relevant role in early diastolic pressure-volume relations and increases during tachycardia.

Adult↗
PubMed1980

Recovery from circulatory depression after coronary artery bypass surgery.

The direct traumatic effects of coronary artery bypass surgery may counter-balance the expected improvement of myocardial function in the early postoperative period. In 55 patients, the regional shortening fraction was measured over 12 months using radiopaque epicardial markers pairs implanted during surgery in the newly perfused regions. The time course of cardiothoracic ratio, heart rate and cuff blood pressure was documented. All patients were catheterized before surgery and 1 year afterwards. There is an initial depression in myocardial function lasting up to 3 months after surgery which is not directionally related to changes in loading conditions or chronotropic state, but most likely to recovery of the myocardium from perioperative injury. At 1 year after surgery the overall ventricular function is unchanged. The evaluation of ventricular function after coronary artery bypass grafting should be performed no sooner than 3 months after surgery to avoid this transient period of depressed myocardial performance.

Adult↗
PubMed1979

Left ventricular function and compliance in swine during halothane anesthesia.

Halothane (0.05--1.7 vol per cent end-tidal) in nitrous oxide (N2O), 60 per cent: oxygen (O2), 40 per cent was administered to nonmedicated, closed-chest pigs. Ventricular function was analyzed from cardiac output (thermodilution) and left ventricular (LV) pressure indices. Ventricular volumes and compliance were estimated from single and biplane LV angiography. In separate experiments, the effects of N2O, time, and the angiographic dye injections were shown to be minimal. Halothane caused dose-dependent decreases in aortic blood pressure, cardiac output, peak first derivative of left ventricular pressure (LV dP/dt), the in-vivo maximum velocity of fiber shortening (Vmax), and ejection fraction; non-dose-dependent decreases in heart rate and circumferential fiber shortening rate. Although a pronounced dose-related negative inotropic effect of halothane in the pig heart was demonstrated, there was no definite effect on ventricular pressure-volume relationships (compliance). If there was any such effect of halothane, it was obscured by the cardiac depression produced.

Animals↗
PubMed1979

[Regional myocardial shortening and blood flow through the graft after aorto-coronary bypass surgery].

In 56 patients operated on for coronary artery bypass grafting the relation between regional epicardial shortening, bypass flow, reactive hyperemia, and time postoperative was determined. Regional shortening in the newly perfused region was measured by a new technique employing four to six radiopaque markers sutured in pairs to the epicardium juxtaposed by 2 cm, and from 0 to 3 cm distal to the coronary anastomosis. Marker pairs were filmed sequentially at each follow up. Excluding dyskinesia, shortening fraction (ratio of shortening to maximum marker separation) for all graft regions at 1 week was 9.8 p. 100, 1 month 12.8 p. 100, 3 months 13.3 p. 100, and 6 months 13.9 p. 100. Average graft flow was 56 ml/mn and average reactive hyperemia was 25 p. 100 with 37 p. 100 of grafts having no response. There was a positive correlation between shortening fraction and flow, becoming significant (null hypothesis: r = 0) when reactive hyperemia exceeded 20 p. 100. Correlation was greatest at 1 week and 1 month, but became non-significant at 6 months implicating other factors such as new collateral development, bypass closure, new infarction, or altered medical therapy. It appears that bypass flow and reactive hyperemia do have a certain predictive value as to regional shortening up to 1 to 3 months postoperative.

Adult↗
PubMed1979

Regional myocardial shortening in relation to graft-reactive hyperemia and flow after coronary bypass surgery.

Extent of regional shortening of myocardium in areas newly perfused by bypass grafting was determined in 56 patients by a new technique employing four to six radiopaque markers sutured in pairs to the epicardium near the coronary anastomosis. Paradoxical systolic expansion (PSE) was manifest in 16 regions (a 12% incidence) during the follow-up period, and six of these showed spontaneous remission. All cases of PSE were in the region of the left anterior descending artery. Correlation between graft flow measured during operation and regional shortening during the postoperative period revealed that the development of PSE could not be predicted from the hemodynamic measurements. In the majority of cases postoperative myocardial infarction could also be excluded as an explanation. At 1 year after operation most grafts were patent in PSE regions but collaterals, apparent preoperatively, could not be visualized. Excluding PSE, shortening fraction (ratio of shortening to maximum marker separation) for all graft regions at 1 week was 9.8%; 1 month, 12.8%; 3 months, 13.3%; and six months, 13.9%. Average graft flow was 56 ml. per minute and average reactive hyperemia was 25% with 37% of grafts showing no response. For those regions that did not develop PSE there was a positive correlation between shortening fraction and flow that became significant (null hypothesis: r = 0) when reactive hyperemia exceeded 20%. Correlation was greatest at 1 week and 1 month, but became nonsignificant at 6 months. These results are consistent with a simple interpretation of reactive hyperemia: Graft-reactive hyperemia is related to the dependence of viable tissue on the functioning of the graft.

Adult↗
PubMed1978

Direct method for determining regional myocardial shortening after bypass surgery from radiopaque markers in man.

A new method is described for determining localized epicardial shortening in regions newly perfused after saphenous vein bypass grafting. Four to six radiopaque markers are sutured to the ventricular epicardium in pairs, 2 cm apart and 0 to 3 cm distal to the coronary anastomosis. Shortening fraction and time to onset of shortening are reported in 56 patients examined noninvasively with use of cinefluorography 1 week to 6 months after operation. The right coronary bypass region showed the greatest improvement in shortening fraction in 6 months (from 10.1 to 16.7 percent); the left anterior descending region showed the least (but still significant) improvement (from 8.6 to 11.5 percent). Paradoxical systolic expansion occurred predominantly in the region of the left anterior descending coronary bypass (95 percent of all such occurrences). Measurement error, observer variability and beat to beat variability were less important than the physiologic changes in the postoperative period. This technique is a direct method providing heretofore unavailable follow-up information on localized shortening in newly perfused myocardium after coronary bypass grafting.

Adult↗