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Biomedical subjects

B G Brown

Publications and source records attributed to B G Brown.

At least 109 records · Page 6Linked to original sources
PubMed1983

Effects of verapamil on coronary hemodynamic function and vasomobility relative to its mechanism of antianginal action.

The effect of intravenous verapamil on systemic and coronary hemodynamic function was studied at cardiac catheterization in 12 patients with coronary artery disease. Verapamil was administered as a 2-minute bolus (0.145 mg/kg) followed by an infusion (0.005 mg/kg/min). Cardiac output and coronary sinus blood flow were measured by thermodilution techniques. Caliber of the large coronary arteries and of diseased segments was determined from the coronary angiogram using a computer-assisted method. Verapamil reduced mean arterial pressure 14% (p less than 0.001), systemic vascular resistance 21% (p less than 0.01), and stroke work index 16% (p less than 0.001). Coronary vascular resistance decreased 24% (p less than 0.01) with a small increase in coronary sinus blood flow (+13%, difference not significant [NS]). Myocardial oxygen consumption determined in 5 patients showed no significant change with verapamil. Luminal area in 39 coronary lesions was measured in the "normal" portion of the diseased segment and at its maximal constriction, and an estimate of flow resistance in the stenosis was computed. Overall, 50% of "normal" and of diseased coronary segments dilated significantly with verapamil. Stenosis dilation resulted in an average 14% reduction (p less than 0.01) in estimated flow resistance. In 8 patients, the luminal changes (n = 27) induced by sublingual nitroglycerin were compared with those induced by verapamil. Nitroglycerin induced a significantly greater increase in coronary caliber in both normal and diseased segments; estimated stenosis flow resistance decreased 28% with nitroglycerin compared with 14% with verapamil (p less than 0.01). Thus, verapamil moderately dilates the systemic and coronary small vessel resistance bed without apparently increasing myocardial metabolic demand. Furthermore, verapamil mildly dilates large coronary conductance vessels in both "normal" and diseased segments, although significantly less than does nitroglycerin.

Aged↗
PubMed1983

Postoperative treadmill performance and graft patency after myocardial revascularization.

In a prospective study, a random selection of 122 patients who had coronary artery bypass grafting were studied angiographically and given treadmill tests preoperatively and one year after operation, regardless of their symptoms. A total of 397 grafts were performed (average, 3.3 grafts per patient) on all primary and secondary coronary vessels deemed graftable. Complete coronary revascularization (grafts to vessels 1.5 mm or more in diameter with 50% or greater stenosis) was achieved in 104 patients (85%); 18 patients (15%) were considered incompletely revascularized. One hundred sixteen of the 397 grafts (29%) were to the left anterior descending (LAD) coronary artery, 99 (25%) to the right coronary artery, 126 (32%) to the obtuse marginal branch, 52 (13%) to the diagonal branch of the LAD coronary artery, and 4 (1%) to the septal coronary arteries. Overall results showed that patients with positive postoperative treadmill tests had a graft patency of 64%, compared with 86% for patients with negative treadmill tests (p less than 0.001). Completely revascularized patients with all grafts patent had a 4.8% (3/62) incidence of positive treadmill performance, compared with 60% (6/10) for incompletely revascularized patients with all grafts patent (p less than 0.001). Completely revascularized patients with positive treadmill tests had a graft patency of 58% (45/78), while those with negative treadmill evaluations had a graft patency of 86% (227/264) (p less than 0.001). The patency rate for incompletely revascularized patients with positive treadmill performance was 78% (25/32) and 87% (20/23) for those with negative treadmill performance. This difference was not statistically significant. This study shows that postoperative treadmill performance is highly dependent on completeness of revascularization and graft patency. It therefore supports the prognostic importance of regular treadmill exercise testing to monitor continued graft patency.

Adult↗
PubMed1983

Effect of deprival of rete testis fluid on the morphology of efferent ductules.

One week after unilateral cannulation of the rete testis and ligation of the efferent ductules, samples of the proximal, middle and distal segments of the efferent ductules of 6 goats were examined by light and electron microscopy and compared with normal contralateral efferent ductules. The pseudostratified columnar epithelium consisted of ciliated, nonciliated and basal cells. The number of clear vacuoles decreased markedly in the proximal and middle segments following deprivation of androgen-rich rete testis fluid. The epithelium of the distal segment of the cannulated side had few large clear vacuoles compared to the normal side, which had a high concentration of large vacuoles. Since the large vacuoles decreased in all three segments following ligation, they were thought to be absorptive. Some cells of the distal segment of the cannulated side contained a single, huge, basal vacuole. Electron-dense, membrane-bound granules were abundant in the proximal segment of normal ductules. After cannulation these granules were still present. It was concluded that the electron-dense granules were insensitive to rete testis fluid and that they did not arise from the fluid leaving the rete testis.

Androgens↗
PubMed1983

Variability in the measurement of regional left ventricular wall motion from contrast angiograms.

Four types of variability affecting quantification of regional wall motion from contrast left ventriculograms (LVgrams) were studied. These included beat-to-beat variability in 24 LVgrams, intraobserver and interobserver variability in 20 LVgrams, and study-to-study variability in serial LVgrams of 21 patients with stable coronary artery disease. Motion was measured at 100 equidistant chords perpendicular to a center line drawn midway between the end-diastolic and end-systolic contours and normalized for heart size. Variability was computed as the absolute difference between observations. Beat-to-beat, intraobserver, and interobserver variability at the 100 chords were similar, averaging 14%, 14%, and 17%, respectively, of the mean motion in 64 patients with normal ventriculograms. Study-to-study variability was significantly higher, averaging 30% of mean normal motion, but was reduced when regional motion was calculated as the mean motion of chords within a region of interest. Variability peaked at the apex. Realignment to correct for cardiac rotation significantly increased variability. Investigators whose methods of wall motion analysis rely on identification of the apex as a landmark should be aware of this source of potential variability and error.

Arterial Occlusive Diseases↗
PubMed1983

Dilation of coronary artery stenosis: a major mechanism of the effect of nitrates.

The mechanisms of action of nitroglycerin have been studied extensively; but despite this, there is controversy regarding the manner in which this commonly used drug exerts its dramatic beneficial effect. Angina is usually due to inadequate subendocardial perfusion. Improvement in subendocardial ischemia is achieved not by one single mechanism, but by three contributory phenomena. First, nitroglycerin directly dilates most coronary stenoses, with an average 40% reduction in resistance to flow through severely narrowed arterial segments. Second, the drug decreases left ventricular "afterload" and thus reduces the myocardial oxygen demand by an average of 10%. Third, the drug decreases ventricular diastolic filling pressure (preload) an average of 30%, and thereby improves the distribution of coronary blood to the subendocardial zone.

Coronary Disease↗
PubMed1982

Noninvasive detection and localization of coronary stenoses in patients: comparison of resting dipyridamole and exercise thallium-201 myocardial perfusion imaging.

Two noninvasive tests to detect and localize coronary stenoses were compared in a fully blinded protocol. Thallium201 myocardial perfusion imaging (MPI) following maximal treadmill exercise and pharmacologic coronary vasodilation with intravenous dipyridamole (DP) was performed in 33 patients. Thallium201 imaging defects in six myocardial perfusion regions were correlated with stenoses in their respective vascular distributions. Disease severity was determined with coronary arteriograms using a computer-assisted method. 198 myocardial regions were evaluated; 101 were supplied by at least one major artery with a greater than or equal to 50% stenosis (luminal diameter narrowing). The sensitivity and specificity for detecting a greater than or equal to 50% stenosis were 85% and 64% (p less than 0.005), respectively, for DP and 84% and 68% (p less than 0.005) for exercise-thallium201 imaging. A particular combination of anterior and septal imaging defects was useful in detecting left anterior descending artery stenoses proximal to its first septal branch. DP administration was safe in this group of patients; however, 42% experienced transient chest pain. Although the overall sensitivity and specificity of the two methods were not significantly different, DP-MPI appeared more sensitive than exercise-MPI (70% vs 52%, p less than 0.01) in detecting coronary stenoses in the 40% to 60% range. DP-thallium201 MPI provides a useful alternative test for potential coronary disease patients unable to perform maximal exercise.

Adult↗
PubMed1982

Hemodynamic effect of myocardial revascularization in the impaired ventricle.

The hemodynamic effect of myocardial revascularization with saphenous vein grafts (mean 3.3 per patient) was analyzed 1 year after operation in 111 patients. Operations were performed using one continuous period of aortic cross-clamping with hyperkalemic cardioplegia for distal anastomoses in 84% of patients; 16% had arrest with topical and systemic hypothermia for myocardial protection. Group I (N = 18) had normal ventricles (ejection fraction [EF] greater than 50%; left ventricular end-diastolic pressure [LVEDP] less than or equal to 12 torr); Group II (N = 64) had ischemic ventricles (EF greater than 50%, LVEDP greater than 13 torr); and Group III (N = 30) had abnormal ventricles (EF less than 50%, LVEDP greater than 13 torr). Hemodynamic measurements were obtained before and 1 year after operation. Fifteen of 18 patients (83%) in Group I did not show significant hemodynamic changes, but in three EF decreased by greater than or equal to 10% and LVEDP increased by greater than 10% over preoperative levels. In Group II, EF was unchanged or slightly better in 89% (57/64) and worse in seven patients. Improvement in cardiac index (p less than 0.01) and LVEDP (p less than 0.001) was significant. Worsening of EF in 10 of 82 patients in Groups I and II was attributed to graft closure and/or poor myocardial protection. In Group III, significant improvement in cardiac index (p less than 0.001), EF (p less than 0.001), and LVEDP (p less than 0.01) was also noted. A subset of nine patients with EF less than or equal to 35% showed postoperative improvement in 56%. Of the remaining 20 patients with an EF of greater than 35% to less than 50%, half had greater than or equal to 20% improvement in postoperative EF. Operative mortality was 3.3% (1/30) for Group III. Late mortality was 1.5% (1/64) for Group II and 10% (3/29) for Group III. Significant improvement was noted postoperatively in 67% (57/85) of all patients who had preoperative treadmill tests (p less than 0.001). This study shows that myocardial revascularization significantly improved left ventricular performance in most patients with ischemic and abnormal ventricles. Previous studies that fail to show improvement may be related to incomplete revascularization and/or poor myocardial preservation. These data, therefore, justify the need for revascularization of the impaired ventricle.

Adult↗
PubMed1981

Coronary vasospasm. Observations linking the clinical spectrum of ischemic heart disease to the dynamic pathology of coronary atherosclerosis.

Patients with angina, myocardial infarction, and sudden death almost always have demonstrable coronary atherosclerosis. Furthermore, there is mounting evidence that coronary artery "spasm" is a contributing feature of these different coronary ischemic syndromes. Using quantitative angiography and two modes of alpha-adrenergic stimulation in patients with spontaneous most angina, vasomotor hyperreactivity was shown to be localized only to the region of a preexisting coronary atheroma. These observations support the hypothesis that a dynamic interaction between the histopathologic features of coronary atherosclerosis and "normal" amounts of coronary smooth-muscle shortening accounts for the clinical features in the great majority of cases in the spectrum of ischemic heart disease. There are stenosis, each with different therapeutic implications.

Angina Pectoris↗
PubMed1981

Intravenous dipyridamole combined with isometric handgrip for near maximal acute increase in coronary flow in patients with coronary artery disease.

Twenty-four patients with coronary artery disease were studied during cardiac catheterization to determine the effects of sustained isometric handgrip exercise and intravenous dipyridamole and their combination on coronary and systemic hemodynamics and measured coronary luminal caliber. During 4 to 5 minutes of 25 percent maximal handgrip, blood pressure and heart rate increased 24 and 19 percent, respectively, coronary sinus flow increased to 1.7 x baseline value, and epicardial coronary arteries constricted to increase predicted flow resistance by 40 percent in 36 diseased arterial segments. After a 4 minute intravenous infusion of dipyridamole (0.56 mg/kg body weight), systemic pressure decreased 8 percent, heart rate increased 23 percent, coronary sinus flow increased to 2.4 x baseline value and coronary luminal caliber was unchanged. During isometric handgrip initiated 6 minutes after the infusion of dipyridamole, systemic pressure and heart rate increased to 14 and 31 percent, respectively, above control values, coronary sinus flow increased to 3.3 x baseline value (3.8 x baseline value in patients with normal anterior perfusion) and stenotic flow resistance increased by 36 percent. The response of coronary flow to the combined stresses was 68 percent greater than the response to dipyridamole alone (p less than 0.02); these flow levels exceed values previously reported for the human coronary circulation. Aminophylline plus nitroglycerin appears to assure patient safety.

Acute Disease↗
PubMed1981

The mechanisms of nitroglycerin action: stenosis vasodilatation as a major component of the drug response.

The effect of sublingual or intracoronary nitroglycerin (NTG) on luminal caliber in normal and diseased portions of epicardial coronary arteries was determined in 85 lesions from 57 typical patients with ischemic heart disease. Measurements were made from coronary angiograms, using a computer-assisted method and a carefully blinded protocol for analysis of the pre- and post- NTG angiograms. Luminal area in the "normal" portion of the diseased segment and at its maximum constriction and an estimate of flow resistance in the stenosis were computed. Luminal area increased 1.27 mm2 (p less than 0.001) in the "normal" regions, an average increase of 18% over the control area. Dilation with NTG depended strongly on vessel size; area increased 35% in normal vessels of 1.6-2.3 mm luminal diameter and only 9% in vessels 4.0-5.0 mm in diameter. Lesions were grouped into four levels of severity by percent stenosis. Minimum luminal area increased 0.35 mm2 (p less than 0.01) at the narrowest point in moderate lesions, a 22% area increase, and 0.14 mm2 (p less than 0.001) in severe lesions, a 36% area increase. Stenosis dilation resulted in an average 25% reduction (p less than 0.01) in estimated stenosis flow resistance in moderate lesions and a 38% reduction (p less than 0.001) in severe lesions. A statistically significant resistance reduction of greater than 20% occurred in 15 to 20 severe stenoses; only two of 20 showed no measurable dilation. We reviewed recent literature on hemodynamic responses to NTG and determined that changes of this magnitude are among the largest reported. We conclude that vasodilation of epicardial coronary stenosis is usually a major component of the beneficial response to NTG. We support that conclusion by demonstrating a striking improvement in ischemic left ventricular compliance abnormalities after low-dose intracoronary NTG.

Constriction, Pathologic↗
PubMed1980

Method for intermittent collection of large volumes of lymph by means of an exteriorized visceral lymphatic truck shunt.

A surgical technique involving a cannulation of the visceral lymphatic truck of the calf was developed to improve the intermittent collection of large volumes of lymph. Catheters were inserted in the visceral lymphatic duct and ligated to form an external loop. Large numbers of pure lymphocytes (2 to 5 x 10(9)) were collected from the lymphatic duct in less than 45 minutes. Drainage from the cannula was maintained on the average for 5 to 7 weeks to periods of up to 14 weeks. Visceral trunk cannulation in calves offers several advantages over the previously described thoracic duct-venous shunt techniques for collection of lymph and entry into the lymphatic circulation.

Animals↗
PubMed1980

Clinical approach to determine the contribution of the palmar and palmar metacarpal nerves to the innervation of the equine fetlock joint.

To determine the sensory nerve supply of the metacarpophalangeal joint, lameness was induced in eight horses by injecting the joint with a glycerin suspension of glass micropheres. When the medial and lateral palmar nerves were anesthetized in 4 horses, there was noticeable improvement in the gait, but each horse remained lame. When the medial and lateral palmar metacarpal nerves were also anesthetized, 3 of the 4 horses became sound. To confirm the results of local anesthesia, neurectomies were performed on a second group of four horses. The lameness was alleviated only upon resection of both the palmar nerves and the palmar metacarpal nerves.

Anesthesia, Local↗
PubMed1979

Factors influencing patency of saphenous vein grafts.

To determine factors affecting saphenous vein graft patency, 218 grafts in 66 unselected patients were studied angiographically 1 year after operation. Fourteen variables were extracted from the angiograms, electrocardiograms, and intraoperative flow measurements to assess their predictive value. Preoperative coronary vessel diameter and degree of proximal stenosis measured angiographically correlated significantly with graft patency. Graft patency for vessels greater than 1.5 mm in diameter with greater than 70% stenosis was 93% (98 out of 105). Vessel size at operation and the presence of reactive hyperemia greater than 20 ml per minute also correlated significantly with graft patency. Reactive hyperemia increased significantly as the severity of the vessel stenosis proximal to the graft increased, thus suggesting a mechanism for the improved patency rate of grafts to more stenotic vessels. The patency rate of the end-to-side component of a continuity graft (left anterior descending coronary artery and diagonal or marginal artery in 1 graft) was 100% and of the side-to-side component, 77%. This study shows that the patency rate for saphenous vein grafts compares favorably with the reported patency for internal mammary grafts when critical factors such as vessel size (greater than 1.5 mm) and degree of stenosis (greater than 70%) are considered in bypass selection.

Coronary Angiography↗
PubMed1979

Quantitative coronary angiography: measurement of the "critical" stenosis in patients with unstable angina and single-vessel disease without collaterals.

Quantitative angiographic assessment of proximal coronary artery stenosis was performed in 15 patients with consecutive presentations in two categories defined by clinical and angiographic criteria. Group 1 consisted of 10 patients who had new onset of refractory rest angina and ischemic ST-T changes, but no infarction, single-vessel coronary disease without collateralization, and normal left ventricular (LV) angiograms. Group 2 consisted of five patients who were similar to patients in group 1, but had subendocardial infarction (SEI). Quantitative coronary arteriography, using paired perpendicular angiographic views and digital computation, yielded statistically different lesion dimensions and hemodynamic predictions for the two groups. Minimum stenosis diameters were 0.88 +/- 0.14 (SD) and 0.64 +/- 0.08 mm, respectively, for groups 1 and 2. This corresponded to 72% and 78% diameter reduction and 92% and 95% cross-sectional area reduction for the two groups. These small dimensional differences among lesions in the two groups resulted in large differences in their hemodynamic impact as predicted from classic fluid mechanics theory. We conclude that there are characteristic lesion dimensions for the isolated "critical" stenosis in these selected patients with rest angina. Further small increases in lesions severity result in SEI. Certain practical applications and limitations of these observations are discussed.

Angina Pectoris↗