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Biomedical subjects

T C Gibson

Publications and source records attributed to T C Gibson.

At least 19 recordsLinked to original sources
PubMed1990

Cardiac and skeletal muscle adaptations to training in systemic hypertension and effect of beta blockade (metoprolol or propranolol).

Cardiovascular and peripheral adaptations to an aerobic conditioning program were studied in 30 hypertensive adults taking either placebo, beta 1-selective beta-adrenergic blocker (metoprolol) or beta 1-nonselective beta-adrenergic blocker (propranolol). The placebo group increased aerobic capacity (VO2max) 24% (p less than 0.002), largely explained by an increased peripheral arteriovenous (AV) oxygen difference with minimal changes in cardiac size and function. Resting blood pressure and total systemic resistance also decreased. The group taking a beta 1-selective beta blocker increased VO2max 8% (p less than 0.05), reduced resting blood pressure but had no significant change of AV oxygen difference or cardiac size or function. The group taking the beta 1-nonselective beta blocker propranolol had no increase in VO2max, no decrease in resting blood pressure and no cardiovascular or peripheral adaptations to the exercise program. Thus, beta 1-selective and beta 1-nonselective beta blockers attenuate conditioning in hypertensive patients to differing degrees, in each case by blocking peripheral mechanisms of conditioning.

Adaptation, Physiological↗
PubMed1988

ECG abnormalities during excretory urography: the effect of stress.

ECG alterations occurring during IV infusion of contrast agents have been well documented, although the specific causes of these alterations are unknown. Stress and anxiety have been considered important factors, but no prospective evaluation of their impact on ECG alterations has been reported. In order to separate ECG changes resulting from anxiety associated with the procedure itself from those caused by the contrast agent, ECG monitoring was done during IV urography, first when patients were given saline and then again during and after contrast infusion. In both circumstances, the patients were told that they were being given contrast material. One hundred fifty patients undergoing infusion excretory urography with meglumine diatrizoate were studied. Preliminary 12-lead ECGs identified those with initially normal (71) and abnormal (79) tracings. Lead II rhythm strip ECGs were then obtained at 1 and 3 min during a saline infusion and again during contrast infusion; final 12-lead ECGs were done after the contrast infusion. During contrast infusion, PR prolongation (greater than 0.02 sec) occurred in 44% of patients, a change in heart rate (greater than +/- 10 beats/min) occurred in 26%, and benign arrhythmias (premature atrial and ventricular contractions, less than 5/min) occurred in 9%. Saline alone caused no statistically significant ECG alterations (only a single instance of premature atrial contractions). The hypothesis that stress or anxiety may adversely affect ECG reactivity in IV urography is unproved. Although we do not offer proof that it cannot occur, we found no evidence in a study of 150 patients to confirm that stress is an important factor. Only the contrast agent, not saline, produced measurable ECG changes during urography.

Adult↗
PubMed1987

Vascular access for acute haemodialysis.

Vascular access for acute haemodialysis was required on 29 occasions in 26 children over a six year period. Comparison was made of the forms of vascular access employed, these being the Scribner shunt, the Hickman line, and percutaneous polyvinylchloride cannulae. The Hickman catheter was used to provide vascular access in 17 patients (mean age 8.8 years (range 2.5-16 years) and mean weight 25.5 kg (range 7.7-60 kg)) and allowed adequate haemodialysis to occur. Only one catheter had to be removed because of infection, and no other serious complications were encountered. These results show the superiority of the Hickman catheter as vascular access for acute haemodialysis in children.

Adolescent↗
PubMed1986

The ear lobe crease sign and coronary artery disease in aortic stenosis.

Ear lobe creases have been proposed as useful indirect markers of coronary artery disease. To test such a hypothesis, this physical sign was evaluated in 100 patients with symptomatic aortic stenosis undergoing cardiac catheterization to establish the hemodynamic severity of the obstruction and the degree of coronary artery involvement. This is a disorder where the coexistence of cardiac ischemia may play an important part in diagnosis and management. Criteria were established for the degree of ear lobe involvement with a grading of mild (Grade 1), moderate (Grade 2), and severe (Grade 3). Significant coronary artery disease was defined as narrowing greater than or equal to 50% and a coronary score was established. Sensitivity, specificity, positive and negative predictive values were calculated, using Bayesian analysis for three levels of assumed coronary artery disease prevalence. An ear lobe crease score was correlated with a coronary artery disease score, taking into account the variables of age, sex, and body mass index. No useful statistical correlations were found and it is concluded that this physical sign is of little practical value in this clinical setting.

Adult↗
PubMed1986

A new echocardiographic model for quantifying three-dimensional endocardial surface area.

A new technique for quantitatively mapping the three-dimensional left ventricular endocardial surface was developed, using measurements from standard cross-sectional echocardiographic images. To validate the accuracy of this echocardiographic mapping technique in an animal model, the endocardial areas of 15 excised canine ventricles were calculated using measurements made from echocardiographic studies of the hearts and compared with areas determined with latex casts of the same ventricles. Close correlation (r = 0.87, p less than 0.001) between these two measures of endocardial area provided preliminary confirmation of the accuracy of the maps. To further characterize the mapping algorithm, it was translated into computer format and used to map the surfaces of idealized hemiellipsoids. Areas measured with this mapping technique closely approximated the actual areas of idealized surfaces with a wide spectrum of shapes; maps were particularly accurate for ellipsoids with shapes similar to those of undistorted human ventricles. Also, the accuracies of area calculations were relatively insensitive to deviation from the assumed positions of the echocardiographic short-axis planes. Finally, although the accuracy of the mapping technique improved as data from more transverse planes were added, the procedure proved reliable for estimating surface areas when data from only three planes were used. These studies confirm the accuracy of the echocardiographic mapping technique, and they suggest that the resulting planar plots might be useful as templates for localizing and quantifying the overall extent of abnormal wall motion.

Animals↗
PubMed1986

Unruptured sinus of Valsalva aneurysm with right ventricular outflow obstruction diagnosed by two-dimensional and Doppler echocardiography.

This report presents a case of an unusually large unruptured sinus of Valsalva aneurysm complicated by right ventricular outflow tract obstruction, right coronary artery occlusion and incomplete right bundle branch block. Two-dimensional and Doppler echocardiography were instrumental in preoperative diagnosis and postoperative follow-up.

Aortic Aneurysm↗
PubMed1985

Method for estimating right ventricular volume by planes applicable to cross-sectional echocardiography: correlation with angiographic formulas.

Right ventricular (RV) volumes determined by echocardiography were compared with those measured using established angiographic formulas. RV cast displacement volumes were first correlated with data derived from radiographic images of the casts corresponding to standard angiographic RV views. Four established angiographic formulas (Ferlinz, Boak, Fisher and Thilenius) correlated well with cast volume, with the corrected prism method of Fisher showing a best fit (r = 0.98, y = 1.1 + 0.9 x, standard error of the estimate = 3.6). Cast volumes calculated using our echocardiographic formula were then examined relative to the volumes derived from radiographic images of the RV casts. Volumes calculated using the corrected area-length Thilenius formula correlated best with those obtained using our derived 2-dimensional echocardiographic formula (r = 0.96, y = 4.6 + 1.0 x, standard error of the estimate = 6.8). These data confirm that volume calculated using the suggested optimal echocardiographic formula correlates well with volume obtained using derived angiographic data. Accordingly, confirmation in humans by the use of angiography is a rational step.

Adult↗
PubMed1984

Clinical significance of incomplete tricuspid valve closure seen on two-dimensional echocardiography.

Incomplete closure of the tricuspid valve without apparent cusp disease was noted on two-dimensional echocardiography in 31 patients. This abnormality was defined as a failure of the tricuspid valve leaflet tips to reach the plane of the tricuspid valve anulus by at least 1 cm in the standard apical four chamber view at the point of maximal systolic closure. This resulted in a final systolic leaflet position deeper within the right ventricular cavity than is normally seen. The finding was present in the following diagnostic subgroups: Group A, pulmonary hypertension (11 patients); Group B, rheumatic heart disease (4 patients); Group C, dilated cardiomyopathy (9 patients) and Group D, previous myocardial infarction (7 patients). Right atrial, right ventricular and tricuspid anulus measurements were made and compared with those from a group of 67 normal subjects. The results were as follows: right atrial endsystolic area = 27.2 +/- 8.6 cm2 (normal = 13.4 +/- 2.0); right ventricular end-systolic area = 25.6 +/- 8.7 cm2 (normal = 10.9 +/- 2.9); right ventricular end-diastolic area = 31.5 +/- 9.1 cm2 (normal = 20.1 +/- 4.9) and tricuspid valve anular end-systolic dimension = 4.0 +/- 0.6 cm (normal = 2.2 +/- 0.3). The differences from the normal data were all statistically significant (p less than 0.001). Incomplete closure of the tricuspid valve, although a nonspecific diagnostic finding, is primarily associated with right-sided chamber enlargement. Tricuspid regurgitation may be present. The mechanism could be related to geometric changes in valve apparatus dynamics secondary to right-sided cardiac enlargement and tricuspid valve anular dilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1982

The effect of amyl nitrite on the mitral valve echocardiogram in presumably healthy young adults.

We analyzed the use of amyl nitrite as a provocative factor in the diagnosis of mitral valve prolapse in a population of healthy young adults. Sixty-five men and 11 women underwent continuous M-mode echocardiographic and phonocardiographic monitoring before, during and after the administration of inhaled amyl nitrite. All of the 76 subjects had normal baseline echocardiograms, and all had a satisfactory hemodynamic response to amyl nitrite. Mitral valve prolapse, defined by echocardiography and phonocardiography, was not provoked in any of the subjects. Therefore, we concluded that, although this technique may be difficult, significant false-positive results should not occur if adherence to strict diagnostic criteria takes place.

Adult↗
PubMed1980

Presumptive tricuspid valve malfunction induced by a pacemaker lead: a case report and review of the literature.

A 23-year-old woman developed 3 degrees AV block with syncope. Insertion of a permanent pacemaker lead was followed by the onset of a persistent murmur in late systole preceded by single or multiple clicks. The murmur was best heard at the left sternal edge, grade 3-4/6 with two major frequencies (60-250 Hz), increased with inspiration and on assuming the erect posture. It was considered to be tricuspid in origin and related to interference of the tricuspid valve apparatus by the pacemaker lead resulting in tricuspid regurgitation. No tricuspid valve prolapse or flutter was seen on echocardiography. Withdrawal of the pacemaker lead resulted in immediate disappearance of the new auscultatory findings. Review of the literature suggests that the appearance of such a murmur following pacemaker insertion could be associated with later complications in relation to tricuspid valve dysfunction. It is therefore recommended that, under these circumstances, permanent pacemaker leads should be appropriately repositioned.

Adult↗
PubMed1978

Blood pressure levels in acute myocardial infarction.

Serial blood pressure recordings were taken for 72 hours in 112 patients with acute myocardial infarction and in 96 patients with cardiac ischemia, admitted to hospital no more than 6 hours after the onset of chest pain. During the first hour of admission 66 (31.7%) had a blood pressure recorded 160/100 or greater. By the sixth hour, without specific antihypertensive therapy, this number had fallen to 13 (6.3%). This fall was subsequently maintained with very similar trends for both acute myocardial infarction and cardiac ischemia. Such an early blood pressure fall in acute myocardial infarction may indicate that this is too labile a measurement to determine the need for, or efficacy of, antihypertensive therapy aimed at the preservation of myocardium. The hospital course and mortality rate of patients with acute myocardial infarction and early hypertension, as defined, did not differ significantly from the non-hypertensive group.

Acute Disease↗