Search PubMed⌕ Search

Biomedical subjects

D G Gibson

Publications and source records attributed to D G Gibson.

At least 127 records · Page 7Linked to original sources
PubMed1989

Effect of temperature on rate of left ventricular pressure fall in humans.

The time constant (T) of left ventricular pressure fall is widely used as an index of ventricular "relaxation". It is not known whether its rate limiting step is deactivation, an enzymic energy consuming reaction whose rate is therefore sensitive to temperature, or elastic recoil. To distinguish between these possibilities, the time constant was measured by simple logarithmic (Tlog) and exponential (Texp) methods in 12 patients during cooling before coronary artery grafting. Ventricular loading conditions were altered by transfusion from bypass to maintain arterial and left atrial pressures constant in individual patients, though heart rate fell from 86 (8.4) to 68 (10) beats/min. Tlog increased from 49 (10) ms mean (SD), at 37 degrees C to 86 (15) ms at 31 degrees C, and Texp from 63(14) at 37 degrees C to 112 (23) ms at 31 degrees C with intermediate values at 34 degrees C. Texp proved sensitive to "noise" at low temperatures, but the overall change in Tlog with temperature was 9% per degree C--considerably less than that observed experimentally for the rate of tension decline of isolated myocardium, and possibly itself an overestimate because of the concomitant fall in heart rate. The relatively small effect of temperature on Tlog in humans, associated with a considerable load sensitivity appearing under hypothermic conditions, does not favour simple dependence on deactivation as the rate limiting step of left ventricular pressure fall, but suggests that its determinants may be complex.

Adult↗
PubMed1989

Impairment of diastolic function by shortened filling period in severe left ventricular disease.

A dilated left ventricle with reduced ejection fraction is usually attributed to impaired systolic function. To investigate the possibility that ventricular filling might also be disturbed, M mode echocardiograms, phonocardiograms, and Doppler cardiograms were recorded in 30 patients with ventricular disease of varying cause. All but four had functional mitral regurgitation. The size of the left ventricular cavity was increased in all and peak velocity of circumferential fibre shortening was reduced. Diastolic abnormalities included a short isovolumic relaxation time, and, on digitised M mode, a reduced rate of dimension increase and of posterior wall thinning. Although the timing of aortic valve closure was normal, mitral regurgitation persisted beyond it by 95 (35) ms and beyond mitral valve opening by 60 (40) ms. This reduced the effective filling time (the interval when the mitral valve was open and mitral regurgitation was absent) to less than 200 ms in seven patients. The effective filling time correlated closely with the RR interval, the regression equation indicating a reduction of 80 ms for each 100 ms fall in RR interval. It was also independently shortened by 2 ms a year with increasing age. The effective left ventricular filling time may thus be very short in patients with left ventricular cavity dilatation and functional mitral regurgitation. It is suggested that when diastolic function is also abnormal, this short filling time may physically limit ventricular inflow. Its close relation to heart rate might contribute to the therapeutic effect of beta blockade in such patients.

Adolescent↗
PubMed1989

Quantitative effects of speckle reduction on cross sectional echocardiographic images.

Speckle is prominent on all cross sectional echocardiograms. In order to assess its effects on image quantification, frames from a sector scanner with a six bit grey scale were stored and processed off line to identify and smooth the speckle by means of an adaptive filter based on fully developed speckle. In 14 controls, 12 patients with hypertrophic cardiomyopathy, and 12 with secondary left ventricular hypertrophy, filtering significantly reduced the standard deviation of echo intensity, which was used as a measure of the scatter of pixel amplitude, in all three groups (by 52%, 46%, and 46% respectively). The mean value of back-scattered echo intensity itself, however, was reduced by only 7%, 5%, and 8% respectively, and median values were not affected at all. Mean (SD) left ventricular cavity areas on the apical four chamber view were significantly increased from 26 (15) to 30 (17) cm2. The valve dimensions in the parasternal minor axis in 10 patients with mitral stenosis were significantly increased by 11% laterally, but were unaffected anteroposteriorly. Subjective image quality was appreciably modified: endocardial boundaries in apical views were enhanced and the septal "ground glass" appearance was lost in hypertrophic cardiomyopathy. Speckle reduction therefore greatly reduced the scatter of pixel values, with little effect on the mean regional back scattered echo amplitude. It also modified the perceived image texture. Improved boundary definition consistently increased the area estimates, particularly when these depended on lateral rather than range resolution.

Cardiomegaly↗
PubMed1989

Right ventricular function 10 years after the Mustard operation for transposition of the great arteries: analysis of size, shape, and wall motion.

Biplane right ventriculograms were obtained in 18 symptom free patients 109 (26) months (mean (SD)) after Mustard repair of transposition of the great arteries. Ventricular size, shape, and wall motion were measured from the digitised angiograms and compared with previously published data on left ventricular function after anatomical correction of transposition of the great arteries, with right ventricular function in controls, and with patients before repair of tetralogy of Fallot. Global indices of ventricular function were depressed after Mustard repair and wall motion abnormalities were common. The presence of wall motion abnormalities in this group was associated with a reduction in ejection fraction and ventricular filling rates. In four of five patients in whom an appropriate preoperative angiogram was available a similar pattern of wall motion was seen before the Mustard operation, suggesting that preoperative events may be important in determining eventual outcome.

Child↗
PubMed1989

Cardiac involvement in Churg-Strauss syndrome shown by echocardiography.

To define the range of cardiac involvement in the Churg-Strauss syndrome, M mode, continuous wave Doppler, and cross sectional echocardiograms were recorded in twelve patients with the disorder. The M mode recordings were digitised and the cross sectional images were recorded with standardised gain settings to determine regional myocardial echo amplitude. Left ventricular end diastolic and end systolic dimensions were increased above the normal 95% confidence interval in four patients, three of whom showed a depressed shortening fraction. Mitral regurgitation was present in six patients; this was severe enough to need valve replacement in two. Mean echo amplitude in both the septum and the posterior wall was significantly increased above normal by a mean (SD) of 4.87 (2.57) dB, suggesting the presence of myocardial fibrosis. There was no evidence of subendocardial involvement as there is in other hypereosinophilic syndromes. Mitral regurgitation is common in the Churg-Strauss syndrome. This cannot be ascribed to involvement of the cusps or chordae and it occurs even when ventricular function is well preserved. It is suggested that mitral regurgitation is caused by diffuse myocardial fibrosis.

Churg-Strauss Syndrome↗
PubMed1988

Controlled clinical trial of complete open surgical drainage and of prednisolone in treatment of tuberculous pericardial effusion in Transkei.

240 patients with active tuberculous pericardial effusion received a 4-drug daily antituberculosis regimen for 6 months and have been studied for 24 months or longer. Those willing were randomly allocated to open pericardial biopsy and complete drainage of pericardial fluid on admission or percutaneous pericardiocentesis as required. All patients were randomly allocated to prednisolone or matching placebo for the first 11 weeks, on a double-blind basis. Complete open drainage on admission abolished the need for pericardiocentesis (p less than 0.01) but did not influence the need for pericardiectomy for subsequent constriction or the risk of death. Among patients who did not have open drainage on admission, 2 (3%) of 76 given prednisolone compared with 10 (14%) of 74 given placebo died of pericarditis (p less than 0.05), 6 (8%) and 9 (12%) respectively required pericardiectomy, 7 (9%) and 17 (23%) repeat pericardiocentesis (p less than 0.05), and 3 (4%) and 7 (9%) open surgical drainage. By 24 months, apart from the 16 who died from pericarditis, all but 3 patients (2%) had a favourable status.

Adolescent↗
PubMed1988

What stops the flow of blood from the heart?

The determinants of aortic pressure and flow are generally studied using impedance methods, the results of which indicate that reflected waves are important, particularly during aortic flow deceleration. An alternative analysis of measured aortic pressure and velocity, using the method of characteristics to calculate the energy flux per unit area of the waves, suggests a different conclusion. We suggest that aortic deceleration is caused by a discrete expansion wave propagating from the left ventricle, and that energy thus recovered by the ventricle may be coupled to early filling of the ventricle.

Aorta, Thoracic↗
PubMed1988

Diagnostic and therapeutic problems in two patients with antiphospholipid antibodies, heart valve lesions, and transient ischaemic attacks.

Two young women (aged 32 and 25 years) with systemic lupus erythematosus and heart valve lesions in association with antiphospholipid antibodies are presented. In addition to the presence of the 'lupus anticoagulant' and false positive Venereal Disease Research Laboratory (VDRL) tests, both patients had high levels of IgG anticardiolipin antibodies. The first patient additionally had contraceptive induced chorea, chorea gravidarum, seven miscarriages, livedo reticularis, pulmonary embolism, and thrombocytopenia and developed culture negative endocarditis as well as hypertension. The second patient, who had presented with hypertension, developed aortic and mitral regurgitation, suspected myocarditis, manifested transient ischaemic attacks, and responded well to anticoagulation and steroid treatment.

Adult↗
PubMed1988

Correction of left ventricular asynchrony by coronary artery surgery.

To investigate the effect of coronary artery bypass grafting on the timing of regional left ventricular wall motion, contrast left ventriculograms from 27 patients were digitised frame by frame before and after operation. End diastolic and end systolic volumes, ejection fraction, and peak ejection and filling rates showed no significant change. The commonest preoperative abnormality was delayed onset of inward wall motion during ejection, which was present in 14 patients over 10% (range 5-40%) of the cavity outline, leading to a pattern of "diagonal contours". After operation this pattern had resolved completely in 12 patients and partially in two. Minor abnormalities appeared postoperatively in five but overall the mean (1SD) area affected was reduced by 5 (8)%. The time span between the onset of inward motion in different regions of the cavity also fell significantly after surgery from 190 (50) to 130 (50) ms. Regional hypokinesis (6 cases) and abnormal wall motion during isovolumic contraction (4 cases) or isovolumic relaxation (5 cases) were not consistently affected. Thus successful coronary artery surgery is without consistent effect on overall left ventricular function, overall hypokinesis, or abnormal wall motion during the isovolumic periods. It does, however, strikingly reduce the asynchrony of wall motion during ejection, suggesting that before operation this abnormality may directly reflect impaired coronary blood flow. The results emphasise the potential value of analysing regional wall motion to elucidate functional abnormalities associated with coronary artery disease.

Adult↗
PubMed1988

Regional left ventricular wall motion in pacing induced angina.

Left ventricular cineangiograms (30 degrees right anterior oblique projection) and high fidelity left ventricular pressure were recorded at rest in 10 individuals with normal hearts and at rest and during an episode of angina provoked by rapid atrial pacing in 14 patients with obstructive coronary artery disease. Angiograms were digitised frame by frame. The ventricular perimeter was divided into 40 segments and regional ventricular function was examined by means of isometric and contour plots and by the construction of segmental pressure-wall displacement loops. In 10 patients 12 abnormal resting regions were identified. The commonest (11 regions) was delayed onset of inward endocardial motion during systole which was manifest by diagonal contour lines on the contour plot. Six regions (five with associated delay in onset of inward motion) showed resting hypokinesis. Angina was associated with the development of 19 new regions of abnormal wall motion in 12 patients. Fourteen of these regions of abnormality were thought to be primary events occurring as a consequence of ischaemia and five to be secondary events occurring in normally perfused regions of myocardium. Hypokinesis occurred in 12 regions, developing in a region with normal amplitude at rest in seven and as an extension of resting hypokinesis in five. In 10 out of 12 cases the region of hypokinesis developed in a region showing diagonal contour lines at rest. Asynchrony with delay in the timing of peak inward displacement relative to minimum volume occurred with angina in eight regions (in six cases concomitant with hypokinesis and in two cases in isolation). In contrast with hypokinesis the pattern of wall motion at rest did not permit regions developing asynchrony with angina to be identified. Pressure-displacement loops show that regional hypokinesis is associated with reduced segmental work and that regional asynchrony (delayed or premature timing of peak inward endocardial displacement) is associated with a loss of efficiency of energy transfer between the myocardium and the circulation. These observations illustrate the complex nature of wall motion abnormalities occurring with angina.

Adult↗
PubMed1988

Patterns of diastolic dysfunction in left ventricular hypertrophy.

The relative sensitivities of and interrelations between different measurements of diastolic function were studied in 50 patients with left ventricular hypertrophy diagnosed on anatomical grounds. Isovolumic relaxation time, the interval from minimum cavity dimension to mitral valve opening and relative dimension increase during this period, and the peak rate of dimension increase and wall thinning during rapid ventricular filling were measured by digitised M mode echocardiography. The relative heights of peak early diastolic and atrial velocities (a/E) and the time for decline of early diastolic velocity to half its peak value (velocity half time) were measured on continuous wave and pulsed Doppler and the relative height of the "a" wave was measured by apexcardiogram. All sets of values except those of the interval from minimum dimension to mitral opening were unimodally distributed, and all differed significantly from those in 20 age matched controls. The relative height of the "a" wave on the apexcardiogram (90% values were abnormal) was the most sensitive method of studying left ventricular diastolic function and peak rate of dimension increase was the least sensitive. Though none of the correlations was high, there were individual associations between peak rate of dimension increase, a/E, peak wall thinning rate, and velocity half time, and independently between delay in mitral valve opening and dimension change during this period. Other values seemed to be independent of one another, suggesting a different physiological basis. It is concluded that these various abnormal values do not reflect a single underlying disturbance of diastolic function. There are at least four possible discrete abnormalities: prolongation of isovolumic relaxation; incoordination during isovolumic relaxation; reduced rate of rapid filling; and an increase in the relative amplitude of the "a" wave probably caused by increased passive stiffness. These may be present singly or in combination in any patient.

Adolescent↗
PubMed1988

Angina pectoris treated by ventricular plication.

Objective analysis of the left ventricular angiogram in a patient with angina but normal coronary arteries showed an appreciable disturbance of regional wall movement. Because of persistent symptoms refractory to medical treatment left ventricular plication was undertaken. This resulted in a return to normal of a series of disturbances of left ventricular wall motion commonly found in patients with obstructive coronary disease, and a striking improvement in the patient's symptoms. The patient remains symptom free five years after operation.

Angina Pectoris↗
PubMed1988

Assessment of the severity of mitral regurgitation from the dynamics of retrograde flow.

Sixty four consecutive patients with isolated mitral regurgitation referred for Doppler echocardiography were divided into three groups: group 1, 20 patients with severe mitral regurgitation that required operation; group 2, 22 patients with severe left ventricular dysfunction and secondary mitral regurgitation; and group 3, 22 patients with mild to moderate mitral regurgitation that did not require valve operation. M mode and continuous wave Doppler traces with a simultaneous electrocardiogram and phonocardiogram were analysed to identify time intervals that could be used to distinguish patients who needed valve operation from those who did not. An interval of less than 55 ms between the aortic component of the second heart sound (A2) and the cessation of mitral retrograde flow was a powerful predictor that the patient required operation (sensitivity 100% and specificity 86%). The mean (SD) value of this variable in group 1 (40(15) ms) was significantly lower than in group 2 (90(35)ms) and group 3 (75(20)ms). Mean isovolumic relaxation time was less than normal in group 1 but did not differ significantly between groups. Deceleration of regurgitant velocity at end ejection was greater in group 1. The pressure drop from the left ventricle to the left atrium at A2 of less than 50% of the peak gradient also identified patients who needed valve operation (sensitivity 75% and specificity 68%). These findings may help to identify patients who require operation. They suggest that there are significant differences in the dynamics of flow velocities in patients with mitral regurgitation, possibly related to the relative resistances to retrograde and anterograde and anterograde flow.

Angiography↗
PubMed1987

Controlled trial of prednisolone as adjuvant in treatment of tuberculous constrictive pericarditis in Transkei.

In Transkei, 143 patients with active tuberculous constrictive pericarditis without significant pericardial effusion all received the same daily 6-month antituberculosis regimen of streptomycin, isoniazid, rifampicin, and pyrazinamide for 14 weeks followed by isoniazid and rifampicin. They were randomly allocated to receive in addition either prednisolone or placebo for the first 11 weeks; the comparison was double-blind throughout treatment and follow-up. In the 114 patients assessable up to 24 months, improvement was significantly more rapid in the prednisolone group, as shown by the rate of fall in the mean pulse rate and the rate at which jugular venous pressure and level of physical activity became normal. During follow-up, 2 (4%) of the 53 prednisolone and 7 (11%) of the 61 placebo patients died from pericarditis, and 11 (21%) and 18 (30%), respectively, required pericardiectomy. By 24 months 50 (94%) prednisolone and 52 (85%) placebo patients had a favourable status. 3 patients (1 prednisolone, 2 placebo) were normally active but were classified as not having achieved a favourable status. It is recommended that, in the absence of a specific contraindication, antituberculosis chemotherapy should be initially supplemented by steroids.

Adolescent↗
PubMed1987

The myocardium in ankylosing spondylitis. A clinical, echocardiographic, and histopathological study.

Cardiac function was investigated in men with ankylosing spondylitis (AS) age 21-65 years who had no cardiorespiratory symptoms or known abnormalities of heart or lungs. Chest radiographs and standard electrocardiograms were normal in 73 of 74 subjects. In echocardiographs of 30 men, left atrial size and left ventricular cavity size and wall thickness were normal. Minor abnormalities in the valve roots were present in 3 older men. Early diastolic abnormalities of the left ventricle were demonstrated in 16 of 30 subjects. This finding was confirmed by repetition of the echocardiography a year later in 15 subjects and by comparison of 11 probands with their healthy brothers. Myocardial tissue obtained at necropsy from 28 AS patients without ischaemic or valvular heart disease or hypertension was studied. A mild, diffuse increase of interstitial connective tissue was seen but there was no inflammatory change or amyloid. Computerised image analysis showed 30.7% interstitial reticulin compared with 17.7% in age/sex matched controls (p less than 0.0001).

Adult↗
PubMed1986

Computer assisted echocardiographic assessment of left ventricular function before and after anatomical correction of transposition of the great arteries.

Left ventricular function before and after anatomical correction of transposition of the great arteries was assessed by computer assisted analysis of 78 echocardiographs from 27 patients obtained one year before to five years after operation. Sixteen patients had simple transposition, and 11 had complex transposition with additional large ventricular septal defect. Immediately after correction mean shortening fraction fell from 46(9)% to 33(8)%. There was a corresponding drop in normalised peak shortening rate from 5.4(3.7) to 3.3(1.1) s-1 and normal septal motion was usually absent. Systolic shortening fraction increased with time after correction and left ventricular end diastolic diameter increased appropriately for age. The preoperative rate of free wall thickening was significantly higher in simple (5.6(2.8) s-1) and complex transposition (4.5(1.8) s-1) than in controls (2.9(0.8) s-1). After operation these values remained high in both the short and long term. Thus, computer assisted analysis of left ventricular dimensions and their rates of change before and after anatomical correction showed only slight postoperative changes which tended to become normal with time. Septal motion was commonly absent after operation. This was associated with an increase in the rate of posterior wall thickening that suggested normal ventricular function associated with an altered contraction pattern. Computer assisted echocardiographic analysis may be helpful in the long term assessment of ventricular function after operation for various heart abnormalities.

Child↗