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Biomedical subjects

D B Longmore

Publications and source records attributed to D B Longmore.

At least 55 records · Page 3Linked to original sources
PubMed1988

Magnetic resonance velocity mapping in aortic dissection.

We describe three patients with chronic aortic dissection in whom both spin-echo magnetic resonance imaging (MRI) and cine field-echo imaging were performed. The field even-echo rephasing (FEER) sequence showed the intimal flaps much more clearly than the spin-echo sequence and provided a distinction between thrombus and static blood. Velocity mapping allowed flow measurements in the true and false lumens. The management of the three patients was based upon the information provided by MRI. It is suggested that MRI may avoid invasive investigation and be the method of choice in haemodynamically stable patients with aortic dissection provided that the FEER sequence is used.

Aged↗
PubMed1987

Magnetic resonance velocity mapping: clinical application of a new technique.

Magnetic resonance velocity mapping is a new technique which provides a display of velocity within the cardiovascular system at any point of the cardiac cycle. A short field echo sequence with even echo rephasing is used to obtain a signal from rapidly moving blood and a cine display is provided by rapid repetition of the sequence. The amplitude image shows the anatomy, with blood giving a high signal and areas of turbulent flow no signal. The phase image is a map of velocities at each point in the image plane. Thirteen cases are described in which the technique either provided a diagnosis or helped in functional assessment. Flow through atrial and ventricular septal defects was seen, although turbulent flow distal to the ventricular shunts led to some loss of quantitative information. In three patients with valve disease jets of abnormal flow were seen because of signal loss and it is suggested that the size of the area of turbulence may be used to quantify the severity of regurgitation. Velocities were measured in four coronary artery bypass grafts in two patients, and low velocity was seen in a graft with distal disease that supplied the infarcted territory. Velocity was reduced distal to an aortic coarctation and it was increased at the site of narrowing caused by thrombosis in a deep vein. The speed and direction of flow in the central vessels in a patient with complex congenital heart disease helped to establish the anatomy. The technique provides useful information in a wide range of disorders of the cardiovascular system, and in some cases may avoid the need for invasive investigation.

Adolescent↗
PubMed1987

Blood flow patterns in the human aorta studied by magnetic resonance.

Magnetic resonance velocity mapping by the field even echo rephasing sequence was used to provide two dimensional velocity profiles in the ascending and the descending aorta. Flow patterns were studied in ten healthy volunteers by a display method that gave clear details of the profiles. Velocity profiles in the ascending aorta were skewed in systole with an axis of skew roughly symmetrical about the plane of the aortic arch. During diastole flow was reversed along the posterior left wall of the ascending aorta while it continued forwards at the anterior right wall. In the descending aorta plug flow occurred but with minimal skew. Flow along the right wall was reversed during diastole. Turbulent flow did not occur in the ascending or descending aorta of any healthy subject. Magnetic resonance velocity mapping is a very powerful tool for the study of cardiovascular physiology. Its non-invasiveness, its quantitative two-dimensional data, its accuracy, and its high spatial resolution make it suitable for clinical use.

Aorta↗
PubMed1987

Magnetic resonance imaging of the pulmonary arteries and their systemic connections in pulmonary atresia: comparison with angiographic and surgical findings.

Patients with pulmonary atresia require several investigations and operations. The role of magnetic resonance imaging in assessing the anatomy of the central pulmonary arteries, the origin and course of systemic collateral arteries, and the patency of surgical shunts has been studied with the aim of reducing the need for invasive angiography. Transverse, coronal, and sagittal images were obtained in ten adult patients and assessed without knowledge of surgical and angiographic data. Central pulmonary artery anatomy varied from full development to complete absence. Transverse slices showed hypoplastic arteries particularly well and the findings accorded with surgical and angiographic data in all patients. The origin and proximal course of 15 large collaterals were identified on the magnetic resonance images and 18 were identified by surgical and angiographic data. Magnetic resonance imaging did not show their distal connections; if such information is required angiography will be needed. Five surgical shunts were shown to be patent and two occluded at surgery and angiography, and this was confirmed on the magnetic resonance images. The patency of a further four shunts was uncertain, but they were not seen by magnetic resonance and were presumed to be occluded.

Adult↗
PubMed1987

Colour display of quantitative blood flow and cardiac anatomy in a single magnetic resonance cine loop.

A method of displaying on a single image both the anatomical and the quantitative blood-flow information obtainable from cardiac magnetic resonance has been developed. Anatomical and parametric blood velocity images are combined to produce a computer-processed composite image suitable for display with a specially designed colour scale. Methods for dealing with imperfections in the input images and for obviating technical problems encountered in computer cine display are described. The clinical application of the method is illustrated using eight coronal frames from a normal subject.

Blood Flow Velocity↗
PubMed1986

Assessment of regional left ventricular function by magnetic resonance.

The ability of magnetic resonance to determine regional left ventricular function was investigated in 18 patients--13 with coronary artery disease (nine with previous infarction), one with congestive cardiomyopathy, one with mitral stenosis, one with an atrial septal defect, and two without detectable cardiac abnormality. Coronal magnetic resonance images were acquired through the aortic valve and sagittal images were acquired in the plane of widest diameter of the left ventricle seen in the coronal image, both at end diastole and end systole. Regional wall motion assessed by magnetic resonance was compared with the results of anteroposterior and left lateral x ray ventriculograms by two independent observers. The left ventricular wall was divided into three segments in each plane and the motion of the segments was classified as normal, hypokinetic, akinetic, or dyskinetic. Muscle thickness was measured in each segment of the magnetic resonance images and was considered to be abnormal if in the systolic images it was less than 75% of that in neighbouring segments or if it failed to increase by at least 25% between diastole and systole. Wall motion assessments by the two methods agreed in 68 of 105 segments analysed, but differed by one class in 32 segments and by two classes in five segments. The differences can be explained by the conditions under which the investigations were performed and by the disparity between a tomographic section and an x ray projection. Magnetic resonance showed 25 segments to have abnormal wall thickness. Only one patient with infarction did not have an area of wall thinning and no patient without infarction had an area of thinning. It is concluded that magnetic resonance allows an accurate non-invasive assessment of left ventricular wall motion and thickness.

Adult↗
PubMed1986

Magnetic resonance assessment of aortic and mitral regurgitation.

Magnetic resonance imaging provides an accurate method for the measurement of left and right ventricular volume. The ratio of left ventricular stroke volume to right ventricular stroke volume was calculated from contiguous transverse magnetic resonance images and was used to measure the severity of regurgitation in 18 patients with aortic regurgitation and 10 with mitral regurgitation. Cardiac anatomy was well demonstrated, allowing an assessment of relative chamber volumes and associated abnormalities, although valve abnormality was not well seen. There was a weak correlation between magnetic resonance measurements of left ventricular end diastolic volume and stroke volume ratio. The stroke volume ratio differed significantly in four groups with increasing angiographic severity of regurgitation, and all but the group with trivial regurgitation differed significantly from normal. There was good correlation between magnetic resonance and radionuclide measurements of left ventricular ejection fraction and stroke volume ratio, although the stroke volume ratio was consistently overestimated by radionuclide ventriculography. Correlation was less good for the right ventricular ejection fraction, which was underestimated by radionuclide ventriculography. It is concluded that magnetic resonance imaging provides valuable information in patients with valvar regurgitation, and serves as a suitable standard by which to judge conventional techniques.

Adolescent↗
PubMed1986

[Left and right ventricular dimensions and functions measured by ECG-gated NMR cardiac imaging].

Experimental studies using static and dynamic phantoms have shown that nuclear magnetic resonance cardiac imaging (MRI) can provide accurate measurements of left ventricular wax cast volumes, wax cavity volumes and pumping volumes. Ventricular dimensions and functions of 15 normal volunteers were quantitatively studied. A multislice spin echo (SE) sequence with ECG-gating identified end-diastole and end-systole. Ventricular volumes were calculated by summing the areas of the cavities in multiple contiguous transverse sections. Stroke volume, cardiac output, and ejection fraction were consequently calculated. The right and left ventricular dimensions and functions were compared using these method. The stroke volumes of the right (71.3 +/- 13.5 ml) and left ventricles (72.5 +/- 12.1 ml) were identical. Accordingly, the cardiac outputs of the right (4.8 +/- 0.9 l/min) and left ventricles (4.9 +/- 0.8 l/min) were identical. Right ventricular end-diastolic volumes (133.6 +/- 18.6 ml) and end-systolic volumes (62.3 +/- 10.0 ml) were significantly larger than the corresponding left ventricular volumes (120.2 +/- 15.9 ml and 47.7 +/- 9.7 ml, respectively) (p less than 0.001). Right ventricular ejection fraction (53.1 +/- 5.4%) was significantly less than left ventricular ejection fraction (60.8 +/- 6.2%) (p less than 0.001). Using MRI, measurements of right and left ventricular dimensions and functions were simultaneously obtained, accurately and non-invasively.

Adult↗
PubMed1985

Dimensional accuracy of magnetic resonance in studies of the heart.

Magnetic resonance (MR) can provide high-resolution tomographic images of the heart at any part of the cardiac cycle. Tests on static and dynamic phantoms showed that the technique can give accurate measurements of ventricular wall thickness, cavity volume, and stroke volume. In 20 patients with angina pectoris, electrocardiographically gated MR images of the left ventricle were compared with X-ray contrast ventriculograms. There was good correlation with the anteroposterior ventriculogram, but poorer correlation in the lateral projection because of difficulty in locating the aortic valve precisely on the ventriculogram. In 20 normal subjects, left and right ventricular volumes at end-diastole and end-systole were measured by summing the areas of the cavities in multiple contiguous sections. Stroke volumes and ejection fractions were thus calculated, and the ratio of left to right ventricular stroke volume was very close to the theoretical value of 1, in all cases. In any individual volume measurement, the error was approximately 2%. MR therefore provides an accurate non-invasive method of studying cardiac dimensions and function.

Animals↗
PubMed1984

Measurement of flow with NMR imaging using a gradient pulse and phase difference technique.

A method for determining flow by nuclear magnetic resonance (NMR) imaging is described. A conventional spin-echo imaging sequence is employed with the addition of balanced gradient pulses on either side of the pi radiofrequency pulse. Flow velocities in the direction orthogonal to the image plane are determined by the phase shifts in the NMR image. Experimental validation of the technique in vitro was achieved with a phantom designed to give a continuous flow of water. The flow rate measured by NMR agreed well with the volume flow rate through the phantom. In vivo, NMR flow measurements on the carotid and femoral arteries of two volunteers were compared with Doppler ultrasound results. Velocity measurements were in general agreement. Rapid changes in flow are difficult to follow with the NMR method unless particular care is taken in gradient profile design. The technique can readily be used in existing NMR imaging machines and may have a useful clinical role.

Blood Flow Velocity↗
PubMed1983

Nuclear magnetic resonance imaging of the heart. Current status and future prospects.

The basic principles and current status of proton nuclear magnetic resonance imaging are outlined. Nuclear magnetic resonance images of the heart have improved in quality with advances in technique and better gating but clinical experience remains very limited. Myocardial infarction has been shown in animals and man, and plaques of atheroma have been seen with nuclear magnetic resonance flow studies. Further improvements in image quality, faster examination times, 23Na imaging, and the use of paramagnetic contrast agents are advances that are anticipated in the near future.

Animals↗
PubMed1983

The effects of plasma from patients with Graves' disease on foetal mouse hearts in organ culture.

Plasma, obtained during plasma exchange therapy, from 3 euthyroid patients with Graves' disease and severe progressive exophthalmos induced an increase in heart rate and then early death when applied to foetal mouse hearts maintained in isolated organ culture. All plasma samples which induced an increase in foetal heart rate had high titres of thyroid stimulating immunoglobulins. Plasma samples obtained after exchange had a much diminished effect. These studies may indicate a previously unrecognized non-thyroidal action of the abnormal immunoglobulins associated with Graves' disease and suggest that chronic thyroid heart disease may be due, at least in part, to the effect of these immunoglobulins especially when not associated with elevated thyroid hormones concentrations.

Animals↗
PubMed1981

Experience with prostacyclin in cardiopulmonary bypass in dog and man.

The activation and disruption of platelets resulting from contact with bypass equipment is responsible for bleeding problems after open-heart surgery and for vascular injury leading to cerebral damage. This paper presents experimental and clinical evidence for the benefits of the preservation of platelets by prostacyclin (PGI2) during cardiopulmonary bypass operations. Work with dogs showed that PGI2 was more effective than heparin in maintaining the numbers and aggregability of the platelet population, but by far the most effective was a combination of the two agents. A subsequent double-blind clinical trial on 24 patients undergoing coronary vein grafts, in which the combination was compared with heparin alone, confirmed these findings in man. In the presence of PGI2, platelet numbers and aggregability were preserved, with a consequent reduction in blood loss. Significantly fewer reinforcing doses of heparin were required by the PGI2 group. The integrity of platelets in the presence of PGI2 was reflected by the lack of micro-aggregates and fibrin deposits on arterial line filters. In both the human and dog studies, PGI2 was shown, by the cultured foetal mouse heart test, to prevent the release of circulating cardiotoxic factors during bypass. The known vasodilator effect of PGI2 was observed but caused no clinical problems. An unexpected feature was the maintenance of perfusion pressure without the need for additional fluid. This may indicate that PGI2 reduces capillary permeability.

Adult↗
PubMed1981

Prostacyclin administration during cardiopulmonary bypass in man.

In a double-blind trial prostacyclin was given to 12 of 23 patients undergoing coronary vein grafting. The treatment group showed a preservation of platelet number and function, with a halving of blood loss in the first 18 h postoperatively. The heparin sparing effect of prostacyclin was confirmed, as were the vasodilator effects which were not troublesome.

Adult↗
PubMed1979

Prostacyclin: a solution to some problems of extracorporeal circulation. Experiments in greyhounds.

In cardiopulmonary-bypass experiments in greyhounds the effects of adding prostacyclin, prostacyclin plus heparin, and heparin alone to the extracorporeal circulation were compared. With heparin alone platelet count and function were reduced, the pressure differential across the arterial filters rose, platelet deposits were found on the arterial filters, and plasma-fibrinogen levels fell. Plasma from these dogs was toxic to fetal-mouse hearts in culture. With prostacyclin alone, fibrinogen levels fell, but the platelets were preserved. With a combination of prostacyclin and heparin, platelet count and function were maintained, there was no consumption of fibrinogen, and there was little deposition on the arterial filters.

Animals↗