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Biomedical subjects

M R Roach

Publications and source records attributed to M R Roach.

At least 109 records · Page 6Linked to original sources
PubMed1968

Vasomotor responses in the hind limbs of foetal and new-born lambs to asphyxia and aortic chemoreceptor stimulation.

1. Hind limb blood flow was measured in lambs of from 91 days gestation (delivered by Caesarean section) to 1 month after birth (term is about 147 days), under chloralose anaesthesia. Vascular resistance/100 g wet wt. increased progressively with age. There was reflex femoral vascular tone from the earliest age studied, as shown by vasodilatation on cutting the sciatic nerve.2. On asphyxia by cord occlusion reflex femoral vasoconstriction began earlier and was somewhat greater in older foetal lambs. At all ages, and after denervation of the hind limb, there was vasodilatation after local ischaemia, and a vasoconstriction of delayed onset during asphyxia attributed to release of noradrenaline into the circulation. The vasoconstrictor effect of noradrenaline in immature lambs was at least as great as at term or in the new-born.3. Injections of minimal effective doses of cyanide were used to localize possible chemoreceptor sites in foetal lambs. Injection into the left atrium caused a rise of arterial pressure, femoral vasoconstriction and a complex change in heart rate (usually bradycardia) but rarely any respiratory movement. After atropine, cyanide caused a large tachycardia. All responses were much reduced or abolished by cervical vagotomy.4. Injection of the same doses of cyanide into a jugular vein, the right ventricle, pulmonary or common carotid arteries of foetal lambs caused negligible cardiovascular or respiratory effects, whereas injection into the carotids of new-born lambs caused a profound hyperpnoea.5. It is concluded that the aortic chemoreceptors are active in the foetus, are supplied from the left heart, and that they probably represent the primary defence in blood gas homeostasis by their effects on the circulation.

Acetylcholine↗
PubMedDate not supplied

A quantitative study of the localization of atherosclerotic lesions in the rabbit aorta.

A quantitative study of the size and location of early sudanophilic lesions has been carried out on the aortae of five rabbits. The atherosclerotic lesions were induced by feeding an average of 114 (+/- 3.7) egg yolks over an average period of 83 (+/- 1.7) days. The aortic lesions were visualuized by gross staining with Sudan III and measured by the polar coordinate method. The lesions were almost entirely around orifices: their size was directly proportional to the area of the associated ostium (P less than 0.005). The sudanophilic deposits were located downstream from the ostia in areas believed to experience high shear stresses. The area of the intercostal ostia increased as one proceeded down the thoracic aorta (P less than 0.005). A deviation from the distal distribution pattern was observed where local flow and shear stresses were disturbed. The coronary lesions completely surrounded the ostia, the coeliac lesions had significant proximal components and the left renal and inferior mesenteric lesions were skewed to the right. The study suggests that hemodynamic forces and particularly high shear stress is of considerable importance in both the initiation and localization of early atherosclerotic lesions.

Animals↗
PubMedDate not supplied

Effect of unilateral nephrectomy of the localization of aortic sudanophilic lesions in cholesterol-fed rabbits.

The method of polar coordinate mapping of lesions on the aortic wall around orifices was used to study the effect of unilateral nephrectomy on sudanophilic lesions in rabbits. Four groups of six rabbits each were studied. Group I had a right nephrectomy with a short renal artery stump. Group II had a sham right nephrectomy. Group III had a left nephrectomy with a short renal artery stump and Group IV a sham left nephrectomy. All groups were allowed to recover for one week and were then fed rabbit chow enriched with 2% cholesterol and 6% corn oil for a four-week period. Groups I and III showed a marked alteration in lesions around the stump with both proximal and distal peaks. Group I also showed the development of skewing of the left renal lesion to the left, presumably because of a change in aortic flow due to removal of the proximal right renal flow. The right renal artery had a lesion skewed to the right; this was not altered by left nephrectomy and was probably due to coeliac flow. The data provides strong evidence that sudanophilic lesions in rabbit aortas are altered by local flow disturbances.

Animals↗
PubMedDate not supplied

A digital-radiographic technique for in vitro tissue thickness measurement using iodine displacement.

A novel digital radiographic method has been developed for measuring the thickness of a tissue sample by iodine displacement. This simple, accurate method is useful both in medical research and in the comparison of pathological and clinical findings. Radiographic measurements of tissue samples in air suffer from the limitation that the quantity measured depends on the product of both thickness and radiographic attenuation coefficient. This technique allows one to obtain thickness measurements from a digital radiograph of a tissue sample suspended in a bath of radio-opaque contrast agent. The attenuation of the iodinated contrast agent is much higher than that of tissue or calcium. Thus the resulting image is determined largely by the contour of the surrounding bath, and is only slightly influenced by the composition of the tissue. This technique improves both the accuracy and precision of radiographic thickness determination. In this paper the iodine displacement technique is described and the accuracy and precision of thickness measurements in appropriate phantoms are quantified. This technique has been used with both image intensifier and screen-film based imaging systems to obtain thickness maps of calcified human aorta, with precision better than 4% and spatial resolution of 2.5 mm-1.

Aged↗
PubMedDate not supplied

Flow disturbances at the apex and lateral angles of a variety of bifurcation models and their role in development and manifestations of arterial disease.

Dye flow patterns were studied in 12 glass model bifurcations with angles of 45, 90, 135, and 180 degrees, and area ratios of 0.78, 1.03 and 1.27. At the apex, the dye formed a saddle zone, and streamlines from the core which entered this region were swept over the upper and lower surfaces to enter the lateral angles. Qualitatively, the shape and size of the apex played a key role in this effect. Boundary layer separation occurred in the lateral angles, and increased as flow into the branch was reduced. If the branch was occluded, a complex vortex developed in the first few diameters of the branch, and no flow occurred beyond this, even though the occlusion was about 20 diameters downstream. The results were comparable with steady and pulsatile flow. The implications of these results for the localization of atherosclerosis are discussed.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Fenestrations in the internal elastic lamina at bifurcations of human cerebral arteries.

Measurements of fenestrations (or windows) in the internal elastic lamina at the bifurcation of human cerebral arteries, were obtained from photomicrographs (scanning electron microscope). Thirteen of 28 bifurcations revealed regions of enlarged fenestrations among the normal fenestrations in the vicinity of the apex. The mean diameter of the enlarged fenestrations (7.0 +/- 0.34 SEM micrometer) was significantly greater than the mean diameter (2.1 +/- 0.13 SEM micrometer) of the normal fenestrations. The number of fenestrations per sq mm was less (2606 +/- 284 SEM per sq mm) for the enlarged fenestrations than for the normal fenestrations (4518 +/- 397 SEM per sq mm). The proportion of the area of internal elastic lamina comprised of fenestrations increased to 15.0 +/- 1.1 SEM percent for the enlarged fenestrations from a mean of 1.8 +/- 0.16 SEM percent for the normal fenestrations. Fenestrations from bifurcations without enlarged fenestrations, demonstrated characteristics similar to the normal fenestrations. More than 80% of the specimens exhibited a gap in the internal elastic lamina in the apical region of the bifurcation. Based on a comparison of stress concentration factors, we propose that the presence of enlarged fenestrations represents a weakness in the internal elastic lamina at the bifurcation apex which may contribute to the initiation of microaneurysms.

Aged↗
PubMedDate not supplied

Shape changes at the apex of isolated human cerebral bifurcations with changes in transmural pressure.

The geometry of arterial bifurcations appears to play a significant role in the development of vascular disease. We have investigated the changes in bifurcation geometry with changes in distending pressure over the range 0.0 to 190.0 mm Hg. Five cerebral arterial bifurcations from human subjects were studied. The investigation focussed on the shape and on changes in the shape of the leading edge of the flow divider (internal apical curve). The curve outline at each transmural pressure increment (each 10.0 mm Hg) was photographed and digitized. The curves were plotted serially on an expanded scale. Visual comparison of the curves indicated flattening in the central region and broadening of the shoulders of the curves with increasing transmural pressure. Regression analysis using second order polynomials was used to obtain coefficients for equations defining short, overlapping segments of each curve. Twenty-four coordinates were used for each successive regression. Each curve was characterized by 85 to 100 digitized coordinates. The regression equations for each curve were used to calculate the curvature parameter, K, and the radius of curvature, R. Three of the five bifurcations demonstrated a negative correlation of K with increasing transmural pressure (p less than .001). This result supports the visual observation that the internal apical curve flattens with increasing transmural pressure. Flattening of the internal apical curve together with thinning of the arterial wall with increasing transmural pressure would contribute to a stress concentration at the apex of a cerebral bifurcation. This stress concentration would be more pronounced in the presence of a medial gap at the apex of the bifurcation. It is on or near this region of stress concentration that aneurysms develop.

Adult↗
PubMedDate not supplied

A physical model for the formation of evaginations: a prospective precursor to the creation of saccular aneurysms.

The actual spatial geometry of separate regions of normal and enlarged fenestrations from the internal elastic lamina of human cerebral arteries have been replicated in sheets of latex rubber from scanning electron microscope (SEM) photomicrographs. Geometrical models which assume a constant diameter for the fenestrations, a constant ligament efficiency for the regions of fenestrations and a uniform array of rows and columns have also been created in sheets of latex rubber. The stress (load per unit of cross-sectional area) and strain (percent elongation) were computed for each of the samples during uniaxial stretching. The elongation of the sample representing the region of enlarged fenestrations increased an average of 47% compared to the similar representation of normal fenestrations, at the same increments of stress. This suggests that regions of enlarged fenestrations would form a bulge, indicative of an evagination of the internal elastic lamina. The model configurations demonstrate very similar stress/strain characteristics to the replications. This finding justified the use of the modelling technique using equivalent ligament efficiencies, to represent the actual spatial geometry. During elongation, the average area of the enlarged fenestrations increased at a rate which was an order of magnitude greater than the normal fenestrations. Since a number of observations associated with the development of intracranial saccular aneurysms can be correlated to a region of enlarged fenestrations, the region of enlarged fenestrations may be a defect in the internal elastic lamina which could play a prominent role in the development of intracranial saccular aneurysms.

Elasticity↗