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Biomedical subjects

R Jacob

Publications and source records attributed to R Jacob.

At least 217 records · Page 12Linked to original sources
PubMed1976

Fractures of the hip in childhood.

Twenty hip fractures in 19 children aged 2 1/2 to 18 were analyzed in a ten-year retrospective review at the University of Alabama Hospitals in Birmingham, Ala. There was one epiphyseal, one intertrochanteric, 4 subtrochanteric, and 14 intracapsular fractures. The mechanism of injury was usually severe trauma with 31% of the patients sustaining other associated major injuries. Avascular necrosis occurred in three intracapsular fractures (23%), all seemingly related to inadequate internal fixation. Coxa vara occurred in 30% of the patients; all were treated by closed methods, and delayed union and nonunion occurred in 10% of the series. Nine patients developed discrepancies of limb length between 1/2 and 13/4 inches. It was thought that intracapsular fractures should be treated with prompt open reduction and internal fixation with multiple pins; whereas, extracapsular fractures may be treated by either open or closed methods.

Adolescent↗
PubMed1976

Concentration and adenosinetriphosphatase activity on left ventricular actomyosin in Goldblatt rats during the compensatory stage of hypertrophy.

Left ventricular myocardia of Goldblatt rats with an average increase in arterial blood pressure to about 200 mm Hg showed a progressive reduction of the Ca-activated specific acotmyosin ATPase activity 4 -12 weeks after the coarctation of one renal artery, as compared with controls of the same age. During the same period, a significant increase in the concentration of contractile proteins was noticeable, whereas the content of nonprotein substances and of water corresponded to the control values. The hydroxyproline concentration, as a measure of the collagen tissue content, increased only after 24 weeks. The time course of the specific ATPase activity was closely parallel to the decrease in the unloaded myocardial shortening velocity, as estimated at the same stage by our group. This is in accordance with the assumption of a fundamental relationship between the two values. The reduced rate of energy turnover and of the shortening velocity is regarded as an adaptive mechanism which, however, has a negative effect in advanced hypertrophy when further diminution takes place. The decrease in the specific enzymatic activity of actomysin is not necessarily linked to a large increase in myocardial mass, but is already apparent at moderate degrees of hypertrophy (34%).

Actomyosin↗
PubMed1976

[Maximum velocity of load-free shortening Vmax, myocardial capacity and "contractility indices" in the hypertrophic myocardium].

Based upon literature and our own experimentation on Goldblatt rats, the significance of a decrease of the maximal shortening velocity of the myocardium at zero load (Vmax) in the hypertrophied, chronically pressure-loaded heart is discussed. In the hypertrophied myocardium with varying concentrations of the contractile structures, the developed tension under isometric conditions (sigma) and the maximum rate of tension development (d sigma/dtmax) can indicate significant deviations from the values of controls of the same age, without, however, making it possible to draw from these changes absolute conclusions about the elementary contractile process. With the enhanced concentration of contractile proteins, the mentioned isometric values, as well as the maximum instantaneous power (cross-sectionally related) of the myocardium can be increased during a stage of hypertrophy in which Vmax is already reduced. The decrease of Vmax shows a rough correlation with the reduction of the specific ATPase activity of actomyosin and is already observed at moderate degrees of hypertrophy (30 to 50%). The time course of the change of both parameters in experimental hypertrophy suggests a causal relation between the changes of those two parameters and the failure of the myocardium in later stages of a chronic overload. Under the condition of reliable estimation, Vmax allows for, also with changed actomyosin concentration, an assessment of the elementary contractile process. On the other hand, Vmax does not present a sufficient measure for the cross-sectionally related power capacity of the hypertrophied myocardium. The possible dissociation between the unloaded shortening velocity and the cross-sectionally related power capacity could, in certain cases, explain an unsatisfactory correlation between Vmax and the clinical state of the heart. The so-called empirical indices of contractility, which are not always clearly related to basic physiological characteristics of the myocardium, should be interpreted with particular reserve in relation to the hypertrophied cardiac muscle.

Actomyosin↗
PubMed1976

Selective ascending lumbosacral venography in the assessment of lumbar-disc herniation. An anatomical study and clinical experience.

Epidural venography was performed in 110 patients with suspected lumbar-disc herniation by catheterization of the ascending lumbar and ascending sacral veins. The findings by venography and by myelography were compared with those revealed by operative exploration. Only sixty-one patients had venography, myelography, and operative exploration. In fifty of these patients with no previous disc surgery, the diagnostic accuracy of venography was 98 per cent and of myelography, 90 per cent. Venography had limited value in the other eleven patients who had had one or more prior disc operations because it did not distinguish between scarring and recurrent disc herniation at the levels previously explored. Selctive ascending lumbosacral venography is indicated both in patients who have not had a prior disc operation, as a guide to whether myelography should be performed when the clinical picture is ambiguous, and in patients whose myelogram is normal or equivocal but whose signs and symptoms are strongly suggestive of disc herniation.

Adolescent↗
PubMed1975

The effect of sudden stretches on length-tension-and force-velocity relations of mammalian cardiac muscle.

In the isotonically beating cat papillary muscle, a sudden augmentation of the preload initiates a visco-elastic strain retardation, in the course of which the preparations show a marked increase in their isotonic mechanogram amplitudes. It is preceded in the first seconds by a short-term decline. These effects correspond well with the phenomena of stress relaxation. When applying these post-stretch phenomena to the length-tension diagram, it is shown that the isometric and isotonic length-tension curves are significantly shifted to greater distances with respect to the resting length-tension curve, involving even a doubling of the myocardial working capacity in certain cases. Stretch-induced alterations in Vmax which were obtained from damped quick-releases, initiated during isometric contractions are almost negligible. On the other hand Vmax obtained from quick-releases which were started immediately after the onset of isotonic contractions are strongly affected by sudden stretches. The stair-like decline of the mechanograms in the initial phase of relaxation or retardation is assumed to be mediated by a stretch-induced alteration in the time course of the action potential. The additional reduction in myocardial performance superimposed on this, is consistent with the hypothesis of a stretch-induced transient inactivation or a delayed activation of contractile interaction sites.

Action Potentials↗
PubMed1975

Length-tension diagram and force-velocity relations of mammalian cardiac muscle under steady-state conditions.

Length-tension diagrams and force-velocity relations of isolated cat papillary muscles were measured under strictly stationary conditions: any analysis of isometric mechanograms was carried out only in stable isometric beats; each measurement in beats under any condition different from the isometric one was determined in the very first contraction after a period of stabilization under isometric conditions. The length-tension diagrams show a clear distinction between isometric and isotonic length-tension curves. Force-velocity curves on the basis of afterloaded isotonic, as well as of damped quick-release contractions, could be satisfactorily approximated by a polynomial of the 5th order. Vmax estimated on the basis of afterloaded and of damped quick-releases in the course of isometric and isotonic contractions, was significantly dependent on preload. This is also valid in a range of muscle length which is regarded as physiological.

Animals↗
PubMed1975

Use of polymethylmethacrylate to enhance screw fixation in bone.

Pull-out testing of screws inserted into cement and bone under various conditions showed that the cement-screw complex was significantly stronger when the screw was placed in soft cement and the cement was allowed to polymerize without further manipulation. When screw fixation in osteoporotic bone was reinforced with cement, the bone was the weakest component in the system. Fixation under these conditions should be enhanced by increasing the area of contact between the cement and bone. By cooling the cement to prolong its working time, it could be injected with a syringe in such a way that maximum endosteal and periosteal contact was provided.

Bone Cements↗