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Biomedical subjects

H Hamann

Publications and source records attributed to H Hamann.

At least 73 records · Page 4Linked to original sources
PubMed1987

[Determination of the degree of stenosis in carotid artery stenoses: ultrasound and i.v. DSA in comparison to surgical findings].

The specimens from 116 consecutive carotid thrombendarterectomies were taken as "gold standard" to evaluate the accuracy of ultrasound methods (duplex scanning + extra-/transcranial Doppler sonography) and intravenous digital subtraction angiography (i.v. DSA) in carotid artery stenoses. In 65 cases, in which the specimens could be gauged reliably, sonography estimated the degree of stenosis in 85% within a range of +/- 10%, in 97% within +/- 20% i.v. DSA was accurate in 52 respectively in 94%. High-grade stenoses were correctly assessed by ultrasound in 90%, by i.v. DSA in 64%. Sonography identified 4/10 kinkings and coilings of the carotid artery, i.v. DSA 9/10. Current available ultrasound methods enable estimation of the diameter reduction of carotid artery stenoses with low deviations. I.v. DSA seems to be less reliable, but can be used favourably as a complementary method to sonography.

Carotid Artery Diseases↗
PubMed1987

[Role of digitalized angiography by venous route in the study of carotid bifurcation. Value in the diagnosis of ulcerated lesions].

Intravenous DSA was performed in 149 patients with suspected arteriosclerotic disease of the carotid bifurcation. These patients were submitted to 163 endarterectomies. The radiological and surgical findings were correlated in a retrospective analysis. The sensitivity of the angiographic method in determination of the correct percentage stenosis was 79%, but only 36% for the diagnosis of ulcerated lesions. Sonography exhibited a sensitivity of 79% with respect to the degree of stenosis and 23% in the diagnosis of ulcerated plaques. The present paper demonstrates the limiting factors of DSA and sonography. Furthermore, it reveals the valuable complementary effect of both methods in detecting arteriosclerotic lesions of the carotid bifurcation.

Arteriosclerosis↗
PubMed1987

Insulin as a growth regulator of arterial smooth muscle cells: effect of insulin of I.G.F.I.

The proliferation of smooth muscle cells in the vessel wall plays an important role in the development of an atherosclerosis. The insulin-like growth factor I (I.G.F.I) is an important growth factor for cultivated arterial smooth muscle cells. The plasma I.G.F.I level is controlled by growth hormone and insulin--both factors seem to be important for the development of a diabetic macroangiopathy. In order to evaluate whether I.G.F.I is associated with the development of a macroangiopathy we measured the serum I.G.F.I level in type 2 diabetics with and without macroangiopathy and in non diabetic patients with atherosclerosis and in healthy controls. The range of the individual I.G.F.I levels was wide and the I.G.F.I level between the various groups was not statistically significant. However, our studies with cultured cells show that modulation of the cellular responsiveness to I.G.F.I is as important in the growth control as are changes in the plasma I.G.F.I level. We observed that cultured smooth muscle cells were able to produce an I.G.F.I-like factor. The synthesis and secretion of this factor was dependent on insulin. These findings explain one mechanism by which insulin may influence the growth of smooth muscle cells in the vessel wall.

Adult↗
PubMed1986

[Carotid endarterectomy in vertebrobasilar insufficiency].

In 45 patients with uni- or bilateral stenoses of the internal carotid artery in association with symptomatic vertebro-basilar occlusive disease 61 carotid endarterectomies had been performed. 28 patients had at least one patent posterior communicating artery (PCA) visualized angiographically (group A). Of these, 26 patients (93%) became asymptomatic or improved postoperatively. Of the 17 other patients in whom the PCA did not visualize by preoperative angiography, only 8 (47%) subsequently became asymptomatic or were improved (p less than 0.05). Thus, identification of the PCA (angiographically or by transcranial Dopplersonography) is important in predicting those patients in whom carotid endarterectomy may be strongly recommended.

Carotid Artery Diseases↗
PubMed1985

[Recurrent stenoses following carotid TEA].

Follow-up of 798 patients by Duplex scanning or digital venous angiography 6 months to 13 years after carotid endarterectomy revealed a recurrent stenosis rate of 3.4%. The incidence of the recurrent lesions showed a clear correlation with the operative technique: after closure of the arteriotomy directly (continuous suture) or with a vein patch (303 pat.) the recurrent stenosis rate was 4 times higher than after closure with a dacron patch (495 pat.). Our investigations indicate that recurrent stenosis and occlusions after carotid endarterectomy are largely avoidable. Sufficient length of arteriotomy (5-8 cm), dilatation of the distal internal carotid artery and lumen congruent closure of the arteriotomy with a dacron patch are the pivots of success.

Blood Vessel Prosthesis↗
PubMed1985

Desmoplastic fibroma of the rib.

We present a 17-year-old male patient who had a desmoplastic fibroma. The diagnosis is histologically verified and differentiated from other tumors. The rare localization of this benign lesion in the rib is of particular interest.

Adolescent↗
PubMed1985

[Transvenous digital subtraction angiography of the thoracic aorta after surgical correction of isthmic stenosis].

25 patients (normotensive n = 19, hypertensive n = 6) underwent DSA control following corrective surgery of a coarctation of the thoracic aorta to exclude vascular complications. Simultaneously pressure gradients were determined between upper and lower extremities using the doppler-sonography. DSA was diagnostic in all patients. 2 cases showed a patch-dependent dilatation, in 1 case an anastomotic aneurysm could be demonstrated. In 6 patients with hypoplastic aortic arch and 2 patients with a slight reduction of the diameter in the anastomotic region a pathological pressure-gradient was measured. In these patients the ratio of aortic arch rsp. anastomosis/descending aorta was reduced in diameter (less than 0,66) and area (less than 44). Hypertension could not be related to pressure gradients or vascular disorders.

Adolescent↗
PubMed1985

[Transvenous DSA following surgery of the supra-aortic trunks].

This paper presents our experience using transvenous DSA for control of vascular, prosthetic or bypass patency following operative intervention in the supraaortic branches. The results in 33 cases examined under outpatient conditions demonstrate that DSA via transvenous administration of a contrast material with high iodine concentration is useful to produce images of diagnostic quality (32/33 patients). The pre-condition is a good patient's cooperation and a sufficient cardiac output. Using this minimal invasive method the operative results can be evaluated and vascular complications can be excluded.

Adult↗
PubMed1985

[Aortofemoral bifurcation bypass--effect of the anesthesia procedure (NLA, thoracic continuous catheter peridural anesthesia) on circulation, respiration and metabolism. Intraoperative circulatory reactions].

51 patients who were selected for aorto-bifemoral bypass operation (infrarenal aortic aneurysm, iliac or iliofemoral occlusive disease) were randomized into two groups. 26 patients were operated on under neuroleptanaesthesia and 25 patients had a continuous thoracic epidural, which was supplemented with a light general anaesthesia during the operation. All patients were optimally volume loaded prior to surgery. The most marked haemodynamic alterations (tachycardia, arterial hypertension, increase of cardiac index, left ventricular stroke work index and cardiac minute work) were provoked by eventration of the gut. In the epidural group, these changes were attenuated and in contrast to the neuroleptanaesthesia group, there were a few patients who had a serious fall in blood pressure. These reactions were regularly accompanied by a generalized flush which led to the hypothesis that they were caused by the release of intestinal hormones, reactive peptides and neurotransmitters, from the mechanically irritated gut. Clamping of the aorta was relatively uneventful. Heart rate and cardiac index decreased in both groups but mean arterial pressure and pulmonary capillary wedge pressure remained stable. Systemic vascular resistance increased slightly in the neuroleptanaesthesia, but not in the epidural group. Declamping was followed by significant but transient falls in systemic vascular resistance and arterial pressure in both groups, despite sufficient volume loading before opening the clamp. In the neuroleptanaesthesia group these changes spontaneously returned to normal; in the epidural group 6 patients received vasopressors or positive inotropic drugs. These results indicate the following: Epidural anaesthesia prevents hypertension and tachycardia and lowers cardiac minute work. Eventration of the gut, acute blood losses and declamping of the aorta may be critical situations, which can lead to profound hypotension. Under neuroleptanaesthesia eventration of the gut is followed by tachycardia and hypertension whereas blood losses and declamping are not as critical as when an epidural is used. Only experienced anaesthetists should use epidural anaesthesia for aortic surgery. An intensive monitoring of haemodynamic function during this form of anaesthesia is mandatory.

Adult↗
PubMed1982

Physicochemical properties of salt-soluble, unsheared chromatin. Molecular weight studies.

A chromatin fraction, which can reproducibly be extracted from rat liver nuclei at moderate salt concentration (0.1 M (NH4)2SO4, 0.1 M Tris-HCl, 2 mM MnCl2, pH 7.9), was analyzed with regard to changes of its molecular weight in the range of (NH4)2SO4 concentrations between 0.1 M and 0.4 M. With the transition from 0.1 M to 0.2 M (NH4)2SO4 histone H1 is released and the molecular weight obtained from both sedimentation-viscosity and light scattering is reduced by approximately one-half. A spatial expansion of the resulting half-molecules is observed with further increasing salt concentration. On the basis of these results a double-fibrillar structure of this chromatin fraction is proposed.

Animals↗
PubMed1981

[Replacement of small caliber arteries with synthetic transplants].

Under comparable biological and hemodynamical conditions two different types of arterial prostheses (USCI-Sauvage Filamentous Vascular Prostheses versus Gore-Tex expanded PTFE-prostheses) were implanted in 32 dogs in aorto-iliacal (14 animals) respectively in carotid position (18 animals). The graft length was 8--10 cm, the diameter 4 mm. Followed-up to 24 weeks the expanded PTFE-prostheses had a statistically higher failure rate than the filamentous Dacron-prostheses (67% respectively 52%). Light microscope and scanning electronmicroscope evaluations 2, 4, 8, 12, 20 and 24 weeks postoperatively showed a complete ingrowth of fibrous tissue through the wall of the filamentous Dacron-prostheses with a fibrous neo-intimal layer. At the same time the luminal surface of the expanded PTFE-prostheses was covered with fibrin. Tissue invasion was limited to the outer one third of the graft wall. With increasing time interval a thickening of the inner layer with consecutive narrowing of the lumen could be observed in the filamentous Dacron-prostheses. A neo-intimal thickening of more than 600 mu always leads to a thrombotic graft occlusion. The expanded PTFE-prostheses showed even after 24 weeks no complete ingrowth of fibrous tissue. A fibrous neo-intima with an endothelial lining had only developed near the anastomoses. The remaining surface of the graft was covered by a fibrin layer. Endothelial islands apart of the anastomoses could be observed only in some Dacron-prostheses. The presented results indicate that long term patency of synthetic grafts for reconstruction of small arteries (less than 6 mm) is in the first place limited by the quality of the neo-intimal layer. Further research should be directed therefore to the improvement of the inner surface (for instance by coating with an antithrombogenic layer) and to a better quality of the synthetic wall (compliance, flexibility, etc.).

Animals↗
PubMed1980

Temperature behaviour of human serum albumin.

Structural alterations of albumin, their dependence on concentration and the role of free --SH groups at thermal denaturation, as well as the reversibility of thermally induced structural changes, were studied. Application of various physical methods provides information on a series of structural parameters in a major concentration range. Apart from changes of the helix content, heat treatment gives rise to beta structures which are amplified on cooling and which are correlated with the aggregation of albumin. With rising temperature and concentration the proportion of beta structures and aggregates increases. At degrees of denaturation of up to 20% complete renaturation is possibly in every case. The structure content is concentration-dependent even at room temperature. It may be that intermolecular interactions induce additional alpha-helix structures which are less stable, however, than the ones stabilized by intramolecular interactions. Unfolding of the pocket containing the free --SH group of cysteine-34 enables disulphide bridges to be formed leading to stable aggregates and irreversible structural alterations. Through binding of N-ethymaleimide to free --SH groups, which blocks the formation of disulphide bridges, it is possible to prevent aggregation and irreversible conformational changes. At temperatures below 65--70 degrees C, oligomers are formed mainly via intermolecular beta structures.

Circular Dichroism↗
PubMed1979

[Vascular replacement with plastics (author's transl)].

The plastic substitution of the aorta and its large branches may be considered largely solved today. For this purpose preference is given to highly porous, thin-walled double velour prostheses. The search for a biocompatible plastic substitute for small caliber arteries and the large veins of the body (portal vein, vena cava, iliac veins) is proceeding in two directions at the present time: on the one hand towards optimized bioprostheses and on the other hand towards plastics which apply the principle of microporosity or impermeability with the creation of antithrombogenic inner surfaces. In this respect expanded polytetrafluoroethylene and coating with carbon are very promising.

Biocompatible Materials↗