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Biomedical subjects

U Schulz

Publications and source records attributed to U Schulz.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Quantitative evaluation of retrograde arterial flow in chronic experimental arteriovenous fistulas.

A 2 cm long iliac av. fistula is established in 13 dogs. Flow measurements are performed in the fistula limbs and the adjacent arteries immediately (stage I), as well as 3 months (stage II) and 6 to 12 months (stage III) post-shunt. The following results are obtained: 1) In the acute stage, average flow in the distal fistula artery is very small but directed towards the periphery. In stages II and III a progressively increasing retrograde flow directed towards the fistula is regularly measured in the distal fistula artery. 2) Even in the acute stage a considerable retrograde flow is measured in the distal fistula artery when the proximal artery is clamped. Likewise, in stages II and III, this "free" retrograde flow (after occlusion of proximal fistula artery) is 40 to 60% higher than the spontaneous retrograde flow. 3) In chronic av. fistulas, the "free" retrograde flow in the distal fistula artery decreases significantly after occlusion of the adjacent tail artery and the contralateral iliac artery. It can thus be calculated that in chronic iliac av. fistulas the tail artery contributes approximately 44% and the contralateral iliac artery 22% to retrograde arterial fistula flow. The remaining 34% of retrograde flow are mainly derived from collaterals connecting side-branches of the abdominal aorta with the distal arterial limb. 4) These extensive collaterals adjacent to a chronic iliac av. fistula are demonstrated angiographically and by post-mortem vascular casts. 5) In all stages, occlusion of the proximal fistula artery simultaneously increases flow in the tail artery and contralateral iliac artery by more than 50%. This stresses the major contribution of these arteries to retrograde arterial fistula flow. 6) Successive occlusion of the tail artery and the contralateral iliac artery in stages II and III results in a nearly identical per cent decrease in "free" retrograde flow and in pressure (measured in the distal fistula artery). Even in the pre-fistula control stage, this occlusion experiment induces the same relative pressure-drop in the distal iliac artery. The proportional contribution of the collateral pathways to retrograde arterial fistula-flow and -pressure remains unchanged in the chronic stages post-fistula in spite of the tremendous expansion of collateral vessels within one year. These findings indicate that the three main collateral networks adjacent to the iliac artery all expand proportionally to their pre-fistula status in the months following construction of a large iliac av. fistula. This strongly suggests that the extensive interarterial anastomoses in a chronic av. fistula are all preformed collaterals which have gradually expanded.

Acute Disease↗
PubMedDate not supplied

Stereological changes in the capillary network and nerve cells of the aging human brain.

Stereologic parameters of the capillaries and nerve cells of the brain cortex and putamen were investigated. Thirty-eight brains from subjects aged between 19 and 94 years were examined. All cases were free of metabolic, neurologic and psychiatric diseases. It is demonstrated that the capillary diameter remains unchanged during aging in both brain cortex and putamen. However, in the putamen the total capillary length per unit volume and the capillary volume fractions increase (approximately 60%) progressively with age. Consequently the mean inter-capillary distances in the putamen decrease (approximately 15%). These age-induced changes in the putamen indicate shrinking of subcortical brain structures. In contrast to those of the putamen, the morphometric data of the capillaries in the cortex remain unchanged during the aging process. Stereologic investigations of nerve cells in the brain cortex and putamen revealed that only in brains over 85 years of age can a significant decrease in nerve cell size be demonstrated. A correlation of all the data by a correspondence analytical procedure showed that only the surface/volume ratio of the capillaries correlates with the nerve cell size. This observation suggests a functional interaction between the nerve cells and the capillaries. From the data presented it becomes apparent that the shrinkage of the gyri in the aging brain is not a change in the volume of the cortex, but a decrease in the volume of subcortical structures.

Adult↗