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Biomedical subjects

M Wolgast

Publications and source records attributed to M Wolgast.

At least 73 records · Page 4Linked to original sources
PubMed1982

Experimental obstructive hydronephrosis in newborn rats. II. Long-term effects on renal blood flow distribution.

Partial obstruction of one ureter was created in newborn rats. The weights and blood flows (using the 86Rb-extraction method) of the cortex and outer and inner medulla were examined nine weeks later, i.e., in the adult. The obstructed pelvis was found to be enlarged 7-fold. The whole kidney blood flow on the hydronephrotic side was reduced by 10%; this was compensated by an increase on the contralateral side. There was a tendency to redistribution of flow from the cortex to the outer medulla; no other effects on regional flow were observed. The weight of the hydronephrotic kidneys was the same as that of the kidneys in control rats; hence no apparent atrophy was present. In contrast, the contralateral intact kidney was hypertrophied. The weight distribution of the different regions remained unaltered. Thus, the inner medullary weight was unaffected also on the obstructed side, although it showed considerable deformation. In the discussion, it is proposed that atrophy of the hydronephrotic kidney was probably present, but it was not detected because of the biological variation and the small number of observations. This presumed atrophy was uniform in all the regions and parallel with the reduction of whole kidney blood flow; hence the regional flows were relatively unaffected. It is concluded that unilateral partial obstruction in the newborn rat causes (i) discrete, parallel reductions of hydronephrotic kidney weight and flow, which are (ii) unrelated to the size of the obstructed pelvis and (iii) completely compensated by increases in the contralateral intact kidney.

Animals↗
PubMed1981

Influence of renal nerve activity on arteriolar resistance, ultrafiltration dynamics and fluid reabsorption.

In anaesthetized 300 g rats, the influence of sympathetic nerve activity on the renal hemodynamics, glomerular filtration and fluid reabsorption was studied with direct stimulation at frequencies of 2 Hz and 5 Hz. The single nephron plasma flow at control conditions was 164 nl/min decreasing to 138 nl/min during 2 Hz and 68 nl/min during 5 Hz, reaching complete glomerular ischemia at about 10 Hz. At 2 Hz, the pressure drop over the two arterioles remained essentially unchanged, indicating an equal response to sympathetic discharge. At higher frequencies the afferent tone showed a more marked increase. The glomerular ultrafiltration decreased in parallel to the blood flow. The filtration fraction remained thereby constant at about 0.33. The fractional proximal fluid reabsorption up to the puncture site in early distal tubules showed a clear increase; the Tf/P-Inulin increasing from 6.0 to 7.1 and 7.2 for 2 Hz and 5 Hz, respectively. The absolute reabsorption decreased, however, and indeed not far from the decrement in glomerular filtration. It is concluded that sympathetic nerve activity acts in the direction of fluid conservation, by reducing the glomerular filtration and increasing the fractional reabsorption. The hemodynamic effects will play the dominant role even at 2 Hz stimulation.

Adrenergic Fibers↗
PubMed1981

Functional characteristics of the renal interstitium.

The renal interstitial space analyzed as "inulin space" comprises about 13% in the rat. The Starling forces of this compartment are governed by the balance between tubular and capillary fluid transport and also by the leakage of plasma proteins from the blood side. Protein transport will occur in a large-pore system in the peritubular capillary membrane. During control antidiuresis, the interstitial hydrostatic pressure is 2-4 mmHg. The colloid osmotic pressure shows a larger variability but is generally about 5 mmHg. During conditions of depressed capillary reabsorption but unchanged tubular reabsorption, as in saline expansion, the interstitial hydrostatic pressure rises 3-4 times, whereas the colloid osmotic pressure will show a steep fall resulting from the increased fluid entry and unchanged protein transport. The interstitial volume increases only slightly, since it is compressed by the expanding tubules. The influence of interstitial physical forces on tubular transport remains unclear, mainly due to the inaccessibility of the lateral interspaces to direct measurement of relevant parameters.

Albumins↗
PubMed1981

Regional renal function measured by videodensitometry.

The videodensitometric method was applied for the determination of regional renal blood flow and filtration fraction using 2 contrast agents, where Thorotrast represented an intravascular indicator and Angiografin will be distributed in the intravascular and interstitial space and, in addition being freely filtrable in the glomeruli. The contrast density was continuously monitored from the light intensity on a TV-screen, where the region to be analyzed could be outlined by a light pen. The passage time of Angiografin analyzed from the videodensitometric curve was compared to that of 125I-labelled Angiografin as analyzed in the venous effluent. The two methods yielded almost identical values. Knowing the volume of distribution of the agents, the regional blood flow could be calculated and was found to be the same for the two contrast agents used. The curves for Thorotrast showed a rapid passage with a rapid declination towards the base-line. For Angiografin the curves ended in an almost horizontal plateau reflecting the fraction of the Angiografin filtered and remaining into the tubular system. The height of the plateau was then used for the determination of the filtration fraction. The figure obtained was compared to that obtained by conventional clearance techniques, and was found to yield similar values. It is concluded that the videodensitometric method allows for evaluation of the functional characteristics of the kidney in addition to the anatomical information given by the conventional angiography performed in parallel to the videodensitometric measurements.

Animals↗
PubMed1978

Carotid ligation for the treatment of carotid artery aneurysms. Pre- and peroperative studies of the cerebral blood flow with an intravenous isotope technique.

Carotid ligation was performed in a series of 30 consecutive cases of infraclinoid aneurysms, of which 6 had not ruptured, and 9 cases of supraclinoid aneurysms. Fifteen of the ruptured aneurysms were operated on before, and 18 after, the eleventh day after bleeding. The internal carotid artery was primarily ligated in four cases, with two deaths, and in one case lasting hemiparesis occurred. In the rest of the cases, the common carotid artery was primarily ligated without operative mortality. After varying intervals, the internal carotid artery was ligated both in the neck and intracranially in 25 cases. In three cases late complications occurred due to embolus and thrombosis, resulting in one death. In four cases there were transient symptoms caused by insufficient cerebral circulation. The cerebral circulation was investigated in 23 cases using an intravenous isotope technique before and after ligation of the common carotid artery. In each of the cases the circulatory values were sufficient, with a slight diminishing of the flow on the ligated side. After ligation of the internal carotid artery at a later stage the flow in both hemispheres increased. This finding has been interpreted as being due to the interruption by internal carotid ligation of the retrograde internal carotid flow that occurs after common carotid ligation. In five cases aorto-cervical angiography was performed some months after ligation of the common carotid artery, and in four a retrograde flow in the internal carotid artery on the ligated side was shown. In accordance with the results obtained suggestions are made for carotid ligation in the treatment of carotid aneurysms not accessible for neck ligation.

Adult↗
PubMed1978

Intrarenal hemodynamics in the transplanted rat kidney.

Regional and single glomerular blood flow conditions in the transplanted rat kidney after various periods of cold ischemia were investigated with use of the microsphere method. Intravascular injection of a silicon rubber compound (Microfil) allowed identification and sampling of single glomeruli. The periods of ischemia were two hours (minor damage), 12 hr (intermediate damage), and 16 hr (severe damage). After two hours of cold ischemia, the regional and total renal blood flows were fairly normal. After 12 hr and 16 hr of cold ischemia, the total and regional blood flows were reduced five minutes after recirculation, the reduction being pronounced in the deep cortex and juxtamedullary glomeruli. In the 12-hr group, the blood flow showed complete restitution after 65 min, whereas in the 16-hr group, the blood flow in the inner cortex and juxtamedullary glomeruli remained decreased. An impairment of medullary circulation would seem to be an important component in the pathophysiology of acute renal failure in this model.

Animals↗
PubMed1978

Nephron function of the transplanted rat kidney.

Tubular function in the early phase (one to three hours) after transplantation of rat kidneys was analyzed with respect to glomerular filtration, vascular and tubular pressures, and excretory variables. Kidneys exposed to a short period of cold ischemia (two hours) functioned almost normally, except for a polyuria. After 12 and 16 hr of cold ischemia, nephron heterogeneity appeared with 1) "normal" tubules, 2) dilated tubules, and 3) collapsed tubules. In the "normal" tubules, the pressure was increased to 20 mm Hg, and the filtration was reduced in proportion to the mean net driving force. The dilated tubules had no filtration due to a more or less complete tubular obstruction, probably located in the thin loop of Henle and in the collecting ducts. The collapsed tubules had no filtration due to glomerular ischemia, which in turn might be the consequence of afferent arteriolar constriction. The total GFR was greatly reduced since only the "normal" tubules contributed to the total filtration. Concentrating ability and potassium secretion were also impaired. We interpreted this impairment as being due to medullary dysfunction, which would explain the isosthenuria and the impaired potassium transport.

Animals↗
PubMed1977

Blood flow in the rabbit tracheal mucosa under normal conditions and under the influence of tracheal intubation.

Isotope labelled microspheres were used to study the capillary blood perfusion of the rabbit tracheal mucosa. Under resting conditions the perfusion was about 0.3 ml/min - g (i.e. about 60% of the relative cerebral blood flow). Irritation of the tracheal mucosa by an endotracheal tube caused a steep rise in blood flow, tenfold or more. This was probably due to relaxation of the arterioles caused by a release of histamine-like substances. When an endotracheal tube is equipped with a small cuff (small resting diameter, low residual volume), the part of the mucosa in contact with the cuff, i.e. the mucosa covering the surface and edges of the cartilages, will be ischaemic at a cuff to tracheal wall pressure (C-T pressure) of greater than 30 millimeters of mercury. This abrupt ischaemia threshold contributes to the risk of deep mucosal damage with subsequent tracheal scarring, possibly proceeding to stenosis. Our present studies indicate that the ideal large cuff, with properties resembling those of an air cushion, will allow the major part of the arterial pressure to be propagated as far down as the capillaries. Under these conditions the cuff would permit some of the capillary blood perfusion of the tracheal mucosa covering the cartilages also at C-T pressures exceeding 30 mmHg. Although this investigation supports the concept that the ideal thin-walled large cuff interferes much less with the mucosal blood perfusion than the small cuff, we recommend that the cuff pressure be monitored and kept below 20 mmHg.

Animals↗
PubMed1977

Measurements of total and regional renal blood flow by videodensitometry.

Videodensitometry has made it possible to determine not only total but also regional blood flow within the kidney. In animal experiments good agreement was found between the measurements by videodensitometry and isotope technique, taking vein samples, using 125I-labelled Angiografin. The blood flow in 21 human kidney has been determined by both videodensitometry and Xe wash-out method. The correlation was fairly good.

Adult↗
PubMed1977

On the theory of an intravenous isotope method for cerebral blood flow measurements.

The theoretical basis of the intravenous isotope method has been examined with particular emphasis on the physiological significance of the area of the curves obtained and the meaning of the peak activity. It is concluded that the area is proportional to the volume of distribution of the indicator within the monitored volume, and inversely related to the cardiac output. The peak activity will be a measure of the fractional blood flow to the brain. It will be affected, however by the extension of the input bolus to the brain but also by the transit time within the brain itself. An unexpected low cardiac output, for instance, will lead to an over-estimation of the cerebral blood flow as derived from the peak activity even though the concomitant prolongation of the input bolus will reduce the error. The theory thus suggests that central circulatory variables will have an influence on the curves obtained and thus also will influence the validity of the method. The validity can be substantially improved by (1) the determination of the input bolus by, for instance, a gamma detector focused over the aortic arch, and (2) by the determination of the cardiac output; this can theoretically be carried out if a true intravascular indicator is used and the investigation is expanded to include the determination of the systemic blood volume.

Blood Volume↗
PubMed1977

The validity of an intravenous isotope method for cerebral blood flow measurements. An experimental study.

The intravenous isotope method has been examined. The method uses 99Tc as the indicator with recording of the radioactivity with two gamma-dectors placed bilaterally over the skull and oriented over the bifurcation of the middle cerebral artery. 65% of the total curve obtained was found to be generated by activity passing in the ipsilateral internal carotid artery, 25% in the contralateral internal carotid artery and less than 10% by activity passing in the two external carotid arteries. The counting rate efficiency for an intracerebral location was 19.4 +/- 1.8 times the count rate from the same activity placed at 1 m distance in air which in turn was 5 cps/muCi. The variability in efficiency from patient to patient was thus estimated at +/- 9%. The duration of the input bolus had a marked influence on the vurve, which will be of importance since it showed a rather large variability from patient. Using the peak activity as an index of the cerebral blood flow the intravenous method showed a surprisingly good correlation with the 133Xe wash-out method; the correlation coefficient was 0.93 and the variability at slightly subnormal values estimated at +/- 15%. It is concluded that the method can be used in the case of limited demands on the accuracy of the cerebral blood flow determinations.

Brain↗
PubMed1976

Hydrostatic pressures within the vascular structures of the rat kidney.

The pressure conditions at the distal end of the interlobular arteries and in the interlobular veins were investigated from the pressures obtained in superficial small arteries and veins, accidentally found on the kidney surface, during the subsequent blockade of the blood stream in the down-stream and up-stream direction, respectively. The results suggested a hydrostatic pressure in the distal end of the interlobular arteries of about 85 mm Hg under normotensive conditions-a pressure which remained fairly constant when the perfusion pressure in the renal artery was decreased within the autoregulation range. The results indicate a considerable pressure drop of about 40 mm Hg along the interlobular arteries. During hypotension this pressure drop decreased, implying a decreased resistance in the interlobular arteries, i.e. a typical autoregulative response. The pressure in the interlobular veins amounted to about 5 mm Hg, which is a few mm Hg higher than that in the renal vein and about 7 mm lower than that in the peritubular capillary network. The results suggest a flow resistance located somewhere between the peritubular capillaries and the intrarenal veins. This resistance is not influenced by vasoactive substances but it is decreased when the systemic venous pressure is raised above 10 mm Hg. The resistance seems to act in the direction of protecting the peritubular capillaries from minor changes in the central venous pressure.

Animals↗
PubMed1975

The pressure-flow relationship of different nephron populations in the rat.

The mechanisms behind the autoregulation of the total renal blood flow and the glomerular filtration rate are unclear. In this investigation a modified microsphere technique was applied to measure the blood flow at different depths in the renal cortex during normotensive and hypotensive conditions. No autoregulation was found in the outer cortex while it was well pronounced in the inner one. During similar conditions, glomerular capillary pressure, welling point pressure and intratubular pressure were recorded. By combining these results with the blood flow data, the preglomerular and postglomerular resistances were calculated. It was then found that the preglomerular resistance decreased and the postglomerular resistance increased when the blood pressure was lowered. The results indicate a redistribution of blood flow from the outer parts to the inner parts of the cortex when the blood pressure is decreased. The redistribution of the blood flow might explain the well known linear relationship between the arterial pressure and the urine flow. The single nephron filtration rate of the outermost glomeruli could be calculated and the results seem to indicate a non-equilibrium at the end of the glomerular capillaries.

Biological Transport, Active↗
PubMed1975

Regional and single glomerular blood flow in the rat kidney prepared for micropuncture. A methodological study.

Regional renal and single glomerular blood flow was investigated in rats using 141-Ce and 85-Sr labelled microspheres. The kidneys were prepared for micropuncture and also the artery was catheterized with a steel cannula in order to make injections of 133-Xenon and vasoactive substances selectively into one kidney. The microspheres were first separated by sedimentation into a narrow fraction and then injected as a plasma suspension into the carotid arter; the two batches were infused at half an hour intervals. Single glomeruli were sampled from kidney sections with the aid of silicon rubber casts allowing the identification of the glomeruli both with respect to their localisation and their postglomerular appearance. The results showed a relatively high blood flow in the superficial and juxtamedullary glomeruli of above 100 nl/min per 100 g rat whereas in the other glomeruli the blood flow was about 70 nl/min per 100 g rat. No differences could be observed between the right untouched kidney and the left prepared for micropuncture. Futhermore no discrepancies between the results from the two injections could be found. The data on the total renal blood flow obtained by the 133-Xenon wash-out method agreed well with the microsphere method.

Animals↗
PubMed1975

Kinetics of the glomerular ultrafiltration in the rat kidney. A theoretical study.

The glomerular filtration process was evaluated theoretically from micropuncture data obtained from Sprague-Dawley rats. The hydrostatic pressures in the glomerular capillaries and Bowman's space minus the oncotic pressure in systemic plasma gave the net driving force at the proximal end of the glomerular capillary. From the single nephron filtration fraction the mean net driving force over the glomerular membrane was calculated to be 20 mm Hg during normotension, decreasing to 12 mm Hg during a perfusion pressure of 80 mm Hg. The hydraulic permeability for one glomerulus was 0.7-0.8 nl/min-100 g b.wt. mmHg. The pressures at the distal end of the glomerular capillaries were 13 and 6 mm Hg under the above two conditions, indicating non-equilibrium of the filtration process at the end of the glomerular capillary. It was shown that the glomerular filtration rate is mainly influenced by the driving pressures. During hypotension an increased plasma flow dependency was evident. Brenner et al. found a filtration equilibrium and a plasma flow dependent glomerular filtration rate in a mutant Wistar rat strain. The discrepancy between their results and ours is due to the low glomerular plasma flow and hydrostatic pressures in the Wistar rats. It is concluded from our results that both pre- and postglomerular resistances may influence the glomerular filtration rate and glomerular plasma flow independently.

Animals↗