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Biomedical subjects

B Flemming

Publications and source records attributed to B Flemming.

At least 19 recordsLinked to original sources
PubMed2003

The step response: a method to characterize mechanisms of renal blood flow autoregulation.

Response of renal vasculature to changes in renal perfusion pressure (RPP) involves mechanisms with different frequency characteristics. Autoregulation of renal blood flow (RBF) is mediated by the rapid myogenic response, by the slower tubuloglomerular feedback (TGF) mechanism, and, possibly, by an even slower third mechanism. To evaluate the individual contribution of these mechanisms to RBF autoregulation, we analyzed the response of RBF to a step increase in RPP. In anesthetized rats, the suprarenal aorta was occluded for 30 s, and then the occlusion was released to induce a step increase in RPP. Three dampened oscillations were observed; their oscillation periods ranged from 9.5 to 13 s, from 34.2 to 38.6 s, and from 100.5 to 132.2 s, respectively. The two faster oscillations correspond with previously reported data on the myogenic mechanism and the TGF. In accordance, after furosemide, the amplitude of the intermediate oscillation was significantly reduced. Inhibition of nitric oxide synthesis by Nomega-nitro-l-arginine methyl ester significantly increased the amplitude of the 10-s oscillation. It is concluded that the parameters of the dampened oscillations induced by the step increase in RPP reflect properties of autoregulatory mechanisms. The oscillation period characterizes the individual mechanism, the dampening is a measure for the stability of the regulation, and the square of the amplitudes characterizes the power of the respective mechanism. In addition to the myogenic response and the TGF, a third rather slow mechanism of RBF autoregulation exists.

Animals↗
PubMed2002

Influence of baroreflex on volume elasticity of heart and aorta in the rabbit.

Optimal ventriculoaortic coupling includes tuning of elastic properties. The ratio of effective arterial elastance and left ventricular endsystolic elastance is often taken as a measure for mechanical and energetical efficiency. The present study determined the time course of ventricular and aortic volume elasticity (VE = dp/dV) throughout a complete heartbeat. This was achieved by using changes of eigenfrequency of two catheter-transducer systems under closed chest conditions in rabbits. Short-term VE modulation was studied by a baroreflex response, as induced by pressure changes applied to the carotid sinus. Long-term changes were studied in atherosclerotic rabbits (12 wk of high-cholesterol feeding). The time course and mean values of ventricular and aortic VE were changed by the baroreflex stimulus. Cholesterol feeding diminished the response. The degree of ventriculoaortic coupling, as quantified by VE(Aorta)/VE(Ventricle) ratio, varied during a single ejection period. The large span allows either maximal energetical efficiency or maximal stroke work. Although normal rabbits adjusted their ventriculoaortic coupling during baroreflex input, the cholesterol-fed rabbits failed to do so.

Animals↗
PubMed2000

Coupling of left ventricular and aortic volume elasticity in the rabbit.

Changes in volume elasticity (VE) of the left ventricle and aorta could be important for blood flow. A procedure is presented to rapidly assess VE of the left ventricle and aorta by analyzing changes in the eigenfrequency. Six control rabbits and 11 rabbits with atheromatosis (12 wk of high-cholesterol feeding) were studied. In control rabbits, during the first half of the systole, left ventricular VE continuously increased to +43% (P < 0.05). Then VE gradually declined to an end-diastolic minimum (20% of the average systolic levels, P < 0.05). Aortic VE changes were in the opposite direction to the ventricle. Aortic VE continuously decreased throughout the systole; the last value was 20% lower than at the beginning of the systole (P < 0.05). Conversely, diastolic VE of the aorta took on greater values. This inverse time course between ventricle and aorta may reduce energy requirements for conveying blood. High cholesterol-fed rabbits did not reveal the inverse behavior of ventricular and aortic VE, e.g., aortic VE increased during the systole (119%, P < 0.05).

Animals↗
PubMed1998

Accuracy of screening compression ultrasonography and clinical examination for the diagnosis of deep vein thrombosis after total hip or knee arthroplasty.

OBJECTIVE: To determine whether compression ultrasonography or clinical examination should be considered as screening tests for the diagnosis of deep vein thrombosis (DVT) after total hip or knee arthroplasty in patients receiving warfarin prophylaxis postoperatively. DESIGN: A prospective cohort study. SETTING: A single tertiary care orthopedic centre. PATIENTS: One hundred and eleven patients who underwent elective total hip or knee arthroplasty were enrolled. Postoperatively the warfarin dose was adjusted daily to maintain the international normalized ratio between 1.8 and 2.5. Eighty-six patients successfully completed the study protocol. INTERVENTION: Before they were discharged from hospital, patients were assessed for DVT by clinical examination, bilateral compression ultrasonography of the proximal venous system and bilateral contrast venography. RESULTS: DVT was found in 29 patients (34%; 95% confidence interval [CI] 24% to 45%), and 6 patients (7%; 95% CI 3% to 15%) had proximal DVT. DVT developed in 18 (40%) of 45 patients who underwent total knee arthroplasty and in 11 (27%) of 41 patients who underwent total hip arthroplasty. The sensitivity of compression ultrasonography for the diagnosis of proximal DVT was 83% (95% CI 36% to 99%) and the specificity was 98% (95% CI 91% to 99%). The positive predictive value of compression ultrasonography was 71%. In contrast, clinical examination for DVT had a sensitivity of 11% (95% CI 2% to 28%) and a positive predictive value of 25%. CONCLUSIONS: DVT is a common complication after total hip or knee arthroplasty. Compression ultrasonography appears to be a relatively accurate noninvasive test for diagnosing postoperative proximal DVT. In contrast, clinical examination is a very insensitive test. Whether routine use of screening compression ultrasonography will reduce the morbidity of venous thromboembolism after joint arthroplasty requires confirmation in a prospective trial involving long-term follow-up of patients.

Aged↗
PubMed1997

Ultrasonographic screening before hospital discharge for deep venous thrombosis after arthroplasty: the post-arthroplasty screening study. A randomized, controlled trial.

BACKGROUND: The clinical significance of asymptomatic deep venous thrombosis that develops after joint arthroplasty and the value of screening tests to detect thrombi are uncertain. OBJECTIVES: To determine 1) the rate of symptomatic deep venous thrombosis or pulmonary embolism occurring after hospitalization for joint arthroplasty and 2) the value of screening compression ultrasonography. DESIGN: Double-blind, randomized, controlled trial. SETTING: Tertiary care hospital. PATIENTS: 1024 patients undergoing elective total hip or knee arthroplasty who received warfarin prophylaxis. INTERVENTION: Patients were randomly assigned to undergo either bilateral compression ultrasonography or a sham procedure before hospital discharge. Patients with a diagnosis of asymptomatic deep venous thrombosis were treated after discharge with standard anticoagulant therapy; other patients had warfarin therapy discontinued at discharge. All patients were followed for 90 days. RESULTS: In the screening group, asymptomatic proximal deep venous thrombosis was detected in 13 of 518 patients (2.5%). Another 4 patients subsequently developed symptomatic proximal deep venous thrombosis, and 1 patient treated for asymptomatic deep venous thrombosis developed major bleeding, for a total outcome event rate of 1.0% (5 of 518 patients). In the placebo group, 3 patients developed symptomatic proximal deep venous thrombosis and 2 had nonfatal pulmonary embolism, for a total event rate of 1.0% (5 of 506 patients) (difference, 0 percentage points [95% CI, -1.2 to 1.2 percentage points]). CONCLUSIONS: In patients undergoing total hip or knee arthroplasty, the use of warfarin prophylaxis during hospitalization results in a very low rate of symptomatic deep venous thrombosis or pulmonary embolism after hospital discharge. The use of screening compression ultrasonography at hospital discharge does not seem to be justified in this setting.

Algorithms↗
PubMed1996

Ventricular volume elasticity: a component of cardiovascular control?

According to Koepchen, stimulation of different receptors within a complex network produces typical patterns of effector responses. We investigated whether the dynamical volume elasticity of the heart chamber is an independent component of cardiovascular control. The measurement of the dynamical volume elasticity was calculated by changes of the eigenfrequency of a modified catheter transducer system. The carotid baro- and chemoreflex affected end-diastolic pressure, contractility and calculated diastolic and systolic elasticity to different extents. In conclusion, cardiac volume elasticity is an independent element interacting with other parameters in cardiovascular control.

Animals↗
PubMed1990

The volume elasticity of the heart: a method for its evaluation under closed chest conditions.

A method is described for measuring the volume elasticity of the heart under closed chest conditions by simply inserting a catheter in the left ventricle. The heart as a system capable of oscillations detunes an external oscillating system. The shift in resonance frequency is a measure of the volume elasticity. The time course of diastolic volume elasticity values during one filling phase shows that active mechanisms are involved in the filling. The method can be applied to human beings: it allows the measurement of the volume elasticity of the whole ventricle and of small areas of the myocardium.

Blood Pressure↗
PubMed1989

[Physiological parameters of guinea pigs under long-term anesthesia with controlled respiration].

56 guinea pigs were anesthetized with a mixture of alpha-chloralose and a small dose of ethyl urethane injected i.p. in order to compare the chloralose-urethane anesthesia with neuroleptanesthesia, a mixture of droperidol-fentanyl and a small induction dose of Na-pentobarbital was injected i.p. to 14 animals. All animals were maintained at constant body temperature of 38 degrees C and artificially respirated via a tracheal cannula monitoring the end expiratory CO2 concentration. Mean arterial blood pressure (carotid artery) and heart rate were continuously recorded. Arterial acid-base status and pO2 were tested. Mean arterial blood pressure and heart rate were found to be somewhat higher in the neuroleptanesthetized animals. Under chloralose-urethane anesthesia and neuroleptanesthesia the mean arterial blood pressure amounted to 56 and 62 mm Hg, respectively. These findings correspond to data given in the literature concerning the mean pressure in unanesthetized guinea pigs. The mean heart rates of 295 and 316 min-1, respectively are somewhat higher compared to the normal range. Under both anesthesias, the arterial acid-base status was within the normal limits of unanesthetized animals. The mean arterial pO2 of 80.9 and 76.5 mm Hg was relatively low. The present studies have shown that chloralose-urethane as well as droperidol-fentanyl with pentobarbital are useful, under controlled artificial respiration, to achieve long-term anesthesia maintaining nearly normal systemic circulatory and respiratory conditions.

Anesthesia↗
PubMed1989

[Kidney function in the course of compensatory hypertrophy following unilateral nephrectomy in the Wistar rat].

Unilateral nephrectomy was performed in 109 male Wistar rats, 35 animals served as controls. Determinations of glomerular filtration rate (GFR) using slope clearance of 99mTc-DTPA and of tubular function using an orally water-loading test were made. The tests were performed 2 and 5 days as well as 2, 4, 5 and 6 weeks after nephrectomy. In all examinations the GFR was more than 50% of the level of two-kidney control animals. Fractional maximum diuresis was increased in the first 2 examinations after nephrectomy from 8.9 +/- 2.1 to 15.4 +/- 4.2% of the GFR and fractional clearance of osmotically free water from 6.8 +/- 1.9 to 10.9 +/- 3.5%. In the fourth and sixth week the proximal tubular reabsorption was increased and the glomerulo-tubular balance had been recovered. However, the minimal urine osmolarity was increased to 107.8 +/- 17.7 mmol/l and the osmotic load of the nephrons remained elevated. Possible clinical implications of the results are discussed.

Animals↗
PubMed1988

Determination of the acid-base status in blood of patients on chronic haemodialysis and of bicarbonate in dialysate: comparison of three techniques and their mathematically derived values.

The study deals with the comparison of acid-base parameters in blood of patients on chronic haemodialysis and of bicarbonate dialysate determined by Gas-Check AVL 945, equilibration technique (ET), and a titrimetric method. The results show that an acceptable agreement exists between AVL and ET with respect to measurements of pH, pCO2, HCO3-, and base excess. However, the values obtained for total buffer base related to the actual haemoglobin concentration are significantly lower (P less than 0.001) when determined by AVL. A titrimetric method is proposed for routine measurement of HCO3- in bicarbonate dialysate. Values obtained using this method are 3-4 mmol/l higher than those determined by AVL and ET. However, when the values for pK1' and for the solubility coefficient used in the Henderson-Hasselbalch equation are replaced by those for saline-bicarbonate solutions, results obtained using the titrimetric determined values agree well with those obtained by AVL and ET.

Acetates↗
PubMed1988

The influence of mixed venous pO2 on the natriuretic activity of cat plasma.

Plasma was taken from anaesthetised cats with high or low mixed venous pO2. Different plasma fractions were then administered to anaesthetised rats to examine the effect on sodium excretion. It was found that only the low molecular weight fraction of the plasma from cast with high mixed venous pO2 showed any natriuretic activity. A lipid soluble extract from the same plasma also increased sodium excretion. It is concluded that an increase in mixed venous pO2 in anaesthetised cats leads to the release or activation of a natriuretic factor, which has a molecular weight below 700 and is lipid soluble.

Animals↗
PubMed1987

Erythrocyte sodium transport in normotensive and hypertensive patients on chronic hemodialysis, acute effect of treatment.

Patients on chronic hemodialysis were divided into two groups: normotensive patients (group I) and renal hypertensive patients treated with antihypertensives (group II). The sodium and potassium contents in red blood cells ([Na+]i, [K+]i), ouabain-resistant net sodium uptake (ORNa+ uptake, phi Na), the relative ORNa+ uptake (k), the mean cell hemoglobin concentration (MCHC), and acid-base status were examined just before and after dialysis. The results indicate that in treated renal hypertensive patients k is stimulated and causes lower red blood cell sodium content. The reason for this increase remains obscure: the pattern of alterations of the sodium transport components during dialysis is similar in all patients: [Na+]i and phi Na increase significantly during dialysis, and the increases in [Na+]i are closely related to increases in pH and bicarbonate.

Antihypertensive Agents↗
PubMed1986

Long-term effect of repeated short oxygen exposition on blood pressure development and erythrocyte sodium content in SHR and WKY.

Repeated short oxygen exposition (60 min weekly, beginning at the 1st week of age up to the 18th week of age) induced in male spontaneously hypertensive rats (SHR) a diminished blood pressure rise. Oxygen exposed SHR had also lower heart rates than SHR without oxygen exposition. No significant differences were found in both these parameters in normotensive rats (WKY). Furthermore oxygen exposition decreased the erythrocyte sodium content of SHR.

Aging↗
PubMed1985

[Relation of glucose tolerance and intracellular sodium concentration].

In rabbits with standard diet, in cholesterolaemic rabbits, in pregnant women with physiological hyperinsulinism and in a control group with lower peripheral insulin concentrations after glucose load negative correlations were found between the intracellular sodium content and the KG-value of the intravenous glucose tolerance test. The hormonally regulated blood glucose regulating circle was a prerequisite for these relations, since in vitro a high sodium concentration in the erythrocytes was connected with a high glucose uptake rate. The findings in the total organism were explained by cell membrane properties which stabilise the level of the intracellular sodium concentration as well as are important for functions of the blood glucose regulating circle. As a link between the carbohydrate metabolism and the electrolyte metabolism the SH-groups of the cell membrane were discussed. This concept was used for a pathophysiological explanation of the higher erythrocytic sodium concentrations proved in manifest diabetics.

Animals↗
PubMed1985

[Effect of changes in central venous oxygen partial pressure on kidney function in anesthetized cats].

An extracorporeal veno-venous bypass utilizing an oxygenator to alter mixed venous blood gases was used in experiments on chloralose anesthetized cats. The gas mixture in the oxygenator was alternate 95% O2 or 95% N2 with additional 5% CO2. The produced difference of pO2 in the right ventricle (pO2v-) was 1.3 kPa. The arterial acid base status and the blood gases were not affected by this procedure. Comparing the alterations of pO2v- the higher level of pO2v- was connected with an increase of the mean arterial blood pressure, of the clearances of inulin and PAH, and of the sodium and the potassium excretion. These experiments demonstrate that the alterations of pO2v- have influence on the renal function.

Anesthesia, General↗
PubMed1982

[Correlation of erythrocyte sodium concentration and the KG-value in variable peripheral insulin levels].

In pregnant women with physiological hyperinsulinism and in a control group with lower peripheral insulin concentrations after glucose load was investigated, whether differences in the peripheral insulin content involve different relations between the KG-value and the sodium concentration of the erythrocytes. Despite the differences in the peripheral insulin content during the intravenous glucose tolerance test negative correlations between the KG-value and the sodium concentration of the erythrocytes were found in the groups investigated. From this was concluded that these correlations are not based on changes of the peripheral insulin level, as they were established in the present examinations. A conception was presented issuing from the fact that the negative correlation between the KG-value and the sodium concentration is based on properties of the cell membrane which influence the intracellular sodium concentration as well as the effect of insulin in the cell.

Adult↗
PubMed1982

The sublethal effects of a polychlorinated biphenyl (Aroclor 1254) diet on the Atlantic cod (Gadus morhua).

The effects of diet levels of 1, 5, 10, 25 and 50 micrograms Aroclor 1254/g on the Atlantic cod Gadus morhua were determined after a feeding period of 5 1/2 months. Altered steroid biosynthetic patterns in vitro were observed in the testes and head kidneys (adrenal homologue) of the fish that were fed various levels of PCB in vivo. Histological examination of tissues revealed abnormalities in the testes, gills, and livers of the PCB-fed fish. Various testicular abnormalities including slight-to-marked derangement of lobules, hyperplasia of lobule walls and disintegration and/or fatty necrosis of spermatogenic elements were observed in the testes of PCB-fed fish. Hyperplasia of the epithelial layer of the secondary lamellae was observed in the gills of fish on the 5 to 50 micrograms Aroclor 1254/g diet. Fatty degeneration was observed in the livers of all PCB-fed fish. The PCB content of testes, livers and head kidneys were directly proportional to the level of Aroclor 1254 in the diet. It is apparent that sublethal levels of PCB have a detrimental effect on the physiology of the Atlantic cod.

Animals↗