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Biomedical subjects

P J Blankestijn

Publications and source records attributed to P J Blankestijn.

At least 37 records · Page 2Linked to original sources
PubMed1998

Presyncope during progressive hypovolaemia simulated by lower body negative pressure is not prevented by high-dose naloxone.

BACKGROUND: The haemodynamic response to progressive hypovolaemia, whether simulated by lower body negative pressure (LBNP) or head-up tilt, or induced by haemorrhage or haemodialysis, has a typical biphasic pattern: a first, sympathoexcitatory, phase of vasoconstriction, tachycardia, and stable blood pressure, and a second, sympathoinhibitory, phase of vasodilatation, bradycardia, and hypotension. The opioid system is involved in this response, since animal studies showed that opioid antagonism by naloxone can attenuate hypovolaemic hypotension. In humans, this finding could not be confirmed. We hypothesized that this could result from inadequate dosing. METHODS: Six healthy subjects underwent LBNP at -45 mmHg until presyncope before and after administration of naloxone 2 mg/kg. During the study, blood pressure, heart rate, vascular resistance, cardiac output, and plasma beta-endorphin were measured. RESULTS: LBNP caused an immediate increase in vasoconstriction and heart rate, resulting in stable blood pressure. After 12 +/- 3.5 min, vasodilatory hypotension followed, accompanied by a modest increase in plasma beta-endorphin. Naloxone did not alter the first or the second phase of the circulatory response, and tolerance to LBNP even tended to decrease (hypotension after 7.5 +/- 2.0 min, NS). Pre-LBNP plasma beta-endorphin as well as hypotensive levels were increased after naloxone. CONCLUSIONS: Our results suggest that naloxone, in a sufficient dose to interfere with the opioid system, does not influence the circulatory response to simulated hypovolaemia in humans is not influenced by naloxone. Given the mechanistic resemblance of LBNP hypotension to dialysis-induced hypotension, we propose that high-dose naloxone is not useful to treat the latter form of hypotension.

Adult↗
PubMed1998

Hemodynamic response during lower body negative pressure: role of volume status.

Sudden dialysis-related hypotension is characterized by paradoxical vasodilation, suggestive of sympathoinhibition. A similar hypotensive reaction can be evoked by lower body negative pressure (LBNP), which thus allows the study of the numerous factors involved in dialysis hypotension separately. This article examines the influence of changes in volume status on the hemodynamic response to LBNP (45 mmHg up to the iliac crest, maximum 60 min) in 12 healthy subjects. LBNP caused a decrease in cardiac index and pulse pressure, and an increase in heart rate and total peripheral resistance, most of which developed within the first 3 min of LBNP. Six subjects developed sudden hypotension characterized by vasodilation after 9 +/- 4 min of LBNP. After saline expansion (25 ml/kg), which increased blood volume by approximately 8%, five subjects endured LBNP for the full 60 min. However, after 60 min of LBNP, the circulatory parameters suggested a similar critical situation as that observed before presyncope in their first experiment. The other six subjects endured the full 60 min of LBNP. After furosemide-induced volume reduction associated with 1.6 +/- 0.2 kg weight loss and approximately 7% blood volume reduction, five of them developed vasodilatory presyncope after 17 +/- 5 min of LBNP. Comparison of presyncopal and nonpresyncopal experiments within subjects, as well as between subjects, showed that the early (3 min) response to LBNP was different: Despite similar decreases in cardiac index, the values for systolic pressure, pulse pressure, peripheral resistance, and stroke volume were lower, and the heart rate was higher in the experiments ending in presyncope. It is concluded that the volume status is a determinant of the tolerance to LBNP, probably by affecting the vasoconstrictive response. By inference, this study suggests that the vasoconstrictive response to the hemodynamic stress of hemodialysis is also influenced by the volume status.

Adult↗
PubMed1997

Cold stress provokes sympathoinhibitory presyncope in healthy subjects and hemodialysis patients with low cardiac output.

BACKGROUND: Sudden hypotension in progressive hypovolemia or during hemodialysis is attributed to sudden inhibition of sympathetic activity. Critical ventricular underfilling seems responsible for this paradox, but it is unknown why the transition from sympathoactivation accompanying hypovolemia to sympathoinhibition is so abrupt. We studied whether brief fluctuation of sympathetic activity induced by cold pressor test (CPT) evokes sympathoinhibition if applied during low cardiac output. METHODS AND RESULTS: Fourteen healthy subjects underwent CPT, lower-body negative pressure (LBNP; -45 mm Hg for 60 minutes), or the combination thereof. CPT alone caused vasoconstriction and increased muscle sympathetic nerve activity, followed by uneventful relaxation. When applied during reduced cardiac output, tachycardia, and vasoconstriction induced by prior LBNP for 6 minutes, CPT again caused vasoconstriction, now followed by acute hypotension in 10 subjects, and was associated with vasorelaxation, relative bradycardia, and fall in muscle sympathetic nerve activity. Eight subjects also experienced acute LBNP-induced hypotension in the absence of CPT, but not until 17 +/- 6 minutes of LBNP. We also performed CPT before and in the final phase of hemodialysis in 8 patients. Before dialysis, the patients tolerated CPT uneventfully, but during hemodialysis, CPT provoked acute hypotension in 5 cases, showing similar withdrawal of vasoconstriction. CONCLUSIONS: This is the first study showing that brief cold stress, tolerated well in normal circulatory conditions, can provoke sudden sympathoinhibition and hypotension when applied during decreased cardiac output induced by LBNP or hemodialysis. We suggest that during conditions of a decreased cardiac output, subtle sympathetic relaxation such as follows cold stress triggers self-enhancing relaxation that cannot be controlled.

Adult↗
PubMed1997

Pressure or flow recordings for the surveillance of hemodialysis grafts.

Venous pressures (VP) measured by the dialysis machine are widely used for access surveillance and have significantly improved outcomes. VP reflect the resistance in the venous outflow tract, which will rise in the presence of stenosis. Low graft flow caused by high graft resistance predicts thrombosis. In this study we investigated whether high VP coincides with low graft flow (measured by ultrasound dilution technique). Of 70 forearm bridge grafts in 42 chronic hemodialysis patients, 31 had an angiographically proven outflow stenosis. VP at 200 ml/min blood flow (VP200), total graft resistance and venous outflow resistance were higher whereas graft flow was lower in patients with venous outflow tract stenosis as compared to patients without stenosis. Diagnostic power of the tests for identifying patients with venous stenosis showed no important differences. However, arterial inflow resistance, which is not reflected in VP measurements, represented a substantial and, more importantly, a highly variable percentage of total graft resistance. As a result graft flow showed no correlation with VP measurements. In conclusion, although patients with venous outflow stenosis may be identified accurately using venous pressure assessments, graft flow measurements seem to be more suitable for selecting patients at risk for thrombosis.

Angiography↗
PubMed1997

Pulmonary embolism after thrombolysis of hemodialysis grafts.

The aim of this study was to determine the incidence of pulmonary embolization occurring after mechanical or pharmacomechanical percutaneous intravascular thrombolysis in 23 patients with occluded hemodialysis grafts. In all patients, pulmonary perfusion scintigraphy was performed before and immediately after thrombolysis. In eight (35%) of the patients, there was evidence of pulmonary embolism resulting from the interventional procedure; however, in only one was there clinical symptoms. It is concluded that there is substantial risk of pulmonary embolism in patients undergoing percutaneous intravascular thrombolysis for an occluded hemodialysis graft.

Catheters, Indwelling↗
PubMed1996

Growth hormone responses to growth hormone-releasing hormone and clonidine in patients with type I diabetes and in normal controls: effect of age, body mass index and sex.

OBJECTIVE: Increased plasma concentrations of GH and increased GH responses to provocative stimuli are reported in patients with poorly controlled type I diabetes and are suggested to be related to complications. Our aim was to investigate GH concentrations in moderately controlled patients. PATIENTS AND MEASUREMENTS: We have investigated IGF-I concentrations and fasting GH concentrations and the response to 1 microgram/kg body weight GH-releasing hormone (GHRH) intravenously and/or to 150 micrograms clonidine intravenously in 77 moderately controlled patients with type I diabetes and in 46 healthy controls. RESULTS: Median HbA1c in the patients was 8.5% (upper level of normal 6.3%). Fasting GH and GH concentrations after the administration of GHRH were not significantly different in patients with type I diabetes compared with normal controls. Fasting and stimulated GH concentrations after the administration of clonidine were significantly higher in the patients, but this could be explained by their lower age and body mass index compared with controls. In controls but not in patients there was a negative correlation between GH and glucose concentrations. IGF-I was significantly lower in patients with diabetes than in controls, even after correction for age, body mass index and sex. CONCLUSIONS: Patients with moderately controlled type I diabetes mellitus have normal baseline and stimulated GH concentrations after the administration of GHRH or clonidine compared with healthy controls, when corrected for age, body mass index and sex. However, these 'normal' GH concentrations must be considered inappropriately high in view of the hyperglycaemia in these patients. The low plasma IGF-I concentrations might be responsible for the GH over-production.

Adolescent↗
PubMed1996

No change in automatic function tests during uncomplicated haemodialysis.

Uraemic autonomic dysfunction is reckoned to participate in dialysis hypotension, but a clear relationship has not been established. However, autonomic function is usually tested at rest, and possibly autonomic dysfunction arises or worsens during dialysis. We therefore performed easily repeatable tests of efferent sympathetic function, that is static exercise test and parasympathetic function, that is heart rate variability during Valsalva manoeuvre and deep breathing, at successive stages of a standard haemodialysis session; before dialysis, 20 min after dialysis without ultrafiltration, after 3 h of dialysis combined with ultrafiltration, and 20 min after dialysis. Studies were performed in 22 patients on chronic haemodialysis on a cuprophane dialyser. The mean ultrafiltration volume was 2.2 +/- 0.61. We found that blood pressure elevation upon static exercise, and heart rate variability during Valsalva or deep breathing test remained unaltered at the various stages of dialysis. On past performance the patients were divided into hypotension prone (n = 6) or resistant (n = 16). Hypotension prone patients showed a greater blood pressure drop during dialysis, but also showed an appropriately enhanced heart rate acceleration. The occurrence of autonomic dysfunction was not elevated in this group, nor did such dysfunction develop along dialysis. Predialysis parasympathetic function tests were abnormal in 10 patients. These patients also showed an augmented intradialytic blood pressure decrease, but no enhanced acceleration in heart rate. Their parasympathetic dysfunction did not worsen during dialysis. Based upon the predialysis exercise test, low responding patients (blood pressure increase 5 +/- 2 mmHg, n = 11) were distinguished. These subjects were not characterized by a greater blood pressure decrease or different heart rate acceleration. Generally, the responses upon exercise, whether low or high, remained unaltered during dialysis. we conclude that haemodialysis has no systematic effect on autonomic function. Hypotension-prone patients are not distinguished by a disturbed predialytic or intradialytic autonomic blood pressure control.

Adult↗
PubMed1996

Access flow measurements in hemodialysis patients: in vivo validation of an ultrasound dilution technique.

In this study, access flow in hemodialysis patients with bridge grafts was measured by a newly developed device. The technique is based on the measurement of changes in the ultrasound characteristics of blood. These changes were initiated by an injection of isotonic saline and measured in the tubes of the extra-corporeal circuit. The access flow rate (mean +/- standard variation) was 880 +/- 440 mL/min (range, 166 to 1740) (N = 46). The mean coefficient of variation was 13.4 +/- 6.8% (median, 13.0%; range 3.5 to 29.4%). Measurements correlated well (r = 0.91, N = 22, P < 0.001) with flow rates determined by magnetic resonance angiography and by a technique based on intra-access flow-pressure curves (r = 0.84, N = 14, P < 0.001). In conclusion, access flow can be measured easily, noninvasively, and reliably by the ultrasound dilution device.

Blood Pressure↗
PubMed1995

The results of denatured homologous vein grafts as conduits for secondary haemodialysis access surgery.

OBJECTIVES: To determine the value of denatured homologous vein grafts as a conduit for secondary haemodialysis access. DESIGN: Retrospective clinical study. SETTING: 2 University Hospitals. MATERIALS AND METHODS: One-hundred-and-twenty-five patients received 195 grafts over a period of five years. Fifty-six first grafts (45%) functioned without complications throughout the study period of 5.8 years. MAIN RESULTS: Primary patency was 57% after 1 year and 25% after 3 years of follow-up. Of the initial grafts, 69 (55%) needed 161 interventions, for thrombosis (n = 59), stenosis (n = 43), failure beyond repair (n = 40), aneurysm (n = 12), infection (n = 4), steal syndrome (n = 1), and other causes (n = 2). Secondary patency was 76% at 1 year and 52% at 3 years of follow-up. A major advantage of these grafts was the low rate (2.6%) of infection. Aneurysm formation occurred 17 times in 195 grafts (8.7%). CONCLUSIONS: Denatured homologous vein graft is a good alternative in secondary access surgery.

Arteriovenous Shunt, Surgical↗
PubMed1995

Hemodynamic and biochemical effects of the AT1 receptor antagonist irbesartan in hypertension.

We studied the hemodynamic, neurohumoral, and biochemical effects of the novel angiotensin type 1 (AT1) receptor antagonist irbesartan in 86 untreated patients with essential hypertension on a normal sodium diet. According to a double-blind parallel group trial, patients were randomized to a once-daily oral dose of the AT1 receptor antagonist (1, 25, or 100 mg) or placebo after a placebo run-in period of 3 weeks. Randomization medication was given for 1 week. Compared with placebo, 24-hour ambulatory blood pressure did not change with the 1-mg dose, and it fell (mean and 95% confidence interval) by 7.0 (4.2-9.8)/6.1 (3.9-8.1) mm Hg with the 25-mg dose and by 12.1 (8.1-16.2)/7.2 (4.9-9.4) mm Hg with the 100-mg dose. Heart rate did not change during either dose. With the 25-mg dose, the antihypertensive effect was attenuated during the second half of the recording, and with the 100-mg dose, it was maintained for 24 hours. Baseline values of renin and the antihypertensive response to the 25- and 100-mg doses were well correlated (r = .68, P < .01). Renin did not change with the 1-mg dose, but it rose threefold to fourfold with the 25-mg dose and fourfold to fivefold with the 100-mg dose 4 to 6 hours after administration. With the 100-mg dose, renin was still elevated twofold 24 hours after dosing. The changes in renin induced by the AT1 receptor antagonist were associated with parallel increments in angiotensin I and angiotensin II. Aldosterone, despite AT1 receptor blockade, did not fall.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Hypertension after renal transplantation. Calcium channel or converting enzyme blockade?

We compared the effects of 4 weeks of calcium channel blockade (amlodipine) or converting enzyme inhibition (lisinopril) on blood pressure and renal hemodynamics in a double-blind crossover trial in a group of 20 hypertensive cyclosporine-treated renal transplant patients. Amlodipine (10 mg) was more effective than the same dose of lisinopril in controlling hypertension (mean 24-hour arterial pressure, 111 +/- 9 and 115 +/- 9 mm Hg, respectively; P < .05). Blood pressure during both treatments was lower than during placebo (124 +/- 12 mm Hg, P < .05). Compared with placebo, amlodipine treatment was associated with a significant increase in glomerular filtration rate (10 +/- 20%, P < .05) and effective renal plasma flow (27 +/- 20%, P < .01) and a decrease in renal vascular resistance (23 +/- 18%, P < .01). Renal hemodynamics did not change during lisinopril. Neither drug had an effect on proteinuria. The data indicate that amlodipine is more effective than lisinopril in controlling hypertension in cyclosporine-treated patients and that treatment with amlodipine but not with lisinopril is accompanied by an increase in glomerular filtration rate and effective renal plasma flow and a decrease in renal vascular resistance. The data suggest that the renin-angiotensin system does not play a main role in determining cyclosporine-associated changes in renal hemodynamics and has a limited role in determining cyclosporine-associated hypertension.

Adult↗
PubMed1995

High-flux dialysis membranes improve lipid profile in chronic hemodialysis patients.

In a controlled prospective trial, the effect of a switch from cellulose-based, low-flux dialysis membranes to polysulphone, high-flux membranes on lipid parameters was evaluated. Baseline values of lipid parameters were identical in the study group and the control group in which the dialysis membrane remained unchanged. After 6 wk, total triglyceride, very low-density lipoprotein (VLDL) triglyceride, and VLDL cholesterol decreased, respectively, 28 +/- 17 (P < 0.01), 38 +/- 17 (P < 0.01), and 24 +/- 21% (P < 0.05), and the proportion of total cholesterol that was high-density lipoprotein cholesterol increased from 15 +/- 5 to 18 +/- 5% (P < 0.05) in the high-flux polysulphone group, whereas these variables remained unchanged in the control group. Low-density lipoprotein and total cholesterol as well as Kt/V, protein catabolic rate, parathyroid hormone, albumin, and body weight did not change. No change in lipoprotein lipase activity was found. In a second study, the effects of a single hemodialysis session with high-flux polysulphone and low-flux, cellulose-based membranes on lipid parameters and lipolytic activity were compared in a cross-over fashion. Treatment with both membranes resulted in a significant decrease in plasma triglyceride, VLDL triglyceride, and VLDL cholesterol. Lipoprotein lipase activity increased during hemodialysis. Changes in lipid parameters and lipolytic activity were identical during the two treatments.

Adult↗
PubMed1995

Optimising glomerular filtration rate and effective renal plasma flow measurements using a simple pharmacokinetic model.

We applied an open one compartment pharmacokinetic model for the determination of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) based on a rapid intravenous loading dose followed by a constant infusion of 125I-iothalamate and 131I-orthoiodohippurate in order to ensure constant plasma levels of the two clearance markers. The loading dose was based on the assumption that the volume of distribution of the two markers equals the extracellular volume (25% of the body weight). The infusion rate as calculated after the clearance of thalamate was estimated from body weight, age, sex and serum creatinine using Cockcrofts formula. The clearance of hippurate was assumed to be four times that of thalamate. We studied the reliability of this model in 212 patients with insulin dependent diabetes mellitus (IDDM; n = 74), nephrotic syndrome (NS; n = 18) and heart (HTX; n = 69) or kidney (KTX; n = 51) transplants. A steady state concentration was obtained in all patient groups, even when GFR was markedly depressed. In patients with diabetes, we observed more variance between plasma and urinary clearances of thalamate, which could be due to inaccuracies in urine sampling. In these patients, GFR should be measured using a method that is not dependent on urine collection. Also, the estimation of GFR by means of Cockcrofts equation seems to underestimate GFR in diabetic subjects.

Glomerular Filtration Rate↗