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Biomedical subjects

J van Loon

Publications and source records attributed to J van Loon.

28 records · Page 2Linked to original sources
PubMed1994

Muscle- and pneumatic-powered counterpulsating LVADs: a pilot study.

There is a worldwide interest in supporting the failing heart with a skeletal muscle by either wrapping it around the natural heart (dynamic cardiomyoplasty) or by constructing a skeletal muscle ventricle (SMV) used for counterpulsation. Conventional cardiomyoplasty in many clinics carries an operative mortality rate of 15-20% partly because it requires 6 weeks to train the muscle to contract continually. A flexible, pear-shaped blood pump with an inflatable air chamber was designed and made around which a muscle can be wrapped. The advantage of our design is that it can also be driven by pneumatic power, immediately supporting the circulation of a seriously ill patient while that patient is still on the operating table. After a period of time to allow for revascularization and the subsequent training of the muscle, the external pneumatic power can be gradually discontinued. Then the assisted patient becomes tether-free. If, at any time, the muscle power fails, the pneumatic-powered mechanism can be reactivated. In the preferred approach, the blood pump is connected to the aorta for diastolic counterpulsation. A muscle can either be wrapped around the blood pump directly, or around one of two separate muscle pouches connected to the blood pump. To facilitate surgery, a large pouch is inserted under the musculus latissimus dorsi, which is connected to a blood pump. When stimulated, the muscle will contract over the pouch compressing it and providing power to the blood pump. If it is found that the pressure generated in the pouch cannot meet the aortic blood pressure, it can be augmented by using a pressure amplifier.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Controversies in the management of spontaneous cerebellar haemorrhage. A consecutive series of 49 cases and review of the literature.

We have reviewed our experience with a series of 49 consecutive patients with spontaneous cerebellar haematoma, treated according to a standardized management protocol. Seventeen patients were managed conservatively, 30 underwent ventricular drainage, and in six patients the haematoma was evacuated. The indications for the different modes of treatment are discussed. The most significant prognostic factors determining the outcome at one month were the grade of quadrigeminal cistern obliteration on the initial CT scan and the Glasgow Coma Scale on admission. Patients with normal cisterns had a good outcome, and only needed (temporary) ventricular drainage in case of hydrocephalus. Patients with totally obliterated cisterns had a bad outcome irrespective of treatment. In the patients with compressed cisterns, it is suggested that evacuation of the haematoma might improve outcome; treatment of hydrocephalus alone is insufficient in many cases in this group.

Adolescent↗
PubMed1993

Catecholamine response to a gradual increase of intracranial pressure.

To determine the catecholamine response to progressive intracranial hypertension, intracranial pressure (ICP) was raised gradually by continuous expansion of an epidural balloon in seven dogs. Hemodynamic parameters, ICP, and cerebral perfusion pressure (CPP) were monitored continuously and serum catecholamine levels began to rise when CPP was in the low-positive range (20 to 30 mm Hg), reaching a peak just after brain death (CPP < or = o mm Hg). There was no correlation between ICP and the catecholamine peak. Compared to control values, the mean increase was 286-fold for epinephrine and 78-fold for norepinephrine. Temporally, the catecholamine peak corresponded well with the observed hemodynamic changes. These results suggest that ischemia in certain parts of the brain stem is responsible for the hemodynamic changes observed in intracranial hypertension (such as the Cushing response), and they show that catecholamines play an important role in these hemodynamic changes.

Animals↗
PubMed1992

Subcortical aphasia from a thalamic abscess.

A patient is reported who was treated successfully for a left thalamic abscess that resulted in subcortical aphasia. A SPECT scan showed large areas of hypoperfusion in the cortex of the left hemisphere. At follow up after seven months there was marked improvement in the language disorder and the cortical hypoperfusion. It is suggested that aphasia in patients with subcortical lesions results from secondary cortical dysfunctions. The evidence is confined to patients with stroke lesions. The possible implications of this case on current theories of pathophysiological mechanisms, in particular the ischaemic penumbra theory and the cortical diaschisis theory, are briefly discussed. Cortical diaschisis may be the appropriate explanation in this patient.

Adult↗
PubMed1991

Multicentre comparison of the Novo Biolabs immunometric CK-MB assay with four established methods.

The analytical performance of a new immunometric CK-MB assay from Novo Biolabs was evaluated in three hospitals. Comparisons were made with another immunometric assay, an immune inhibition/precipitation technique, an immune inhibition method, and a column separation method. The Novo assay exhibited good precision (CV 3-7%) at all concentration levels tested (6-150 micrograms/L) and was found to be linear over the range 0-200 micrograms/L. Comparison of the Novo kit with the other methods using patients' sera showed acceptable correlation between the methods over a wide concentration range (r = 0.96-0.99). We conclude that the assay is a useful adjunct to the specific measurement of CK-MB, particularly in routine laboratories with a high throughput of such determinations.

Creatine Kinase↗
PubMed1988

Tamoxifen, serum lipoproteins and cardiovascular risk.

The influence of tamoxifen on plasma lipids and lipoproteins was monitored in 46 postmenopausal and 8 premenopausal women treated for advanced breast cancer up till 6 months. Total cholesterol (total-C) did not significantly change. However, high density lipoprotein cholesterol (HDL-C) and the HDL-C/total-C ratio rose significantly. Low density lipoprotein cholesterol was significantly decreased. Triglycerides and free fatty acids did not change markedly. The concomitant rise of sex hormone binding globulin and thyroxine binding globulin indicates that the increase of HDL-C with prolonged use of tamoxifen is compatible with an intrinsic oestrogenic effect of tamoxifen on the liver. The increased HDL-C/total-C ratio lends no support to the concern that long-term administration of this anti-oestrogenic drug might lead to an increased cardiovascular risk.

Adult↗
PubMedDate not supplied

Risk analysis of thrombo-embolic and recurrent bleeding events in the management of intracranial haemorrhage due to oral anticoagulation.

PURPOSES: Intracranial haemorrhage (ICH) is a rare but potentially devastating complication of oral anticoagulants (OAC). This raises the difficult clinical choice between either permanent cessation of OAC, or continuing OAC and if so, when to restart. To make this choice, one needs to balance the thrombo-embolic risk after cessation of OAC against the risk of recurrent intracranial haemorrhage when OAC are restarted. There are few published data to base this difficult clinical decision on. METHODS: We present an observational study of a consecutive series of 108 patients, collected prospectively and admitted to our department, with an OAC-related intracranial haemorrhage, in whom we assessed the thrombotic event rate and the recurrent intracranial bleeding rate during follow-up. RESULTS: In the 25 patients in whom OAC were reinstituted no new thrombo-embolic events occurred (0/506 unprotected patient-days). In the group of patients in whom OAC were not restarted (n = 81), the thrombo-embolic event rate was 8/11590 unprotected patient-days, of which only 2 were cerebrovascular thrombo-embolisms. The overall risk of a thrombo-embolic complication can be estimated to be 0.66 events/1000 patient-days at risk (95% exact confidence limits of 0.3 to 1.3 events/1000 patient-days at risk). In three patients the thrombo-embolic event was fatal. We saw recurrent intracranial bleeding in eight patients, 2 of which were fatal. Seven of these occurred before the restarting of the OAC. CONCLUSIONS: In OAC-related intracranial haemorrhages, OAC can be stopped safely for a considerable period, with a very low overall thrombotic event rate. The recurrent bleeding risk after restarting OAC is low. Recurrent bleeding mostly occurred before restarting OAC and is probably caused by insufficient or unsustained correction of the initial coagulation deficit. Immediate reversal of anticoagulation provides the patient with the best possible treatment options including surgery. OAC-related intracranial haemorrhages can therefore be actively treated.

Administration, Oral↗
PubMedDate not supplied

The development of a valveless cardiac assist device attached to the ventricular apex.

Konstantinov et al, in October, 1991, published a novel way to bridge a patient for heart transplantation. They proposed to cut off both ventricles high under the atrioventricular groove, leaving the atria, aorta, and pulmonary artery and their valves intact and to attach pneumatically driven, valveless pulsating pouches to assist the heart until a donor could be found. The removal of the ventricles just below the atrioventricular groove is called the "high cut"; it, however, destroys the chordae tendineae rendering the mitral and tricuspid valves insufficient. These have to be replaced by tissue inflow valves. We chose to cut off the ventricles at a lower level (the "low cut") to leave the papillary muscles on both sides intact, thereby saving the integrity of the mitral and tricuspid valves. Pulsating pouches were made to fit the heart at this lower level. They can be easily connected to the remaining heart after a specially disigned cuff has been sutured over the ventricular stumps. The pouches were pumped during the systole of the natural heart, but the myocardium may have to be electrically stimulated during systole to prevent undue distension. If the turgor is too weak to prevent distension, a sleeve over the ventricles is provided. To find the best location for these pouches, human cadaver implantations were done and the pre peritoneal cavity was found to be the most suitable. In vitro testing to determine how much flow could be pumped was done by attaching the pouches to fresh pig hearts and connecting them to a double sided mock circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Output↗