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Biomedical subjects

J Hendrikse

Publications and source records attributed to J Hendrikse.

9 recordsLinked to original sources
PubMed2005

Application of regional perfusion imaging to extra-intracranial bypass surgery and severe stenoses.

Arterial Spin Labeling (ASL) is a non-invasive method to quantitatively measure perfusion without the need of contrast material. Measurement of perfusion is derived from the subtraction of two consecutively acquired scans, with or without radio frequency labeling of the magnetization in the feeding arteries. So far, almost all ASL methods only allowed labeling the entire feeding artery tree of the brain simultaneously, without separation of the individual perfusion territories. In this paper, we describe a newly developed method, Regional Perfusion Imaging, allowing quantitative measurement of perfusion in the watershed of individually labeled arteries (right and left internal carotids, as well as basilar artery and the posterior circulation). Unlike conventional digital subtraction angiography, this new method is completely non-invasive, and allows to selectively measure cerebral perfusion, and not only to get angiograms of the feeding vessels. Regional perfusion was already measured in more than 70 elderly healthy volunteers and over 30 patients with internal carotid disease (severe stenoses and/or after extra-intracranial bypass surgery). A large variation among perfusion territories, even in healthy volunteers, can be appreciated. This method has the potential to increase our understanding of the relationship between collateral flow and regional perfusion in patients with neurovascular diseases.

Basilar Artery↗
PubMed2001

Collateral ability of the circle of Willis in patients with unilateral internal carotid artery occlusion: border zone infarcts and clinical symptoms.

BACKGROUND AND PURPOSE: The circle of Willis is regarded as the major source of collateral flow in patients with severe carotid artery disease. The purpose of the present study was to assess whether the presence of border zone infarcts is related to the collateral ability of the circle of Willis in symptomatic (transient ischemic attack, minor stroke) and asymptomatic patients with unilateral occlusion of the internal carotid artery (ICA). METHODS: Fifty-one patients (35 symptomatic, 16 asymptomatic) and 53 control subjects were investigated. Patients had unilateral occlusion of the ICA and contralateral ICA stenosis between 0% and 69%. The directions of flow, on the side of the ICA occlusion, and the size of the component vessels in the circle of Willis were investigated with MR angiography. RESULTS: On average, 92% of the patients without border zone infarcts (n=26) had willisian collateral flow compared with 60% of patients with border zone infarcts (n=25; P<0.05). This increase in collateral flow was caused by the high prevalence of collateral flow via the posterior communicating artery in patients without border zone infarcts (50% versus 12%; P<0.05). No statistically significant relation was found between the pattern of collateral flow via the circle of Willis and the presence of clinical symptoms. Nevertheless, asymptomatic patients with ICA occlusion demonstrated an increased diameter of the anterior communicating artery (P<0.05). CONCLUSIONS: In patients with unilateral ICA occlusion, the presence of collateral flow via the posterior communicating artery in the circle of Willis is associated with a low prevalence of border zone infarcts. Asymptomatic patients with an ICA occlusion do not have an increased collateral function of the circle of Willis.

Adult↗
PubMed1999

Field-effect flow control for microfabricated fluidic networks

The magnitude and direction of the electro-osmotic flow (EOF) inside a microfabricated fluid channel can be controlled by a perpendicular electric field of 1.5 megavolts per centimeter generated by a voltage of only 50 volts. A microdevice called a "flowFET," with functionality comparable to that of a field-effect transistor (FET) in microelectronics, has been realized. Two flowFETs integrated with a channel junction have been used to generate opposite flows inside a single EOF-pumped channel, thus illustrating the potential of the flowFET as a controlling and switching element in microfluidic networks.

Journal Article↗
PubMed1984

[Artificial reproduction in cattle].

In the first part of the present review paper, not only the current procedures making possible artificial reproduction in cattle are stated, but also the limitations of the methods available for superovulation and sexing, low-temperature preservation and transfer of embryos. In the second part, alternative procedures are reviewed, which may be used to increase the number of embryos per dam to a further extent by methods other than superovulation. Finally, the practical use of these recently acquired methods in breeding and animal products is described.

Animals↗
PubMed1984

[Evaluation of dog sperm].

2,025 ejaculates were screened for correlations between a number of characteristics. There was no difference between the effect of body size or breed. There was a negative correlation between the motility and morphology of the spermatozoa (P = 10(-6), independent of the total number of spermatozoa per ejaculate (P = 0.10). A significant positive correlation was observed between the size of the dog and the number of ejaculated spermatozoa (P = 10(-35) and there was a negative correlation between the age and the number of spermatozoa (P = 0.53 X 10(-3]. No significant differences were observed between the characteristics of the ejaculates, sampled at one- or two-day intervals.

Aging↗
PubMed1978

[Morphology of live and dead spermatozoa of stallions (author's transl)].

Examination of 539 ejaculates of stallions of various breeds showed that approximately 60 per cent of the spermatozoa were completely normal morphologically. Of these morphologically normal spermatozoa, 13 per cent were dead. The total proportion of live spermatozoa was 75 per cent, 32 per cent being obviously abnormal (22 per cent of live and 10 per cent of dead spermatozoa). Separated heads (normal as well as abnormal) were significantly more common among dead spermatozoa. Protoplasmic droplets (both at the neck and at the end of the middle piece) were mainly present in live spermatozoa. As the stallion grow older, the total proportion of abnormal spermatozoa shows only a slight increase. Moreover, this increase is mainly due to an increase in abnormal dead spermatozoa as the live ones show a reduction of abnormal forms. Thus, the proportions of abnormal and separated heads are reduced in live spermatozoa, whereas separated heads show a marked increase in dead spermatozoa. The total number of abnormal spermatozoa is reduced by an average proportion of 4 per cent in second ejaculates, whereas it increases by 8 per cent in live (unstained) spermatozoa.

Age Factors↗