Biomedical subjects

H F Visée

Publications and source records attributed to H F Visée.

4 recordsLinked to original sources

PubMed1998

A transcranial Doppler study of basilar hemodynamics in progressive carotid artery disease.

In carotid artery disease (CAD) the basilar artery (BA) may act as an important intracranial collateral to supply hypoperfused middle cerebral artery (MCA) territories. Transcranial Doppler studies were performed to study the dependency between BA hemodynamics in relation to the MCA perfusion status. BA and MCA blood flow velocities (BFV), pulsatility indices (API) and cerebrovascular reactivity (CVR) were assessed in 40 patients with a progressive MCA hypoperfusion due to progressive CAD. All patients had patent cervical segments of their vertebral arteries with an antegrade vertebral flow profile. Duplex studies were performed to diagnose the severity of CAD. Hypoperfusion of the MCA was diagnosed by the degree of vasoparalysis assessed by a Diamox procedure. Analysis showed that the basilar BFV significantly increased in cases of progressive CAD, the basilar PI decreased but the basilar CVR remained unchanged. However, in cases of bilateral hemodynamic significant CAD and bilateral exhausted CVR in the MCA territory, the basilar artery did not exhibit an increase of BFVs or a decrease of the basilar PI, but the basilar CVR showed a significant decrease. Basilar artery CVR is not impaired if this artery has a function as intracranial collateral in CAD. However in cases of bilateral hypoperfused MCA territories the basilar artery does not function as a collateral pathway. The basilar CVR declines under these circumstances which merely reflects the exhausted hemodynamics in the anterior/posterior borderzones. This situation might lead to an increased stroke risk in the distal basilar supply zones.

Adult↗

PubMed1997

[Asystole due to complex partial epilepsy].

A 56-year-old man was seen in the Emergency Room because of sudden and transient loss of consciousness. An asystole was diagnosed with 10 S duration after which a pacemaker was implanted. The patient had experienced such collapses before, preceded by odd smell sensations. After the implantation of the pacemaker, the patient did not collapse again but still experienced attacks of the same smell sensations combined with a strange feeling in his stomach. An EEG, recorded during such an attack, showed epileptic activity predominantly over the right hemisphere while at the same moment a pacemaker rhythm was observed. After the epileptic activity had stopped, normal sinus rhythm reappeared. On anticonvulsant therapy the attacks disappeared completely.

Electroencephalography↗

PubMed1995

The physiological and clinical significance of nonlinear TCD waveform analysis in occlusive cerebrovascular disease.

In order to compare the results of nonlinear analysis of hemodynamically compromised and noncompromised cerebral circulations we measured consecutive transcranial Doppler (TCD) waveforms of fourteen patients with a unilateral or bilateral occlusion of the internal carotid artery. The cerebral vasomotor reactivity (VMR) to acetazolamide in both middle cerebral artery (MCA) territories was established by using TCD. Conventional TCD data and nonlinear TCD analysis of data were compared. Nonlinear analysis of the TCD time series suggested dynamical chaos based on the fractal dimension of the TCD curve and the positive Lyapunov exponents in the compromised and noncompromised MCA territories. In the areas with the compromised circulation the positive Lyapunov exponents were significantly lower compared to the noncompromised side and in some cases with a negative VMR, the Lyapunov exponent was almost zero. The latter is suggestive for periodic behavior of the impaired cerebral circulation instead of the dynamical chaos which is found under normal conditions. The TCD time series of a hemodynamic compromised cerebral territory not only shows phenomena related to a decreased perfusion pressure (such as a 'damped waveform') but also phenomena which are related to a more prominent periodicity. We speculate that conventional and nonlinear TCD analysis could be used to determine the VMR.

Aged↗

PubMed1994

Dynamical chaos determines the variability of transcranial Doppler signals.

In order to estimate whether or not the variability of a timeseries of transcranial Doppler (TCD) waveforms is the result of a random or a deterministic process the following study was designed. From eight normal volunteers the middle cerebral artery blood flow velocities were measured for 50 sec and the maximum blood flow velocities (or waveforms) were analysed. From these waveforms socalled attractors were reconstructed and shown in a two dimensional phase portrait. The attractor of the TCD timeseries shows the entire range of states the cardiovascular system can display. The geometric structure of the attractor can be estimated by calculation of the correlation dimension D2. The correlation dimension D2 shows that the time evolution of the TCD timeseries is essentially nonperiodic and can be characterized by low dimensional chaos. It has been shown that the D2 value during hypocapnia has a significant higher value compared to the D2 values during normocapnia. The biological and clinical significance of these observations are outlined.

Adult↗