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[Evaluation of cerebral hemodynamics by transcranial Doppler in anesthesia and reanimation]
1Unité INSERM 316, Centre hospitalier et universitaire Trousseau, Tours.
Insights
Doppler technics analyze blood flow to detect vascular diseases like stenosis. This method quantifies hemodynamic parameters, aiding in diagnosing conditions affecting peripheral and intracranial vessels.
Area of Science:
- Medical Imaging
- Cardiovascular Physiology
Background:
- Doppler techniques are essential for peripheral flow investigation.
- Detecting and quantifying vascular diseases such as stenosis and arteriovenous malformations is crucial.
Purpose of the Study:
- To detail the application of Doppler technics for peripheral and intracranial vascular disease detection.
- To explain the quantification of hemodynamic parameters using spectral analysis.
Main Methods:
- Spectral analysis of Doppler signals to determine velocity profiles.
- Quantification of systolic, diastolic, and mean frequencies.
- Calculation of hemodynamic parameters including the Doppler index (R = S-D/S).
Main Results:
- Maximal frequency increases (> 3 kHz) indicate vasospasm.
- Diastolic flow amplitude correlates with vascular resistance.
- Variations in mean Doppler frequency can represent blood flow volume changes when vessel diameter and angle are constant.
Conclusions:
- Doppler technics are versatile for assessing vascular health and disease.
- Hemodynamic parameters derived from Doppler are valuable in anesthesiology and intensive care.
- Limitations exist for intracranial vessel diameter measurement, necessitating alternative approaches during vasospasm.
Abstract:
Doppler technics are widely used for the investigation of the peripheral flows. The main objective of the method is to detect and quantify the vascular disease (stenosis, arterio-venous malformation) at the level of the carotid bifurcation or on the intracranial vessels. The spectral analysis provides informations on the velocity profile, and allows to quantify systolic, diastolic, and mean frequencies from which the usual haemodynamic parameters are determined. In case of vasospasm, the maximal frequency increases significantly (> 3 kHz). The amplitude of the diastolic flow is related to the vascular resistance. Vascular disease or distal vessel compression make the resistance increase; on the contrary vasodilation decreases the vascular resistance. The Doppler index R = S-D/S, with S and D the systolic and diastolic amplitude is generally accepted to change in proportion with the vascular resistance. The blood flow volume can be evaluated from the mean Doppler frequency, the vessel diameter, and the angle theta between the vessel and the Doppler beam. In case of intracranial arteries the diameter cannot be accurately measured by echography. Nevertheless if the diameter does not change and the angle theta remains constant, the variations of the mean frequency represent the blood flow volume changes. If there is a vasospasm, this method cannot be used, and the only possibility to evaluate the cerebral blood flow changes is to measure the variations of the common carotid blood flow or carotid mean frequency. The haemodynamic parameters are used in anesthesiology or in intensive care.(ABSTRACT TRUNCATED AT 250 WORDS)