Evaluation of Cerebrovascular Disease Utilizing a Transcutaneous Doppler Technic

Cerebral blood flow is one of the important parameters in the evaluation of intracranial and extracranial disease processes. Flow determinations are especially useful in atherosclerotic disease, which is becoming more and more prevalent in our aging population. Most flow determinations entail at least blood vessel puncture, one notable exception being the thermographic technic. The need for other atraumatic methods has led the authors to the evaluation of the Doppler velocity technic to study flow in the carotid arteries, the method having been effective in the evaluation of peripheral vascular disease. While velocity is only one factor in the determination of flow, from it there may be inferred abnormal flow patterns that are characteristic of certain disease processes. The work in progress herein presented is only a portion of a larger project; its scope is limited to velocity measurements in the common and internal carotid arteries in patients with cerebrovascular disease. Theoretical Considerations A wave form of specific length will be drawn out or compressed proportionally to the velocity of the sender relative to the receiver (Doppler, 1843). In clinical work, a sonic beam of 5 megacycles is directed along a vessel. The back-scattered waves are slightly more or less than 5 megacycles, depending upon the direction and velocity of the reflecting medium, in this case the red corpuscles. As the flow pattern is one of many velocities, the back-scatter is one of many frequencies. The difference in frequency between the transmitted and received beam is converted into an electrical signal with two useful characteristics. The first is actual frequency (quality of reflected beam) and the second is amplitude which is proportional to the quantity of reflected waves. Material The patients included in the study were adults who were to have or had had arteriography for the evaluation of cerebrovascular disease. The normal controls utilized were either patients who were shown by angiography to have no demonstrable intracranial or extracranial cerebrovascular disease, or they were young asymptomatic adults. Methods The transcutaneous blood velocity meter used was the “Doptone” developed by an American manufacturer. The output is an audible signal of many frequencies and varying intensity. The signal is put into a converter which separates out the two main useful characteristics of the sound waves: amplitude (intensity) and frequency (velocity). One output of the converter is a voltage proportional to the average frequency of the original signal, the other output of the converter is a voltage proportional to the intensity of the original signal. These two signals are displayed on a dual trace oscilloscope and are photographed. An electrocardiographic tracing replaces the frequency tracing during a portion of the examination.