THE EARLY DEVELOPMENT OF NEUROSONOLOGY .3. PULSATILE ECHOENCEPHALOGRAPHY AND DOPPLER TECHNIQUES

From the earliest days of echoencephalography, it was noted that echoes from intracerebral interfaces showed systolic pulsations both in amplitude and range. Recordings of larger pulsations in range could also be obtained from the walls of intracranial arteries. It was hoped that clinical information might be obtained from recording and measuring these pulsations. Since it was easier to build equipment that recorded pulsations in amplitude, most work was confined to the recording of amplitude pulsations. However, such recordings of both amplitude and range pulsations usually used range gates in order.to isolate the echo of interest and movement of the echoes within the gates introduced artefact in the recordings. Such artefact was more easily identified in recordings of range rather than amplitude. None of these types of recordings resulted in the development of a clinically useful examination in either the living or dying patient. However, the recordings of range fluctuations were able to demonstrate the presence of Traube-Hering waves in the blood vessels of the brain thus suggesting that these vessels received an autonomic innervation in addition to their chemical sensitivity. Such range recordings also showed that, as a result of the increase in cerebral volume with the arrival of each systolic pulse wave, the brain moved centripetally to compress the cerebral ventricles and downwards to compress the basal cisterns and venous sinuses. The volume increase in the brain was accomodated by displacing cerebrospinal fluid and venous blood outside the rigid skull. When such a venting mechanism was over-taxed, as may result from increased intracranial pressure, it was postulated that the systolic pulse pressure wave, which could no longer be adequately attenuated by the compensatory venting of blood and cerebrospinal fluid outside the rigid skull, gave rise to shock waves which damaged the periventricular ependymal interface and the underlying brain with the production of progressive hydrocephalus. The development of ultrasonic Doppler techniques was quite a different matter and led to a number of clinically useful examinations as the technology became increasingly developed. The Doppler frequency shifts were displayed in various forms culminating in the display of their whole spectrum. Directional displays added further information and the ability to use short pulses enabled the Doppler shift and velocity of blood flowing in small regions of blood vessels to